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CS75 (Summer 2012) Lecture 0 HTTP Harvard Web Development David Malan — Transcript

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0:09All right
0:10Apologies for the delay
0:12Welcome to computer science S-75 - Building dynamic websites
0:15My name is David. I'll be your instructor this summer
0:18uh... and it said pretty brief summer so we're gonna dive right in tonight into some
0:22material then wall take of breath
0:24a look at the structure of the course, expectations thereof and then conclude with
0:28some additional material
0:30Along the way, please interject with any questions that you might have but first
0:33some questions from me
0:35you go ahead on the internet on your laptop or desktop you pull up your
0:38favorite browser you type in www.google.com and hit enter
0:43What happens? Let's tell this story and we can be as high level or low level
0:47as we want, and I'll steer us in both directions. So you've hit enter.
0:50What happens?
0:52Anything you got?
1:03Oh. Good. So that's the whole story. That's very good.
1:05Let's tease it apart a little bit now and I'll repeat some of the answers
1:08sometimes into the microphone so that our folks who are taking the course
1:11from afar can hear everything
1:13so your computer makes a request through your modem goes to your
1:17ISP, reaches google.com servers and they've replied
1:20with the response, so good.
1:22now let's dive in deeper there, and let's focus on the act of hitting enter
1:26Does someone want to propose, just give me one step
1:29in more technical detail what happens next and then we'll get to that same
1:32endpoint eventually
1:38Perfect. So we first need to translate the name of the site in this case the
1:41www.google.com
1:43into an IP address and, someone else, what is an IP address?
1:53Good, so an IP address identifies a server or computer on the internet
1:58and an IP address is simply a number of this form. Let me go ahead and pull up a
2:02little scratch pad for notes here
2:07so an IP address as you've probably seen as something in the form of w.x.y.z
2:13and little internet trivia:
2:14each of these placeholders can be a digit from what to what?
2:18...or number from what to what?
2:23Perfect. 0-255, and there's some restrictions on what numbers can
2:26be where, but essentially you have number dot number dot number dot number. And each
2:29of those numbers can be again 0-255.
2:32If we've really wanna start pressing deeper here, how many bits is used to
2:36represent an entire IP address under this schema,
2:41for those familiar with bits.
2:4432. So why is that? Well, for though less familiar/unfamiliar, if you
2:49want to represent the number 0 - 255 which is a total
2:52of 256 numbers
2:54you need 8 bits because 2^8=256, But we won't go into
2:57too much detail on along those lines
3:00but if you've seen that IP addresses are just 32 bits
3:03it is because each of these numbers is 8 bits itself so actually let's
3:08go here. There will be much math in this course after at the following sentence
3:11really
3:11but if you have 32 bits: how many possible IP addresses are there
3:16for the world's computers?
3:23so it's to 2^32 which is roughly.. those who are good with math in their heads..?
3:28So it's roughly 4 billion. So that's a lot. But these days most of you have
3:33laptops. Most of you have desktops
3:35Most of you have telephones in your pockets or Ipads or
3:40the like. So there's more to places these days that are consuming
3:43IP adresses
3:43so if you follow the popular media
3:45of late you'll find that people have been freaking out that were about to run
3:49out of IP addresses but that's because we've been using version 4
3:51for far too long.
3:53Thankfully version 6 (u.v.w.x.y.z) has begun to get rolled out
3:55and version 6 (u.v.w.x.y.z) will have 128 bit IP address
3:58..which is great, because that's 2^128
4:01which is huge! Barely pronounceable.
4:04But it will also become a little more complex to break these
4:07things down so we can squeeze a few more years of discussion out of these
4:10addresses but realize the world is
4:12transitioning
4:13now just for the sake of the experience for those at home let me actually pause here
4:17just so we can plug in this recording device so we can capture to another
4:20format so let's leave that is that cliffhanger for just a minute or two and I'll be right back.
4:26Where did we leave off? You've just hit enter. We had proposed that your computer
4:30had translated or needed to translate the hostname www.google.com
4:35into an IP address and then we talked for a moment about various forms
4:39of IP addresses
4:40so let's now push a little harder on how this translation happens
4:43so Google has a numeric address of this form (w.x.y.z)
4:46and as an aside Google actually probably has a whole bunch of IP addresses
4:49of that form. All of which lead to
4:51the same experience but perhaps different servers
4:54so how does your little Mac or PC or Linux computer know
4:58what the IP address of www.google.com actually is?
5:06OK, good. So, it has to do a domain name look up using a DNS server.
5:10For those unfamiliar, DNS is domain name system
5:12and this is an infrastructure on the internet that pretty much does exactly
5:15that. It converts domain names and host names
5:18to IP addresses
5:20and vice versa and will see tonight that it does a few other things in terms of
5:23helping with the routing of email
5:26with validation of ownership of domains and the like
5:29so there are these servers out there now your computer or your home probably
5:32doesn't have its own DNS server
5:34but probably Harvard does if you're on campus or Comcast does or Verizon
5:39or your company does.
5:40Now if you're at a small college for instance and you're not visiting google.com
5:44but your visiting some random website.com It's very possible that you were
5:48the first person on a campus to visit that website ever
5:51or at least in a long time
5:52so what if your small little campus's DNS server has no idea what
5:57this IP addresses is?
5:59Are you sort of out of luck because you went to that school, and not one where
6:02there's more people using that websites
6:05or equivalently, it's kind of the chicken and the egg problem (which came first?) if you're the first person to
6:08ever need to visit that website and therefore your campus's DNS server
6:11has no idea what that mapping is
6:13how do you solve this problem?
6:22Exactly. So there's a hierarchy, thankfully to the DNS system whereby
6:26even though you might have your own DNS server on campus or company
6:30but that doesn't necessarily store all possible domain names and IP addresses in
6:34the world. In fact, that would be quite a large database otherwise and it's just
6:37not efficient to keep all of them around if they're not being accessed at all
6:40or very frequently
6:41but your ISP
6:43knows some bigger fish and maybe that bigger fish knows an even bigger fish that
6:47has its own DNS servers that might know, but in the worst case
6:50if no one along this hierarchy knows, there also exists in the world what are
6:54called root servers
6:55which are spread out geographically across the several continents
6:58and it's those root servers that essentially know
7:01who does know, what the IP addresses of some random website.com
7:06in other words those root servers know
7:08who the authority is for instance for all of the .com's in the world, for all
7:12of the .net's or the like
7:14so that you can have this initial request from little old your computer
7:18bubble up to these very high-level servers and then bubble back down to
7:22some authority
7:23who does actually know
7:25and the reason why that works
7:28is because when you go and buy your own domain name which is a
7:31process will discuss in just a bit
7:33you have to tell the world what the IP address is of
7:37you DNS server, so someone has to be informed proactively once really
7:42and only once when you buy the domain so for now let's come back to our story
7:45We've hit enter
7:46Google.com was in my browsers window. My computer has somehow figured out that
7:50it is 1.2.3.4 or something like that
7:53so now my computer puts together a message to send it across the internet
7:57to Google.com. What does that message look like?
7:59Well in it's simplest form - it's a message that pretty much looks like this. It is
8:03literally the word GET in all caps a space a forward slash ( / ) if you're just
8:07requesting
8:08the root of the web server marked typically with /
8:12and then HTTP /
8:13version number
8:14Now in reality, there is a few more headers, so to speak, HTTP headers that get
8:18sent
8:19from browser to server, and we'll see those in action in just a bit,
8:22but this message captures
8:25really the most important aspect of the request
8:27so your little computer creates a virtual envelope more technically called
8:31a packet of some sort inside of that packet
8:33is a message like this
8:35Put on the front of that virtual envelope is a "To" address namely 1.2.3.4
8:39or whatever Google's IP addresses is.
8:42In the return field of this virtual envelope you know just like you were
8:45mailing something to a human there's the return address who which should be who's
8:49IP address probably?
8:51Your own IP addressing, and your computer does know that if you have an
8:55internet connection
8:56and then your computer sends it out on the internet. Now we can dive deeper and
9:00deeper and deeper but for now assume that your ISP
9:03has what's called the default-gateway
9:05also known as a router
9:07and routers are the computers on the internet that know how to get data from
9:10point "A" to point "B", or if they don't
9:12know precisely how to go for "A" to "B"
9:14they know whom to pass it off to
9:17who can then get it one step closer to point "B"
9:20so in reality a packet, this virtual envelope,
9:23might go from router to router to router to router sometimes as many as thirty
9:26different routers across the globe
9:28until finally it gets to its actual destination Google.com.
9:32Google receives this virtual envelope,
9:34sees that it's for its IP address, opens the envelope up, sees this message
9:38Google.com server happens to be running a web server and so that
9:41webserver looks for the file called "/"
9:44now "/" is typically a synonym for an actual file name like index.html
9:49or index.php or any number of other
9:51default standard file names
9:53so Google grabs that file from its hard drives and then puts it it's an own
9:57virtual envelope
9:58flips the two IP addresses the from and the sender
10:01sends it back to the internet via these routers
10:04it arrives on my computer. My computer, unbeknownst to me, opens this envelope
10:08sees a whole bunch of a language called HTML
10:11renders that HTML top to bottom and I see
10:14the search page for Google's main site
10:22What is the function of the slash?
10:24so whenever you type in a URL
10:27There are several different components to it. HTTP typically
10:31followed by :// followed by something like this (www.google.com/)
10:35and so this is let's say a representative URL, but we can
10:37actually to tease this apart into a few components.
10:40This is the protocol or schema at the beginning,
10:43even though in a browser we almost always used HTTP://
10:47Have folks seen others?
10:50HTTPS, similar, but different, in that it uses cryptography - a topic we'll come back to.
10:56FTP:// SFTP://
11:00WEBCOW:// Some of these are more standardized than
11:05others
11:05but the schema is typically an indicator to some piece of software
11:09how it should view the contents at that address
11:12so what comes after the :// It typically has something called
11:15a hostname
11:17or sub domain name
11:18followed by the domain name, which in this case is google.com
11:21or followed more precisely by a domain name witha TLD - top-level domain
11:26a .com .edu .gov .uk
11:31would be the TLD and then you have what we call a path
11:34and a path specifies exactly what file or folder you wanna access
11:39A single slash means get me the root of my hard drive
11:42and if you come from the windows world this is essentially equivalent to C:\
11:46Or on a mac it's equivalent to that, or on a Linux computer it's
11:50equivalent to that.
11:51So that is truly the root of your hard drive,
11:54the folder in which everything else on your hard drive lives
11:58now it turns out in a browser these days you don't have the type
12:01most of that. you can omit the HTTP:// You can typically omit the www. You can
12:06omit the slash, and things just work
12:08Why is that? both for the most part it's because browsers have just gotten a lot
12:12more user friendly
12:13right there what was the time a few years ago where advertisements
12:17in print and on TV would actually have HTTP://
12:21but then the world kind of realized that you know anytime you see www.
12:24something
12:25probably a website so we started omitting HTTP://
12:29Now the world has gotten acclimated to any mention of .com or .gov so
12:33we don't even really need the www anymore and so whether or not www
12:38works or doesn't work
12:40is actually completely configurable by the system administrators of the website
12:44and in fact
12:46i don't have a
12:47sort of a soapbox to hop on right now but invariably during a semester, I'll
12:51come across some website
12:52for which foo.com or whatever the domain is .com
12:56just doesn't work you have to type in www.something.com
13:01and that's just a foolish technical design decision on their part. We'll talk
13:04today about how you can configure things to just work, and it involves a bit of
13:08DNS
13:09a bit of web server configuration
13:11but typically you don't see that dead end
13:14because browsers these days if you type in foo.com and hit enter and
13:18there is no foo.com IP address out there
13:20the browser will presumptuously or helpfully
13:24prepned "www." to the start of the address
13:27and then retry that one
13:29some browsers if you just type foo will automatically try foo.com, foo.net, foo.gov
13:33some of the most popular ones so in short
13:35a lot of the technical processes that are happening are being sort of hidden
13:39now by browser user friendliness
13:41for better or for worse
13:44So, the story began with hitting enter the story ended with you're seeing the
13:47home page of Google.
13:49Any questions on the various steps in between,
13:51whether high level or lower level?
13:56Allright, so that's the story told from the perspective of a user.
13:59Why don't we tell the story from the perspective now of someone who owns a
14:04website or wants to operate a website so suppose one of your goals in this class
14:08or some other
14:09is to actually have your own presence on the web
14:12to actually buy your own domain name and have your own business or
14:15personal home page or whatever the case may be.
14:18How do you go about doing that? You need more than just a laptop and a browser now
14:22you need a server
14:23on the internet because even though every computer on the internet,
14:26your laptop included
14:27has an IP address
14:29it's not necessarily publicly accessible because even that statement's a bit of an
14:32oversimplification.
