libgo/go/net/rpc/client.go

   1 // Copyright 2009 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 rpc
   6
   7 import (
   8         "bufio"
   9         "encoding/gob"
  10         "errors"
  11         "io"
  12         "log"
  13         "net"
  14         "net/http"
  15         "sync"
  16 )
  17
  18 // ServerError represents an error that has been returned from
  19 // the remote side of the RPC connection.
  20 type ServerError string
  21
  22 func (e ServerError) Error() string {
  23         return string(e)
  24 }
  25
  26 var ErrShutdown = errors.New("connection is shut down")
  27
  28 // Call represents an active RPC.
  29 type Call struct {
  30         ServiceMethod string      // The name of the service and method to call.
  31         Args          interface{} // The argument to the function (*struct).
  32         Reply         interface{} // The reply from the function (*struct).
  33         Error         error       // After completion, the error status.
  34         Done          chan *Call  // Strobes when call is complete.
  35 }
  36
  37 // Client represents an RPC Client.
  38 // There may be multiple outstanding Calls associated
  39 // with a single Client, and a Client may be used by
  40 // multiple goroutines simultaneously.
  41 type Client struct {
  42         codec ClientCodec
  43
  44         sending sync.Mutex
  45
  46         mutex    sync.Mutex // protects following
  47         request  Request
  48         seq      uint64
  49         pending  map[uint64]*Call
  50         closing  bool // user has called Close
  51         shutdown bool // server has told us to stop
  52 }
  53
  54 // A ClientCodec implements writing of RPC requests and
  55 // reading of RPC responses for the client side of an RPC session.
  56 // The client calls WriteRequest to write a request to the connection
  57 // and calls ReadResponseHeader and ReadResponseBody in pairs
  58 // to read responses.  The client calls Close when finished with the
  59 // connection. ReadResponseBody may be called with a nil
  60 // argument to force the body of the response to be read and then
  61 // discarded.
  62 type ClientCodec interface {
  63         // WriteRequest must be safe for concurrent use by multiple goroutines.
  64         WriteRequest(*Request, interface{}) error
  65         ReadResponseHeader(*Response) error
  66         ReadResponseBody(interface{}) error
  67
  68         Close() error
  69 }
  70
  71 func (client *Client) send(call *Call) {
  72         client.sending.Lock()
  73         defer client.sending.Unlock()
  74
  75         // Register this call.
  76         client.mutex.Lock()
  77         if client.shutdown || client.closing {
  78                 call.Error = ErrShutdown
  79                 client.mutex.Unlock()
  80                 call.done()
  81                 return
  82         }
  83         seq := client.seq
  84         client.seq++
  85         client.pending[seq] = call
  86         client.mutex.Unlock()
  87
  88         // Encode and send the request.
  89         client.request.Seq = seq
  90         client.request.ServiceMethod = call.ServiceMethod
  91         err := client.codec.WriteRequest(&client.request, call.Args)
  92         if err != nil {
  93                 client.mutex.Lock()
  94                 call = client.pending[seq]
  95                 delete(client.pending, seq)
  96                 client.mutex.Unlock()
  97                 if call != nil {
  98                         call.Error = err
  99                         call.done()
 100                 }
 101         }
 102 }
 103
 104 func (client *Client) input() {
 105         var err error
 106         var response Response
 107         for err == nil {
 108                 response = Response{}
 109                 err = client.codec.ReadResponseHeader(&response)
 110                 if err != nil {
 111                         break
 112                 }
 113                 seq := response.Seq
 114                 client.mutex.Lock()
 115                 call := client.pending[seq]
 116                 delete(client.pending, seq)
 117                 client.mutex.Unlock()
 118
 119                 switch {
 120                 case call == nil:
 121                         // We've got no pending call. That usually means that
 122                         // WriteRequest partially failed, and call was already
 123                         // removed; response is a server telling us about an
 124                         // error reading request body. We should still attempt
 125                         // to read error body, but there's no one to give it to.
 126                         err = client.codec.ReadResponseBody(nil)
 127                         if err != nil {
 128                                 err = errors.New("reading error body: " + err.Error())
 129                         }
 130                 case response.Error != "":
 131                         // We've got an error response. Give this to the request;
 132                         // any subsequent requests will get the ReadResponseBody
 133                         // error if there is one.
 134                         call.Error = ServerError(response.Error)
 135                         err = client.codec.ReadResponseBody(nil)
 136                         if err != nil {
 137                                 err = errors.New("reading error body: " + err.Error())
 138                         }
 139                         call.done()
 140                 default:
 141                         err = client.codec.ReadResponseBody(call.Reply)
 142                         if err != nil {
 143                                 call.Error = errors.New("reading body " + err.Error())
 144                         }
 145                         call.done()
 146                 }
 147         }
 148         // Terminate pending calls.
 149         client.sending.Lock()
 150         client.mutex.Lock()
 151         client.shutdown = true
 152         closing := client.closing
 153         if err == io.EOF {
 154                 if closing {
 155                         err = ErrShutdown
 156                 } else {
 157                         err = io.ErrUnexpectedEOF
 158                 }
 159         }
 160         for _, call := range client.pending {
 161                 call.Error = err
 162                 call.done()
 163         }
 164         client.mutex.Unlock()
 165         client.sending.Unlock()
 166         if debugLog && err != io.EOF && !closing {
 167                 log.Println("rpc: client protocol error:", err)
 168         }
 169 }
 170
 171 func (call *Call) done() {
 172         select {
 173         case call.Done <- call:
 174                 // ok
 175         default:
 176                 // We don't want to block here.  It is the caller's responsibility to make
 177                 // sure the channel has enough buffer space. See comment in Go().
