From 2ddddbd7c2461610f17763bd8d306824ff42443c Mon Sep 17 00:00:00 2001
From: Duncan Dean <duncangleeddean@gmail.com>
Date: Wed, 29 Mar 2023 22:34:17 +0200
Subject: [PATCH] Use bitcoin wire encoding for witnesses

---
 02-peer-protocol.md | 19 +++++++------------
 03-transactions.md  | 30 ++++++++----------------------
 2 files changed, 15 insertions(+), 34 deletions(-)

diff --git a/02-peer-protocol.md b/02-peer-protocol.md
index aee5cd3..a7efe44 100644
--- a/02-peer-protocol.md
+++ b/02-peer-protocol.md
@@ -388,14 +388,9 @@ the byte size of the input and output counts on the transaction to one (1).
     * [`channel_id`:`channel_id`]
     * [`sha256`:`txid`]
     * [`u16`:`num_witnesses`]
-    * [`num_witnesses*witness_stack`:`witnesses`]
+    * [`num_witnesses*witness`:`witnesses`]
 
-1. subtype: `witness_stack`
-2. data:
-    * [`u16`:`num_witness_elements`]
-    * [`num_witness_elements*witness_element`:`witness_elements`]
-
-1. subtype: `witness_element`
+1. subtype: `witness`
 2. data:
     * [`u16`:`len`]
     * [`len*byte`:`witness_data`]
@@ -413,11 +408,11 @@ The sending node:
 
 The receiving node:
   - MUST fail the negotiation if:
-    - the message contains an empty `witness_stack`
+    - the message contains an empty `witness`
     - the number of `witnesses` does not equal the number of inputs
       added by the sending node
     - the `txid` does not match the txid of the transaction
-    - the witnesses are non-standard
+    - the `witnesses` are non-standard
   - SHOULD apply the `witnesses` to the transaction and broadcast it
   - MUST reply with their `tx_signatures` if not already transmitted
 
@@ -427,8 +422,8 @@ A strict ordering is used to decide which peer sends `tx_signatures` first.
 This prevents deadlocks where each peer is waiting for the other peer to
 send `tx_signatures`, and enables multiparty tx collaboration.
 
-`witness_data` is the data for a witness element in a witness stack, not
-prefixed with its length (since it is already specified in the `len` field).
+The `witness_data` is encoded as per bitcoin's wire protocol (a CompactSize number
+of elements, with each element a CompactSize length and that many bytes following).
 
 While the `minimum fee` is calculated and verified at `tx_complete` conclusion,
 it is possible for the fee for the exchanged witness data to be underpaid.
@@ -1363,7 +1358,7 @@ The sending node:
     - MUST NOT send a `tx_signatures` message
 
 The receiving node:
-  - if the `witness_stack` weight lowers the effective `feerate`
+  - if the `witness` weight lowers the effective `feerate`
     below the the *opener*'s feerate for the funding transaction:
     - SHOULD broadcast their commitment transaction, closing the channel.
   - SHOULD apply `witnesses` to the funding transaction and broadcast it
diff --git a/03-transactions.md b/03-transactions.md
index fd3fa86..1437f8e 100644
--- a/03-transactions.md
+++ b/03-transactions.md
@@ -2940,17 +2940,10 @@ Opener's fees and change:
       channel_id: xxx,
       txid: "5ca4e657c1aa9d069ea4a5d712045d233a7d7c52738cb02993637289e6386057",
       num_witnesses: 1,
-      witness_stack[{
-	num_input_witness: 2,
-	witness_element:[
-	{
-	  len: 32,
-	  witness: "68656c6c6f2074686572652c2074686973206973206120626974636f6e212121"
-	},{
-	  len: 39,
-	  witness: "82012088a820add57dfe5277079d069ca4ad4893c96de91f88ffb981fdc6a2a34d5336c66aff87"
-	}]
-     }]
+      witness[{
+        len: 74,
+        witness_data: "022068656c6c6f2074686572652c2074686973206973206120626974636f6e2121212782012088a820add57dfe5277079d069ca4ad4893c96de91f88ffb981fdc6a2a34d5336c66aff87"
+      }]
   }
 ```
 
@@ -2961,17 +2954,10 @@ Opener's fees and change:
       channel_id: xxx,
       txid: "5ca4e657c1aa9d069ea4a5d712045d233a7d7c52738cb02993637289e6386057",
       num_witnesses: 1,
-      witness_stack[{
-	num_input_witness: 2,
-	witness_element:[
-	{
-	  len: 71,
-	  witness: "304402207de9ba56bb9f641372e805782575ee840a899e61021c8b1572b3ec1d5b5950e9022069e9ba998915dae193d3c25cb89b5e64370e6a3a7755e7f31cf6d7cbc2a49f6d01",
-	},{
-	  len: 33,
-	  witness: "034695f5b7864c580bf11f9f8cb1a94eb336f2ce9ef872d2ae1a90ee276c772484"
-	}]
-     }]
+      witness[{
+        len: 107,
+        witness_data: "0247304402207de9ba56bb9f641372e805782575ee840a899e61021c8b1572b3ec1d5b5950e9022069e9ba998915dae193d3c25cb89b5e64370e6a3a7755e7f31cf6d7cbc2a49f6d0121034695f5b7864c580bf11f9f8cb1a94eb336f2ce9ef872d2ae1a90ee276c772484"
+      }]
   }
 ```