rpc: abstract client and server encodings

R=r
CC=golang-dev, rog
https://golang.org/cl/811046

Author: rsc

src/pkg/rpc/client.go

@@ -33,13 +33,25 @@ type Client struct {
 	shutdown os.Error   // non-nil if the client is shut down
 	sending  sync.Mutex
 	seq      uint64
-	conn     io.ReadWriteCloser
-	enc      *gob.Encoder
-	dec      *gob.Decoder
+	codec    ClientCodec
 	pending  map[uint64]*Call
 	closing  bool
 }
 
+// A ClientCodec implements writing of RPC requests and
+// reading of RPC responses for the client side of an RPC session.
+// The client calls WriteRequest to write a request to the connection
+// and calls ReadResponseHeader and ReadResponseBody in pairs
+// to read responses.  The client calls Close when finished with the
+// connection.
+type ClientCodec interface {
+	WriteRequest(*Request, interface{}) os.Error
+	ReadResponseHeader(*Response) os.Error
+	ReadResponseBody(interface{}) os.Error
+
+	Close() os.Error
+}
+
 func (client *Client) send(c *Call) {
 	// Register this call.
 	client.mutex.Lock()
@@ -59,9 +71,7 @@ func (client *Client) send(c *Call) {
 	client.sending.Lock()
 	request.Seq = c.seq
 	request.ServiceMethod = c.ServiceMethod
-	client.enc.Encode(request)
-	err := client.enc.Encode(c.Args)
-	if err != nil {
+	if err := client.codec.WriteRequest(request, c.Args); err != nil {
 		panic("rpc: client encode error: " + err.String())
 	}
 	client.sending.Unlock()
@@ -71,7 +81,7 @@ func (client *Client) input() {
 	var err os.Error
 	for err == nil {
 		response := new(Response)
-		err = client.dec.Decode(response)
+		err = client.codec.ReadResponseHeader(response)
 		if err != nil {
 			if err == os.EOF && !client.closing {
 				err = io.ErrUnexpectedEOF
@@ -83,7 +93,7 @@ func (client *Client) input() {
 		c := client.pending[seq]
 		client.pending[seq] = c, false
 		client.mutex.Unlock()
-		err = client.dec.Decode(c.Reply)
+		err = client.codec.ReadResponseBody(c.Reply)
 		// Empty strings should turn into nil os.Errors
 		if response.Error != "" {
 			c.Error = os.ErrorString(response.Error)
@@ -110,17 +120,49 @@ func (client *Client) input() {
 // NewClient returns a new Client to handle requests to the
 // set of services at the other end of the connection.
 func NewClient(conn io.ReadWriteCloser) *Client {
-	client := new(Client)
-	client.conn = conn
-	client.enc = gob.NewEncoder(conn)
-	client.dec = gob.NewDecoder(conn)
-	client.pending = make(map[uint64]*Call)
+	return NewClientWithCodec(&gobClientCodec{conn, gob.NewDecoder(conn), gob.NewEncoder(conn)})
+}
+
+// NewClientWithCodec is like NewClient but uses the specified
+// codec to encode requests and decode responses.
+func NewClientWithCodec(codec ClientCodec) *Client {
+	client := &Client{
+		codec:   codec,
+		pending: make(map[uint64]*Call),
+	}
 	go client.input()
 	return client
 }
 
+type gobClientCodec struct {
+	rwc io.ReadWriteCloser
+	dec *gob.Decoder
+	enc *gob.Encoder
+}
+
+func (c *gobClientCodec) WriteRequest(r *Request, body interface{}) os.Error {
+	if err := c.enc.Encode(r); err != nil {
+		return err
+	}
+	return c.enc.Encode(body)
+}
+
+func (c *gobClientCodec) ReadResponseHeader(r *Response) os.Error {
+	return c.dec.Decode(r)
+}
+
+func (c *gobClientCodec) ReadResponseBody(body interface{}) os.Error {
+	return c.dec.Decode(body)
+}
+
+func (c *gobClientCodec) Close() os.Error {
+	return c.rwc.Close()
+}
+
+
 // DialHTTP connects to an HTTP RPC server at the specified network address.
 func DialHTTP(network, address string) (*Client, os.Error) {
+	var err os.Error
 	conn, err := net.Dial(network, "", address)
 	if err != nil {
 		return nil, err
@@ -156,7 +198,7 @@ func (client *Client) Close() os.Error {
 	client.mutex.Lock()
 	client.closing = true
 	client.mutex.Unlock()
-	return client.conn.Close()
+	return client.codec.Close()
 }
 