14:34You do not necessarily have a public IP address. In fact if you go
14:38home
14:39and you have internet access at home, especially wireless
14:41you probably have a home router like an Apple Airport Extreme, or you have a Linksys
14:45router or some device with antennas that gives you wireless internet
14:49access but Comcast or Verizon or whoever you're paying each month to give you
14:53internet access into the house via your cable modem or DSL modem
14:57which in turn is probably connected to that router
15:00if it's not one in the same device which some of the ISPs provide these
15:03all-in-one devices these days
15:05Odds are you have one IP address and if you have 3 brothers and sisters
15:10or parents or grandkids in the house
15:13all of you are sharing
15:15that one IP address
15:16and yet the individual computers in the home still need an IP address.
15:20so what actually is the case is that when you're in a home network you have
15:25what's called generally a private IP address something of a form..
15:29Anyone know what up popular internal IP addresses is?
15:36Exactly. Anything, in fact, starting with 192.168.x.y
15:41is a private IP address, so the folks who invented the internet
15:45along the way decided "You know what? We should probably have some IP addresses
15:48that should never be given out."
15:50So that within the company or home or a little test network
15:53you can have IP addresses that are guaranteed not to exist on the public
15:56internet
15:57so what home routers typically use iss 192.168.0 or 192.168.1
16:02and then the last digit, it can be again between 0-255, but some
16:06exceptions. It really it can't be 0 or 255,
16:08so there are some constraints, but it gives you
16:11roughly 250 or so possible IP addresses
16:15If you don't like that, there's: 172.16.x.y
16:19There's a few more constraints on this one, but then if you really need
16:23a lot of internal IP addresses
16:25you can have what's called a "class a" private network
16:2810.x.y.z is a private address and this actually gives you millions of
16:33IP addresses for your home or your business
16:35or your data center, but in short
16:37any IP addresses beginning with these few other prefixes are considered
16:41private
16:42but the problem then is that even if after this class you know HTML and CSS
16:46all the better. You know PHP, and SQL, and Javascript
16:49and you creates a website and you've run it on your laptop using software
16:53we'll introduce you to. A web server called Apache
16:56no one in the world
16:57is going to be able to visit your website because
17:00your address probably starts with one of these prefixes
17:04and your home router or cable modem or DSL modems is not going to
17:09let outside random people into your home network
17:12to access this IP address
17:14because
17:15frankly there's tens of thousands of people who probably have that exact
17:17same private IP address, so it's just uniquely identifiable
17:21and because your home router
17:23and your cable modem is sometimes a firewall into itself this traffic not
17:26gonna get into your home
17:27so in short that won't work..
17:29but you have at least two options, two alternatives, how can you get your website
17:34out on the internet?
17:43You can. Port forwarding. So let's go there. For those unfamiliar when you use
17:47a protocol like HTTP:// you're actually using other protocols behind the
17:53scenes and in fact you probably at least heard the
17:56the buzzword TCP/IP transmission control protocol internet protocol
18:01It's actually two protocols, two different standards or languages so to speak
18:05that govern how data can be transmitted
18:07on the internet and this is a bit of an oversimplification but for today's
18:10purposes assume
18:11that IP, the internet protocol,
18:13is just a set of conventions that humans came up with years ago
18:17that govern how you associate numeric addresses with computers
18:21so IP address derives from this protocol so IP is just the standard for
18:25assigning computers addresses however just signing someone an address
18:30doesn't mean you can get data to that address for that you need another
18:34standard another protocol
18:36and that's typically TCP transmission control protocol
18:39So TCP
18:40is the standard
18:41that web browsers and web servers speak
18:44in order to actually physically move data or electronically move data
18:48from point "A" to point "B"
18:50using the higher level notion of an IP address to actually uniquely
18:54identify points "A" and point "B"
18:57so for those
18:59who might want to go further in computer science and in networking in particular
19:02there's typically what's called the TCP/IP stack
19:05and so there's topics like there's the transport layer down here there's the
19:09others the IP or addressing layer here
19:12there's the application layer in short much of the internet is the result of
19:16smart people having design things and then design things on top of things on
19:19top of things
19:20and so we just typically over simplify and say TCP/IP.
19:24So what's the point there?
19:25TCP/IP allows not just the web to work but all sorts of applications
19:30There's the web. There's email.
19:32There's instant messaging.
19:34There's things like Spotify. There's dedicated
19:38applications they're using the internet
19:40but aren't necessarily inside of a browser
19:42so
19:43a server can actually do multiple things. It can receive email like Gmail can.
19:48It can be a website and get HTTP:// traffic
19:50so a server because it can do multiple thing somehow needs to be able to
19:54uniquely identify
19:56the various things that it can do
19:58and so the world introduced this notion of port numbers
20:01and typically for a web server
20:04Rather, for HTTP:// it uses this protocol TCP and the world decided some
20:09years ago
20:10the number 80 will arbitrarily but consistently identified this service
20:15so if you have a server and you have a website, and a website uses, as you
20:20probably know, HTTP:// but will look at what that means in a bit
20:23it is running so to speak on port 80 it is listening so to speak on port 80
20:28and the motivation for that
20:30is because you might also have
20:32an email server on the same physical box , right? Gmail, kind of an
20:36oversimplification, but they are both a website and an email service, and if you
20:40want to be able to send email to Gmail you can also used TCP but you have to
20:45use port 25
20:46in other words if you've go to http://www.gmail.com
20:49a with a browser you obviously want to web page back
20:52so even though you, the human,haven't typed 80, it's automatically
20:55inserted for you by your browser, behind the scenes
20:58but if you send an email from Eudora or apple mail or Outlook or whatever
21:02you're using
21:03you again probably don't have to care about this detail but that program
21:06is going to send data still to gmail.com
21:09but specifically to port 25.
21:11So, when a computer's on the internet, a server, and it's listening for traffic all
21:16of that traffic comes in on a specific port
21:19a specific like pathway into the server
21:21so that it knows if it's a webpage or an email, right? Because especially email; emails can
21:25contain HTML now
21:27so you need some way of distinguishing the two fundamentally
21:30so when you propose port forwarding, what does this mean?
21:33Well, if your home network
21:34has a public IP address, and you usually, again, get 1 from your ISP
21:39and that is some address of the form w.x.y.z
21:43and your individual laptop on which you've created your final project that
21:47you wanna make publicly available
21:49is that one of these IP addresses, doesn't really matter what it is,
21:52what you can do is configure your home router AKA firewall AKA cable
21:56modem, it depends on what make and model you have,
21:58but that device,
22:00you can configure it to say
22:01any internet traffic that comes from the internet to my home
22:05on my public IP address
22:07destined for port 80
22:09should be "port forwarded"
22:10to IP address 192.168.x.y
22:15port 80
22:16in other words you can tell this machine to take incoming data on that port
22:20and then route it very specifically to this computer, your's,
22:23so that it just works.
22:26Now, there is one gotcha here.
22:28Especially if you have siblings, for instance or other technically minded family members
22:31or roommates
22:32if you're doing port forwarding in this way
22:35only one of you can operate a webserver
22:38behind your cable modem because you only have one IP address to uniquely
22:43identify your website and if you've already claimed 80 as your own and
22:46that's the default for the world browsers to use pretty much only your
22:49webserver can be accessed
22:52now there is a work around here if your roommates really ticked off at you, you can
22:55say "Fine, fine, fine, I will give you port 81."
22:58but what does that mean? That means the entire world has to type out a URL like
23:04let's say your address was indeed w.x.y.z
23:08this would be your IP address
23:10your URL
23:11your roommates, unfortunately, would be this crazy looking thing (http://w.x.y.z:81/),
23:14right, or any number really.
23:17Now, there are some restrictions on the numbers. Probably can't use 81,
23:20but the point is the same.
23:22This is not standard, and you probably don't want your users having to remember such an
23:26esoteric detail as an arbitrary number.
23:28However if on the internet
23:31you visit any website with :80,
23:34odds are you will get to the website with which you're familiar it's just the
23:38browser is again for user convenience inserting the port number
23:41automatically for you.
23:44and little trivia for HTTPS, the secure version of HTTP, what port number does that use?
23:50443, and you sometimes do see that in the URL and you also see some other
23:53ports commonly like :8080
23:55:8080 is just kind of arbitrary popular port that some companies used to
23:59run certain services but in short using anything non-standard these days
24:03especially for commercial production web sites where you're trying to make money
24:06or trying to stay online up one hundred percent of the time
24:10using non standard ports is bad, because there are certain companies, there are certain
24:13campuses that will pretty much block any ports besides 80 and 443,
24:18but thankfully there's a work around, even if you wanna run some random server
24:21like a bit torrent server, or something like that
24:23all you have to do is change the port number to be 80 or 443
24:27so the reality is that with firewalling and will have this conversation toward the end the
24:31semester, when we talk about security more generally,
24:33in a lot of security mechanisms are kind of a joke because all you need is a
24:36modicum of savy or you know,
24:38having listened to the past 30 seconds of words that I just said
24:41you can circumvent these kinds of
24:43restrictions. Hotels do this a lot, Starbucks does this a lot
24:46the port numbers are really just this very basic
24:49mechanism, and the world and adopted some standards, alright,
24:53so, perfect! We have a solution. All you have to do is somehow figure out
24:57how to download the manual for your Linksys router or Apple Airport
25:02and you can configure all this port forwarding stuff and run a website
25:05from your own,
25:06so not quite. Because if you actually have a popular website, Verizon and Comcast
25:10might very well notice and just shut you off entirely,
25:13because that huge disclosure agreement you probably clicked through and never read when
25:17you signed up for internet service probably said you may not run
25:19a website on your home computer
25:22so plus that this was a pain in the neck to do anyway, plus I might
25:25unplug my laptop sometimes and so my websites gonna go down anytime i go to
25:29go out
25:30so not the best solution even if you have a desktop so let's at least try to
25:33push a little harder and assume that we need to outsource this problem, or we
25:36at least need to put your computer
25:38on the internet itself, in a data center, on the campus, where it can stay plugged in
25:42perpetually, under your desk at work if the system admins allows it,
25:46and moreover i don't want my website to live at w.x.y.z,
25:51or any number for that matter,
25:53I want it to live it david.com or some URL
25:56that is sort of distinctly my brand or my name,
25:59so that begs the question how do you go about
26:02getting your own
26:04domain name?
26:05Has anyone done this before? Yeah, how do you do it?
26:11Okay, where do you purchase them?
26:14Okay, so namecheap.com is a very popular place, fairly inexpensive
26:18Go Daddy is another very popular place
26:21This one (Go Daddy) is kind of riddled with
26:24up-sell attempts, trying to get you to buy everything in the kitchen sink,
26:28but you don't need to do that. There's all there's all sorts of
26:30domain name registrars out there these days. A bunch of years ago
26:34network solutions was the only one,
26:36but then the market was created and so there's a lot of places to buy domain
26:40names.
26:40For the most part, it doesn't matter where you buy your domain name from, but
26:44you do sometimes get different features
26:46in particular you get DNS features sometimes, more control over your DNS
26:50servers.
26:50They might throw in free email accounts, free hosting,
26:53but for the most part, it doesn't matter a huge amount in particular, you don't need to go
26:57to someone like network solutions and pay thirty dollars a year, when you could
27:00go to someone like Go Daddy and pay $9.99 a year or namecheap and
27:04pay $4.99 a year
27:06so in short paying more for domain name
27:08isn't necessarily giving you anything more
27:11uh... in the way of
27:13uh... functionality. It depends on what maybe the add-ons are.
27:17So, how do we go about doing this? Well, let's go to something like Go Daddy.
27:21Go Daddy's kind of a... Well, let's actually try namecheap.
27:23Let's go to namecheap, see what they look like,
27:27much of my friends have indeed used this website.
27:30right so let's see domain name to search and the search for david.com
27:35probably take. Oh,l that is a good price. Already doing better than Go Daddy
27:39All right. So as I expected it is taken as are almost all forms of david.
27:45*Ha* They've suggested I name myself "David John", "David Smith", "David Johnson", "King
27:49David", "David Photography.us"
27:51So one of the hardest things, frankly, of starting a business these days is
27:54finding an available domain name, let alone your own personal vanity domain names
27:57for people's names
27:58but if we found something we like.. Maybe I do want DavidTV... Well, that's atrocious.
28:05$6,000 for this domain but it's not yet taken.
28:09It's probably one of the cheaper ones up above so let's assume we found something
28:12we're happy with
28:14so we add it to our cart and we check out
28:16I now own some domain name, David something.com.
