http: add Hijacker type; remove Hijack from ResponseWriter

The Hijack functionality wasn't removed, but now you have
to test if your ResponseWriter is also a Hijacker:

func ServeHTTP(rw http.ResponseWriter, req *http.Request) {
    if hj, ok := rw.(http.Hijacker); ok {
        hj.Hijack(..)
    }
}

R=rsc
CC=golang-dev
https://golang.org/cl/4245064

src/pkg/http/httptest/recorder.go

@@ -6,17 +6,13 @@
 package httptest
 
 import (
-	"bufio"
 	"bytes"
 	"http"
-	"io"
 	"os"
 )
 
 // ResponseRecorder is an implementation of http.ResponseWriter that
 // records its mutations for later inspection in tests.
-//
-// Note that Hijack is not implemented and simply panics.
 type ResponseRecorder struct {
 	Code    int           // the HTTP response code from WriteHeader
 	Header  http.Header   // if non-nil, the headers to populate
@@ -81,8 +77,3 @@ func (rw *ResponseRecorder) WriteHeader(code int) {
 func (rw *ResponseRecorder) Flush() {
 	rw.Flushed = true
 }
-
-// Hijack is not implemented in ResponseRecorder and instead panics.
-func (rw *ResponseRecorder) Hijack() (io.ReadWriteCloser, *bufio.ReadWriter, os.Error) {
-	panic("Hijack not implemented in ResponseRecorder")
-}

src/pkg/http/server.go

@@ -81,7 +81,10 @@ type ResponseWriter interface {
 
 	// Flush sends any buffered data to the client.
 	Flush()
+}
 
+// A Hijacker is an HTTP request which be taken over by an HTTP handler.
+type Hijacker interface {
 	// Hijack lets the caller take over the connection.
 	// After a call to Hijack(), the HTTP server library
 	// will not do anything else with the connection.

src/pkg/rpc/server.go

@@ -527,7 +527,7 @@ func (server *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 		io.WriteString(w, "405 must CONNECT\n")
 		return
 	}
-	conn, _, err := w.Hijack()
+	conn, _, err := w.(http.Hijacker).Hijack()
 	if err != nil {
 		log.Print("rpc hijacking ", w.RemoteAddr(), ": ", err.String())
 		return

src/pkg/websocket/server.go

@@ -58,7 +58,7 @@ func getKeyNumber(s string) (r uint32) {
 
 // ServeHTTP implements the http.Handler interface for a Web Socket
 func (f Handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
-	rwc, buf, err := w.Hijack()
+	rwc, buf, err := w.(http.Hijacker).Hijack()
 	if err != nil {
 		panic("Hijack failed: " + err.String())
 		return
@@ -184,7 +184,7 @@ func (f Draft75Handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 
-	rwc, buf, err := w.Hijack()
+	rwc, buf, err := w.(http.Hijacker).Hijack()
 	if err != nil {
 		panic("Hijack failed: " + err.String())
 		return