 // Go invokes the function asynchronously.  It returns the Call structure representing

src/pkg/rpc/server.go

@@ -272,7 +272,7 @@ func _new(t *reflect.PtrType) *reflect.PtrValue {
 	return v
 }
 
-func sendResponse(sending *sync.Mutex, req *Request, reply interface{}, enc *gob.Encoder, errmsg string) {
+func sendResponse(sending *sync.Mutex, req *Request, reply interface{}, codec ServerCodec, errmsg string) {
 	resp := new(Response)
 	// Encode the response header
 	resp.ServiceMethod = req.ServiceMethod
@@ -281,13 +281,14 @@ func sendResponse(sending *sync.Mutex, req *Request, reply interface{}, enc *gob
 	}
 	resp.Seq = req.Seq
 	sending.Lock()
-	enc.Encode(resp)
-	// Encode the reply value.
-	enc.Encode(reply)
+	err := codec.WriteResponse(resp, reply)
+	if err != nil {
+		log.Stderr("rpc: writing response: ", err)
+	}
 	sending.Unlock()
 }
 
-func (s *service) call(sending *sync.Mutex, mtype *methodType, req *Request, argv, replyv reflect.Value, enc *gob.Encoder) {
+func (s *service) call(sending *sync.Mutex, mtype *methodType, req *Request, argv, replyv reflect.Value, codec ServerCodec) {
 	mtype.Lock()
 	mtype.numCalls++
 	mtype.Unlock()
@@ -300,17 +301,40 @@ func (s *service) call(sending *sync.Mutex, mtype *methodType, req *Request, arg
 	if errInter != nil {
 		errmsg = errInter.(os.Error).String()
 	}
-	sendResponse(sending, req, replyv.Interface(), enc, errmsg)
+	sendResponse(sending, req, replyv.Interface(), codec, errmsg)
+}
+
+type gobServerCodec struct {
+	rwc io.ReadWriteCloser
+	dec *gob.Decoder
+	enc *gob.Encoder
+}
+
+func (c *gobServerCodec) ReadRequestHeader(r *Request) os.Error {
+	return c.dec.Decode(r)
+}
+
+func (c *gobServerCodec) ReadRequestBody(body interface{}) os.Error {
+	return c.dec.Decode(body)
+}
+
+func (c *gobServerCodec) WriteResponse(r *Response, body interface{}) os.Error {
+	if err := c.enc.Encode(r); err != nil {
+		return err
+	}
+	return c.enc.Encode(body)
 }
 