28:20So what now do I do with it?
28:22How do I associate it with my web server?
28:24and for that matter, how do I get a web server? Let's assume I have a web server, and we'll
28:27cross that bridge in a moment,
28:29but I have a domain name.
28:31What do I need to do with it to start using it? Well I need to tell the world what
28:35my IP address is.
28:36So I need to, somehow, tell the world that my server.. I don't know who's going to be
28:41hosting it, but i know it will have a IP address, by nature of how the web works.
28:45so let's assume I know the IP address is going to be
28:48w.x.y.z.
28:49I somehow have to inform the whole world
28:52that david.com's IP address is w.x.y.z.
28:55So one of the things I'll have to do at namecheap.com or Go Daddy or
28:59networksolutions.com
29:00is I tell the registrar
29:03not what my own computers IP address will be
29:06but rather what the IP address
29:08of my domain names
29:10DNS server's will be
29:13and the convention is typically that every domain name in the world should have
29:162 DNS servers: primary and secondary
29:18so a main one and a backup one.
29:20They can be one in the same, but the world really pushes people having at
29:23least two for the sake of up time and redundancy
29:26so I need to know not my own IP address, per se,
29:29but I need to know the IP address of one and then a second DNS server
29:33Now I don't have my own DNS servers and I want to configure two more
29:36computers in addition to my web server
29:38so this is where web hosting companies come in.
29:41So in addition to buying the domain name I also wanna host my website somewhere
29:45and it could very well be the same exact company. Could be Go Daddy, it could be
29:49Name Cheap
29:50depending on the service that they provide, but
29:53we need to have
29:55a web hosting
29:56option. So what's the web host going to give us? A web host is going to give us
30:00hard drive to put my files on, you know, maybe not hard drive, per se, but some
30:04illusion of storage space
30:05they are going to have their own connections to the internet
30:08this web hosting company
30:10there hopefully gonna have a pool of IP addresses so that I can have at least
30:12one of them.
30:14They're also going to have some RAM. they're also going to have technical
30:17support staff. In short, they're gonna have a server, and all of the things
30:20necessary to keep a server alive on the internet,
30:22and hopefully they're also going to have at least 2 of what..?
30:27DNS servers.
30:28So if I decide to host my website, let's say dreamhost.com. This is a very
30:33popular sort of "El Cheapo" (basic)
30:34kind of web hosting company
30:38that I've used myself in the past like $6.95 or $8.95 a month.
30:42So that's pretty good but again you get what you pay for.
30:45I wouldn't necessarily build a big business on it
30:47So for $8.95 a month
30:49I have the ability to upload my HTML and CSS files and soon PHP and Javascript
30:53files to their server.
30:56Their server has nearby 2 DNS servers, each of which, have their own
31:00IP addresses. So once I know what Dream Host's IP addresses are for its
31:05nameservers, I'd tell Name Cheap
31:07or Go Daddy, or wherever I bought my domain name
31:09and that's it
31:10the only time I have to talk to my registrar again, most likely, is in a
31:13year when they charge me another $5.99 or $99 for my
31:17domain name. Unfortunately, "buying,"
31:19you're really renting your domain name from these registrars.
31:23Now there's a whole bunch more involved in setting up of the web server
31:27and getting my files there
31:28but at least now I've told the world
31:31that if you want to know where david.com is
31:33Ask these people. These two IP addresses of the name server. Either one
31:37and those IP, those DNS servers should hopefully know. Why?
31:42Because so long as I keep paying dreamhost or someone else $8.95
31:45per month
31:46they will ensure that both of those DNS servers
31:48know what my own website's IP address is, and how will they know?
31:52Because of what I'm paying for is some storage space and some internet
31:56connectivity on one of their servers, one of their servers has an IP address
32:00so they just tell their DNS servers that david.com's IP address,
32:03is whatever the IP addresses is of the server
32:05they've told me to put my content on.
32:08and will actually look in little more detail
32:10what's involved in that.
32:13..but any questions?
32:16so in answer to the somewhat
32:20frequent problem where a website does work at www.something.com but not at
32:25something.com
32:27How do you fix something like that? There's usually two pieces to the
32:30solution
32:311. You have to make sure that there's a DNS record for something.com
32:36that is, there's an IP address associated with it. In addition to one being
32:39associated with www.something.com
32:43and you need to configure the webserver to accept requests for either something.com
32:47or
32:48www.something.com
32:51but really let's focus on just this DNS piece for now.
32:56so DNS... turns out the DNS is relatively straightforward and once you
33:00start operating a whole bunch of services on your own website. Maybe you
33:03have an email server,
33:05maybe you want to use hosted services like Google calendar
33:08Google docs. You can do things like
33:12actually for CS75, for this course,
33:14the TFs (teaching fellows) and I
33:15use Gmail essentially to host CS75.net's email
33:20so that's the website as I'll soon reveal
33:23if you haven't pulled up the website,
33:25and we want to be able to have an email list so that each of us can email
33:28everyone else very easily. So we want email addresses of the form [email protected]
33:34Now how do we do this? Well, we could set up a mail server, we could pay
33:37someone to do this, but an amazing service out there is Google apps, some of you
33:41might be familiar and for small fish like us where we only have a few people
33:45on staff
33:46you can actually have hosted Gmail, hosted Google calendar, hosted
33:50Google documents
33:51for I think 20 or fewer people for free
33:54and what you do is you configure your own DNS servers
33:57to map
33:59something like mail.cs75.net
34:02to essentially gmail.com so that whenever we send an email to
34:06something of the form mail.cs75.net, it figures out
34:10via DNS to actually go to Google. We could have calendar.cs75.net
34:13and you hit enter,
34:15you actually end up at Google Calendar, but our copy of
34:17Google calendar, and this is all thanks to DNS and there's only a few
34:21settings with which need to be familiar and we already talked about this one
34:24an NS record
34:26is
34:27a record in a DNS server
34:30that tells the world what the IP address is for that domain.
34:35So, what's inside a DNS server?
34:37Frankly it's a database, and you can think of it as like a database with
34:40excel files so spreadsheets that just have rows and columns
34:44and those columns essentially represents.. In each row, rather, you would
34:49have for instance a domain name and an IP address. Domain name : IP address. Domain name : IP address.
34:53That's really all that's underneath the hood in a DNS
34:56server at least so far as we're concerned.
34:58But there are different types of rows. So one of those rows can be an official
35:02record
35:04that says the name server, NS, for this domain is whatever IP address Dreamhost gave me.
35:09For instance
35:11Now, what else can I have?
35:12Well there's an "A" record. So an "A" record, a row of type "A" in that this
35:17spreadsheet of sorts
35:19is literally
35:20Domain name : IP address it's as simple as that, so if I had something.com
35:23In it's like the address should be xd w dot x dot y dot c
35:26that's what's called in a record
35:28and i can also have mail docs are something dot com or calendar dot
35:33something dot com
35:34and i can associate with an i_q_ dress
35:35and how do i do this they totally depends on your registrar or on your
35:39d_m_s_ provider whether extreme poster go daddy like
35:42but these days it's usually a web interface back in the day
35:44it was a command line you added a text file on the server but these days it's
35:48been made to be more user-friendly but it's essentially
35:50a spreadsheet
35:52thirst to his slightly fancier features
35:55a c name
35:56or canonical name
35:57isn't alias so it turns out with a lot of these webservices like school blacks
36:03where google's providing the service
36:06you don't necessarily want to have to know what google's i_p_ addresses
36:10writers one deep right on the only one who works there and so you can't really
36:13ask them out frankly could run a command in figured out
36:16but if you hard code into your work in a server
36:19the i_p_o_ dress of google dot com implication is that if they ever need to
36:22change their i_q_ address which happens not everyday pretty however few months
36:26few years for whatever technical reasons
36:29now your website goes down
36:30it's common kinda be better
36:32at least like a conceptually if
36:35calendar dot something dot com
36:36didn't resolve to google's likey address but rather what if pounder dot google
36:41dot com could instead resolve more generically too
36:44calendar dot google dot com
36:46so don't have your domain map to a nike address
36:49had your domain name map to someone else's domain
36:53and then let baird cnf server tell the world
36:57what the ac current i_q_ addresses of
36:59calendar dot google dot com
37:00so in other words if you want this layer of obstruction where you don't care what
37:04the i_p_o_ dresses you just care that your domain india synonym for someone
37:08else's domain name
37:09then you use a c name record and what the two columns look like our domain
37:12name domain
37:14instead of the main aim aki address
37:16so it's a wonderful useful feature
37:18especially these days if you look into hosted solutions not just like to
37:21collapse
37:22but companies that have services like
37:25uh... you know i customerservice forums
37:27if you go to a website know often have an address like support dot dell dot com
37:31or the like
37:32well there's a lot of companies days that to provide
37:35our customer service web sites
37:37at but it would look kind of lame if i go to del dot com and i get redirected
37:40to customerservice dot com
37:42del would provide read rather re brand someone else's service
37:46to look like dell even though someone else implemented and is hosting it so
37:50why us by a c name someone like dell could say support dot dell dot com
37:55should actually result to customerservice dot com but the user
37:58should never know that because the oral stage support dot dell dot com so that's
38:02just one of the things you can do
38:04with these things called seanangs
38:05and lastly in annex record as a male exchange record
38:09and mail change record simply states
38:11what is the i_p_o_ dress
38:13of the server or servers that should handle inbound mail
38:17for this domain
38:19and this is great
38:20because when you use your door over gmail or outlook
38:22and you type in the year uh... david mail-in at harvard dot e_d_u_
38:27and hit enter
38:28similarly there you have no idea what harvard's i_q_ dresses
38:31but your computer does but it's not the i_q_ dress of harvard that you do you
38:34per se that your email client needs
38:37it's the acted as a partridge mailserver
38:39so thanks today that's your mac or pc
38:42can ask your icici is deanna server org dot doc dot this whole hierarchy we
38:46discussed earlier
38:47in state what is the annex record for harvard idea
38:50and harvard dot e_d_u_ still means name servers should be able to say send all
38:55mail to the psyche address
38:56and what's nice about annex records as you can have multiple wants with
38:59priorities
39:00so websites orf rather
39:02uh... domains that had very old large numbers of users were you really don't
39:07want their mail servers going down
39:08you could have two or three or ten different mail servers
39:11and the d_n_a_ system all say try this one than this one than this one than
39:15this one
39:15just in case any of those go offline
39:18it's all thanks to d_n_ s and while research take all this for granted
39:22once you start developing your own websites maybe creating your own
39:25companies or confirming back your own school having these abilities is
39:29wonderfully powerful and it really boils down to
39:33basics
39:37any questions
39:41all right so that was kind of a lot want to take out three or so minute break
39:44characters restrooms in the hallway there soda machines i think around the
39:47whole corner
39:48on the move rejoin in about three mins
39:52alright we are back so
39:54why don't we take a look at the course itself and what you are in four and with
39:58the courses expectations are so in terms of prerequisites the official
40:02prerequisites are these so much more years of programming experience as well
40:05as comfort
40:05with html c_s_i_s_
40:07so what does this mean in real terms so summer school is very short since about
40:11six weeks and of course has three na lunch for billy sized projects
40:16and the gold really is to make sure that at the end of this short semester
40:19you feel quite comfortable going off and doing much more on your own in the way
40:23of website development not just html once yes s
40:27informed static websites but really dynamic websites that are driven by
40:30a language like p_h_p_ and javascript back in the database like mysql
40:36so it's a fairly intense course uh...
