rpc: fix issue with null JSON-RPC messages (ethereum#21497)

Author: fjl

rpc/json.go

@@ -194,15 +194,22 @@ func (c *jsonCodec) remoteAddr() string {
 	return c.remote
 }
 
-func (c *jsonCodec) readBatch() (msg []*jsonrpcMessage, batch bool, err error) {
+func (c *jsonCodec) readBatch() (messages []*jsonrpcMessage, batch bool, err error) {
 	// Decode the next JSON object in the input stream.
 	// This verifies basic syntax, etc.
 	var rawmsg json.RawMessage
 	if err := c.decode(&rawmsg); err != nil {
 		return nil, false, err
 	}
-	msg, batch = parseMessage(rawmsg)
-	return msg, batch, nil
+	messages, batch = parseMessage(rawmsg)
+	for i, msg := range messages {
+		if msg == nil {
+			// Message is JSON 'null'. Replace with zero value so it
+			// will be treated like any other invalid message.
+			messages[i] = new(jsonrpcMessage)
+		}
+	}
+	return messages, batch, nil
 }
 
 func (c *jsonCodec) writeJSON(ctx context.Context, v interface{}) error {

rpc/testdata/invalid-batch.js

@@ -10,5 +10,8 @@
 --> [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"}}]
 
+--> [null]
+<-- [{"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-nonobj.js

@@ -2,3 +2,6 @@
 
 --> 1
 <-- {"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}}
+
+--> null
+<-- {"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"invalid request"}}