Merge #15427: Add support for descriptors to utxoupdatepsbt

26fe9b990995f9cb5eee21d40b4daaad19f7181f Add support for descriptors to utxoupdatepsbt (Pieter Wuille)
3135c1a2d2e2fb31bc362c848bd2456d576e408b Abstract out UpdatePSBTOutput from FillPSBT (Pieter Wuille)
fb90ec3c33e824f5abb6a68452c683d6ce8b3e4a Abstract out EvalDescriptorStringOrObject from scantxoutset (Pieter Wuille)
eaf4f887348a08c620732125ad4430e1a133d434 Abstract out IsSegWitOutput from utxoupdatepsbt (Pieter Wuille)

Pull request description:

  This adds a descriptors argument to the `utxoupdatepsbt` RPC. This means:
  * Input and output scripts and keys will be filled in when known.
  * P2SH-witness inputs will be filled in from the UTXO set when a descriptor is provided that shows they're spending segwit outputs.

  This also moves some (newly) shared code to separate functions: `UpdatePSBTOutput` (an analogue to `SignPSBTInput`), `IsSegWitOutput`, and `EvalDescriptorStringOrObject` (implementing the string or object notation parsing used in `scantxoutset`).

ACKs for top commit:
  jnewbery:
    utACK 26fe9b990995f9cb5eee21d40b4daaad19f7181f
  laanwj:
    utACK 26fe9b990995f9cb5eee21d40b4daaad19f7181f (will hold merging until response to promag's comments)
  promag:
    ACK 26fe9b9, checked refactors and tests look comprehensive. Still missing a release note but can be added later.

Tree-SHA512: 1d833b7351b59d6c5ded6da399ff371a8a2a6ad04c0a8f90e6e46105dc737fa6f2740b1e5340280d59e01f42896c40b720c042f44417e38dfbee6477b894b245

1 files changed, 19 insertions, 0 deletions

diff --git a/src/psbt.cpp b/src/psbt.cpp
index d765133190..fe74002e82 100644
--- a/src/psbt.cpp
+++ b/src/psbt.cpp
@@ -212,6 +212,25 @@ bool PSBTInputSigned(const PSBTInput& input)
     return !input.final_script_sig.empty() || !input.final_script_witness.IsNull();
 }
 
+void UpdatePSBTOutput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index)
+{
+    const CTxOut& out = psbt.tx->vout.at(index);
+    PSBTOutput& psbt_out = psbt.outputs.at(index);
+
+    // Fill a SignatureData with output info
+    SignatureData sigdata;
+    psbt_out.FillSignatureData(sigdata);
+
+    // Construct a would-be spend of this output, to update sigdata with.
+    // Note that ProduceSignature is used to fill in metadata (not actual signatures),
+    // so provider does not need to provide any private keys (it can be a HidingSigningProvider).
+    MutableTransactionSignatureCreator creator(psbt.tx.get_ptr(), /* index */ 0, out.nValue, SIGHASH_ALL);
+    ProduceSignature(provider, creator, out.scriptPubKey, sigdata);
+
+    // Put redeem_script, witness_script, key paths, into PSBTOutput.
+    psbt_out.FromSignatureData(sigdata);
+}
+
 bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, int sighash, SignatureData* out_sigdata, bool use_dummy)
 {
     PSBTInput& input = psbt.inputs.at(index);