40:38if you believe takin
40:40something like computer science asks one of the introductory computer science
40:44class
40:45we're just one or two courses i will say from past experience
40:48you'll probably find the core
40:51challenging to say the least and typically willy estimate about thirty
40:55hours per project so there's three projects universally nine days for each
40:59of them
41:00on that's about thirty hours each but that was beyond average so students for
41:03whom programming is a little less familiar or it's been a bunch of your
41:07since you program to read only taken one or two introductory courses but don't
41:11really think of yourself as a programmer
41:13on the course is definitely more challenging so do beware uh... diving in
41:17i will say if you're on that fence and not sure if your comfort level in
41:21background is there
41:23but you can go to c_s_ seventy-five dot tv which is the opencourseware site for
41:27the course
41:28where we have several previous semesters worth of lecture videos handouts of
41:32projects some of which will be are similar to this summer's
41:36so by looking for the past you can perhaps in for as to what this summer
41:40will be like and get a sense then
41:41if the p_b_s_ of pastors projects completely overwhelm you
41:45or completely excites you
41:46so i would try to use that as an additional input tonight
41:49uh... before deciding whether this is the course for you
41:52um... in terms of expectations
41:54and there are these three projects in attending or watching if distant or
41:58unable to make it all in-person the lectures
42:01on the lectures will be structured as follows two tonight our focus is on
42:04h_t_t_p_ and for the mechanics the underlying fundamentals of the internet
42:08that for years you prolly taken for granted
42:10but once you really start building your own website and having to negotiate
42:13things like configurations of servers and coding databases tonight will start
42:17looking at some of those more technical details
42:20on wednesday and han next week will look at p_h_p_
42:23itself so one of p_h_d_'s on most compelling features these days is one
42:29it's in tactically very familiar are very similar to mine which is with which
42:33many of the folks in this room in at home or familiar syntactic lee it's
42:36similar to ciency plus plus
42:39on and other a procedural languages
42:41on this very much in vogue very popular it's pretty only present these days in
42:45terms of the web hosting companies that they're out there and its super easy get
42:48setup even mac o_s_ comes with p_h_p_ an apache the webserver pre-installed
42:53and their packages for windows in the nixon other computers that make it super
42:56simple to get setup on in terms of related languages rop iphone in ruby
43:02you're probably the to close this contenders in terms of popularity with
43:05p_h_p_
43:06and none of these is necessarily better than the others who could very quickly
43:09devolve into a religious debate
43:11but one of the nice things about p_h_p_ is again the omnipresence of support for
43:14a doubt there
43:15and also i think pedagogical e the documentation for p_h_p_ is outstanding
43:19and as you'll see
43:20the p_h_p_ dotnet online reference manual for functions and whatnot is rich
43:25with examples intelligent discussions and so we've just found
43:29that it's a very nice way of diving in deeper to web programming in front of
43:33course like this you should be able to continue on
43:35if you haven't come from that direction are ready to the likes of pipeline
43:38of ruby andrea speed for the job of world they espy's for the windows world
43:44there's a lot of commonalities among them
43:46will transition lecture three
43:48to looking in exile alyssa when it comes time to actually store data whether
43:51statically or dynamically
43:53you don't need a full-fledged database you don't need my sick we don't need
43:55oracle you don't need anything along those lines you could just use text
43:58files
43:58but he'd be nice if it's easy to read and write those text file select some
44:02now
44:03is a very popular language of sorts of metal language with which to right now
44:07textual files and to representative more generally of the topic will come back to
44:11when our javascript lectures
44:12on the document object models so they'll be some commonalities there
44:16uh... as sql are structured query language is what's used by a many
44:21relational databases these days among them my sequel
44:24oracle postgresql theirs
44:26also in vogue these days or are no sequel servers document uh... storage
44:31engines which will look at later in the semester as well
44:33but will primarily used for the courses projects my sequel
44:36will look at lecture six and seven eighths javascript and at this chat more
44:39general technique of ajax the ability to you
44:42whose javascript
44:43to query a server even after pages loaded
44:46to get back more data for instance google maps does this to get more
44:49reptile squares of mapping information when you click and drag
44:53a face book does this to push of live updates from your news feed in the light
44:57i will look toward the end of the semester then
45:00at some higher level concepts like
45:01security which wool interlaced throughout the semester but will really
45:05focus on it
45:06in lecture eight looking at common attacks on web servers on websites on
45:10databases
45:11so as to not necessarily acquaint you with everything they can go wrong
45:15but to at least plant the seeds in your mind of things you should be thinking
45:18about indeed there's so much code out there
45:21that is just one ruble because the people don't think do things like
45:24sanitize user input that is they don't check it for dangerous characters
45:27so we'll talk about things like sequel injection attacks will talk about
45:31uh... prostate scripting attacks in any number of other ways
45:34that are so darn easy to avoid
45:37yet many people just
45:38don't realize it or don't know how inferno typically
45:41simple little function calls conflicts
45:43and in the last lecture will look at scale build so would be of great problem
45:47to have if you've got so much traffic
45:49that all of the lessons you learn from lecture zero two eight
45:53uh... starts at your website search crumbling under the load and so will
45:57conclude the semester by looking at
45:59okay now you have to build now for a few dozen people two hundred people your
46:02school
46:03but several thousand or maybe even several thousand people per second how
46:06you actually scale
46:07from one little webserver to a bigger one
46:10but then once you have the biggest and most expensive available webserver what
46:13do you do
46:14we start to scale as they say poor is awfully so you get multiple servers
46:18maybe even cheaper slower web servers
46:20but you somehow figure out how to balance lowdown so to speak traffic
46:23across them
46:24how do you do that we databases how do you do that geographically
46:28uh... how do you do that with cloud computing a buzzword that's all the rage
46:31these days but has a very interesting technologies inter-lining
46:34will wrap up this master looking at those bigger picture
46:37issues
46:38in addition to second lectures
46:40we will have most weeks on sections in office hours for the course has
46:45uh... for teaching fellows folks who have either taught or take in the course
46:48before
46:48who'll be with us in the form of sections and office are sections will be
46:52a more slightly more intimate opportunities so on wednesdays in
46:55monday's typically right after lecture if you'd like to stick around to dive a
46:58little deeper into that weeks project
47:00so in addition to the pbf specification you'll get of a project
47:03one of its yes will walk you through the week uh... the week's project to give
47:07point now
47:08offer some design tips awesome helpful direction answer any confusion
47:12why did something quite poorly in lecture we can revisit those kinds of
47:15luck topics in sections that you get another perspective altogether
47:18and then office hours which is meant to simply follow
47:21section so one section officially wraps after an hour
47:23uh... office hours will be an opportunity for one-on-one human a with
47:27one or two fifty s
47:28uh... and this will be an opportunity in particular
47:30for questions with the projects if you're having trouble understanding
47:33something trouble chasing down some bug in addition to reaching out to us on
47:37line with a bs in person opportunities for those of you who are local for those
47:40of you were dissent
47:41more on the online opportunities in just a moment
47:45in addition to
47:46um... the courses classes there are projects three of them and they will
47:50outflow
47:51roughly in the order of the topics on the syllabus portal start in terms of
47:55p_h_p_ which would be new to song or most people in the room
47:58then will introduce mid semester databases in my sequel being will
48:02introduce javascript and ajax
48:04and so that all sense would be the tripartite approach
48:07of the courses projects in terms of the topics
48:10um... in terms of grades on projects are graded fairly holistic lead because
48:14you'll be encouraged to make a lot of design decisions on your own
48:18you won't necessarily have to implement per slice lee
48:21what we tell you to rather you'll have to meet certain feature and technical
48:24requirements
48:25so will to evaluate the three projects on these axes cisco will be in axis that
48:30and it'll be a numeric sport that captures how much of the project you
48:33actually attempted
48:35uh... correctness will capture how much of your code works in accordance with us
48:39back
48:39if it's very body that would not be considered very correct
48:42design is more subjective design is pain might work might work perfectly
48:46but does it look like a mass underneath the hood you had like ten nested four
48:50that's that is not good designed for instance
48:52and so designed to be an opportunity for pf particularly qualitative feedback
48:55from the teaching fellows on your code
48:57and style
48:59is the more of the aesthetics or your variables reasonably named are is your
49:03code well commented is it nicely indented
49:05the sordid easy things that are good habits to getting to meet if you're not
49:09yet enough
49:10that's what we define a style
49:11and then just for reference things are weighted in roughly the order the amount
49:15of time that's required to get things right
49:17so for instance this is the formidable used a computer total score for each of
49:21the project
49:22were correctness for instance is weighted more heavily
49:25then style and uh... batch of capture the fact that
49:28inventing a code polish and take you all that long but she seemed on bob's
49:32concert retake
49:33quite a bit of time
49:34so the format was meant to capture
49:37um... the courses website which help open just a moment has everything that
49:41you will need for the course including videos of lectures if you can't make it
49:44some evening work it's tricky because a full time work
49:46totally fine to watch the courses lectures online all the handout
49:49similarly will be available there
49:51what will be rolling out over email this week is access to a tool that actually
49:55uh... we've used in another class of mine concious fifty but it's a
49:58discussion tool that will allow you to interact with classmates with myself
50:02with the courses t_s_ online
50:04sab online discussion forms of sorts but using some of the same technologies that
50:08will talk about
50:09in the class including a jackson similar
50:11on so you will soon receive emails from us with invitations of sorts to create
50:15accounts within the uh... website
50:18so that we can you can start directing questions to classmates poor privately
50:21to the staff
50:22biopsy is fifty discuss
50:24so any questions on the structure expectations of
50:27but here in the right place
50:30must of course itself
50:34in terms of
50:39attendance is uh... expected and encourage bucks not factored
50:44so see it in a sense of protracted
50:47uh...
50:48then in terms of lecture typically we reese were slated for three fifteen to
50:51six fifteen i think will rarely go lol three hours typically the same course
50:55during the year on these two hours of classical typically have a little bit of
50:58wiggle room and let me not commit to just two hours per night
51:02on but we will typically not go i think as many as three hours for the frankly a
51:05lot to take and com twice a week no less
51:08uh... so uh...
