rpc: decode Miniscript descriptor when possible in decodescript

The descriptor inference logic would previously always use a dummy
signing provider and would never analyze the witness script of a P2WSH
scriptPubKey.

Note even a valid Miniscript might not always be decodable from Script
without more contextual information (for instance the key preimage for a
pk_h).

src/core_io.h

@@ -15,6 +15,7 @@ class CBlockHeader;
 class CScript;
 class CTransaction;
 struct CMutableTransaction;
+class SigningProvider;
 class uint256;
 class UniValue;
 class CTxUndo;
@@ -52,7 +53,7 @@ UniValue ValueFromAmount(const CAmount amount);
 std::string FormatScript(const CScript& script);
 std::string EncodeHexTx(const CTransaction& tx, const int serializeFlags = 0);
 std::string SighashToStr(unsigned char sighash_type);
-void ScriptToUniv(const CScript& script, UniValue& out, bool include_hex = true, bool include_address = false);
+void ScriptToUniv(const CScript& script, UniValue& out, bool include_hex = true, bool include_address = false, const SigningProvider* provider = nullptr);
 void TxToUniv(const CTransaction& tx, const uint256& block_hash, UniValue& entry, bool include_hex = true, int serialize_flags = 0, const CTxUndo* txundo = nullptr, TxVerbosity verbosity = TxVerbosity::SHOW_DETAILS);
 
 #endif // BITCOIN_CORE_IO_H

src/core_write.cpp

@@ -147,13 +147,13 @@ std::string EncodeHexTx(const CTransaction& tx, const int serializeFlags)
     return HexStr(ssTx);
 }
 
-void ScriptToUniv(const CScript& script, UniValue& out, bool include_hex, bool include_address)
+void ScriptToUniv(const CScript& script, UniValue& out, bool include_hex, bool include_address, const SigningProvider* provider)
 {
     CTxDestination address;
 
     out.pushKV("asm", ScriptToAsmStr(script));
     if (include_address) {
-        out.pushKV("desc", InferDescriptor(script, DUMMY_SIGNING_PROVIDER)->ToString());
+        out.pushKV("desc", InferDescriptor(script, provider ? *provider : DUMMY_SIGNING_PROVIDER)->ToString());
     }
     if (include_hex) {
         out.pushKV("hex", HexStr(script));

src/rpc/rawtransaction.cpp

@@ -522,15 +522,17 @@ static RPCHelpMan decodescript()
         if (can_wrap_P2WSH) {
             UniValue sr(UniValue::VOBJ);
             CScript segwitScr;
+            FillableSigningProvider provider;
             if (which_type == TxoutType::PUBKEY) {
                 segwitScr = GetScriptForDestination(WitnessV0KeyHash(Hash160(solutions_data[0])));
             } else if (which_type == TxoutType::PUBKEYHASH) {
                 segwitScr = GetScriptForDestination(WitnessV0KeyHash(uint160{solutions_data[0]}));
             } else {
                 // Scripts that are not fit for P2WPKH are encoded as P2WSH.
+                provider.AddCScript(script);
                 segwitScr = GetScriptForDestination(WitnessV0ScriptHash(script));
             }
-            ScriptToUniv(segwitScr, /*out=*/sr, /*include_hex=*/true, /*include_address=*/true);
+            ScriptToUniv(segwitScr, /*out=*/sr, /*include_hex=*/true, /*include_address=*/true, /*provider=*/&provider);
             sr.pushKV("p2sh-segwit", EncodeDestination(ScriptHash(segwitScr)));
             r.pushKV("segwit", sr);
         }

test/functional/data/rpc_decodescript.json

@@ -69,7 +69,7 @@
             "p2sh": "2N34iiGoUUkVSPiaaTFpJjB1FR9TXQu3PGM",
             "segwit": {
                 "asm": "0 96c2368fc30514a438a8bd909f93c49a1549d77198ccbdb792043b666cb24f42",
-                "desc": "addr(bcrt1qjmprdr7rq522gw9ghkgfly7yng25n4m3nrxtmdujqsakvm9jfapqk795l5)#5akkdska",
+                "desc": "wsh(raw(02eeee))#gtay4y0z",
                 "hex": "002096c2368fc30514a438a8bd909f93c49a1549d77198ccbdb792043b666cb24f42",
                 "address": "bcrt1qjmprdr7rq522gw9ghkgfly7yng25n4m3nrxtmdujqsakvm9jfapqk795l5",
                 "type": "witness_v0_scripthash",

test/functional/rpc_decodescript.py

@@ -263,6 +263,16 @@ class DecodeScriptTest(BitcoinTestFramework):
             rpc_result = self.nodes[0].decodescript(script)
             assert_equal(result, rpc_result)
 
+    def decodescript_miniscript(self):
+        """Check that a Miniscript is decoded when possible under P2WSH context."""
+        # Sourced from https://github.com/bitcoin/bitcoin/pull/27037#issuecomment-1416151907.
+        # Miniscript-compatible offered HTLC
+        res = self.nodes[0].decodescript("82012088a914ffffffffffffffffffffffffffffffffffffffff88210250929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0ad51b2")
+        assert res["segwit"]["desc"] == "wsh(and_v(and_v(v:hash160(ffffffffffffffffffffffffffffffffffffffff),v:pk(0250929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0)),older(1)))#gm8xz4fl"
+        # Miniscript-incompatible offered HTLC
+        res = self.nodes[0].decodescript("82012088a914ffffffffffffffffffffffffffffffffffffffff882102ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffacb2")
+        assert res["segwit"]["desc"] == "wsh(raw(82012088a914ffffffffffffffffffffffffffffffffffffffff882102ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffacb2))#ra6w2xa7"
+
     def run_test(self):
         self.log.info("Test decoding of standard input scripts [scriptSig]")
         self.decodescript_script_sig()
@@ -272,6 +282,8 @@ class DecodeScriptTest(BitcoinTestFramework):
         self.decoderawtransaction_asm_sighashtype()
         self.log.info("Data-driven tests")
         self.decodescript_datadriven_tests()
+        self.log.info("Miniscript descriptor decoding")
+        self.decodescript_miniscript()
 
 if __name__ == '__main__':
     DecodeScriptTest().main()