Abstract out UpdatePSBTOutput from FillPSBT

Author: sipa

src/psbt.cpp

@@ -215,6 +215,25 @@ 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);

src/psbt.h

@@ -565,6 +565,12 @@ bool PSBTInputSigned(const PSBTInput& input);
 /** Signs a PSBTInput, verifying that all provided data matches what is being signed. */
 bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, int sighash = SIGHASH_ALL, SignatureData* out_sigdata = nullptr, bool use_dummy = false);
 
+/** Updates a PSBTOutput with information from provider.
+ *
+ * This fills in the redeem_script, witness_script, and hd_keypaths where possible.
+ */
+void UpdatePSBTOutput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index);
+
 /**
  * Finalizes a PSBT if possible, combining partial signatures.
  *

src/wallet/psbtwallet.cpp

@@ -44,16 +44,7 @@ TransactionError FillPSBT(const CWallet* pwallet, PartiallySignedTransaction& ps
 
     // Fill in the bip32 keypaths and redeemscripts for the outputs so that hardware wallets can identify change
     for (unsigned int i = 0; i < psbtx.tx->vout.size(); ++i) {
-        const CTxOut& out = psbtx.tx->vout.at(i);
-        PSBTOutput& psbt_out = psbtx.outputs.at(i);
-
-        // Fill a SignatureData with output info
-        SignatureData sigdata;
-        psbt_out.FillSignatureData(sigdata);
-
-        MutableTransactionSignatureCreator creator(psbtx.tx.get_ptr(), 0, out.nValue, 1);
-        ProduceSignature(HidingSigningProvider(pwallet, true, !bip32derivs), creator, out.scriptPubKey, sigdata);
-        psbt_out.FromSignatureData(sigdata);
+        UpdatePSBTOutput(HidingSigningProvider(pwallet, true, !bip32derivs), psbtx, i);
     }
 
     return TransactionError::OK;