Merge #13932: Additional utility RPCs for PSBT

540729e Implement analyzepsbt RPC and tests (Andrew Chow)
77542cf Move PSBT UTXO fetching to a separate method (Andrew Chow)
cb40b3a Figure out what is missing during signing (Andrew Chow)
08f749c Implement joinpsbts RPC and tests (Andrew Chow)
7344a7b Implement utxoupdatepsbt RPC and tests (Andrew Chow)

Pull request description:

  This PR adds 3 new utility RPCs for interacting with PSBTs.

  `utxoupdatepsbt` updates a PSBT with UTXO information from the node. It only works with witness UTXOs because full transactions (as would be needed for non-witness UTXOs) are not available unless txindex is enabled.

  `joinpsbts` joins the inputs from multiple distinct PSBTs into one PSBT. e.g. if PSBT 1 has inputs 1 and 2, and PSBT 2 has inputs 3 and 4, `joinpsbts` would create a new PSBT with inputs 1, 2, 3, and 4.

  `analyzepsbt` analyzes a PSBT and determines the current state of it and all of its inputs, and the next step that needs to be done.

Tree-SHA512: 3c1fa302201abca76a8901d0c2be7b4ccbce334d989533c215f8b3e50e22f2f018ce6209544b26789f58f5980a253c0655111e1e20d47d5656e0414c64891a5c

src/psbt.cpp

@@ -42,6 +42,40 @@ bool PartiallySignedTransaction::IsSane() const
     return true;
 }
 
+bool PartiallySignedTransaction::AddInput(const CTxIn& txin, PSBTInput& psbtin)
+{
+    if (std::find(tx->vin.begin(), tx->vin.end(), txin) != tx->vin.end()) {
+        return false;
+    }
+    tx->vin.push_back(txin);
+    psbtin.partial_sigs.clear();
+    psbtin.final_script_sig.clear();
+    psbtin.final_script_witness.SetNull();
+    inputs.push_back(psbtin);
+    return true;
+}
+
+bool PartiallySignedTransaction::AddOutput(const CTxOut& txout, const PSBTOutput& psbtout)
+{
+    tx->vout.push_back(txout);
+    outputs.push_back(psbtout);
+    return true;
+}
+
+bool PartiallySignedTransaction::GetInputUTXO(CTxOut& utxo, int input_index) const
+{
+    PSBTInput input = inputs[input_index];
+    int prevout_index = tx->vin[input_index].prevout.n;
+    if (input.non_witness_utxo) {
+        utxo = input.non_witness_utxo->vout[prevout_index];
+    } else if (!input.witness_utxo.IsNull()) {
+        utxo = input.witness_utxo;
+    } else {
+        return false;
+    }
+    return true;
+}
+
 bool PSBTInput::IsNull() const
 {
     return !non_witness_utxo && witness_utxo.IsNull() && partial_sigs.empty() && unknown.empty() && hd_keypaths.empty() && redeem_script.empty() && witness_script.empty();
@@ -171,13 +205,12 @@ 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;
@@ -217,9 +250,14 @@ 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);
@@ -230,6 +268,14 @@ 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;
 }
 

src/psbt.h

@@ -389,9 +389,19 @@ struct PartiallySignedTransaction
       * same actual Bitcoin transaction.) Returns true if the merge succeeded, false otherwise. */
     NODISCARD bool Merge(const PartiallySignedTransaction& psbt);
     bool IsSane() const;
+    bool AddInput(const CTxIn& txin, PSBTInput& psbtin);
+    bool AddOutput(const CTxOut& txout, const PSBTOutput& psbtout);
     PartiallySignedTransaction() {}
     PartiallySignedTransaction(const PartiallySignedTransaction& psbt_in) : tx(psbt_in.tx), inputs(psbt_in.inputs), outputs(psbt_in.outputs), unknown(psbt_in.unknown) {}
     explicit PartiallySignedTransaction(const CMutableTransaction& tx);
+    /**
+     * Finds the UTXO for a given input index
+     *
+     * @param[out] utxo The UTXO of the input if found
+     * @param[in] input_index Index of the input to retrieve the UTXO of
+     * @return Whether the UTXO for the specified input was found
+     */
+    bool GetInputUTXO(CTxOut& utxo, int input_index) const;
 
     template <typename Stream>
     inline void Serialize(Stream& s) const {
@@ -542,7 +552,7 @@ 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.

src/rpc/client.cpp

@@ -112,6 +112,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "createpsbt", 2, "locktime" },
     { "createpsbt", 3, "replaceable" },
     { "combinepsbt", 0, "txs"},
+    { "joinpsbts", 0, "txs"},
     { "finalizepsbt", 1, "extract"},
     { "converttopsbt", 1, "permitsigdata"},
     { "converttopsbt", 2, "iswitness"},