Merge #15899: rpc: Document iswitness flag and fix bug in converttopsbt

fa499b5f027f77c0bf13699852c8c06f78e27bef rpc: bugfix: Properly use iswitness in converttopsbt (MarcoFalke)
fa5c5cd141f0265a5693234690ac757b811157d8 rpc: Switch touched RPCs to IsValidNumArgs (MarcoFalke)

Pull request description:

  When a serialized transaction has inputs, there is no risk in only trying to deserialize it with witness allowed. (This is how all transactions from p2p are deserialized.) In fact, it would avoid a common issue where a transaction with inputs can be deserialized in two ways:
  * Fixes #12989
  * Fixes #15872
  * Fixes #15701
  * Fixes #13738
  * ...

  When a serialized transaction has no inputs, there is no risk in only trying to deserialze it with witness disallowed. (A transaction without inputs can't have corresponding witness data)

ACKs for commit fa499b:
  meshcollider:
    utACK https://github.com/bitcoin/bitcoin/pull/15899/commits/fa499b5f027f77c0bf13699852c8c06f78e27bef
  ryanofsky:
    utACK fa499b5f027f77c0bf13699852c8c06f78e27bef. Changes since last review: consolidating commits and making iswitness documentation the same across methods.
  PastaPastaPasta:
    utACK fa499b5f027f77c0bf13699852c8c06f78e27bef

Tree-SHA512: a64423a3131f3f0222a40da557c8b590c9ff01b45bcd40796f77a1a64ae74c6680a6be9d01ece95c492dfbcc7e2810409d2c2b336c2894af00bb213972fc85c6

3 files changed, 43 insertions, 24 deletions

diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index 0aad60c743..9da24afe79 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -426,14 +426,17 @@ static UniValue createrawtransaction(const JSONRPCRequest& request)
 
 static UniValue decoderawtransaction(const JSONRPCRequest& request)
 {
-    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
-        throw std::runtime_error(
-            RPCHelpMan{"decoderawtransaction",
+    const RPCHelpMan help{"decoderawtransaction",
                 "\nReturn a JSON object representing the serialized, hex-encoded transaction.\n",
                 {
                     {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction hex string"},
-                    {"iswitness", RPCArg::Type::BOOL, /* default */ "depends on heuristic tests", "Whether the transaction hex is a serialized witness transaction\n"
-            "                         If iswitness is not present, heuristic tests will be used in decoding"},
+                    {"iswitness", RPCArg::Type::BOOL, /* default */ "depends on heuristic tests", "Whether the transaction hex is a serialized witness transaction.\n"
+                        "If iswitness is not present, heuristic tests will be used in decoding.\n"
+                        "If true, only witness deserialization will be tried.\n"
+                        "If false, only non-witness deserialization will be tried.\n"
+                        "This boolean should reflect whether the transaction has inputs\n"
+                        "(e.g. fully valid, or on-chain transactions), if known by the caller."
+                    },
                 },
                 RPCResult{
             "{\n"
@@ -480,7 +483,11 @@ static UniValue decoderawtransaction(const JSONRPCRequest& request)
                     HelpExampleCli("decoderawtransaction", "\"hexstring\"")
             + HelpExampleRpc("decoderawtransaction", "\"hexstring\"")
                 },
-            }.ToString());
+    };
+
+    if (request.fHelp || !help.IsValidNumArgs(request.params.size())) {
+        throw std::runtime_error(help.ToString());
+    }
 
     RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VBOOL});
 
@@ -1417,19 +1424,20 @@ UniValue createpsbt(const JSONRPCRequest& request)
 
 UniValue converttopsbt(const JSONRPCRequest& request)
 {
-    if (request.fHelp || request.params.size() < 1 || request.params.size() > 3)
-        throw std::runtime_error(
-            RPCHelpMan{"converttopsbt",
+    const RPCHelpMan help{"converttopsbt",
                 "\nConverts a network serialized transaction to a PSBT. This should be used only with createrawtransaction and fundrawtransaction\n"
                 "createpsbt and walletcreatefundedpsbt should be used for new applications.\n",
                 {
                     {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The hex string of a raw transaction"},
-                    {"permitsigdata", RPCArg::Type::BOOL, /* default */ "false", "If true, any signatures in the input will be discarded and conversion.\n"
+                    {"permitsigdata", RPCArg::Type::BOOL, /* default */ "false", "If true, any signatures in the input will be discarded and conversion\n"
                             "                              will continue. If false, RPC will fail if any signatures are present."},
                     {"iswitness", RPCArg::Type::BOOL, /* default */ "depends on heuristic tests", "Whether the transaction hex is a serialized witness transaction.\n"
-                            "                              If iswitness is not present, heuristic tests will be used in decoding. If true, only witness deserializaion\n"
-                            "                              will be tried. If false, only non-witness deserialization will be tried. Only has an effect if\n"
-                            "                              permitsigdata is true."},
+                        "If iswitness is not present, heuristic tests will be used in decoding.\n"
+                        "If true, only witness deserialization will be tried.\n"
+                        "If false, only non-witness deserialization will be tried.\n"
+                        "This boolean should reflect whether the transaction has inputs\n"
+                        "(e.g. fully valid, or on-chain transactions), if known by the caller."
+                    },
                 },
                 RPCResult{
                             "  \"psbt\"        (string)  The resulting raw transaction (base64-encoded string)\n"
@@ -1440,8 +1448,11 @@ UniValue converttopsbt(const JSONRPCRequest& request)
                             "\nConvert the transaction to a PSBT\n"
                             + HelpExampleCli("converttopsbt", "\"rawtransaction\"")
                 },
-            }.ToString());
+    };
 