51:11where we end up its act
51:13any other questions
51:15olin over there are two sections
51:17the implication of that detail
51:19is that sections will not start necessarily eta preordained time what
51:22will try to do is the test will come a bit early
51:24so if we do end up wrapping up a lecture we'll take a short break the band i've
51:27been right outright immediately to section
51:30an office hours so that you don't sit here awkwardly just waiting for an
51:34arbitrary time to come around
51:38for the distance students sections will be filmed as well and we will be making
51:42ample use of online interactions for students who are primarily distance on
51:46and we've also experiment in the past with things like skype in video
51:50conferencing or
51:51online chats com were quite flexible for whatever works uh... pedagogical for
51:55folks
52:00good question and typically not for distance jeans with sections we do film
52:03them but there is some leniency in when we post them we may experiment with
52:07trying to straighten some things online but this room is not equipped for that
52:10so i shouldn't makeup promises to that just yet
52:13but either way things will be available in synchronously after the fact
52:18the office hours will typically be right after sections on mondays and wednesdays
52:22which are right after lectures
52:25uh... the motivation being especially for folks who commutes
52:27we figured we try to compact things from mondays and wednesdays you'll have to
52:30come to campus yet again
52:32and we're flexible too if for instance
52:34you're really struggling in the class you have lots of questions or
52:37your schedule you have a nighttime class right after work
52:39'em were happy to do things by appointment as well
52:42soldier will will meet you half way as best we can
52:47somewhat hosting companies we talked earlier about d_n_a_ aspin sort of
52:50getting traffic to some destination b
52:53but once they get their what's waiting for the use or where are your rates tim
52:56allen's yes essence in p_h_p_ files actually store
52:59so this is a little screenshot from this one company dreamhost and i don't
53:02necessarily recommend them over any others
53:04but they're popular among our own and super cheap and just to give you a sense
53:07of what you get
53:09and what you don't really get
53:10here's a screenshot of what you get for parity for eight ninety five per month
53:14so you'd have to get unlimited tera bites
53:17of disc storage space
53:19uh... you get unlimited tera bites of monthly bandwidth you get an unlimited
53:23number of domains hosted and you get an unlimited number of user counts email
53:27account bicycle databases
53:29and at the turn of the distribution of the next fall back
53:32took ourselves to good to be true
53:34so what is the capture
53:36but that's an amazing deal for eight ninety five
53:39unlimited everything
53:41so what are some of the taxes are what are they doing here technologically to
53:44make this possible
53:51exactly so a lot of these web hosting companies are shared services whereby
53:56you might get this
53:57but they're also promising the exact same thing to ten other people to one
54:00hundred other people
54:02now turns out that its g_d_p_ the protocol we discussed earlier
54:06there is a future for these days for what's called virtual hosting
54:09so back in the day for the web every website needed unique i_p_ address
54:13essentially so that when you type in something dot com
54:16you went to one web sites and that website madonna server that server had a
54:19nike address and if you want to the second website
54:22you better get a second server or these give that computer a second i_p_ address
54:26however in more recent versions of h_t_t_p_
54:29will see through some experimentation with actual browsers
54:31browsers send and other issue to be hatter they don't just send gets
54:36they also send a reminder to the web server as to what the user typed into
54:39the u r l
54:40so that you can now have these days multiple websites foo dot com bardot
54:45combats dot com all living on the same physical server
54:48at the exact same like he address
54:51and because the browser's remind the server what the user typed in
54:55from dot com or bar dot com or about dot com
54:58the server
54:59even though it's receiving traffic for three different websites
55:01can figure out from those so-called headers what was requested
55:05and then return the appropriate
55:07domains
55:07homepage
55:08so in this case
55:11that's great 'cause it makes this possible we only have four billion i_p_
55:15addresses in the world in the are legitimately running out and so this is
55:18great that we can multiplex servers in this way and put multiple people
55:23multiple websites on the same mikey address
55:25but there's a couple dot that's what's the implication of yes
55:29the fact that multiple customers on the same machine
55:38goods of the mission crashes now all of you are affected rather than just the
55:41one
55:44contention for resources right so you're kind of in bad luck a bad place it for
55:49instance when the other customers on the website server is face book dot com or
55:53something then take xiv unexpected popularity on all of a sudden
55:56or maybe it's a web site that's really
55:58text someone off
56:00and is getting some kind of internet-based attacked like a denial of
56:03service attack
56:04because people going after that website and just because your server your web
56:08site on the same server
56:09now you are down or otherwise offline as well
56:12moreover at one of the res one of the ways in which these
56:16uh... companies offer such discounted prices this 'cause it's not just you and
56:20to other websites as prime not ten
56:21it could be a hundred could be a thousand other customers on the same
56:25server
56:26and so there must be some fine print hopefully there's some fine print
56:29somewhere
56:30that does say this is subject to something right they don't have infinite
56:33tera bites on their web service infinite bandwidth there's gotta be some catch
56:37here
56:38otherwise the world monopoly thousands of dollars a month to host a real
56:41large-scale websites
56:43so you again sort of get what you pay for
56:46and this is actually expense of years ago i signed up for some fly-by-night
56:48operation for like two ninety five by year
56:52um... to host my website and it was a website that i did not care much for and
56:56that was good because it went down quite a bit um... so what they're not
56:59guaranteeing here's unlimited uptime
57:01for instance so there some
57:03some doctors
57:04but frankly if you're just starting small you just one experiment you need
57:07it
57:07place for testing website or
57:09you don't you're eight ninety five is more compelling than several hundreds of
57:13dollars or even more
57:14um... this is certainly fights compelling
57:18but as an aside things like emailing calendar and what not there's another
57:21alternatives you don't need to get those thirty-year west coast when places like
57:25google exist
57:26but suppose you are
57:28not so comfortable with that approach and you suppose to
57:31that you're not comfortable also with the fact that
57:34we used to not have any control over a dreamhost like server
57:38because it's being shared by other people in it because it's being managed
57:40by other people
57:41which is to say if they are running p_h_p_ five point two which is a few
57:45years old
57:46so rio like you're running p_h_d_ five point even if you want to take the
57:50advantage of new language features they were introduced in p_h_p_ five three
57:53and more recently p_h_p_ five four
57:55you're outta luck like you're gonna have to other funny web poster just deal with
57:58it you can't just install it yourself typically
58:01so similar they can you not upgrade different versions of software you can
58:04assist early reconfigured the webserver at will
58:07now they might give you some form of control but you'll reach a point perhaps
58:11we're just too frustrating not to have administrative access to the server
58:14so you can still achieve that so virtual private servers d_p_s_ is or an
58:19alternative to shared web hosting model
58:22and the d_p_s_ world
58:23you get a dedicated server to yourself
58:27lasorda
58:28you get the allusion of the dedicated server to yourself so thanks to a
58:31technology generically known as virtualization
58:34these days you can park by our server with like a bunch of six user a bunch of
58:39course lots of ram lost of disk space
58:42and then you can run virtualization software on it uh... something known
58:45janet generally is a hyper by sir
58:47like vmware or parallels or virtualbox there's a whole bunch of these products
58:52free in commercial like out there
58:54that once you run them
58:56and install them on the server
58:58on top of that software you can then install multiple instances of windows
59:02multiple instances of lyrics multiple instances if they allowed it of mac o_s_
59:07so you can create the illusion of multiple distinct computers
59:10each of which has its own usernames and passwords its own administrative or
59:14so-called route account
59:15and even though they're sharing the physical hardware
59:18they are not sharing the same software
59:21so what you would get as the customer is the root login or the administrator
59:25login to your machine
59:26now there's still the risk of resource contention
59:29because these players to go to the quick over provision freshly if your pet
59:32spending
59:33in nineteen ninety five a month and not a hundred and fifty-nine ninety four
59:36ninety five months
59:38you're prolly gonna be on the server with fewer resources or with more
59:41customers
59:41but at least here you gain something
59:44and if you've been following along
59:46what is it fundamental you're gaining
59:47from a d_p_s_ that you didn't get from a web host
59:54exactly
59:55control you can to keep things up to date you can install whatever you want
59:59and also
1:00:00it's all morning altar servers compromised
1:00:03all it's our your words
1:00:04might not p
1:00:05whereas if the web hosting server is compromised everything on that server
1:00:10is potentially for durable
1:00:12so still not perfect because the reality is too
1:00:15even though you are the only one now with through ordnance traded access
1:00:18because it's a dedicated albeit virtual server for you
1:00:22that she was kind of a white lie who else has access
1:00:26the people there
1:00:27even if they don't know your password they have physical access the machines
1:00:32easier physical access to any machine in the world pretty much
1:00:35you can't compromise that you can do analytics computer for instance can be
1:00:38glued in what's called single user mode
1:00:40by pretty much any letter x when its booting up
1:00:43and that sort of bands any request for password at which point you can even
1:00:46change it
1:00:47um... even on p_c_s in computers you can usually reset certain passwords by
1:00:50opening the case up
1:00:52putting a little metal connector onto pins in a short circuits out the
1:00:55password and clears it out
1:00:57so in short physical access bat for security so you're not gaining more
1:01:00security off fundamentally
1:01:03you're just making it less likely that someone else's compromise will affect
1:01:08you
1:01:08and in some of these systems some software
1:01:11that system administrators we'll have the password or at least access to the
1:01:16root account on your server
1:01:17so in short we should just assumed that this is for you
1:01:21but probably at least one other person could physically access
1:01:24your conscience
1:01:26so what do you get uh... for the money
1:01:28well here and frankly these numbers are a little more compelling 'cause it's not
1:01:31on limited so what you're kind of inclined to believe a bit more about the
1:01:35quality of service for getting here
1:01:36but twenty gigabytes of storage no that's fine for typical website unless
1:01:40your website
1:01:41has a ridiculous amount of traffic in database traffic and logs which could
1:01:44build up and start taking mags are bigger bites of space
1:01:47uh... or if you're allow users to upload files are photos then you might need a
1:01:51lot of space
1:01:52but many websites even if they are dynamic this is probably planning
1:01:56transfers an interesting one twenty two hundred gigabytes per month
1:02:00for most websites that's probably fine and less your website is a photo website
1:02:04or worse a video website
1:02:07then you have to start to do the math and figure out exactly how much traffic
1:02:10data will be coming in and out of your server
1:02:12based on users patterns and moreover there's also corner cases this will
1:02:15discuss toward the end of semester you gotta worry about the bad guys out there
1:02:19if someone just unlike you words board or download some free piece of software
1:02:23that bangsar bangs the heck out of your computer
1:02:26they could just you've got your monthly allotment of bandwidth
1:02:29just by sending bogus traffic or downloading the same video again and
1:02:32again and again
1:02:33so there's very interesting adversarial tax
1:02:36when you have
1:02:37finances somehow tied to usage so you need to be where that especially with
1:02:42cloud computing
1:02:43uh... and let's see you get some amount of ran five hundred twelve megabytes
1:02:46here
1:02:47and so forth one of the things will look at the ring the semesters we start
1:02:49playing with apache
1:02:51is all give you a sense of uh... how you can assess how much ran your computers
1:02:54using image disk space it's using
1:02:56i dare say when the most common platforms for web hosting these days
1:03:00whether it's a vp s
1:03:01or it's is a
1:03:03uh... sir by post
1:03:05izla nixon some form whether it's debbie in or for the world war ubuntu war red
1:03:09hatter sent offer any number of versions of the next
1:03:12will happen to use the door of the class but it's representative of many a
1:03:16similar
1:03:17operating systems
1:03:18you can use mac o_s_ but it's not really use commercially to host websites just
1:03:22'cause that's not really xoxo
1:03:24geared toward that
1:03:25you can use windows on but you really there's no good reason
1:03:28there's no
1:03:29come technically compelling reason to use a windows machine to host things
1:03:32like p_h_p_ your python ruby
1:03:34'cause you're paying money for windows license to run free software so it's not
1:03:37necessarily compelling unless you are a powerful licenses and have the machines
1:03:41uh... generally going with
1:03:43these open-source tools is uh... quick comment compelling because none of the
1:03:47software reviews in the course
1:03:49uh... cost any money whatsoever and that's nonetheless quite popular and
1:03:53robust
1:03:55so
1:03:56went out
1:03:58declines so we will introduce it tonight but we will in the form of the first
1:04:01project so that you have an experience
1:04:03in the class that is as realistic as possible what will actually have each of
1:04:07you do
1:04:08is run your own webserver and run your own database server and actually run
1:04:12your own copy of lennox itself
1:04:14for this will use another tool that i use another possible i'm told this is
1:04:16that the appliance and this will be a downloadable file
1:04:20that inside of which he is in installation of land expat or lennox
1:04:23pacific lee
1:04:24but also installed for you in advance will be apache which is web server
1:04:27software my sequel which is database software
1:04:30p_h_p_ as well as support for a bunches of other languages in standard tools and
1:04:35the like
1:04:35and the up side of this is that rather than have you connect for instance to
1:04:38some random harbored servers on which you only have
1:04:41temporary access
1:04:42this is a virtual machine that you'll have a new computer for as long as you
1:04:45want to keep it around and it's very representative of the configuration
1:04:48you would find added d_p_s_
1:04:50or at a commercial web host and because you'll have a real access on its
1:04:54and because it will be live on your machine only you'll have perfectly
1:04:57secure access to it
1:04:59ominous your laptop or desktop is compromised
1:05:01and you'll be able to configure apache and p_h_p_ and really tinker with things
1:05:05and best yet best yet
1:05:07if you showed up
1:05:08that's fine used on the new and you're back to sort of beginning comes along as
1:05:12you've saved your code somewhere which will
1:05:14encourage you a how and where to do
1:05:16so more on that in a week or so
1:05:19and how would you connect to this kind of thing uh...
