rpc: respond to invalid JSON

rpc/client.go

@@ -612,6 +612,9 @@ func (c *Client) drainRead() {
 func (c *Client) read(codec ServerCodec) {
 	for {
 		msgs, batch, err := codec.Read()
+		if _, ok := err.(*json.SyntaxError); ok {
+			codec.Write(context.Background(), errorMessage(&parseError{err.Error()}))
+		}
 		if err != nil {
 			c.readErr <- err
 			return

rpc/errors.go

@@ -36,6 +36,13 @@ func (e *subscriptionNotFoundError) Error() string {
 	return fmt.Sprintf("no %q subscription in %s namespace", e.subscription, e.namespace)
 }
 
+// Invalid JSON was received by the server.
+type parseError struct{ message string }
+
+func (e *parseError) ErrorCode() int { return -32700 }
+
+func (e *parseError) Error() string { return e.message }
+
 // received message isn't a valid request
 type invalidRequestError struct{ message string }
 

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"}}
+