Merge bitcoin/bitcoin#28492: RPC: descriptorprocesspsbt returns hex encoded tx if complete

a99e9e6 doc: add release note (ismaelsadeeq)
2b4edf8 test: check `descriptorprocesspsbt` return hex encoded tx (ismaelsadeeq)
c405207 rpc: `descriptorprocesspsbt` return hex encoded tx (ismaelsadeeq)

Pull request description:

  Coming from [#28414 comment](bitcoin/bitcoin#28414 (review)) Same thing also for `descriptorprocesspsbt`.

  Before this PR `descriptorprocesspsbt` returns a boolean `complete` which indicates that the psbt is final, users then have to call `finalizepsbt` to get the hex encoded network transaction.

  In this PR if the psbt is complete the return object also has the hex encoded network transaction ready for broadcast with `sendrawtransaction`.

  This save users calling `finalizepsbt` with the descriptor, if it is already complete.

ACKs for top commit:
  achow101:
    ACK a99e9e6
  pinheadmz:
    ACK a99e9e6
  ishaanam:
    ACK a99e9e6

Tree-SHA512: c3f1b1391d4df05216c463127cd593f8703840430a99febb54890bc66fadabf9d9530860605f347ec54c1694019173247a0e7a9eb879d3cbb420f9e8d9839b75

Author: achow101

doc/release-notes-28414.md

@@ -1,5 +1,6 @@
 RPC Wallet
 ----------
 
-- RPC `walletprocesspsbt` return object now includes field `hex` (if the transaction
-is complete) containing the serialized transaction suitable for RPC `sendrawtransaction`. (#28414)
+- RPC `walletprocesspsbt`, and `descriptorprocesspsbt` return object now includes field `hex` (if the transaction
+is complete) containing the serialized transaction suitable for RPC `sendrawtransaction`.
+

src/rpc/rawtransaction.cpp

@@ -1949,6 +1949,7 @@ RPCHelpMan descriptorprocesspsbt()
                     {
                         {RPCResult::Type::STR, "psbt", "The base64-encoded partially signed transaction"},
                         {RPCResult::Type::BOOL, "complete", "If the transaction has a complete set of signatures"},
+                        {RPCResult::Type::STR_HEX, "hex", /*optional=*/true, "The hex-encoded network transaction if complete"},
                     }
                 },
                 RPCExamples{
@@ -1989,7 +1990,14 @@ RPCHelpMan descriptorprocesspsbt()
 
     result.pushKV("psbt", EncodeBase64(ssTx));
     result.pushKV("complete", complete);
-
+    if (complete) {
+        CMutableTransaction mtx;
+        PartiallySignedTransaction psbtx_copy = psbtx;
+        CHECK_NONFATAL(FinalizeAndExtractPSBT(psbtx_copy, mtx));
+        CDataStream ssTx_final(SER_NETWORK, PROTOCOL_VERSION);
+        ssTx_final << mtx;
+        result.pushKV("hex", HexStr(ssTx_final));
+    }
     return result;
 },
     };

test/functional/rpc_psbt.py

@@ -978,17 +978,22 @@ def test_psbt_input_keys(psbt_input, keys):
         test_psbt_input_keys(decoded['inputs'][0], ['witness_utxo', 'non_witness_utxo'])
 
         # Test that the psbt is not finalized and does not have bip32_derivs unless specified
-        psbt = self.nodes[2].descriptorprocesspsbt(psbt=psbt, descriptors=[descriptor], sighashtype="ALL", bip32derivs=True, finalize=False)["psbt"]
-        decoded = self.nodes[2].decodepsbt(psbt)
+        processed_psbt = self.nodes[2].descriptorprocesspsbt(psbt=psbt, descriptors=[descriptor], sighashtype="ALL", bip32derivs=True, finalize=False)
+        decoded = self.nodes[2].decodepsbt(processed_psbt['psbt'])
         test_psbt_input_keys(decoded['inputs'][0], ['witness_utxo', 'non_witness_utxo', 'partial_signatures', 'bip32_derivs'])
 
-        psbt = self.nodes[2].descriptorprocesspsbt(psbt=psbt, descriptors=[descriptor], sighashtype="ALL", bip32derivs=False, finalize=True)["psbt"]
-        decoded = self.nodes[2].decodepsbt(psbt)
+        # If psbt not finalized, test that result does not have hex
+        assert "hex" not in processed_psbt
+
+        processed_psbt = self.nodes[2].descriptorprocesspsbt(psbt=psbt, descriptors=[descriptor], sighashtype="ALL", bip32derivs=False, finalize=True)
+        decoded = self.nodes[2].decodepsbt(processed_psbt['psbt'])
         test_psbt_input_keys(decoded['inputs'][0], ['witness_utxo', 'non_witness_utxo', 'final_scriptwitness'])
 
+        # Test psbt is complete
+        assert_equal(processed_psbt['complete'], True)
+
         # Broadcast transaction
-        rawtx = self.nodes[2].finalizepsbt(psbt)["hex"]
-        self.nodes[2].sendrawtransaction(rawtx)
+        self.nodes[2].sendrawtransaction(processed_psbt['hex'])
 
         self.log.info("Test descriptorprocesspsbt raises if an invalid sighashtype is passed")
         assert_raises_rpc_error(-8, "all is not a valid sighash parameter.", self.nodes[2].descriptorprocesspsbt, psbt, [descriptor], sighashtype="all")