1:05:21so as the states
1:05:22zen one u
1:05:23news
1:05:24so why not use this as a ship
1:05:27status
1:05:29so if you have any specific stands for secure shell
1:05:32and this is a way sort of all school way but now much more secure
1:05:36of connecting to a remote server and executing commands on it so this is just
1:05:40uh... free program that comes with mac o_s_ terminal
1:05:43and there's analogues for the windows world party has a free program for
1:05:47windows that a lot of people like to use
1:05:49and it allows you to open up essentially a black and white window or white and
1:05:52black window
1:05:53and see
1:05:54type in a username and password
1:05:56connect to some remote server and execute commands on it and those
1:05:59commands can be to create files removed files configure the webserver turn the
1:06:03database on or off for the like
1:06:06so what they'll find once we start using the c_s_ fifty appliance a virtual
1:06:09machine albeit running on your own computer not some server
1:06:12is you will be able to connect to that appliance
1:06:15as though it's a remote server looks so that you'd never even need to see the
1:06:19appliance itself literally once you turn it on you can minimize it and pretend
1:06:23that it's a server somewhere else on the internet
1:06:25because once you install it the appliance
1:06:27into a virtual machine
1:06:28is gonna have its own i_p_ address
1:06:30but it's going to be what type of i_p_ address
1:06:34so it'll be private to your own laptop so no one else can you can access it but
1:06:38you'll be able to go through precisely the same motions that you would if you
1:06:41are actually paying some third party to host your website or you own some server
1:06:45outs where on the internet services dates will be one of the techniques that
1:06:48we use
1:06:49s f three p for those unfamiliar this is a screen shot of a popular of windows
1:06:53client for transferring files called secure effects but others exist free
1:06:57ones in particular
1:06:58just listed writing drop files from your computer to a server
1:07:02but in this case the server
1:07:03is going to be a virtual machine running on your own computer that may be
1:07:07maybe or maybe not is minimize but again
1:07:09experience of the precisely the same
1:07:13sold where does that still be bouts so
1:07:16turns out when you are writing
1:07:19html
1:07:20uh... you
1:07:21at fairly static content but you do have these mechanisms and i'm guessing most
1:07:26people in the room have some were a lot of experience with
1:07:28it's you know and basic web sites on the life
1:07:31but these ultimately already
1:07:33basic input mechanisms by which we can start
1:07:36making dynamic websites in other words
1:07:39we have text field password fields hidden fields checkboxes radio buttons
1:07:42drop-down menus
1:07:43so these are the mechanisms by which we can start to get input from users
1:07:48so that when they interact with our website they don't necessarily see the
1:07:51same thing
1:07:51rather they might see different things every time we visit that website so
1:07:55let's do a little
1:07:56example here
1:07:58i'm gonna go ahead and
1:07:59don't download this on your own just yet because we will be posting a newer
1:08:03version soon but i'm gonna go ahead and open up
1:08:07a program coldfusion
1:08:10vmware fusion this is what's called generally again a hyper visor
1:08:14virtualization software
1:08:16and what i've just done is essentially run lynn x on my own that
1:08:20and you too can do this i'm gonna actually use the lyrics desktop discuss
1:08:23its here but i could similarly minimize it as i will just few minutes and will
1:08:27connect to his well so now i'm running lyrics on my syndicator and notice i
1:08:31currently have no idea dress that they should change in a few seconds once
1:08:34identity there we go
1:08:36so my lyrics computer virtual machine has just asks for the network give me i
1:08:41p address and it came
1:08:42uh... the protocol
1:08:43the computers use to get idea dresses dynamically does anyone know
1:08:48dac p are dynamic host configuration protocol that's what did that
1:08:52it's also how your own personal computer works at home and gets a nike address
1:08:55from your links this router or airport extreme so i'm gonna go ahead and to do
1:09:01with this first let me go to mike back to my mac
1:09:04i'm gonna open up the simplest the program's text edit which is what we
1:09:07used earlier
1:09:08animated just make a very simple web page on first thing i do doctype
1:09:13html so in the course will use html five which is the sort of the latest and
1:09:18greatest
1:09:19version of html
1:09:23and so i'm gonna say hello
1:09:25now let's do this
1:09:26let's call this
1:09:30and then body
1:09:33and close body
1:09:35and then on to say cool
1:09:38on ok gonna save this ominous go ahead and save it on my desktop as google dot
1:09:43html
1:09:45i'm gonna say yes uses two million of the text file
1:09:48and now i'm going to go ahead and pull up
1:09:49google dot html
1:09:52so i'm not exactly google just yet i can do a little better so let's make this a
1:09:56little different slowly going here
1:09:59did style text align center
1:10:04so into any of this looks completely critical new these are the kinds of
1:10:07things that we will take for granted and of course that the stuff looks familiar
1:10:10so let me say the relocate now looks a little more like a low but it certainly
1:10:14lacking in some key features among them
1:10:18i searched far right so let's go there so let me start to make a simple web
1:10:22page that i get on thirty many of you could have done are ready cuz you know
1:10:25html and forms and what not so
1:10:27let's go ahead and do this it down here on an essay form
1:10:31close by for a minute ago and fear
1:10:34and i needed inputs
1:10:36tight equals taxed
1:10:38and i prolly need a summit by hand so let me did
1:10:43input by you poor summits if this about you starts with
1:10:48victory it as best we can saved
1:10:50reload okay so now it's getting there
1:10:53this isn't the prettiest things so let me go ahead and do style wear flats sade
1:11:00two hundred pixels
1:11:02school back here and say it it still looks a little small three hundred
1:11:05pixels
1:11:06uh... looks more global alike
1:11:07and we really want to be an all here
1:11:10we could do this
1:11:14line lucky
1:11:16so now we've got roughly google but in black and white
1:11:18so unfortunately takes away more work to implement the back end of this website
1:11:23writes a front-end pretty easy were pretty much done other than some colors
1:11:26and some other features these days
1:11:27but what about the back end so if i actually wanted a patch into google
1:11:31let's see if we can now revisit that conversation we started earlier when i
1:11:34tried to dublin dub dot google dot com is the answer
1:11:36what really is happening let's take a look underneath the hood let's look at
1:11:39the age to be traffic and think about what it is we're gonna start building
1:11:42next week in terms of the actual back and so let's
1:11:46suspend this mental thread
1:11:48pull up the actual global dot com
1:11:51and take a look at what's is here
1:11:53i'm gonna go ahead first so that this is
1:11:57new lightning think it is
1:12:02we have the disabled this annoying instant search feature
1:12:06select this
1:12:08here i come
1:12:11search settings
1:12:14google instance disabling
1:12:19never showed instant results so the reason i wanna do this is ready to talk
1:12:22about javascript and ajax the technologies that nobody's on
1:12:26annoying or beneficial instant search feature we wanted to sort of all swollen
1:12:29she d p
1:12:30searches right now
1:12:31sub disabled that's so now hopefully i can save
1:12:36okay now i'm gonna go back to build a dot com is what it is like five years
1:12:39ago when you want a search for something on the internet
1:12:41so now i'm going to go ahead and take for instance harper
1:12:44so it's still doing auto complete but it's not immediately showing me the
1:12:47search results
1:12:48so now notice before here's the or l on that
1:12:51dub dub dub dot google dot com
1:12:53and now after early hit enter
1:12:55now known as the oracle
1:12:57so they're this is now hinting
1:12:59at the fundamental functionality of h_t_t_p_ we had just issued one of those
1:13:04debt requests we had two of them in fact the first one came up when i visited the
1:13:08home page then i hit enter in it appears that another get request has been sent
1:13:12wide because when you are all changed so generally anytime the
1:13:16keyword get is involved
1:13:17it's because the orals changed
1:13:19or equivalent leave the aural changes you just to get
1:13:21most likely
1:13:22so there's a whole lot of distracting stuff up there but what is relevant in
1:13:26uh... what looks familiar up there
1:13:29in the u r ellen gray
1:13:33i have no idea what h_l_ is
1:13:35site so i don't know source i don't know but what looks familiar
1:13:39okay harbor
1:13:40so let me delete manually all the stuff that i had no idea about what it means
1:13:44at least not yet so mummy i don't know what this is
1:13:47q equals harvard that i did
1:13:49okay legals harvard apple q i don't know i'm just gonna
1:13:53presumptuous the whittle it down to that analysis answer
1:13:56so interestingly still works
1:13:58and what's nice is that there's much less distraction we can have the same
1:14:01story boat with fewer distractions in detail so it looks like
1:14:06when hitting enter on the previous page if i throw away the distractions
1:14:10i have now been fitted snot slash but slash search
1:14:14question mark
1:14:15q equals harbor so what is q she was generally known as the h_t_t_p_
1:14:19parameter so it isn't input to a web server
1:14:22that's generally comes from a four but as we'll see a few weeks ago also
1:14:25confirm javascript doesn't have to come from a form per se
1:14:28harvard is obviously what i typed in so what is slash search
1:14:31well it's not obvious here what programming language google uses before
1:14:35on face book we would probably see search dot p_h_p_ his face book is known
1:14:38for using p_h_p_ there also known for not hiding their file tensions which is
1:14:42very easy to do but they just don't for some reason
1:14:45gold does hide their file tension but a lot of google's code at least run-in has
1:14:49written a currently in python
1:14:51or in some other languages so
1:14:52it's not clear what language is on the server but slash search
1:14:56is referring to some files or some folder on the server
1:15:00what is the question mark the no
1:15:06the start of the parameters so anytime you have a question mark in your old
1:15:10that the marks the path
1:15:12and the preceding part of you are all
1:15:13from all of the parameters and parameters are key value pairs something
1:15:17equal something and if you have multiple parameters what separates them even
1:15:21though i already deleted the others
1:15:26ends the ampersand say assemble so if i had it deleted all of that
1:15:30recall that we saw something like this just a moment though and
1:15:34boat hwy quills harvard and i don't know what took you is but
1:15:37that's how you would separate parameters with m percent
1:15:40so this means we have submitted
1:15:43uh... ke of q anna value of harvard to the server
1:15:46so now let's use a fairly common tool built into chrome it's also built into
1:15:50safari
1:15:51firefox or something similar when we recommend something called fire bug on
1:15:54the courses website
1:15:56with which to do the same kind of thing but i'm in a good of you
1:15:59developer
1:16:01and developer tools and i will say these days certainly when using lamp clinics
1:16:05apache mysql and p_h_p_ which is this courses focused
1:16:09uh... many people are increasingly using chrome one because it's popular too
1:16:13because it's faster because it comes with some developer tools
1:16:16i would say firefox is also wonderfully convenient for doing development the
1:16:20mifsud certainly task on multiple browsers as well
1:16:23uh... require in one of the prep in the first project spec
1:16:26on you can get windows of rather intern explores getting better about having
1:16:29some integrated development tools from the course of perspective
1:16:32we don't care what browser you use because you'll be using again the
1:16:34appliance as a server
1:16:36you can use whatever browser whatever operations from on your own computer
1:16:39that you're most comfortable with but
1:16:42you are coming to this with some
1:16:45i'd say uh...
1:16:46less familiarity uh... with various tools
1:16:50chrome is pretty popular in firefox tend to be packing better for development
1:16:53purposes in indonesia task on all of them
1:16:55so one of my senior i'd just opened the developer tabs
1:16:59and now i have elements resources network scripts timeline profiles audits
1:17:03and consul we're not gonna use all of these but if you would never quite
1:17:05helpful one
1:17:07the elements have shows you the page's html
1:17:09but it pretty princess for u and it makes of hierarchical so that with those
1:17:12little triangles
1:17:13you can dive in deeper n c
1:17:15even though if we look at you source for the page
1:17:18it is an automatically of the page afaik uh...
1:17:23over here
1:17:25and view page source
1:17:26this is what came back from the server
1:17:28and i would argue this is not very readable
1:17:33unanimity actually still al
1:17:35even the html not that readable color coded maybe still not useful
1:17:39so what is this still
1:17:40x the developer toward actually parses it for you see can start to navigate and
1:17:45this is actually wonderfully compelling whether it's your site or someone else's
1:17:47if it's someone else's
1:17:49it's a wonderful way of learning how they did something or how they stylized
1:17:52something if it's your own site so wonderful way of chasing down bugs
1:17:55and also as you'll see changing on the fly some of the aesthetics
1:17:59without having to change actual files and then relo
1:18:02notary upload so we don't care so much about elements right now
1:18:06we do care about network so let me go to the networks have and what this tableau
1:18:10do first is
1:18:12uh...
