gc: better error messages for interface failures, conversions

x.go:13: cannot use t (type T) as type Reader in assignment:
	T does not implement Reader (Read method requires pointer receiver)
x.go:19: cannot use q (type Q) as type Reader in assignment:
	Q does not implement Reader (missing Read method)
		have read()
		want Read()
x.go:22: cannot use z (type int) as type Reader in assignment:
	int does not implement Reader (missing Read method)

x.go:24: too many arguments to conversion to complex: complex(1, 3)

R=ken2
CC=golang-dev
https://golang.org/cl/1736041

src/pkg/rpc/server.go

@@ -158,6 +158,12 @@ type Response struct {
 	Error         string // error, if any.
 }
 
+// ClientInfo records information about an RPC client connection.
+type ClientInfo struct {
+	LocalAddr  string
+	RemoteAddr string
+}
+
 type serverType struct {
 	sync.Mutex // protects the serviceMap
 	serviceMap map[string]*service
@@ -208,7 +214,7 @@ func (server *serverType) register(rcvr interface{}) os.Error {
 		}
 		// Method needs three ins: receiver, *args, *reply.
 		// The args and reply must be structs until gobs are more general.
-		if mtype.NumIn() != 3 {
+		if mtype.NumIn() != 3 && mtype.NumIn() != 4 {
 			log.Stderr("method", mname, "has wrong number of ins:", mtype.NumIn())
 			continue
 		}
@@ -238,6 +244,13 @@ func (server *serverType) register(rcvr interface{}) os.Error {
 			log.Stderr(mname, "reply type not public:", replyType)
 			continue
 		}
+		if mtype.NumIn() == 4 {
+			t := mtype.In(3)
+			if t != reflect.Typeof((*ClientInfo)(nil)) {
+				log.Stderr(mname, "last argument not *ClientInfo")
+				continue
+			}
+		}
 		// Method needs one out: os.Error.
 		if mtype.NumOut() != 1 {
 			log.Stderr("method", mname, "has wrong number of outs:", mtype.NumOut())
@@ -288,13 +301,19 @@ func sendResponse(sending *sync.Mutex, req *Request, reply interface{}, codec Se
 	sending.Unlock()
 }
 
-func (s *service) call(sending *sync.Mutex, mtype *methodType, req *Request, argv, replyv reflect.Value, codec ServerCodec) {
+func (s *service) call(sending *sync.Mutex, mtype *methodType, req *Request, argv, replyv reflect.Value, codec ServerCodec, ci *ClientInfo) {
 	mtype.Lock()
 	mtype.numCalls++
 	mtype.Unlock()
 	function := mtype.method.Func
 	// Invoke the method, providing a new value for the reply.
-	returnValues := function.Call([]reflect.Value{s.rcvr, argv, replyv})
+	var args []reflect.Value
+	if mtype.method.Type.NumIn() == 3 {
+		args = []reflect.Value{s.rcvr, argv, replyv}
+	} else {
+		args = []reflect.Value{s.rcvr, argv, replyv, reflect.NewValue(ci)}
+	}
+	returnValues := function.Call(args)
 	// The return value for the method is an os.Error.
 	errInter := returnValues[0].Interface()
 	errmsg := ""
@@ -329,7 +348,7 @@ func (c *gobServerCodec) Close() os.Error {
 	return c.rwc.Close()
 }
 
-func (server *serverType) input(codec ServerCodec) {
+func (server *serverType) input(codec ServerCodec, ci *ClientInfo) {
 	sending := new(sync.Mutex)
 	for {
 		// Grab the request header.
@@ -376,7 +395,7 @@ func (server *serverType) input(codec ServerCodec) {
 			sendResponse(sending, req, replyv.Interface(), codec, err.String())
 			break
 		}
-		go service.call(sending, mtype, req, argv, replyv, codec)
+		go service.call(sending, mtype, req, argv, replyv, codec, ci)
 	}
 	codec.Close()
 }
@@ -387,7 +406,7 @@ func (server *serverType) accept(lis net.Listener) {
 		if err != nil {
 			log.Exit("rpc.Serve: accept:", err.String()) // TODO(r): exit?
 		}
-		go ServeConn(conn)
+		go ServeConn(conn, &ClientInfo{conn.LocalAddr().String(), conn.RemoteAddr().String()})
 	}
 }
 
@@ -419,14 +438,14 @@ type ServerCodec interface {
 // 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)})
+func ServeConn(conn io.ReadWriteCloser, ci *ClientInfo) {
+	ServeCodec(&gobServerCodec{conn, gob.NewDecoder(conn), gob.NewEncoder(conn)}, ci)
 }
 
 // ServeCodec is like ServeConn but uses the specified codec to
 // decode requests and encode responses.
-func ServeCodec(codec ServerCodec) {
-	server.input(codec)
+func ServeCodec(codec ServerCodec, ci *ClientInfo) {
+	server.input(codec, ci)
 }
 
 // Accept accepts connections on the listener and serves requests
@@ -452,7 +471,11 @@ func serveHTTP(c *http.Conn, req *http.Request) {
 		return
 	}
 	io.WriteString(conn, "HTTP/1.0 "+connected+"\n\n")
-	ServeConn(conn)
+	ci := &ClientInfo{
+		LocalAddr:  conn.(net.Conn).LocalAddr().String(),
+		RemoteAddr: c.RemoteAddr,
+	}
+	ServeConn(conn, ci)
 }
 
 // HandleHTTP registers an HTTP handler for RPC messages.