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

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