Merge #568: psbt: Rewrite input replacement to avoid forgetting fields

c50bdf8 psbt: Rewrite input replacement to avoid forgetting fields (Steven Roose)

Pull request description:

  The way it was written seemed very prone to forgetting fields if new ones would be added. Like this it just keeps the required fields and all the rest is set to `Default::default()`.

ACKs for top commit:
  sanket1729:
    utACK c50bdf8
  apoelstra:
    ACK c50bdf8

Tree-SHA512: 80bbd74ec6ed5e72786400a3ef1ca0330047423ca881efc0203f499b1f0aa544d9d2cc0743ecc03273b2ca2949c196fa7a94c8c965439db8993a9f69113b10fd

Author: apoelstra

src/psbt/finalizer.rs

@@ -8,6 +8,8 @@
 //! `https://github.com/bitcoin/bips/blob/master/bip-0174.mediawiki`
 //!
 
+use core::mem;
+
 use bitcoin::hashes::hash160;
 use bitcoin::key::XOnlyPublicKey;
 use bitcoin::secp256k1::{self, Secp256k1};
@@ -415,8 +417,10 @@ pub(super) fn finalize_input<C: secp256k1::Verification>(
     // Now mutate the psbt input. Note that we cannot error after this point.
     // If the input is mutated, it means that the finalization succeeded.
     {
+        let original = mem::replace(&mut psbt.inputs[index], Default::default());
         let input = &mut psbt.inputs[index];
-        //Fill in the satisfactions
+        input.non_witness_utxo = original.non_witness_utxo;
+        input.witness_utxo = original.witness_utxo;
         input.final_script_sig = if script_sig.is_empty() {
             None
         } else {
@@ -427,25 +431,6 @@ pub(super) fn finalize_input<C: secp256k1::Verification>(
         } else {
             Some(witness)
         };
-        //reset everything
-        input.partial_sigs.clear(); // 0x02
-        input.sighash_type = None; // 0x03
-        input.redeem_script = None; // 0x04
-        input.witness_script = None; // 0x05
-        input.bip32_derivation.clear(); // 0x05
-                                        // finalized witness 0x06 and 0x07 are not clear
-                                        // 0x09 Proof of reserves not yet supported
-        input.ripemd160_preimages.clear(); // 0x0a
-        input.sha256_preimages.clear(); // 0x0b
-        input.hash160_preimages.clear(); // 0x0c
-        input.hash256_preimages.clear(); // 0x0d
-                                         // psbt v2 fields till 0x012 not supported
-        input.tap_key_sig = None; // 0x013
-        input.tap_script_sigs.clear(); // 0x014
-        input.tap_scripts.clear(); // 0x015
-        input.tap_key_origins.clear(); // 0x16
-        input.tap_internal_key = None; // x017
-        input.tap_merkle_root = None; // 0x018
     }
 
     Ok(())