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// Copyright 2010 The Go 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 jsonrpc implements a JSON-RPC ClientCodec and ServerCodec
// for the rpc package.
package jsonrpc

import (
        "encoding/json"
        "fmt"
        "io"
        "net"
        "net/rpc"
        "sync"
)

type clientCodec struct {
        dec *json.Decoder // for reading JSON values
        enc *json.Encoder // for writing JSON values
        c   io.Closer

        // temporary work space
        req  clientRequest
        resp clientResponse

        // JSON-RPC responses include the request id but not the request method.
        // Package rpc expects both.
        // We save the request method in pending when sending a request
        // and then look it up by request ID when filling out the rpc Response.
        mutex   sync.Mutex        // protects pending
        pending map[uint64]string // map request id to method name
}

// NewClientCodec returns a new rpc.ClientCodec using JSON-RPC on conn.
func NewClientCodec(conn io.ReadWriteCloser) rpc.ClientCodec {
        return &clientCodec{
                dec:     json.NewDecoder(conn),
                enc:     json.NewEncoder(conn),
                c:       conn,
                pending: make(map[uint64]string),
        }
}

type clientRequest struct {
        Method string         `json:"method"`
        Params [1]interface{} `json:"params"`
        Id     uint64         `json:"id"`
}

func (c *clientCodec) WriteRequest(r *rpc.Request, param interface{}) error {
        c.mutex.Lock()
        c.pending[r.Seq] = r.ServiceMethod
        c.mutex.Unlock()
        c.req.Method = r.ServiceMethod
        c.req.Params[0] = param
        c.req.Id = r.Seq
        return c.enc.Encode(&c.req)
}

type clientResponse struct {
        Id     uint64           `json:"id"`
        Result *json.RawMessage `json:"result"`
        Error  interface{}      `json:"error"`
}

func (r *clientResponse) reset() {
        r.Id = 0
        r.Result = nil
        r.Error = nil
}

func (c *clientCodec) ReadResponseHeader(r *rpc.Response) error {
        c.resp.reset()
        if err := c.dec.Decode(&c.resp); err != nil {
                return err
        }

        c.mutex.Lock()
        r.ServiceMethod = c.pending[c.resp.Id]
        delete(c.pending, c.resp.Id)
        c.mutex.Unlock()

        r.Error = ""
        r.Seq = c.resp.Id
        if c.resp.Error != nil {
                x, ok := c.resp.Error.(string)
                if !ok {
                        return fmt.Errorf("invalid error %v", c.resp.Error)
                }
                if x == "" {
                        x = "unspecified error"
                }
                r.Error = x
        }
        return nil
}

func (c *clientCodec) ReadResponseBody(x interface{}) error {
        if x == nil {
                return nil
        }
        return json.Unmarshal(*c.resp.Result, x)
}

func (c *clientCodec) Close() error {
        return c.c.Close()
}

// NewClient returns a new rpc.Client to handle requests to the
// set of services at the other end of the connection.
func NewClient(conn io.ReadWriteCloser) *rpc.Client {
        return rpc.NewClientWithCodec(NewClientCodec(conn))
}

// Dial connects to a JSON-RPC server at the specified network address.
func Dial(network, address string) (*rpc.Client, error) {
        conn, err := net.Dial(network, address)
        if err != nil {
                return nil, err
        }
        return NewClient(conn), err
}