Use pre-segwit transaction serialization for fundrawtransaction (#2865)

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),

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)]

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 {
@@ -243,7 +245,26 @@ impl Api for Server {
     options: Option<FundRawTransactionOptions>,
     _is_witness: Option<bool>,
   ) -> Result<FundRawTransactionResult, jsonrpc_core::Error> {
-    let mut transaction: Transaction = deserialize(&hex::decode(tx).unwrap()).unwrap();
+    let options = options.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,
+      Some(transaction.output.len().try_into().unwrap())
+    );
 
     let state = self.state();
 
@@ -294,7 +315,7 @@ 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;