wallet rpc: return final tx hex from walletprocesspsbt if complete

src/wallet/rpc/spend.cpp

@@ -1566,6 +1566,7 @@ RPCHelpMan walletprocesspsbt()
                     {
                         {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{
@@ -1609,6 +1610,14 @@ RPCHelpMan walletprocesspsbt()
     ssTx << psbtx;
     result.pushKV("psbt", EncodeBase64(ssTx.str()));
     result.pushKV("complete", complete);
+    if (complete) {
+        CMutableTransaction mtx;
+        // Returns true if complete, which we already think it is.
+        CHECK_NONFATAL(FinalizeAndExtractPSBT(psbtx, mtx));
+        CDataStream ssTx_final(SER_NETWORK, PROTOCOL_VERSION);
+        ssTx_final << mtx;
+        result.pushKV("hex", HexStr(ssTx_final));
+    }
 
     return result;
 },

test/functional/rpc_psbt.py

@@ -217,12 +217,21 @@ class PSBTTest(BitcoinTestFramework):
 
         self.nodes[0].walletpassphrase(passphrase="password", timeout=1000000)
 
-        # Sign the transaction and send
-        signed_tx = self.nodes[0].walletprocesspsbt(psbt=psbtx, finalize=False)['psbt']
-        finalized_tx = self.nodes[0].walletprocesspsbt(psbt=psbtx, finalize=True)['psbt']
-        assert signed_tx != finalized_tx
-        final_tx = self.nodes[0].finalizepsbt(signed_tx)['hex']
-        self.nodes[0].sendrawtransaction(final_tx)
+        # Sign the transaction but don't finalize
+        processed_psbt = self.nodes[0].walletprocesspsbt(psbt=psbtx, finalize=False)
+        assert "hex" not in processed_psbt
+        signed_psbt = processed_psbt['psbt']
+
+        # Finalize and send
+        finalized_hex = self.nodes[0].finalizepsbt(signed_psbt)['hex']
+        self.nodes[0].sendrawtransaction(finalized_hex)
+
+        # Alternative method: sign AND finalize in one command
+        processed_finalized_psbt = self.nodes[0].walletprocesspsbt(psbt=psbtx, finalize=True)
+        finalized_psbt = processed_finalized_psbt['psbt']
+        finalized_psbt_hex = processed_finalized_psbt['hex']
+        assert signed_psbt != finalized_psbt
+        assert finalized_psbt_hex == finalized_hex
 
         # Manually selected inputs can be locked:
         assert_equal(len(self.nodes[0].listlockunspent()), 0)