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// Copyright 2009 The Go Authors. All rights reserved.
// Copyright 2012 The Gorilla Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package json
import (
var null = json.RawMessage([]byte("null"))
// ----------------------------------------------------------------------------
// Request and Response
// ----------------------------------------------------------------------------
// serverRequest represents a JSON-RPC request received by the server.
type serverRequest struct {
// A String containing the name of the method to be invoked.
Method string `json:"method"`
// An Array of objects to pass as arguments to the method.
Params *json.RawMessage `json:"params"`
// The request id. This can be of any type. It is used to match the
// response with the request that it is replying to.
Id *json.RawMessage `json:"id"`
// serverResponse represents a JSON-RPC response returned by the server.
type serverResponse struct {
// The Object that was returned by the invoked method. This must be null
// in case there was an error invoking the method.
Result interface{} `json:"result"`
// An Error object if there was an error invoking the method. It must be
// null if there was no error.
Error interface{} `json:"error"`
// This must be the same id as the request it is responding to.
Id *json.RawMessage `json:"id"`
// ----------------------------------------------------------------------------
// Codec
// ----------------------------------------------------------------------------
// NewCodec returns a new JSON Codec.
func NewCodec() *Codec {
return &Codec{}
// Codec creates a CodecRequest to process each request.
type Codec struct {
// NewRequest returns a CodecRequest.
func (c *Codec) NewRequest(r *http.Request) rpc.CodecRequest {
return newCodecRequest(r)
// ----------------------------------------------------------------------------
// CodecRequest
// ----------------------------------------------------------------------------
// newCodecRequest returns a new CodecRequest.
func newCodecRequest(r *http.Request) rpc.CodecRequest {
// Decode the request body and check if RPC method is valid.
req := new(serverRequest)
err := json.NewDecoder(r.Body).Decode(req)
return &CodecRequest{request: req, err: err}
// CodecRequest decodes and encodes a single request.
type CodecRequest struct {
request *serverRequest
err error
// Method returns the RPC method for the current request.
// The method uses a dotted notation as in "Service.Method".
func (c *CodecRequest) Method() (string, error) {
if c.err == nil {
return c.request.Method, nil
return "", c.err
// ReadRequest fills the request object for the RPC method.
func (c *CodecRequest) ReadRequest(args interface{}) error {
if c.err == nil {
if c.request.Params != nil {
// JSON params is array value. RPC params is struct.
// Unmarshal into array containing the request struct.
params := [1]interface{}{args}
c.err = json.Unmarshal(*c.request.Params, &params)
} else {
c.err = errors.New("rpc: method request ill-formed: missing params field")
return c.err
// WriteResponse encodes the response and writes it to the ResponseWriter.
// The err parameter is the error resulted from calling the RPC method,
// or nil if there was no error.
func (c *CodecRequest) WriteResponse(w http.ResponseWriter, reply interface{}, methodErr error) error {
if c.err != nil {
return c.err
res := &serverResponse{
Result: reply,
Error: &null,
Id: c.request.Id,
if methodErr != nil {
// Propagate error message as string.
res.Error = methodErr.Error()
// Result must be null if there was an error invoking the method.
res.Result = &null
if c.request.Id == nil {
// Id is null for notifications and they don't have a response.
res.Id = &null
} else {
w.Header().Set("Content-Type", "application/json; charset=utf-8")
encoder := json.NewEncoder(w)
c.err = encoder.Encode(res)
return c.err