1:18:13smith
1:18:14all of the network traffic between my browser and the server
1:18:17and will show each peacekeeping request one per line at the bomb
1:18:20some gonna leave this window open and click reload
1:18:23and again this is my u r l
1:18:28that's a lot i'd only hit reload once but why in the world that so many rose
1:18:32appear down here
1:18:38by clicking wants
1:18:39but look how much stuff just happened
1:18:42each of those again represents an eighty d p requests or virtual on bola from
1:18:46browser to server and back yet
1:18:50what does that mean behind the scenes
1:19:02okay good civil winnie support other things to me and concrete example of
1:19:05something as the polar
1:19:08so inside of the
1:19:10htmldiff initially downloaded there could be an image tag outsource tackling
1:19:14two tak two si es esta javascript images could be flash files
1:19:18could be a whole bunch of other assets so to speak
1:19:20and to get those the browser is predefined
1:19:23to sort of a personal ego get those assets so if it sees a source tagore
1:19:26image tag
1:19:27it will send another virtual envelope requesting that file specifically it
1:19:31might do it over the same network connection the same t_c_ p socket so to
1:19:34speak
1:19:35but each of these rose represents a different file that was downloaded
1:19:38ironically it seems that's harvard's not behaving well win the terms of the auto
1:19:43previews but that's good another day we can look at why
1:19:46uh... but let's look at the first one because that's the one that will be the
1:19:48most enlightening for now
1:19:50and when i click on this
1:19:52there's a few details so one
1:19:53the preview is just what was returned
1:19:55and here's another big mess of results from the web server but we don't care so
1:19:59much about that
1:20:00i care about the headers
1:20:01so many zoom in on this
1:20:04and rather than look at this fairly pretty printed version of it i want to
1:20:07look at the brawl source over diving in deep sort of uh... intellectually here
1:20:11so let me look at the source
1:20:13now this
1:20:14is what was literally sent
1:20:16in that virtual envelope
1:20:18that we started tonight's discussion with
1:20:20so there's the top-line debt slash search question mark you week was
1:20:24harvard stay safety p slash version number so that was in the envelope
1:20:28and we did promise to some other stuff in there
1:20:30second line
1:20:31is a reminder to the server
1:20:33as to what the user type and so what is the hostname
1:20:36now frankly but was not sharing their servers with other companies most likely
1:20:39so this doesn't really matter there but for shared web hosting companies the
1:20:43fact that i'm being reminded what do u r l was means i can serve up food dot com
1:20:48or bar dot com about us dot com so thankfully
1:20:50it's d_p_ does that
1:20:51there some arcane information here
1:20:54related to passing and connections inefficiency
1:20:57only wait my hand it back
1:20:58for now user-agent is interesting
1:21:00you might notice are ready but if you don't every web page of adverb visited
1:21:05is every website you've ever visited
1:21:07knows what computer you have and what opportune system you're running and what
1:21:11browser you were using
1:21:12why is that what browsers by default
1:21:15reveal precisely that information i'd have just told global
1:21:18behind the scenes that i have a mac
1:21:20running mac os x are ten point seven point four and if i scrolled down
1:21:24further or they will be able to infer that i was using chrome versions
1:21:27something or other
1:21:29so why in the world is that useful
1:21:43good so hard to believe this is use full from the bugging purposes useful for
1:21:46demographic purpose is to know who your users are
1:21:56goods
1:21:57so there's some features that could be dictated by what type of o_s_ or browser
1:22:02someone's using for instance if you go to a website that lets you download
1:22:04software
1:22:05it's not necessary that you detect with users opportune system browser are it's
1:22:09kind of a nicer user experience if the server only shows you the mac software
1:22:14because you clearly have a mac as opposed to me having to figure out which
1:22:17of the links to click for lenexa
1:22:18windows or mac o_s_
1:22:20uh... another argument frankly is that this is completely unnecessary and we
1:22:23should never gotten to this habit in the first place because it for uh... it's
1:22:26not necessarily used all that much
1:22:29and indeed
1:22:30writing websites that of require knowing what the user's browser is is actually
1:22:35generally bad practice because there will be certain privacy tools
1:22:38that users can install on the computer glitches hide this information
1:22:41altogether
1:22:42for better or for worse and if you're relying on certain headers to be sent
1:22:45your own website could misbehave
1:22:47so they work turns out there's other tricks for doing detection
1:22:50and typically is will see in javascript it's better generally to detect
1:22:54whether a browser has a certain feature
1:22:56rather than is that a specific operating system for specific version of a browser
1:23:01however databases for the billboards this
1:23:03that allow you to figure out based on the so-called user agents strings
1:23:08what version
1:23:10of browser inopportune system some answers because frankly this is a little
1:23:13hard to read so softer exist that simplifies this
1:23:16so you can just check a boolean variable is mac ortiz pc
1:23:19our butts below
1:23:20so more pain details that always my hand that
1:23:23cookies will come back to in a week or two when we have to start using them to
1:23:26our advantage but will also talk about the security implications of them
1:23:29but in a nutshell
1:23:30all of these headers just text is what was inside of
1:23:34that virtual on book and the most important one arguably was the very
1:23:37first one 'cause that tells people what to return
1:23:39but now we see that it's not just last
1:23:41it's a full path
1:23:43so google has hopefully parks that string
1:23:46so-to-speak slash search question mark cubicles harbor
1:23:49and then you
1:23:50lustig you equals harvard as import
1:23:52to its database or what not
1:23:53to return customized results to me
1:23:56now if you scroll down let's see how google reply
1:23:59so this is just a chrome thing
1:24:01it is just kind of dumb down display of the query string printers justice useful
1:24:05specially for developer you can see it more easily this way
1:24:08but let me go ahead and use source now for response headers
1:24:11this is what the server responded with
1:24:13so turns out
1:24:15many of you have seen numbers return by servers who has ever seen message four
1:24:19oh four comeback
1:24:21it was for foreman
1:24:24file not found right so it's a nation's bee status code it's an arbiter number
1:24:28the world decided on years ago that means files not found what are some
1:24:31others you might have seen
1:24:33sizes
1:24:36five oh one so internal server error of some sort
1:24:39five oh three audience another internal error
1:24:42or resource are forbidden
1:24:44there's four oh three rather which is forbidden
1:24:47uh...
1:24:51three oh one and three oh two are redirects which are actually quite
1:24:54useful will start using those in the next lecturer to such aren't there some
1:24:57codes that you've probably seen for four th may be the most popular
1:25:00two hundred you might not have ever seen because the best one of all
1:25:03two hundred is literally ok in these everything worked out well see just
1:25:07don't see it
1:25:08because it indicates success as those little green icon that we
1:25:11uh... saw a moment ago before i expanded this so this is the servers response two
1:25:16hundred means found what you're looking for here it is
1:25:18now what else comes down
1:25:20we have the date from the server which might be useful
1:25:23uh... expires in past controls so directives to the browser saying do or
1:25:27don't pass this even though these are not necessarily reliable talk about this
1:25:31when we get the p_h_p_
1:25:32uh... this is interesting set cookie
1:25:34set cookie is amazingly powerful if not a little unsettling especially northern
1:25:38advertising in tracking but we'll talk about that in the context of p_h_p_
1:25:42notice that the servers telling us that it supports jeez it which is like uh...
1:25:46compression utility
1:25:47which is a compression utility in this just means a you can compress your date
1:25:51of june from me
1:25:52uh...
1:25:53the name of the server g_w_ s probably good google web services
1:25:57and then some headers that they use for some the security things will talk about
1:26:01later in the semester so that's what school was returned
1:26:03in addition to
1:26:05the content that has come back from the server
1:26:07so let's see this outside the scope of a browser on the boat open
1:26:11uh... a program called terminal
1:26:13the switches comes with mac o_s_ for those of you with windows padi as
1:26:16another option will look at that
1:26:18uh... or encourage that info my music supply
1:26:22uh... bull book at that
1:26:24or recommend that for future projects an interim program call telnet telnet is
1:26:28like associates put uninfected now that's a bit of an oversimplification
1:26:31i'm gonna go ahead and tell that to google dot com
1:26:34and nothing actually happens but he did figure out the was likely address so
1:26:38that's interesting
1:26:39but tell that by the fall uses port twenty uh...
1:26:43has been so long
1:26:45twenty-one
1:26:46tom is a sport twenty want to see people are twenty-one bikes there's no tone
1:26:50that server their tone it used to be to send messages and connected email
1:26:53servers in the like
1:26:54but what if i instead say eighty
1:26:56so there's no colin in this program there is in a browser
1:26:59but this is going to connect from my laptop to google dot com on ccp port
1:27:02eighty
1:27:04so this is interesting
1:27:05now i've connected to their server
1:27:07wine are how do i know that
1:27:09stony connected to tell doubly dot dot dot l dot google dot com
1:27:13where did this all come from
1:27:14the days of the n_ s_ trickery tally for load balancing purposes they had
1:27:17multiple server so they're fraud gotten one of them specifically
1:27:20but i'm gonna pretend to be a browser unless they get me slash
1:27:24using issue d_p_ version one point one
1:27:26and the answer
1:27:27and then if that's the last of my headers i have to hit entered twice
1:27:31and wala
1:27:32what do i see
1:27:33well the fonts kind of big in the html javascript kind of mina five but that's
1:27:37exactly what my browser got back but if i keep going up and open up and up
1:27:41notice i can say
1:27:43exactly what the servers response was
1:27:45so i see my age to be headers they came back from the server
1:27:48uh... set cookie and all those same lines exactly what i saw on the browser
1:27:52so i just pretended really
1:27:53to be a browser and we can do this with any websites
1:27:56and it's more than just a curiosity can actually help with the bugging great
1:28:00actually seeing what's coming back from a server
1:28:02i can do dot dot dot dot harvard dot e_d_u_ eighty
1:28:06death slap
1:28:07slashes vp one point uh... one
1:28:10answer answer
1:28:11so interesting bad request
1:28:14now why is that said we see some html is this the webserver assumes that a
1:28:18browser will typically be doing this
1:28:20why might this be a bad requests
1:28:26i'm actually in a guest here let's try this gets slash is tepee one point one
1:28:31post
1:28:32prioritize u
1:28:34so it didn't like the fact that i did not say
1:28:37the host hatter
1:28:38which means harvard's web servers probably using something called virtual
1:28:42hosting which is that feature i alluded to earlier when a website
1:28:46can support molt when webserver can support local websites
1:28:50bought for that to work browsers have to cooperate and the fact that i did not
1:28:54send that had her meant that the server didn't know who's hoping to return
1:28:57so we gave me that
1:28:58four hundred response of i don't know what to do
1:29:01now let's try one other thing on the cancelled s
1:29:04and let me do
1:29:05telnet sue not dubbed the dubbed a harbored idea let's try this one to see
1:29:09what happens
1:29:10so get slash h_d_t_v_ one point one answer answer
1:29:14they didn't like that so let's fix this again
1:29:16so gets slash uh... issue the p one point one
1:29:21post harbor dot you do you answer answer
1:29:25interested
1:29:25this is not the home page where i get this time
1:29:30some message about
1:29:31it's moved
1:29:32harbor but you do has moved permanently you know that's and if i scroll up
1:29:36more esoteric lian headers is one of different status code three oh one which
1:29:40you mentioned earlier three oh one these permanent redirect
1:29:43if a browser receives a three oh one
1:29:46it should never asked that question again
1:29:48it should just remember harbor dot e_d_u_ moved
1:29:50any move to wear
1:29:52to the value of the location field which should also be included in the response
1:29:55centers
1:29:56how did that happen
1:29:58well some system administrator gene at harvard just decided arbitrarily
1:30:01that's but reasonably
1:30:03that we don't want to standardize on harbor dot e_d_u_ ann arbor authors in
1:30:06people's browsers we want them automatically to be redirected to dub
1:30:09dub dub dot harvard dot the id a dot harvard dot e_d_u_ white
1:30:13one printing minutes one
1:30:16it's perfectly reasonable
1:30:17to more technologically it can be better for
1:30:20securities a bit of an overstatement but for technical reasons having the w_w_w_
1:30:24means your cookies can be isolated to w_w_w_ dot harvard dot e_d_u_
1:30:29whereas if your cookies were instead sent to harvard that you do you that
1:30:33means your cookies could be read really bite any websites so including c asp dot
1:30:37harvard dot e_d_u_ or xd summer dot harvard dot you do you so they sing
1:30:41doubly david w
1:30:42you're also forcing uh... released by default cookies to be more precisely
1:30:46define so there's some technical reasons as well
1:30:48only a year or two ago was this problem fixed on the recent a few years back
1:30:52someone on a new came to harbor tour on the news office and one of her first
1:30:55things
1:30:56i one of her first acts was to fix
1:30:58eucharistic omission for years recovered that you do you did not exist
1:31:02devito v_w_ dot harvard dot e_d_u_ existed and they weren't even
1:31:05redirecting south that is a bug that's now been
1:31:09uh...
1:31:11and questions then
1:31:12uh... what just happened
1:31:14and one of the terminal window open the meat offer up some other troubleshooting
1:31:17tips
1:31:17anissa lookup nameserver lookup is a wonderful way
1:31:21of doing those d_m_s_ lookups we talked about before what i've just done is
1:31:25asked the nearest city in a server which happens to be this
1:31:28because that's how harvard's configured the campus that's the deanna server
1:31:31and i've asked what's the idea dress of harvard i do u and it's given me the
1:31:35psyche address
1:31:36so far we get curious that we do that's uh... they should be peak on five slash
1:31:41i can address
1:31:42interesting
1:31:44whatever why this is not working will again be hosting like the website is not
1:31:47configured to understand mikey addresses by default
1:31:50however let's try another one and it's lookup cnn.com
1:31:54what c_n_n_ dot com
1:31:57interesting
1:31:58so it turns out we denounce you can also do what's called round robin you can
1:32:01return multiple mikey addresses
1:32:03for web server and those can rotate literally in the order in which their
1:32:06return
1:32:07to do but balance
1:32:08and we'll discuss that topping again for the end of the semester and scale
1:32:11ability but let me just one of these
1:32:12and c_n_n_ either pretty day on guessing they don't really share with some other
1:32:16websites so let's just go to their i_p_ address
1:32:19and indeed
1:32:20there's works
1:32:21now notice my you are all hasn't changed
1:32:23so now if i really want to get sort of phone
1:32:26uh...
1:32:28i really want to get sort of
1:32:31uh... creative i'm gonna do this on my mac and you can do this on a windows
1:32:35machine is well there's typically file on macs in my next computers is called
1:32:39at sea coasts which is a text file bitmaps that hard cuts
1:32:43ita dresses
1:32:44four
1:32:45domain names
1:32:46this is useful generally for internal corporate used for development purposes
1:32:50so will be able to do this with projects as well
1:32:53uh... i'm gonna go ahead and uh... sent the case here
1:32:57just a text file and noticed this is some basic ones that come with the
1:33:01system this is my t_v_ six version six address written in a
1:33:04uh... crazy form
1:33:05i'm gonna go ahead and paste in not that u r l
1:33:08but the i_q_ dress of c_n_n_ and i'm gonna say this is
1:33:13david news dot com
1:33:15so this is like manually overriding
1:33:17the mapping bataya ki address to something else here only for my own
1:33:21computer i'm not running again a server
1:33:23it's just that my
1:33:24opportune system ako s in windows is supposed to look at a file like this
1:33:27before asking india nasser
1:33:30so now let's see
1:33:31if this works doesn't work with all websites but let me go to
1:33:35h_t_t_p_ colon slash slash
1:33:37david news dot com
1:33:45kamon
1:33:47areas
1:33:48i'd just made my own
1:33:49or new site
1:33:51frankly this is kind of stupid of them um...
