Figure out what is missing during signing

When signing an input, figure out what was requested for but was unable
to be found and store it in a SignatureData.

Return this information in SignPSBTInput.

4 files changed, 34 insertions, 7 deletions

diff --git a/src/psbt.cpp b/src/psbt.cpp
index 424b92cfb5..0734edcf8e 100644
--- a/src/psbt.cpp
+++ b/src/psbt.cpp
@@ -191,13 +191,12 @@ void PSBTOutput::Merge(const PSBTOutput& output)
     if (redeem_script.empty() && !output.redeem_script.empty()) redeem_script = output.redeem_script;
     if (witness_script.empty() && !output.witness_script.empty()) witness_script = output.witness_script;
 }
-
 bool PSBTInputSigned(PSBTInput& input)
 {
     return !input.final_script_sig.empty() || !input.final_script_witness.IsNull();
 }
 
-bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, int sighash)
+bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, int sighash, SignatureData* out_sigdata, bool use_dummy)
 {
     PSBTInput& input = psbt.inputs.at(index);
     const CMutableTransaction& tx = *psbt.tx;
@@ -237,9 +236,14 @@ bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction&
         return false;
     }
 
-    MutableTransactionSignatureCreator creator(&tx, index, utxo.nValue, sighash);
     sigdata.witness = false;
-    bool sig_complete = ProduceSignature(provider, creator, utxo.scriptPubKey, sigdata);
+    bool sig_complete;
+    if (use_dummy) {
+        sig_complete = ProduceSignature(provider, DUMMY_SIGNATURE_CREATOR, utxo.scriptPubKey, sigdata);
+    } else {
+        MutableTransactionSignatureCreator creator(&tx, index, utxo.nValue, sighash);
+        sig_complete = ProduceSignature(provider, creator, utxo.scriptPubKey, sigdata);
+    }
     // Verify that a witness signature was produced in case one was required.
     if (require_witness_sig && !sigdata.witness) return false;
     input.FromSignatureData(sigdata);
@@ -250,6 +254,14 @@ bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction&
         input.non_witness_utxo = nullptr;
     }
 
+    // Fill in the missing info
+    if (out_sigdata) {
+        out_sigdata->missing_pubkeys = sigdata.missing_pubkeys;
+        out_sigdata->missing_sigs = sigdata.missing_sigs;
+        out_sigdata->missing_redeem_script = sigdata.missing_redeem_script;
+        out_sigdata->missing_witness_script = sigdata.missing_witness_script;
+    }
+
     return sig_complete;
 }
 
diff --git a/src/psbt.h b/src/psbt.h
index 982fb803d5..cc4882c580 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -544,7 +544,7 @@ struct PartiallySignedTransaction
 bool PSBTInputSigned(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);
+bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, int sighash = SIGHASH_ALL, SignatureData* out_sigdata = nullptr, bool use_dummy = false);
 
 /**
  * Finalizes a PSBT if possible, combining partial signatures.
diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index 9d6a390ea2..320956d0c4 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -83,6 +83,8 @@ static bool CreateSig(const BaseSignatureCreator& creator, SignatureData& sigdat
         assert(i.second);
         return true;
     }
+    // Could not make signature or signature not found, add keyid to missing
+    sigdata.missing_sigs.push_back(keyid);
     return false;
 }
 
@@ -116,17 +118,24 @@ static bool SignStep(const SigningProvider& provider, const BaseSignatureCreator
     case TX_PUBKEYHASH: {
         CKeyID keyID = CKeyID(uint160(vSolutions[0]));
         CPubKey pubkey;
-        if (!GetPubKey(provider, sigdata, keyID, pubkey)) return false;
+        if (!GetPubKey(provider, sigdata, keyID, pubkey)) {
+            // Pubkey could not be found, add to missing
+            sigdata.missing_pubkeys.push_back(keyID);
+            return false;
+        }
         if (!CreateSig(creator, sigdata, provider, sig, pubkey, scriptPubKey, sigversion)) return false;
         ret.push_back(std::move(sig));
         ret.push_back(ToByteVector(pubkey));
         return true;
     }
     case TX_SCRIPTHASH:
-        if (GetCScript(provider, sigdata, uint160(vSolutions[0]), scriptRet)) {
+        h160 = uint160(vSolutions[0]);
+        if (GetCScript(provider, sigdata, h160, scriptRet)) {
             ret.push_back(std::vector<unsigned char>(scriptRet.begin(), scriptRet.end()));
             return true;
         }
+        // Could not find redeemScript, add to missing
+        sigdata.missing_redeem_script = h160;
         return false;
 
     case TX_MULTISIG: {
@@ -154,6 +163,8 @@ static bool SignStep(const SigningProvider& provider, const BaseSignatureCreator
             ret.push_back(std::vector<unsigned char>(scriptRet.begin(), scriptRet.end()));
             return true;
         }
+        // Could not find witnessScript, add to missing
+        sigdata.missing_witness_script = uint256(vSolutions[0]);
         return false;
 
     default:
diff --git a/src/script/sign.h b/src/script/sign.h
index 64eb3eb8e5..e229c375c7 100644
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -117,6 +117,10 @@ struct SignatureData {
     CScriptWitness scriptWitness; ///< The scriptWitness of an input. Contains complete signatures or the traditional partial signatures format. scriptWitness is part of a transaction input per BIP 144.
     std::map<CKeyID, SigPair> signatures; ///< BIP 174 style partial signatures for the input. May contain all signatures necessary for producing a final scriptSig or scriptWitness.
     std::map<CKeyID, std::pair<CPubKey, KeyOriginInfo>> misc_pubkeys;
+    std::vector<CKeyID> missing_pubkeys; ///< KeyIDs of pubkeys which could not be found
+    std::vector<CKeyID> missing_sigs; ///< KeyIDs of pubkeys for signatures which could not be found
+    uint160 missing_redeem_script; ///< ScriptID of the missing redeemScript (if any)
+    uint256 missing_witness_script; ///< SHA256 of the missing witnessScript (if any)
 
     SignatureData() {}
     explicit SignatureData(const CScript& script) : scriptSig(script) {}