From 94b51b6629980c49b71f0e2a7c1982343db0226e Mon Sep 17 00:00:00 2001
From: Casey Rodarmor <casey@rodarmor.com>
Date: Sat, 16 Dec 2023 00:30:28 +0800
Subject: [PATCH 1/2] Use pre-segwit tx serialization for fundrawtransaction

---
 src/lib.rs                         | 14 +++++++++++++-
 test-bitcoincore-rpc/src/lib.rs    |  2 ++
 test-bitcoincore-rpc/src/server.rs |  9 ++++++++-
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 7b8921141f..c18bf58866 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -160,15 +160,27 @@ fn fund_raw_transaction(
   fee_rate: FeeRate,
   unfunded_transaction: &Transaction,
 ) -> Result<Vec<u8>> {
+  let mut buffer = Vec::new();
+
+  {
+    unfunded_transaction.version.consensus_encode(&mut buffer)?;
+    unfunded_transaction.input.consensus_encode(&mut buffer)?;
+    unfunded_transaction.output.consensus_encode(&mut buffer)?;
+    unfunded_transaction
+      .lock_time
+      .consensus_encode(&mut buffer)?;
+  }
+
   Ok(
     client
       .fund_raw_transaction(
-        unfunded_transaction,
+        &buffer,
         Some(&bitcoincore_rpc::json::FundRawTransactionOptions {
           // NB. This is `fundrawtransaction`'s `feeRate`, which is fee per kvB
           // and *not* fee per vB. So, we multiply the fee rate given by the user
           // by 1000.
           fee_rate: Some(Amount::from_sat((fee_rate.n() * 1000.0).ceil() as u64)),
+          change_position: Some(unfunded_transaction.output.len().try_into()?),
           ..Default::default()
         }),
         Some(false),
diff --git a/test-bitcoincore-rpc/src/lib.rs b/test-bitcoincore-rpc/src/lib.rs
index 3a3a1560a2..b12cf61fbf 100644
--- a/test-bitcoincore-rpc/src/lib.rs
+++ b/test-bitcoincore-rpc/src/lib.rs
@@ -162,6 +162,8 @@ impl From<OutPoint> for JsonOutPoint {
 struct FundRawTransactionOptions {
   #[serde(with = "bitcoin::amount::serde::as_btc::opt")]
   fee_rate: Option<Amount>,
+  #[serde(skip_serializing_if = "Option::is_none")]
+  change_position: Option<u32>,
 }
 
 #[derive(Deserialize, Clone, PartialEq, Eq, Debug, Serialize)]
diff --git a/test-bitcoincore-rpc/src/server.rs b/test-bitcoincore-rpc/src/server.rs
index 4655939f92..93b67a7bdc 100644
--- a/test-bitcoincore-rpc/src/server.rs
+++ b/test-bitcoincore-rpc/src/server.rs
@@ -243,8 +243,15 @@ impl Api for Server {
     options: Option<FundRawTransactionOptions>,
     _is_witness: Option<bool>,
   ) -> Result<FundRawTransactionResult, jsonrpc_core::Error> {
+    let options = options.unwrap();
+
     let mut transaction: Transaction = deserialize(&hex::decode(tx).unwrap()).unwrap();
 
+    assert_eq!(
+      options.change_position,
+      Some(transaction.output.len().try_into().unwrap())
+    );
+
     let state = self.state();
 
     let output_value = transaction
@@ -294,7 +301,7 @@ impl Api for Server {
       script_pubkey: ScriptBuf::new(),
     });
 
-    let fee = if let Some(fee_rate) = options.and_then(|options| options.fee_rate) {
+    let fee = if let Some(fee_rate) = options.fee_rate {
       // increase vsize to account for the witness that `fundrawtransaction` will add
       let funded_vsize = transaction.vsize() as f64 + 68.0 / 4.0;
       let funded_kwu = funded_vsize / 1000.0;

From 301dcc23429682e50106caafbf8ed0f315277bd6 Mon Sep 17 00:00:00 2001
From: Casey Rodarmor <casey@rodarmor.com>
Date: Sat, 16 Dec 2023 08:59:39 +0800
Subject: [PATCH 2/2] Implement decoding

---
 test-bitcoincore-rpc/src/server.rs | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/test-bitcoincore-rpc/src/server.rs b/test-bitcoincore-rpc/src/server.rs
index 93b67a7bdc..3ec18b188d 100644
--- a/test-bitcoincore-rpc/src/server.rs
+++ b/test-bitcoincore-rpc/src/server.rs
@@ -1,9 +1,11 @@
 use {
   super::*,
   bitcoin::{
+    consensus::Decodable,
     secp256k1::{rand, KeyPair, Secp256k1, XOnlyPublicKey},
     Witness,
   },
+  std::io::Cursor,
 };
 
 pub(crate) struct Server {
@@ -245,7 +247,19 @@ impl Api for Server {
   ) -> Result<FundRawTransactionResult, jsonrpc_core::Error> {
     let options = options.unwrap();
 
-    let mut transaction: Transaction = deserialize(&hex::decode(tx).unwrap()).unwrap();
+    let mut cursor = Cursor::new(hex::decode(tx).unwrap());
+
+    let version = i32::consensus_decode_from_finite_reader(&mut cursor).unwrap();
+    let input = Vec::<TxIn>::consensus_decode_from_finite_reader(&mut cursor).unwrap();
+    let output = Decodable::consensus_decode_from_finite_reader(&mut cursor).unwrap();
+    let lock_time = Decodable::consensus_decode_from_finite_reader(&mut cursor).unwrap();
+
+    let mut transaction = Transaction {
+      version,
+      input,
+      output,
+      lock_time,
+    };
 
     assert_eq!(
       options.change_position,