Add bool PSBTInputSigned

Refactor out a "PSBTInputSigned" function to check if a PSBT is signed,
for use in subsequent commits.

Also improve a related comment.

2 files changed, 9 insertions, 2 deletions

diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index bcf110896..5cdc0112d 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -239,10 +239,14 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
     return sigdata.complete;
 }
 
+bool PSBTInputSigned(PSBTInput& input)
+{
+    return !input.final_script_sig.empty() || !input.final_script_witness.IsNull();
+}
+
 bool SignPSBTInput(const SigningProvider& provider, const CMutableTransaction& tx, PSBTInput& input, int index, int sighash)
 {
-    // if this input has a final scriptsig or scriptwitness, don't do anything with it
-    if (!input.final_script_sig.empty() || !input.final_script_witness.IsNull()) {
+    if (PSBTInputSigned(input)) {
         return true;
     }
 
diff --git a/src/script/sign.h b/src/script/sign.h
index 381e2eb12..35f7630f4 100644
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -730,6 +730,9 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
 bool SignSignature(const SigningProvider &provider, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType);
 bool SignSignature(const SigningProvider &provider, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType);
 
+/** Checks whether a PSBTInput is already signed. */
+bool PSBTInputSigned(PSBTInput& input);
+
 /** Signs a PSBTInput, verifying that all provided data matches what is being signed. */
 bool SignPSBTInput(const SigningProvider& provider, const CMutableTransaction& tx, PSBTInput& input, int index, int sighash = SIGHASH_ALL);