rpc: Allow named and positional arguments to be used together

It's nice to be able to use named options and positional arguments together.

Most shell tools accept both, and python functions combine options and
arguments allowing them to be passed with even more flexibility. This change
adds support for python's approach so as a motivating example:

    bitcoin-cli -named createwallet wallet_name=mywallet load_on_startup=1

Can be shortened to:

    bitcoin-cli -named createwallet mywallet load_on_startup=1

JSON-RPC standard doesn't have a convention for passing named and positional
parameters together, so this implementation makes one up and interprets any
unused "args" named parameter as a positional parameter array.

doc/JSON-RPC-interface.md

@@ -5,6 +5,28 @@ The headless daemon `bitcoind` has the JSON-RPC API enabled by default, the GUI
 option. In the GUI it is possible to execute RPC methods in the Debug Console
 Dialog.
 
+## Parameter passing
+
+The JSON-RPC server supports both _by-position_ and _by-name_ [parameter
+structures](https://www.jsonrpc.org/specification#parameter_structures)
+described in the JSON-RPC specification. For extra convenience, to avoid the
+need to name every parameter value, all RPC methods accept a named parameter
+called `args`, which can be set to an array of initial positional values that
+are combined with named values.
+
+Examples:
+
+```sh
+# "params": ["mywallet", false, false, "", false, false, true]
+bitcoin-cli createwallet mywallet false false "" false false true
+
+# "params": {"wallet_name": "mywallet", "load_on_startup": true}
+bitcoin-cli -named createwallet wallet_name=mywallet load_on_startup=true
+
+# "params": {"args": ["mywallet"], "load_on_startup": true}
+bitcoin-cli -named createwallet mywallet load_on_startup=true
+```
+
 ## Versioning
 
 The RPC interface might change from one major version of Bitcoin Core to the

doc/release-notes-19762.md

@@ -0,0 +1,19 @@
+JSON-RPC
+---
+
+All JSON-RPC methods accept a new [named
+parameter](JSON-RPC-interface.md#parameter-passing) called `args` that can
+contain positional parameter values. This is a convenience to allow some
+parameter values to be passed by name without having to name every value. The
+python test framework and `bitcoin-cli` tool both take advantage of this, so
+for example:
+
+```sh
+bitcoin-cli -named createwallet wallet_name=mywallet load_on_startup=1
+```
+
+Can now be shortened to:
+
+```sh
+bitcoin-cli -named createwallet mywallet load_on_startup=1
+```

src/rpc/client.cpp

@@ -277,11 +277,13 @@ UniValue RPCConvertValues(const std::string &strMethod, const std::vector<std::s
 UniValue RPCConvertNamedValues(const std::string &strMethod, const std::vector<std::string> &strParams)
 {
     UniValue params(UniValue::VOBJ);
+    UniValue positional_args{UniValue::VARR};
 
     for (const std::string &s: strParams) {
         size_t pos = s.find('=');
         if (pos == std::string::npos) {
-            throw(std::runtime_error("No '=' in named argument '"+s+"', this needs to be present for every argument (even if it is empty)"));
+            positional_args.push_back(rpcCvtTable.convert(strMethod, positional_args.size()) ? ParseNonRFCJSONValue(s) : s);
+            continue;
         }
 
         std::string name = s.substr(0, pos);
@@ -296,5 +298,9 @@ UniValue RPCConvertNamedValues(const std::string &strMethod, const std::vector<s
         }
     }
 
+    if (!positional_args.empty()) {
+        params.pushKV("args", positional_args);
+    }
+
     return params;
 }

