Fermah Pay - T1 Walkthrough — Transcript

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1. 0:00Hey, I'm Maxi, Rust protocol engineer at
2. 0:02Firma, and this is a quick walkthrough
3. 0:04of Trans 1 from Obelus Teller.
4. 0:06Trans 1 was the prepaid ledger. It's a
5. 0:10sovereign contract where a buyer
6. 0:12deposits USDC 1s, and a seller charges
7. 0:15small amounts against that balance.
8. 0:18On top of it, there's a gateway that
9. 0:20sends every transaction and pays the
10. 0:22network fees. So, the buyer never pays a
11. 0:25fee. This is the contract on testnet.
12. 0:29Um down here, you can see its activity,
13. 0:31deposits, charge, batches, and
14. 0:34withdrawals.
15. 0:36It shows three versions because we
16. 0:38upgraded it in place, so the hash here
17. 0:41is the current one. But, the address and
18. 0:44the balance stay the same.
19. 0:46This is a deposit. Up here, the source
20. 0:49account is ours. It's the account that
21. 0:52sends the transaction, and this one is
22. 0:54the fee source account. It's a separate
23. 0:57one um
24. 0:59that paid the fee for this transaction
25. 1:01through a fee bump, so the buyer paid
26. 1:04nothing.
27. 1:05Here is the deposit call. This address
28. 1:10right here is the the buyer, and this is
29. 1:13the amount. It's point um
30. 1:1603 USDC
31. 1:18since USDC has seven decimals here.
32. 1:22In the details right here, you can see
33. 1:24the USDC coming out of the buyer's
34. 1:27wallet and going into our treasury.
35. 1:31And here, um
36. 1:33the contract
37. 1:35credits the buyer's balance in the
38. 1:37ledger, which is what the seller charges
39. 1:39against.
40. 1:41The USDC transfer only happens with the
41. 1:44buyer's authorization, and this is the
42. 1:47line. Um the buyer's signed
43. 1:50authorization gets used up with the with
44. 1:53this nonce, so nobody can replay it.
45. 1:56Now here, in signatures, there's only
46. 1:58our key. That's because the buyer never
47. 2:00signed this transaction itself. They
48. 2:02just signed that one authorization for
49. 2:04the deposit once. So, next, a charge.
50. 2:08Um here is the charge call.
51. 2:10As you can see, it's the same buyer. Um
52. 2:13this is the charge ID.
53. 2:16And
54. 2:17this is the amount. It's .01 USDC, and
55. 2:21this last number is the latest ledger it
56. 2:24can settle in. So, a charge can sit
57. 2:26there and forever.
58. 2:28Charges need the operator roles
59. 2:31authorization, and this is it.
60. 2:34Um the operator's nonce getting used up.
61. 2:37As you can see here, um
62. 2:40the event at the end has a zero.
63. 2:43Right here. Um which in the contract
64. 2:46means charge it.
65. 2:48And um here
66. 2:51the
67. 2:52the buyer's balance in the ledger goes
68. 2:54down. Um no USDC moves in that charge.
69. 2:58It's just the ledger moving the amount
70. 3:00the amount from the buyer's um balance
71. 3:02to the seller's revenue.
72. 3:06>> [snorts]
73. 3:06>> And lastly, this right here, as you can
74. 3:10see,
75. 3:12um
76. 3:13this line's the important one for the
77. 3:16next part because the contract
78. 3:19um keeps a record of every charge ID
79. 3:21with with its um outcome. So, the same
80. 3:25charge can never be taken twice.
81. 3:28Now the duplicate. Um this is a batch of
82. 3:3298 charges that had already been um
83. 3:37settled.
84. 3:38We sent it a second time on purpose.
85. 3:41It's the same setup as before, as you
86. 3:43can see.
87. 3:45Um each entry is a buyer, a charge ID,
88. 3:49an amount, and the last ledger. The same
89. 3:51shape as the single charge before, just
90. 3:5398 of them in one transaction.
91. 3:57Um the transaction um
92. 4:01goes through,
93. 4:02but this error is um what the contract
94. 4:06returned. One result uh per charge.
95. 4:09Every single one is free, which in the
96. 4:11contract means uh duplicate because
97. 4:13those um charge IDs were already
98. 4:16recorded.
99. 4:18>> [snorts]
100. 4:18>> And if you send a single duplicate
101. 4:20charge straight um to the contract, it's
102. 4:23refused before it even reached the the
103. 4:26chain. So, there's no transaction at
104. 4:28all. So, this is the CI. This runs on
105. 4:32every change to main.
106. 4:34It's an end-to-end test against testnet
107. 4:37that goes through the gateway API, the
108. 4:39same way a real seller would use it.
109. 4:42This is the
110. 4:44the shop summary list.
111. 4:46Um as you can see, it lists every step
112. 4:50with its um transaction.
113. 4:53First, it creates uh a new buyer. It
114. 4:56funds it with testnet USDC.
115. 4:59It deposits with one buyer signature, um
116. 5:03and it settles free charges.
117. 5:06Then, it checks the
118. 5:09the duplicate both ways. Um our retry
119. 5:13charge through the API just returns the
120. 5:15original one, and the same charge sent
121. 5:18um straight to the contract gets refused
122. 5:21before submission.
123. 5:23And at the end, um
124. 5:26it checks that the gateway's balance
125. 5:28match the the contract's to the to the
126. 5:31unit.
127. 5:32>> [snorts]
128. 5:33>> Every hash um links to the explorer, so
129. 5:37anyone can check it themselves, as you
130. 5:39can see,
131. 5:40right here. Trench two builds on top of
132. 5:43it with four pieces.
133. 5:45First is recurring
134. 5:48um charges,
135. 5:50which is the buyer authorize a monthly
136. 5:53charge once and the seller can charge
137. 5:55each period without asking again until
138. 5:58the mandate expires.
139. 6:01Second is
140. 6:03um settlement interface compatible with
141. 6:06um X402.
142. 6:09So, any third-party facilitator can
143. 6:12check a buyer's balance and settle
144. 6:15against it.
145. 6:17Third
146. 6:18um is on-chain monitoring with um
147. 6:22with alerts for each risk we identify we
148. 6:25identify and so on. And fourth, it's a
149. 6:28testnet integration with um ecosystem
150. 6:31partner.
151. 6:33Well, so the first two already run here
152. 6:36on every change to main and we are
153. 6:38closing the the other two now.