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      1 // Copyright 2010 The Go Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 // Package jsonrpc implements a JSON-RPC ClientCodec and ServerCodec
      6 // for the rpc package.
      7 package jsonrpc
      8 
      9 import (
     10 	"encoding/json"
     11 	"fmt"
     12 	"io"
     13 	"net"
     14 	"net/rpc"
     15 	"sync"
     16 )
     17 
     18 type clientCodec struct {
     19 	dec *json.Decoder // for reading JSON values
     20 	enc *json.Encoder // for writing JSON values
     21 	c   io.Closer
     22 
     23 	// temporary work space
     24 	req  clientRequest
     25 	resp clientResponse
     26 
     27 	// JSON-RPC responses include the request id but not the request method.
     28 	// Package rpc expects both.
     29 	// We save the request method in pending when sending a request
     30 	// and then look it up by request ID when filling out the rpc Response.
     31 	mutex   sync.Mutex        // protects pending
     32 	pending map[uint64]string // map request id to method name
     33 }
     34 
     35 // NewClientCodec returns a new rpc.ClientCodec using JSON-RPC on conn.
     36 func NewClientCodec(conn io.ReadWriteCloser) rpc.ClientCodec {
     37 	return &clientCodec{
     38 		dec:     json.NewDecoder(conn),
     39 		enc:     json.NewEncoder(conn),
     40 		c:       conn,
     41 		pending: make(map[uint64]string),
     42 	}
     43 }
     44 
     45 type clientRequest struct {
     46 	Method string         `json:"method"`
     47 	Params [1]interface{} `json:"params"`
     48 	Id     uint64         `json:"id"`
     49 }
     50 
     51 func (c *clientCodec) WriteRequest(r *rpc.Request, param interface{}) error {
     52 	c.mutex.Lock()
     53 	c.pending[r.Seq] = r.ServiceMethod
     54 	c.mutex.Unlock()
     55 	c.req.Method = r.ServiceMethod
     56 	c.req.Params[0] = param
     57 	c.req.Id = r.Seq
     58 	return c.enc.Encode(&c.req)
     59 }
     60 
     61 type clientResponse struct {
     62 	Id     uint64           `json:"id"`
     63 	Result *json.RawMessage `json:"result"`
     64 	Error  interface{}      `json:"error"`
     65 }
     66 
     67 func (r *clientResponse) reset() {
     68 	r.Id = 0
     69 	r.Result = nil
     70 	r.Error = nil
     71 }
     72 
     73 func (c *clientCodec) ReadResponseHeader(r *rpc.Response) error {
     74 	c.resp.reset()
     75 	if err := c.dec.Decode(&c.resp); err != nil {
     76 		return err
     77 	}
     78 
     79 	c.mutex.Lock()
     80 	r.ServiceMethod = c.pending[c.resp.Id]
     81 	delete(c.pending, c.resp.Id)
     82 	c.mutex.Unlock()
     83 
     84 	r.Error = ""
     85 	r.Seq = c.resp.Id
     86 	if c.resp.Error != nil || c.resp.Result == nil {
     87 		x, ok := c.resp.Error.(string)
     88 		if !ok {
     89 			return fmt.Errorf("invalid error %v", c.resp.Error)
     90 		}
     91 		if x == "" {
     92 			x = "unspecified error"
     93 		}
     94 		r.Error = x
     95 	}
     96 	return nil
     97 }
     98 
     99 func (c *clientCodec) ReadResponseBody(x interface{}) error {
    100 	if x == nil {
    101 		return nil
    102 	}
    103 	return json.Unmarshal(*c.resp.Result, x)
    104 }
    105 
    106 func (c *clientCodec) Close() error {
    107 	return c.c.Close()
    108 }
    109 
    110 // NewClient returns a new rpc.Client to handle requests to the
    111 // set of services at the other end of the connection.
    112 func NewClient(conn io.ReadWriteCloser) *rpc.Client {
    113 	return rpc.NewClientWithCodec(NewClientCodec(conn))
    114 }
    115 
    116 // Dial connects to a JSON-RPC server at the specified network address.
    117 func Dial(network, address string) (*rpc.Client, error) {
    118 	conn, err := net.Dial(network, address)
    119 	if err != nil {
    120 		return nil, err
    121 	}
    122 	return NewClient(conn), err
    123 }
    124