Merge pull request #26 from dunxen/add-2419

Add 2419

Author: dunxen

_posts/2023-09-29-#2618.md renamed to _posts/2023-10-13-#2618.md

@@ -0,0 +1,45 @@
+---
+layout: pr
+date: 2023-11-10
+title: "Interactive Transaction Construction"
+pr: 2419
+authors: [jurvis]
+components: ["InteractiveTxConstructor", "splicing", "dual-funding"]
+host: dunxen
+status: upcoming
+commit:
+---
+
+## Notes
+
+* The interactive transaction construction protocol, outlined in [lightning/bolts#851], allows parties to collaboratively
+  construct a bitcoin transaction by exchanging inputs and outputs for that transaction. It finds its first practical use
+  in the dual-funding protocol where both parties A and B can contribute to the value of the channel during establishment.
+  An example interactive transaction construction session (from the spec) could look like the following:
+
+        +-------+                         +-------+
+        |       |--(1)- tx_add_input ---->|       |
+        |       |<-(2)- tx_complete ------|       |
+        |       |--(3)- tx_add_output --->|       |
+        |       |<-(4)- tx_complete ------|       |
+        |       |--(5)- tx_add_input ---->|       |
+        |   A   |<-(6)- tx_add_input -----|   B   |
+        |       |--(7)- tx_remove_output >|       |
+        |       |<-(8)- tx_add_output ----|       |
+        |       |--(9)- tx_complete ----->|       |
+        |       |<-(10) tx_complete ------|       |
+        +-------+                         +-------+
+
+* Splicing also makes use of the interactive transaction construction protocol for constructing splice-in and splice-out transactions.
+* This PR implements the interactive transaction construction protocol as a type-safe state machine.
+
+## Questions
+1. Did you review the PR? [Concept ACK, approach ACK, tested ACK, or NACK](https://github.com/lightningdevkit/rust-lightning/blob/master/CONTRIBUTING.md#peer-review)?
+1. What is the `SerialId` of an input or output and how is it chosen in this implementation? What is the `SerialId` parity constraint and why is it used?
+1. Why are the number of inputs and outputs for the constructed transaction limited to 252 each?
+1. If we already have the limit for inputs and outputs above, why do we place a limit of 4096 on received `TxAddInput` and `TxAddOutput` messages?
+1. How are the state transitions defined using the `define_state_transitions` macro and what is the purpose of doing so in this way? How does it help holders
+   of an `InteractiveTxConstructor`?
+1. What transaction fees are paid by the non-initiator of the interactive construction protocol?
+
+[lightning/bolts#851]: https://github.com/lightning/bolts/pull/851