-func (server *serverType) input(conn io.ReadWriteCloser) {
-	dec := gob.NewDecoder(conn)
-	enc := gob.NewEncoder(conn)
+func (c *gobServerCodec) Close() os.Error {
+	return c.rwc.Close()
+}
+
+func (server *serverType) input(codec ServerCodec) {
 	sending := new(sync.Mutex)
 	for {
 		// Grab the request header.
 		req := new(Request)
-		err := dec.Decode(req)
+		err := codec.ReadRequestHeader(req)
 		if err != nil {
 			if err == os.EOF || err == io.ErrUnexpectedEOF {
 				if err == io.ErrUnexpectedEOF {
@@ -319,13 +343,13 @@ func (server *serverType) input(conn io.ReadWriteCloser) {
 				break
 			}
 			s := "rpc: server cannot decode request: " + err.String()
-			sendResponse(sending, req, invalidRequest, enc, s)
-			continue
+			sendResponse(sending, req, invalidRequest, codec, s)
+			break
 		}
 		serviceMethod := strings.Split(req.ServiceMethod, ".", 0)
 		if len(serviceMethod) != 2 {
-			s := "rpc: service/method request ill:formed: " + req.ServiceMethod
-			sendResponse(sending, req, invalidRequest, enc, s)
+			s := "rpc: service/method request ill-formed: " + req.ServiceMethod
+			sendResponse(sending, req, invalidRequest, codec, s)
 			continue
 		}
 		// Look up the request.
@@ -334,27 +358,27 @@ func (server *serverType) input(conn io.ReadWriteCloser) {
 		server.Unlock()
 		if !ok {
 			s := "rpc: can't find service " + req.ServiceMethod
-			sendResponse(sending, req, invalidRequest, enc, s)
+			sendResponse(sending, req, invalidRequest, codec, s)
 			continue
 		}
 		mtype, ok := service.method[serviceMethod[1]]
 		if !ok {
 			s := "rpc: can't find method " + req.ServiceMethod
-			sendResponse(sending, req, invalidRequest, enc, s)
+			sendResponse(sending, req, invalidRequest, codec, s)
 			continue
 		}
 		// Decode the argument value.
 		argv := _new(mtype.argType)
 		replyv := _new(mtype.replyType)
-		err = dec.Decode(argv.Interface())
+		err = codec.ReadRequestBody(argv.Interface())
 		if err != nil {
 			log.Stderr("rpc: tearing down", serviceMethod[0], "connection:", err)
-			sendResponse(sending, req, replyv.Interface(), enc, err.String())
-			continue
+			sendResponse(sending, req, replyv.Interface(), codec, err.String())
+			break
 		}
-		go service.call(sending, mtype, req, argv, replyv, enc)
+		go service.call(sending, mtype, req, argv, replyv, codec)
 	}
-	conn.Close()
+	codec.Close()
 }
 
 func (server *serverType) accept(lis net.Listener) {
@@ -363,7 +387,7 @@ func (server *serverType) accept(lis net.Listener) {
 		if err != nil {
 			log.Exit("rpc.Serve: accept:", err.String()) // TODO(r): exit?
 		}
-		go server.input(conn)
+		go ServeConn(conn)
 	}
 }
 
@@ -376,10 +400,34 @@ func (server *serverType) accept(lis net.Listener) {
 // suitable methods.
 func Register(rcvr interface{}) os.Error { return server.register(rcvr) }
 
-// ServeConn runs the server on a single connection.  When the connection
-// completes, service terminates.  ServeConn blocks; the caller typically
-// invokes it in a go statement.
-func ServeConn(conn io.ReadWriteCloser) { server.input(conn) }
+// A ServerCodec implements reading of RPC requests and writing of
+// RPC responses for the server side of an RPC session.
+// The server calls ReadRequestHeader and ReadRequestBody in pairs
+// to read requests from the connection, and it calls WriteResponse to
+// write a response back.  The server calls Close when finished with the
+// connection.
+type ServerCodec interface {
+	ReadRequestHeader(*Request) os.Error
+	ReadRequestBody(interface{}) os.Error
+	WriteResponse(*Response, interface{}) os.Error
+
+	Close() os.Error
+}
+
+// ServeConn runs the server on a single connection.
+// ServeConn blocks, serving the connection until the client hangs up.
+// The caller typically invokes ServeConn in a go statement.
+// ServeConn uses the gob wire format (see package gob) on the
+// connection.  To use an alternate codec, use ServeCodec.
+func ServeConn(conn io.ReadWriteCloser) {
+	ServeCodec(&gobServerCodec{conn, gob.NewDecoder(conn), gob.NewEncoder(conn)})
+}
+
+// ServeCodec is like ServeConn but uses the specified codec to
+// decode requests and encode responses.
+func ServeCodec(codec ServerCodec) {
+	server.input(codec)
+}
 
 // Accept accepts connections on the listener and serves requests
 // for each incoming connection.  Accept blocks; the caller typically
@@ -404,7 +452,7 @@ func serveHTTP(c *http.Conn, req *http.Request) {
 		return
 	}
 	io.WriteString(conn, "HTTP/1.0 "+connected+"\n\n")
-	server.input(conn)
+	ServeConn(conn)
 }
 
 // HandleHTTP registers an HTTP handler for RPC messages.