1:33:53they go i was just joking with some friends the other day that you could
1:33:55kind of have fun with this and make
1:33:57fairly offensive domain names of the only to c_n_n_ somehow uh... and why is
1:34:01this
1:34:01so this is trivial defects frankly in a web server i a web server could be
1:34:05configured as you will be able to do with features of the past you before
1:34:08long
1:34:09of checking
1:34:10upon receipt of one of those virtual envelopes what was in the to field
1:34:14if the to field does not match something that were happy with
1:34:17redirect the user how you respond with what sascha
1:34:22three oh one
1:34:23somebody's actually trivial to fix this kind of things that could still be they
1:34:27can't stop david news dot com from needing to c_n_n_ dot com
1:34:30but they can stop the browser from staying there or the spy encouraging it
1:34:34without three oh one to redirect elsewhere
1:34:36and this redirection is super com and not just for harbor dot you do you
1:34:39but even the courses own website if i go to issue p
1:34:43colon slash slash two seventy five dotnet and hit enter
1:34:47notice what the oral changes too
1:34:51a few things happen there
1:34:52so this is the courses website what are some of the things that got answered in
1:34:55automatically it seems
1:35:01deaf indeed so idea then just go to the dub dub dub version i also went to the
1:35:06secure person why
1:35:07we've just gone into the habit and i personally guns out of using us as offer
1:35:10everything it's relatively cheap to do it's relatively trivial to turn on
1:35:14and it's only getting cheaper it's accuser getting faster and
1:35:17some of you might be familiar with about a year-and-a-half ago uh... toolkit
1:35:21caught fire shape was released
1:35:23which was a wonderfully free proof of concept of something called the a
1:35:26session hijacking attack something we'll talk about in a few weeks time in the
1:35:29context of security
1:35:31long story short if you are visiting the website that uses h_t_t_p_ colon slash
1:35:35slash
1:35:36it is fairly trivial
1:35:38for someone in your nearby wireless vicinity whether in this room at
1:35:41starbucks even in your own home if you have adversarial for gaza blends are
1:35:46roomates
1:35:47to can't login to your facebook account or your google account or i cannot go
1:35:51facebook account twitter account or any websites that's not using h_t_t_p_ ass
1:35:56and that is because
1:35:57if you're not using a g_p_s_
1:35:59nothing's infected known
1:36:00probably knew that but among the things that are infected or things called
1:36:03cookies so if you are just broadcasting cookies
1:36:07and cookies it turns out is hosting a weaker to hard the mechanism by which
1:36:10users are remembered as being logged into websites if you're just sending
1:36:15that cookie tool website again and again to remind unlike n on login on login
1:36:20that sign creek did anyone in starbucks can sniff that cookie
1:36:23and with the right technical savvy as you will soon have senate has their own
1:36:27another log into whatever you work
1:36:29doesn't mean they know your password
1:36:31but it doesn't mean they can hijack your current sessions so to speak
1:36:35so a protracted google because global about a year or two ago thanks to some
1:36:39of the issues in china they had with crack hacking and whatnot
1:36:42they transition all their services to a steep yes at least if you opt into at
1:36:45face book also find the offers this
1:36:47but again we come back to this uh... you a few more weeks of insecurity in your
1:36:50lives if you don't mind
1:36:52but will come back to this and talk about how you can have certain defenses
1:36:55up
1:36:55and i tragically
1:36:57even websites that redirect
1:37:00strong law
1:37:01the uninfected version to the infected version might still be vulnerable
1:37:05because many of those websites will first do a redirect
1:37:08that sends your cooking in the clear and then it realizes all of this to be
1:37:12secure
1:37:13by then it's too late so even though banking websites almost always uses
1:37:16there have been certain banks to be known
1:37:18to be not to technically
1:37:19uh... savvy
1:37:21who are still leaking cookies
1:37:22on four uh... reasons that will soon reveal so i said the duh duh duh based
1:37:27ups and then this stupid main page which is a media with the thing which is the
1:37:30tool we use for the courses website it's free with the software
1:37:33and that's not really intellectually interesting just their own software
1:37:38contact any questions on a cd p
1:37:41will delete david news dot com
1:37:44and again that wouldn't work with all websites in fact harvard's probably
1:37:46would not work for us
1:37:50so which is the party's hdv headers still become in invaluable resource when
1:37:54it comes time to chase down blogs are features in your own code
1:37:57let me take another quick look at something within krone's
1:38:00uh... developer toolbar in more than one last thing with regard to google and see
1:38:05if we can implement a little more of our own version of the world
1:38:08so let me go to
1:38:09the elements tab
1:38:11and just as a proof of concept here goes what's adds a little complex underneath
1:38:15the hood
1:38:16but let me go ahead and right-click on harvard university and they choose
1:38:19inspect elements
1:38:22and inspect element is nice because it's going to jump me right too
1:38:25the part of the html
1:38:27that relates to that portion of the page which is wonderful useful for diving in
1:38:31deeper to specific place
1:38:32so that is the a_h_ wrath that got me at harvard university link
1:38:36now suppose i'm actually google's designer
1:38:39and we're not quite happy with the shade of blue where the font size or font face
1:38:42it so i want to take over the website
1:38:44but frankly i don't have to log into the server and change font size and save the
1:38:47file dinh reload the browser
1:38:49and go thro the suit
1:38:51kinda like to do it
1:38:52uh...
1:38:53in line in the browser albeit at without saving any changes
1:38:56so notice you're on the right if you've not used from before
1:39:00that gordon developer tool bar
1:39:02notice on the right you have a summary
1:39:04of all of the styles that relate to that specific elements in the web page
1:39:09so from top to bottom here's the cv uh... there's the ciency assessed
1:39:14cascading top-to-bottom
1:39:15here all of the rules that apply to that all so
1:39:19there's apparently somewhere and google cssc apparently the file called search
1:39:23online sex
1:39:25and a link uh... dot w class mention in all of this where they're specifying the
1:39:29color of the link in the cursor that should be used over it
1:39:32so let me just right for text legally here
1:39:35let me just change this to
1:39:37let's say something we the
1:39:40random like or just
1:39:41so that is what i've done a their change who was elected or of course non
1:39:45permanently and only for the links in the page for which that csrs rule
1:39:48applies but the point here is that this is just a wonderfully quick and dirty
1:39:51way of experimenting especially if you're quite evil
1:39:54and you want to get let the pics alignment perfect in something
1:39:57being able to just tweaked it ever so slightly here and then figure out the
1:40:01values are and then write down in the actual file on the server
1:40:05just wonderfully useful
1:40:06also too if you're trying to figure out what font website uses
1:40:10i mean fighting the computed stop as this can be a little overwhelming like
1:40:13my god there's so many rules that apply to this element because of the cascading
1:40:16nature of c_s_ s
1:40:18let me just look at the computed styles which is a summary of the end result of
1:40:22all of these styles that have been applied
1:40:24enough i look for font-family
1:40:27indeed this is
1:40:29uh... appliances aerial followed by sensor so i know what font now google
1:40:35said just the debugging trick if you've not used it
1:40:37this and the networks have one abusing
1:40:39quite a bit
1:40:40most likely
1:40:41so now back to our own version of google unfortunately if i typed and harbored
1:40:46at google search
1:40:48doesn't go anywhere sort of the kind of did where did it end up
1:40:52urals almost the same it's a crazy looking you are opposite is obviously a
1:40:56file on my hard drive not on the internet but what the change in the oro
1:40:59yeah
1:41:02good so the question mark unattended
1:41:04but nope rameters got sent
1:41:07so let me go ahead and take a look at my file o
1:41:11well no predators were sent to them and give any of the main so let me go back
1:41:14and fix this restrict the fought so we can see more once
1:41:17and the need to input name equal skew here
1:41:21and let me go back over here and reload the page
1:41:25and now we go ahead and take harbor and now clickable search
1:41:29so now we have some progress
1:41:30so this is interesting
1:41:32now unfortunately google dot html is not a website
1:41:35nor is that dynamic it's literally just a static files you can send any
1:41:38parameters you want
1:41:39it's just you know inorg everytime
1:41:41but what is byproducts each year
1:41:43i'm kind of in a hurry to implement my own search engine uh... you know i read
1:41:46uh... knocked off my own new sites
1:41:49now would you mind search engine
1:41:50well i can actually do this form
1:41:53action should actually go to let's say dot dot dot dot google dot com slash
1:41:58search
1:41:59and i'm gonna say math the equals and get in all our case here
1:42:04slight inconsistency
1:42:06with what we've seen before
1:42:07now let me go back to this page
1:42:11reload
1:42:12and now mimetype harbored and watch the oral as i could answer
1:42:16uh... now i have implemented my own version of gul but how
1:42:20right all i did was i constructed a form
1:42:22on a specified a method of deaths inaction that happens to be a point b
1:42:26elsewhere
1:42:27but because of its dpm because a browser knows how to handle foreign it compiled
1:42:31all of the
1:42:32key value pairs in this case just want you equal something put it in the oral
1:42:36consented
1:42:37to that action
1:42:38attribute sent it to that particular u r l
1:42:40so now we have implemented
1:42:43our own version approval now of course
1:42:45denies that they were our search results and they were completely cutting corners
1:42:48here
1:42:49but that's where we'll need something like p_h_p_ to do things
1:42:52server-side
1:42:54let me pause for just a moment peter do want to say hello to class peters one of
1:42:57our for teaching fellows the others are at work right now
1:43:00do on a lot too
1:43:01actual hole up i have to come near you with a microphone value what you want to
1:43:05come this way so the cameras
1:43:06little more really available
1:43:08uh... although i a look forward to working with all of you and i will see
1:43:12you on wednesday
1:43:14much
1:43:15any questions that about the wolf
1:43:17faqs
1:43:18pgp
1:43:26precaution that's it
1:43:27had it not been named kit would this be broken so let me go back into here and
1:43:31let's just call a query thinking that's a reasonable name to give a parameter to
1:43:35mini reload mates gml me take that harvard answer
1:43:39and interesting they support we're so
1:43:42let me misspellings
1:43:44and that's probably not supported but maybe let's say
1:43:48family reload type harvard center
1:43:51okay that doesn't work
1:43:52so there's a bar cleary r_k_o_ for whatever backwards compatibility agrees
1:43:57other questions
1:44:08yes and on the entirety apartments campus your sessions can be hijacked
1:44:13so if you have malicious roommates or are you aria this thurs four technical
1:44:18people around you you are vulnerable to this issue hijacking can happen anywhere
1:44:22worker can is not use whether between you and the access points
1:44:25the wireless access point we're between you and the endpoints uh... webserver
1:44:29and i should say especially those of you are from out of town realize that harbor
1:44:32does that fine print in rules about not doing this to other people otherwise
1:44:35they'd
1:44:36that you can solve this problem by expelling people that's one way if you
1:44:39can't do technologically
1:44:41so this is one of these things were returned educators how it can be done
1:44:44but don't go trying this in the dorms on campus
1:44:46which he go home on your own home network
1:44:49other questions
1:44:52so where does this leave so we started by talking about global and we keep
1:44:55talking about who will be discussed so popular but it above the story applies
1:44:58to really any website out there
1:45:00so
1:45:01we talked about the in az and the process of not only booking up a web
1:45:05page is your rayl rather mikey address but also getting your own ita dress and
1:45:09getting your own web server in your own domain name
1:45:12we talked a little bit about html forms which would which you might be tonight
1:45:16are ready to the tools with which you can get a little more comfortable with
1:45:20diagnosing things in debugging things and we've written so that you know
1:45:23that's a that's a form
1:45:24all that we haven't done yet is actually implement the dynamic website for that
1:45:28we've completely outsourced to c_n_n_ and global today
1:45:31one of the first things we will do this coming wednesday is diving deeper to
1:45:34p_h_p_ and things like depts imposed concessions and shopping carts
1:45:38awesome the security implications around them will dive in cbc is fifty appliance
1:45:42in this virtual machine environment with which you get to
1:45:45uh... play you in terms of apache in p_h_p_ and mysql
1:45:48so tonight will turn abid early all stick around with peter for anyone with
1:45:52questions you might happen otherwise we will see you again on wednesday and
1:45:56after wednesday's lecture will flow
1:45:58right intersection office hours if you have questions about
1:46:01contents even though the first project will be released for a week or so
1:46:04sienna couple days

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