 178                 if debugLog {
 179                         log.Println("rpc: discarding Call reply due to insufficient Done chan capacity")
 180                 }
 181         }
 182 }
 183
 184 // NewClient returns a new Client to handle requests to the
 185 // set of services at the other end of the connection.
 186 // It adds a buffer to the write side of the connection so
 187 // the header and payload are sent as a unit.
 188 func NewClient(conn io.ReadWriteCloser) *Client {
 189         encBuf := bufio.NewWriter(conn)
 190         client := &gobClientCodec{conn, gob.NewDecoder(conn), gob.NewEncoder(encBuf), encBuf}
 191         return NewClientWithCodec(client)
 192 }
 193
 194 // NewClientWithCodec is like NewClient but uses the specified
 195 // codec to encode requests and decode responses.
 196 func NewClientWithCodec(codec ClientCodec) *Client {
 197         client := &Client{
 198                 codec:   codec,
 199                 pending: make(map[uint64]*Call),
 200         }
 201         go client.input()
 202         return client
 203 }
 204
 205 type gobClientCodec struct {
 206         rwc    io.ReadWriteCloser
 207         dec    *gob.Decoder
 208         enc    *gob.Encoder
 209         encBuf *bufio.Writer
 210 }
 211
 212 func (c *gobClientCodec) WriteRequest(r *Request, body interface{}) (err error) {
 213         if err = c.enc.Encode(r); err != nil {
 214                 return
 215         }
 216         if err = c.enc.Encode(body); err != nil {
 217                 return
 218         }
 219         return c.encBuf.Flush()
 220 }
 221
 222 func (c *gobClientCodec) ReadResponseHeader(r *Response) error {
 223         return c.dec.Decode(r)
 224 }
 225
 226 func (c *gobClientCodec) ReadResponseBody(body interface{}) error {
 227         return c.dec.Decode(body)
 228 }
 229
 230 func (c *gobClientCodec) Close() error {
 231         return c.rwc.Close()
 232 }
 233
 234 // DialHTTP connects to an HTTP RPC server at the specified network address
 235 // listening on the default HTTP RPC path.
 236 func DialHTTP(network, address string) (*Client, error) {
 237         return DialHTTPPath(network, address, DefaultRPCPath)
 238 }
 239
 240 // DialHTTPPath connects to an HTTP RPC server
 241 // at the specified network address and path.
 242 func DialHTTPPath(network, address, path string) (*Client, error) {
 243         var err error
 244         conn, err := net.Dial(network, address)
 245         if err != nil {
 246                 return nil, err
 247         }
 248         io.WriteString(conn, "CONNECT "+path+" HTTP/1.0\n\n")
 249
 250         // Require successful HTTP response
 251         // before switching to RPC protocol.
 252         resp, err := http.ReadResponse(bufio.NewReader(conn), &http.Request{Method: "CONNECT"})
 253         if err == nil && resp.Status == connected {
 254                 return NewClient(conn), nil
 255         }
 256         if err == nil {
 257                 err = errors.New("unexpected HTTP response: " + resp.Status)
 258         }
 259         conn.Close()
 260         return nil, &net.OpError{
 261                 Op:   "dial-http",
 262                 Net:  network + " " + address,
 263                 Addr: nil,
 264                 Err:  err,
 265         }
 266 }
 267
 268 // Dial connects to an RPC server at the specified network address.
 269 func Dial(network, address string) (*Client, error) {
 270         conn, err := net.Dial(network, address)
 271         if err != nil {
 272                 return nil, err
 273         }
 274         return NewClient(conn), nil
 275 }
 276
 277 func (client *Client) Close() error {
 278         client.mutex.Lock()
 279         if client.closing {
 280                 client.mutex.Unlock()
 281                 return ErrShutdown
 282         }
 283         client.closing = true
 284         client.mutex.Unlock()
 285         return client.codec.Close()
 286 }
 287
 288 // Go invokes the function asynchronously.  It returns the Call structure representing
 289 // the invocation.  The done channel will signal when the call is complete by returning
 290 // the same Call object.  If done is nil, Go will allocate a new channel.
 291 // If non-nil, done must be buffered or Go will deliberately crash.
 292 func (client *Client) Go(serviceMethod string, args interface{}, reply interface{}, done chan *Call) *Call {
 293         call := new(Call)
 294         call.ServiceMethod = serviceMethod
 295         call.Args = args
 296         call.Reply = reply
 297         if done == nil {
 298                 done = make(chan *Call, 10) // buffered.
 299         } else {
 300                 // If caller passes done != nil, it must arrange that
 301                 // done has enough buffer for the number of simultaneous
 302                 // RPCs that will be using that channel.  If the channel
 303                 // is totally unbuffered, it's best not to run at all.
 304                 if cap(done) == 0 {
 305                         log.Panic("rpc: done channel is unbuffered")
 306                 }
 307         }
 308         call.Done = done
 309         client.send(call)
 310         return call
 311 }
 312
 313 // Call invokes the named function, waits for it to complete, and returns its error status.
 314 func (client *Client) Call(serviceMethod string, args interface{}, reply interface{}) error {
 315         call := <-client.Go(serviceMethod, args, reply, make(chan *Call, 1)).Done
 316         return call.Error
 317 }