src/rpc/server.cpp

@@ -401,8 +401,16 @@ static inline JSONRPCRequest transformNamedArguments(const JSONRPCRequest& in, c
     for (size_t i=0; i<keys.size(); ++i) {
         argsIn[keys[i]] = &values[i];
     }
-    // Process expected parameters.
+    // Process expected parameters. If any parameters were left unspecified in
+    // the request before a parameter that was specified, null values need to be
+    // inserted at the unspecifed parameter positions, and the "hole" variable
+    // below tracks the number of null values that need to be inserted.
+    // The "initial_hole_size" variable stores the size of the initial hole,
+    // i.e. how many initial positional arguments were left unspecified. This is
+    // used after the for-loop to add initial positional arguments from the
+    // "args" parameter, if present.
     int hole = 0;
+    int initial_hole_size = 0;
     for (const std::string &argNamePattern: argNames) {
         std::vector<std::string> vargNames = SplitString(argNamePattern, '|');
         auto fr = argsIn.end();
@@ -424,6 +432,24 @@ static inline JSONRPCRequest transformNamedArguments(const JSONRPCRequest& in, c
             argsIn.erase(fr);
         } else {
             hole += 1;
+            if (out.params.empty()) initial_hole_size = hole;
+        }
+    }
+    // If leftover "args" param was found, use it as a source of positional
+    // arguments and add named arguments after. This is a convenience for
+    // clients that want to pass a combination of named and positional
+    // arguments as described in doc/JSON-RPC-interface.md#parameter-passing
+    auto positional_args{argsIn.extract("args")};
+    if (positional_args && positional_args.mapped()->isArray()) {
+        const bool has_named_arguments{initial_hole_size < (int)argNames.size()};
+        if (initial_hole_size < (int)positional_args.mapped()->size() && has_named_arguments) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "Parameter " + argNames[initial_hole_size] + " specified twice both as positional and named argument");
+        }
+        // Assign positional_args to out.params and append named_args after.
+        UniValue named_args{std::move(out.params)};
+        out.params = *positional_args.mapped();
+        for (size_t i{out.params.size()}; i < named_args.size(); ++i) {
+            out.params.push_back(named_args[i]);
         }
     }
     // If there are still arguments in the argsIn map, this is an error.

src/test/rpc_tests.cpp

@@ -17,12 +17,49 @@
 
 #include <boost/test/unit_test.hpp>
 
+static UniValue JSON(std::string_view json)
+{
+    UniValue value;
+    BOOST_CHECK(value.read(json.data(), json.size()));
+    return value;
+}
+
+class HasJSON
+{
+public:
+    explicit HasJSON(std::string json) : m_json(std::move(json)) {}
+    bool operator()(const UniValue& value) const
+    {
+        std::string json{value.write()};
+        BOOST_CHECK_EQUAL(json, m_json);
+        return json == m_json;
+    };
+
+private:
+    const std::string m_json;
+};
+
 class RPCTestingSetup : public TestingSetup
 {
 public:
+    UniValue TransformParams(const UniValue& params, std::vector<std::string> arg_names) const;
     UniValue CallRPC(std::string args);
 };
 
+UniValue RPCTestingSetup::TransformParams(const UniValue& params, std::vector<std::string> arg_names) const
+{
+    UniValue transformed_params;
+    CRPCTable table;
+    CRPCCommand command{"category", "method", [&](const JSONRPCRequest& request, UniValue&, bool) -> bool { transformed_params = request.params; return true; }, arg_names, /*unique_id=*/0};
+    table.appendCommand("method", &command);
+    JSONRPCRequest request;
+    request.strMethod = "method";
+    request.params = params;
+    if (RPCIsInWarmup(nullptr)) SetRPCWarmupFinished();
+    table.execute(request);
+    return transformed_params;
+}
+
 UniValue RPCTestingSetup::CallRPC(std::string args)
 {
     std::vector<std::string> vArgs{SplitString(args, ' ')};
@@ -45,6 +82,29 @@ UniValue RPCTestingSetup::CallRPC(std::string args)
 
 BOOST_FIXTURE_TEST_SUITE(rpc_tests, RPCTestingSetup)
 
