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

Documentation: net/rpc/jsonrpc

  // 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
  
  import (
  	"encoding/json"
  	"errors"
  	"io"
  	"net/rpc"
  	"sync"
  )
  
  var errMissingParams = errors.New("jsonrpc: request body missing params")
  
  type serverCodec struct {
  	dec *json.Decoder // for reading JSON values
  	enc *json.Encoder // for writing JSON values
  	c   io.Closer
  
  	// temporary work space
  	req serverRequest
  
  	// JSON-RPC clients can use arbitrary json values as request IDs.
  	// Package rpc expects uint64 request IDs.
  	// We assign uint64 sequence numbers to incoming requests
  	// but save the original request ID in the pending map.
  	// When rpc responds, we use the sequence number in
  	// the response to find the original request ID.
  	mutex   sync.Mutex // protects seq, pending
  	seq     uint64
  	pending map[uint64]*json.RawMessage
  }
  
  // NewServerCodec returns a new rpc.ServerCodec using JSON-RPC on conn.
  func NewServerCodec(conn io.ReadWriteCloser) rpc.ServerCodec {
  	return &serverCodec{
  		dec:     json.NewDecoder(conn),
  		enc:     json.NewEncoder(conn),
  		c:       conn,
  		pending: make(map[uint64]*json.RawMessage),
  	}
  }
  
  type serverRequest struct {
  	Method string           `json:"method"`
  	Params *json.RawMessage `json:"params"`
  	Id     *json.RawMessage `json:"id"`
  }
  
  func (r *serverRequest) reset() {
  	r.Method = ""
  	r.Params = nil
  	r.Id = nil
  }
  
  type serverResponse struct {
  	Id     *json.RawMessage `json:"id"`
  	Result interface{}      `json:"result"`
  	Error  interface{}      `json:"error"`
  }
  
  func (c *serverCodec) ReadRequestHeader(r *rpc.Request) error {
  	c.req.reset()
  	if err := c.dec.Decode(&c.req); err != nil {
  		return err
  	}
  	r.ServiceMethod = c.req.Method
  
  	// JSON request id can be any JSON value;
  	// RPC package expects uint64.  Translate to
  	// internal uint64 and save JSON on the side.
  	c.mutex.Lock()
  	c.seq++
  	c.pending[c.seq] = c.req.Id
  	c.req.Id = nil
  	r.Seq = c.seq
  	c.mutex.Unlock()
  
  	return nil
  }
  
  func (c *serverCodec) ReadRequestBody(x interface{}) error {
  	if x == nil {
  		return nil
  	}
  	if c.req.Params == nil {
  		return errMissingParams
  	}
  	// JSON params is array value.
  	// RPC params is struct.
  	// Unmarshal into array containing struct for now.
  	// Should think about making RPC more general.
  	var params [1]interface{}
  	params[0] = x
  	return json.Unmarshal(*c.req.Params, &params)
  }
  
  var null = json.RawMessage([]byte("null"))
  
  func (c *serverCodec) WriteResponse(r *rpc.Response, x interface{}) error {
  	c.mutex.Lock()
  	b, ok := c.pending[r.Seq]
  	if !ok {
  		c.mutex.Unlock()
  		return errors.New("invalid sequence number in response")
  	}
  	delete(c.pending, r.Seq)
  	c.mutex.Unlock()
  
  	if b == nil {
  		// Invalid request so no id. Use JSON null.
  		b = &null
  	}
  	resp := serverResponse{Id: b}
  	if r.Error == "" {
  		resp.Result = x
  	} else {
  		resp.Error = r.Error
  	}
  	return c.enc.Encode(resp)
  }
  
  func (c *serverCodec) Close() error {
  	return c.c.Close()
  }
  
  // ServeConn runs the JSON-RPC server on a single connection.
  // ServeConn blocks, serving the connection until the client hangs up.
  // The caller typically invokes ServeConn in a go statement.
  func ServeConn(conn io.ReadWriteCloser) {
  	rpc.ServeCodec(NewServerCodec(conn))
  }
  

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