rpc: implement full bi-directional communication (#18471)

New APIs added:

    client.RegisterName(namespace, service) // makes service available to server
    client.Notify(ctx, method, args...)     // sends a notification
    ClientFromContext(ctx)                  // to get a client in handler method

This is essentially a rewrite of the server-side code. JSON-RPC
processing code is now the same on both server and client side. Many
minor issues were fixed in the process and there is a new test suite for
JSON-RPC spec compliance (and non-compliance in some cases).

List of behavior changes:

- Method handlers are now called with a per-request context instead of a
  per-connection context. The context is canceled right after the method
  returns.
- Subscription error channels are always closed when the connection
  ends. There is no need to also wait on the Notifier's Closed channel
  to detect whether the subscription has ended.
- Client now omits "params" instead of sending "params": null when there
  are no arguments to a call. The previous behavior was not compliant
  with the spec. The server still accepts "params": null.
- Floating point numbers are allowed as "id". The spec doesn't allow
  them, but we handle request "id" as json.RawMessage and guarantee that
  the same number will be sent back.
- Logging is improved significantly. There is now a message at DEBUG
  level for each RPC call served.

rpc/testdata/invalid-badid.js

@@ -0,0 +1,7 @@
+// This test checks processing of messages with invalid ID.
+
+--> {"id":[],"method":"test_foo"}
+<-- {"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}}
+
+--> {"id":{},"method":"test_foo"}
+<-- {"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}}

rpc/testdata/invalid-batch.js

@@ -0,0 +1,14 @@
+// This test checks the behavior of batches with invalid elements.
+// Empty batches are not allowed. Batches may contain junk.
+
+--> []
+<-- {"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"empty batch"}}
+
+--> [1]
+<-- [{"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}}]
+
+--> [1,2,3]
+<-- [{"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}},{"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}},{"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}}]
+
+--> [{"jsonrpc":"2.0","id":1,"method":"test_echo","params":["foo",1]},55,{"jsonrpc":"2.0","id":2,"method":"unknown_method"},{"foo":"bar"}]
+<-- [{"jsonrpc":"2.0","id":1,"result":{"String":"foo","Int":1,"Args":null}},{"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}},{"jsonrpc":"2.0","id":2,"error":{"code":-32601,"message":"the method unknown_method does not exist/is not available"}},{"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}}]

rpc/testdata/invalid-idonly.js

@@ -0,0 +1,7 @@
+// This test checks processing of messages that contain just the ID and nothing else.
+
+--> {"id":1}
+<-- {"jsonrpc":"2.0","id":1,"error":{"code":-32600,"message":"invalid request"}}
+
+--> {"jsonrpc":"2.0","id":1}
+<-- {"jsonrpc":"2.0","id":1,"error":{"code":-32600,"message":"invalid request"}}

rpc/testdata/invalid-nonobj.js

@@ -0,0 +1,4 @@
+// This test checks behavior for invalid requests.
+
+--> 1
+<-- {"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}}

rpc/testdata/invalid-syntax.json

@@ -0,0 +1,5 @@
+// This test checks that an error is written for invalid JSON requests.
+
+--> 'f
+<-- {"jsonrpc":"2.0","id":null,"error":{"code":-32700,"message":"invalid character '\\'' looking for beginning of value"}}
+

rpc/testdata/reqresp-batch.js

@@ -0,0 +1,8 @@
+// There is no response for all-notification batches.
+
+--> [{"jsonrpc":"2.0","method":"test_echo","params":["x",99]}]
+
+// This test checks regular batch calls.
+
+--> [{"jsonrpc":"2.0","id":2,"method":"test_echo","params":[]}, {"jsonrpc":"2.0","id": 3,"method":"test_echo","params":["x",3]}]
+<-- [{"jsonrpc":"2.0","id":2,"error":{"code":-32602,"message":"missing value for required argument 0"}},{"jsonrpc":"2.0","id":3,"result":{"String":"x","Int":3,"Args":null}}]

