Implement joinpsbts RPC and tests

Adds a joinpsbts RPC which combines multiple distinct PSBTs into
one PSBT.

src/psbt.cpp

@@ -42,6 +42,26 @@ 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 PSBTInput::IsNull() const
 {
  return !non_witness_utxo && witness_utxo.IsNull() && partial_sigs.empty() && unknown.empty() && hd_keypaths.empty() && redeem_script.empty() && witness_script.empty();

src/psbt.h

@@ -389,6 +389,8 @@ 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);

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"},

src/rpc/rawtransaction.cpp

@@ -1755,6 +1755,80 @@ UniValue utxoupdatepsbt(const JSONRPCRequest& request)
  return EncodeBase64((unsigned char*)ssTx.data(), ssTx.size());
 }
 
+UniValue joinpsbts(const JSONRPCRequest& request)
+{
+ if (request.fHelp || request.params.size() != 1) {
+ throw std::runtime_error(
+ RPCHelpMan{"joinpsbts",
+ "\nJoins multiple distinct PSBTs with different inputs and outputs into one PSBT with inputs and outputs from all of the PSBTs\n"
+ "No input in any of the PSBTs can be in more than one of the PSBTs.\n",
+ {
+ {"txs", RPCArg::Type::ARR, RPCArg::Optional::NO, "A json array of base64 strings of partially signed transactions",
+ {
+ {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "A base64 string of a PSBT"}
+ }}
+ },
+ RPCResult {
+ " \"psbt\" (string) The base64-encoded partially signed transaction\n"
+ },
+ RPCExamples {
+ HelpExampleCli("joinpsbts", "\"psbt\"")
+ }}.ToString());
+ }
+
+ RPCTypeCheck(request.params, {UniValue::VARR}, true);
+
+ // Unserialize the transactions
+ std::vector<PartiallySignedTransaction> psbtxs;
+ UniValue txs = request.params[0].get_array();
+
+ if (txs.size() <= 1) {
+ throw JSONRPCError(RPC_INVALID_PARAMETER, "At least two PSBTs are required to join PSBTs.");
+ }
+
+ int32_t best_version = 1;
+ uint32_t best_locktime = 0xffffffff;
+ for (unsigned int i = 0; i < txs.size(); ++i) {
+ PartiallySignedTransaction psbtx;
+ std::string error;
+ if (!DecodeBase64PSBT(psbtx, txs[i].get_str(), error)) {
+ throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
+ }
+ psbtxs.push_back(psbtx);
+ // Choose the highest version number
+ if (psbtx.tx->nVersion > best_version) {
+ best_version = psbtx.tx->nVersion;
+ }
+ // Choose the lowest lock time
+ if (psbtx.tx->nLockTime < best_locktime) {
+ best_locktime = psbtx.tx->nLockTime;
+ }
+ }
+
+ // Create a blank psbt where everything will be added
+ PartiallySignedTransaction merged_psbt;
+ merged_psbt.tx = CMutableTransaction();
+ merged_psbt.tx->nVersion = best_version;
+ merged_psbt.tx->nLockTime = best_locktime;
+
+ // Merge
+ for (auto& psbt : psbtxs) {
+ for (unsigned int i = 0; i < psbt.tx->vin.size(); ++i) {
+ if (!merged_psbt.AddInput(psbt.tx->vin[i], psbt.inputs[i])) {
+ throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Input %s:%d exists in multiple PSBTs", psbt.tx->vin[i].prevout.hash.ToString().c_str(), psbt.tx->vin[i].prevout.n));
+ }
+ }
+ for (unsigned int i = 0; i < psbt.tx->vout.size(); ++i) {
+ merged_psbt.AddOutput(psbt.tx->vout[i], psbt.outputs[i]);
+ }
+ merged_psbt.unknown.insert(psbt.unknown.begin(), psbt.unknown.end());
+ }
+
+ CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
+ ssTx << merged_psbt;
+ return EncodeBase64((unsigned char*)ssTx.data(), ssTx.size());
+}
+
 // clang-format off
 static const CRPCCommand commands[] =
 { // category name actor (function) argNames
@@ -1774,6 +1848,7 @@ static const CRPCCommand commands[] =
  { "rawtransactions", "createpsbt", &createpsbt, {"inputs","outputs","locktime","replaceable"} },
  { "rawtransactions", "converttopsbt", &converttopsbt, {"hexstring","permitsigdata","iswitness"} },
  { "rawtransactions", "utxoupdatepsbt", &utxoupdatepsbt, {"psbt"} },
+ { "rawtransactions", "joinpsbts", &joinpsbts, {"txs"} },
 
  { "blockchain", "gettxoutproof", &gettxoutproof, {"txids", "blockhash"} },
  { "blockchain", "verifytxoutproof", &verifytxoutproof, {"proof"} },

test/functional/rpc_psbt.py

@@ -321,6 +321,23 @@ def run_test(self):
  assert "witness_utxo" not in decoded['inputs'][1] and "non_witness_utxo" not in decoded['inputs'][1]
  assert "witness_utxo" not in decoded['inputs'][2] and "non_witness_utxo" not in decoded['inputs'][2]
 
+ # Two PSBTs with a common input should not be joinable
+ psbt1 = self.nodes[1].createpsbt([{"txid":txid1, "vout":vout1}], {self.nodes[0].getnewaddress():Decimal('10.999')})
+ assert_raises_rpc_error(-8, "exists in multiple PSBTs", self.nodes[1].joinpsbts, [psbt1, updated])
+
+ # Join two distinct PSBTs
+ addr4 = self.nodes[1].getnewaddress("", "p2sh-segwit")
+ txid4 = self.nodes[0].sendtoaddress(addr4, 5)
+ vout4 = find_output(self.nodes[0], txid4, 5)
+ self.nodes[0].generate(6)
+ self.sync_all()
+ psbt2 = self.nodes[1].createpsbt([{"txid":txid4, "vout":vout4}], {self.nodes[0].getnewaddress():Decimal('4.999')})
+ psbt2 = self.nodes[1].walletprocesspsbt(psbt2)['psbt']
+ psbt2_decoded = self.nodes[0].decodepsbt(psbt2)
+ assert "final_scriptwitness" in psbt2_decoded['inputs'][0] and "final_scriptSig" in psbt2_decoded['inputs'][0]
+ joined = self.nodes[0].joinpsbts([psbt, psbt2])
+ joined_decoded = self.nodes[0].decodepsbt(joined)
+ assert len(joined_decoded['inputs']) == 4 and len(joined_decoded['outputs']) == 2 and "final_scriptwitness" not in joined_decoded['inputs'][3] and "final_scriptSig" not in joined_decoded['inputs'][3]
 
 
 if __name__ == '__main__':