Source file src/pkg/net/rpc/jsonrpc/server.go

     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
     6	
     7	import (
     8		"encoding/json"
     9		"errors"
    10		"io"
    11		"net/rpc"
    12		"sync"
    13	)
    14	
    15	type serverCodec struct {
    16		dec *json.Decoder // for reading JSON values
    17		enc *json.Encoder // for writing JSON values
    18		c   io.Closer
    19	
    20		// temporary work space
    21		req  serverRequest
    22		resp serverResponse
    23	
    24		// JSON-RPC clients can use arbitrary json values as request IDs.
    25		// Package rpc expects uint64 request IDs.
    26		// We assign uint64 sequence numbers to incoming requests
    27		// but save the original request ID in the pending map.
    28		// When rpc responds, we use the sequence number in
    29		// the response to find the original request ID.
    30		mutex   sync.Mutex // protects seq, pending
    31		seq     uint64
    32		pending map[uint64]*json.RawMessage
    33	}
    34	
    35	// NewServerCodec returns a new rpc.ServerCodec using JSON-RPC on conn.
    36	func NewServerCodec(conn io.ReadWriteCloser) rpc.ServerCodec {
    37		return &serverCodec{
    38			dec:     json.NewDecoder(conn),
    39			enc:     json.NewEncoder(conn),
    40			c:       conn,
    41			pending: make(map[uint64]*json.RawMessage),
    42		}
    43	}
    44	
    45	type serverRequest struct {
    46		Method string           `json:"method"`
    47		Params *json.RawMessage `json:"params"`
    48		Id     *json.RawMessage `json:"id"`
    49	}
    50	
    51	func (r *serverRequest) reset() {
    52		r.Method = ""
    53		if r.Params != nil {
    54			*r.Params = (*r.Params)[0:0]
    55		}
    56		if r.Id != nil {
    57			*r.Id = (*r.Id)[0:0]
    58		}
    59	}
    60	
    61	type serverResponse struct {
    62		Id     *json.RawMessage `json:"id"`
    63		Result interface{}      `json:"result"`
    64		Error  interface{}      `json:"error"`
    65	}
    66	
    67	func (c *serverCodec) ReadRequestHeader(r *rpc.Request) error {
    68		c.req.reset()
    69		if err := c.dec.Decode(&c.req); err != nil {
    70			return err
    71		}
    72		r.ServiceMethod = c.req.Method
    73	
    74		// JSON request id can be any JSON value;
    75		// RPC package expects uint64.  Translate to
    76		// internal uint64 and save JSON on the side.
    77		c.mutex.Lock()
    78		c.seq++
    79		c.pending[c.seq] = c.req.Id
    80		c.req.Id = nil
    81		r.Seq = c.seq
    82		c.mutex.Unlock()
    83	
    84		return nil
    85	}
    86	
    87	func (c *serverCodec) ReadRequestBody(x interface{}) error {
    88		if x == nil {
    89			return nil
    90		}
    91		// JSON params is array value.
    92		// RPC params is struct.
    93		// Unmarshal into array containing struct for now.
    94		// Should think about making RPC more general.
    95		var params [1]interface{}
    96		params[0] = x
    97		return json.Unmarshal(*c.req.Params, &params)
    98	}
    99	
   100	var null = json.RawMessage([]byte("null"))
   101	
   102	func (c *serverCodec) WriteResponse(r *rpc.Response, x interface{}) error {
   103		var resp serverResponse
   104		c.mutex.Lock()
   105		b, ok := c.pending[r.Seq]
   106		if !ok {
   107			c.mutex.Unlock()
   108			return errors.New("invalid sequence number in response")
   109		}
   110		delete(c.pending, r.Seq)
   111		c.mutex.Unlock()
   112	
   113		if b == nil {
   114			// Invalid request so no id.  Use JSON null.
   115			b = &null
   116		}
   117		resp.Id = b
   118		resp.Result = x
   119		if r.Error == "" {
   120			resp.Error = nil
   121		} else {
   122			resp.Error = r.Error
   123		}
   124		return c.enc.Encode(resp)
   125	}
   126	
   127	func (c *serverCodec) Close() error {
   128		return c.c.Close()
   129	}
   130	
   131	// ServeConn runs the JSON-RPC server on a single connection.
   132	// ServeConn blocks, serving the connection until the client hangs up.
   133	// The caller typically invokes ServeConn in a go statement.
   134	func ServeConn(conn io.ReadWriteCloser) {
   135		rpc.ServeCodec(NewServerCodec(conn))
   136	}