rpc/testdata/reqresp-echo.js

@@ -0,0 +1,16 @@
+// This test calls the test_echo method.
+
+--> {"jsonrpc": "2.0", "id": 2, "method": "test_echo", "params": []}
+<-- {"jsonrpc":"2.0","id":2,"error":{"code":-32602,"message":"missing value for required argument 0"}}
+
+--> {"jsonrpc": "2.0", "id": 2, "method": "test_echo", "params": ["x"]}
+<-- {"jsonrpc":"2.0","id":2,"error":{"code":-32602,"message":"missing value for required argument 1"}}
+
+--> {"jsonrpc": "2.0", "id": 2, "method": "test_echo", "params": ["x", 3]}
+<-- {"jsonrpc":"2.0","id":2,"result":{"String":"x","Int":3,"Args":null}}
+
+--> {"jsonrpc": "2.0", "id": 2, "method": "test_echo", "params": ["x", 3, {"S": "foo"}]}
+<-- {"jsonrpc":"2.0","id":2,"result":{"String":"x","Int":3,"Args":{"S":"foo"}}}
+
+--> {"jsonrpc": "2.0", "id": 2, "method": "test_echoWithCtx", "params": ["x", 3, {"S": "foo"}]}
+<-- {"jsonrpc":"2.0","id":2,"result":{"String":"x","Int":3,"Args":{"S":"foo"}}}

rpc/testdata/reqresp-namedparam.js

@@ -0,0 +1,5 @@
+// This test checks that an error response is sent for calls
+// with named parameters. 
+
+--> {"jsonrpc":"2.0","method":"test_echo","params":{"int":23},"id":3}
+<-- {"jsonrpc":"2.0","id":3,"error":{"code":-32602,"message":"non-array args"}}

rpc/testdata/reqresp-noargsrets.js

@@ -0,0 +1,4 @@
+// This test calls the test_noArgsRets method.
+
+--> {"jsonrpc": "2.0", "id": "foo", "method": "test_noArgsRets", "params": []}
+<-- {"jsonrpc":"2.0","id":"foo","result":null}

rpc/testdata/reqresp-nomethod.js

@@ -0,0 +1,4 @@
+// This test calls a method that doesn't exist.
+
+--> {"jsonrpc": "2.0", "id": 2, "method": "invalid_method", "params": [2, 3]}
+<-- {"jsonrpc":"2.0","id":2,"error":{"code":-32601,"message":"the method invalid_method does not exist/is not available"}}

rpc/testdata/reqresp-noparam.js

@@ -0,0 +1,4 @@
+// This test checks that calls with no parameters work.
+
+--> {"jsonrpc":"2.0","method":"test_noArgsRets","id":3}
+<-- {"jsonrpc":"2.0","id":3,"result":null}

rpc/testdata/reqresp-paramsnull.js

@@ -0,0 +1,4 @@
+// This test checks that calls with "params":null work.
+
+--> {"jsonrpc":"2.0","method":"test_noArgsRets","params":null,"id":3}
+<-- {"jsonrpc":"2.0","id":3,"result":null}

rpc/testdata/revcall.js

@@ -0,0 +1,6 @@
+// This test checks reverse calls.
+
+--> {"jsonrpc":"2.0","id":2,"method":"test_callMeBack","params":["foo",[1]]}
+<-- {"jsonrpc":"2.0","id":1,"method":"foo","params":[1]}
+--> {"jsonrpc":"2.0","id":1,"result":"my result"}
+<-- {"jsonrpc":"2.0","id":2,"result":"my result"}

rpc/testdata/revcall2.js

@@ -0,0 +1,7 @@
+// This test checks reverse calls.
+
+--> {"jsonrpc":"2.0","id":2,"method":"test_callMeBackLater","params":["foo",[1]]}
+<-- {"jsonrpc":"2.0","id":2,"result":null}
+<-- {"jsonrpc":"2.0","id":1,"method":"foo","params":[1]}
+--> {"jsonrpc":"2.0","id":1,"result":"my result"}
+

rpc/testdata/subscription.js

@@ -0,0 +1,12 @@
+// This test checks basic subscription support.
+
+--> {"jsonrpc":"2.0","id":1,"method":"nftest_subscribe","params":["someSubscription",5,1]}
+<-- {"jsonrpc":"2.0","id":1,"result":"0x1"}
+<-- {"jsonrpc":"2.0","method":"nftest_subscription","params":{"subscription":"0x1","result":1}}
+<-- {"jsonrpc":"2.0","method":"nftest_subscription","params":{"subscription":"0x1","result":2}}
+<-- {"jsonrpc":"2.0","method":"nftest_subscription","params":{"subscription":"0x1","result":3}}
+<-- {"jsonrpc":"2.0","method":"nftest_subscription","params":{"subscription":"0x1","result":4}}
+<-- {"jsonrpc":"2.0","method":"nftest_subscription","params":{"subscription":"0x1","result":5}}
+
+--> {"jsonrpc":"2.0","id":2,"method":"nftest_echo","params":[11]}
+<-- {"jsonrpc":"2.0","id":2,"result":11}