+BOOST_AUTO_TEST_CASE(rpc_namedparams)
+{
+    const std::vector<std::string> arg_names{{"arg1", "arg2", "arg3", "arg4", "arg5"}};
+
+    // Make sure named arguments are transformed into positional arguments in correct places separated by nulls
+    BOOST_CHECK_EQUAL(TransformParams(JSON(R"({"arg2": 2, "arg4": 4})"), arg_names).write(), "[null,2,null,4]");
+
+    // Make sure named and positional arguments can be combined.
+    BOOST_CHECK_EQUAL(TransformParams(JSON(R"({"arg5": 5, "args": [1, 2], "arg4": 4})"), arg_names).write(), "[1,2,null,4,5]");
+
+    // Make sure a unknown named argument raises an exception
+    BOOST_CHECK_EXCEPTION(TransformParams(JSON(R"({"arg2": 2, "unknown": 6})"), arg_names), UniValue,
+                          HasJSON(R"({"code":-8,"message":"Unknown named parameter unknown"})"));
+
+    // Make sure an overlap between a named argument and positional argument raises an exception
+    BOOST_CHECK_EXCEPTION(TransformParams(JSON(R"({"args": [1,2,3], "arg4": 4, "arg2": 2})"), arg_names), UniValue,
+                          HasJSON(R"({"code":-8,"message":"Parameter arg2 specified twice both as positional and named argument"})"));
+
+    // Make sure extra positional arguments can be passed through to the method implemenation, as long as they don't overlap with named arguments.
+    BOOST_CHECK_EQUAL(TransformParams(JSON(R"({"args": [1,2,3,4,5,6,7,8,9,10]})"), arg_names).write(), "[1,2,3,4,5,6,7,8,9,10]");
+    BOOST_CHECK_EQUAL(TransformParams(JSON(R"([1,2,3,4,5,6,7,8,9,10])"), arg_names).write(), "[1,2,3,4,5,6,7,8,9,10]");
+}
+
 BOOST_AUTO_TEST_CASE(rpc_rawparams)
 {
     // Test raw transaction API argument handling

test/functional/interface_bitcoin_cli.py

@@ -84,6 +84,11 @@ class TestBitcoinCli(BitcoinTestFramework):
         rpc_response = self.nodes[0].getblockchaininfo()
         assert_equal(cli_response, rpc_response)
 
+        self.log.info("Test named arguments")
+        assert_equal(self.nodes[0].cli.echo(0, 1, arg3=3, arg5=5), ['0', '1', None, '3', None, '5'])
+        assert_raises_rpc_error(-8, "Parameter arg1 specified twice both as positional and named argument", self.nodes[0].cli.echo, 0, 1, arg1=1)
+        assert_raises_rpc_error(-8, "Parameter arg1 specified twice both as positional and named argument", self.nodes[0].cli.echo, 0, None, 2, arg1=1)
+
         user, password = get_auth_cookie(self.nodes[0].datadir, self.chain)
 
         self.log.info("Test -stdinrpcpass option")

test/functional/rpc_named_arguments.py

@@ -30,6 +30,9 @@ class NamedArgumentTest(BitcoinTestFramework):
         assert_equal(node.echo(arg1=1), [None, 1])
         assert_equal(node.echo(arg9=None), [None]*10)
         assert_equal(node.echo(arg0=0,arg3=3,arg9=9), [0] + [None]*2 + [3] + [None]*5 + [9])
+        assert_equal(node.echo(0, 1, arg3=3, arg5=5), [0, 1, None, 3, None, 5])
+        assert_raises_rpc_error(-8, "Parameter arg1 specified twice both as positional and named argument", node.echo, 0, 1, arg1=1)
+        assert_raises_rpc_error(-8, "Parameter arg1 specified twice both as positional and named argument", node.echo, 0, None, 2, arg1=1)
 
 if __name__ == '__main__':
     NamedArgumentTest().main()

test/functional/test_framework/authproxy.py

@@ -131,10 +131,12 @@ class AuthServiceProxy():
             json.dumps(args or argsn, default=EncodeDecimal, ensure_ascii=self.ensure_ascii),
         ))
         if args and argsn:
-            raise ValueError('Cannot handle both named and positional arguments')
+            params = dict(args=args, **argsn)
+        else:
+            params = args or argsn
         return {'version': '1.1',
                 'method': self._service_name,
-                'params': args or argsn,
+                'params': params,
                 'id': AuthServiceProxy.__id_count}
 
     def __call__(self, *args, **argsn):

test/functional/test_framework/test_node.py

@@ -719,7 +719,6 @@ class TestNodeCLI():
         """Run bitcoin-cli command. Deserializes returned string as python object."""
         pos_args = [arg_to_cli(arg) for arg in args]
         named_args = [str(key) + "=" + arg_to_cli(value) for (key, value) in kwargs.items()]
-        assert not (pos_args and named_args), "Cannot use positional arguments and named arguments in the same bitcoin-cli call"
         p_args = [self.binary, "-datadir=" + self.datadir] + self.options
         if named_args:
             p_args += ["-named"]