+    if (request.fHelp || !help.IsValidNumArgs(request.params.size())) {
+        throw std::runtime_error(help.ToString());
+    }
 
     RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VBOOL, UniValue::VBOOL}, true);
 
@@ -1450,8 +1461,8 @@ UniValue converttopsbt(const JSONRPCRequest& request)
     bool permitsigdata = request.params[1].isNull() ? false : request.params[1].get_bool();
     bool witness_specified = !request.params[2].isNull();
     bool iswitness = witness_specified ? request.params[2].get_bool() : false;
-    bool try_witness = permitsigdata ? (witness_specified ? iswitness : true) : false;
-    bool try_no_witness = permitsigdata ? (witness_specified ? !iswitness : true) : true;
+    const bool try_witness = witness_specified ? iswitness : true;
+    const bool try_no_witness = witness_specified ? !iswitness : true;
     if (!DecodeHexTx(tx, request.params[0].get_str(), try_no_witness, try_witness)) {
         throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
     }
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index 29880002b3..f9baabeda4 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -3106,9 +3106,7 @@ static UniValue fundrawtransaction(const JSONRPCRequest& request)
         return NullUniValue;
     }
 
-    if (request.fHelp || request.params.size() < 1 || request.params.size() > 3)
-        throw std::runtime_error(
-            RPCHelpMan{"fundrawtransaction",
+    const RPCHelpMan help{"fundrawtransaction",
                 "\nAdd inputs to a transaction until it has enough in value to meet its out value.\n"
                 "This will not modify existing inputs, and will add at most one change output to the outputs.\n"
                 "No existing outputs will be modified unless \"subtractFeeFromOutputs\" is specified.\n"
@@ -3147,8 +3145,13 @@ static UniValue fundrawtransaction(const JSONRPCRequest& request)
                             "         \"CONSERVATIVE\""},
                         },
                         "options"},
-                    {"iswitness", RPCArg::Type::BOOL, /* default */ "depends on heuristic tests", "Whether the transaction hex is a serialized witness transaction \n"
-                            "                              If iswitness is not present, heuristic tests will be used in decoding"},
+                    {"iswitness", RPCArg::Type::BOOL, /* default */ "depends on heuristic tests", "Whether the transaction hex is a serialized witness transaction.\n"
+                        "If iswitness is not present, heuristic tests will be used in decoding.\n"
+                        "If true, only witness deserialization will be tried.\n"
+                        "If false, only non-witness deserialization will be tried.\n"
+                        "This boolean should reflect whether the transaction has inputs\n"
+                        "(e.g. fully valid, or on-chain transactions), if known by the caller."
+                    },
                 },
                 RPCResult{
                             "{\n"
@@ -3167,7 +3170,11 @@ static UniValue fundrawtransaction(const JSONRPCRequest& request)
                             "\nSend the transaction\n"
                             + HelpExampleCli("sendrawtransaction", "\"signedtransactionhex\"")
                                 },
-                            }.ToString());
+    };
+
+    if (request.fHelp || !help.IsValidNumArgs(request.params.size())) {
+        throw std::runtime_error(help.ToString());
+    }
 
     RPCTypeCheck(request.params, {UniValue::VSTR, UniValueType(), UniValue::VBOOL});
 
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index 8a7ea7aa58..430be6dd37 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -152,9 +152,10 @@ class PSBTTest(BitcoinTestFramework):
 
         # Make sure that a non-psbt with signatures cannot be converted
         # Error could be either "TX decode failed" (segwit inputs causes parsing to fail) or "Inputs must not have scriptSigs and scriptWitnesses"
+        # We must set iswitness=True because the serialized transaction has inputs and is therefore a witness transaction
         signedtx = self.nodes[0].signrawtransactionwithwallet(rawtx['hex'])
-        assert_raises_rpc_error(-22, "", self.nodes[0].converttopsbt, signedtx['hex'])
-        assert_raises_rpc_error(-22, "", self.nodes[0].converttopsbt, signedtx['hex'], False)
+        assert_raises_rpc_error(-22, "", self.nodes[0].converttopsbt, hexstring=signedtx['hex'], iswitness=True)
+        assert_raises_rpc_error(-22, "", self.nodes[0].converttopsbt, hexstring=signedtx['hex'], permitsigdata=False, iswitness=True)
         # Unless we allow it to convert and strip signatures
         self.nodes[0].converttopsbt(signedtx['hex'], True)