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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
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 any `json:"result"`
Error any `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 any) 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]any
params[0] = x
return json.Unmarshal(*c.req.Params, ¶ms)
}
var null = json.RawMessage([]byte("null"))
func (c *serverCodec) WriteResponse(r *rpc.Response, x any) 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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