websocket: include *http.Request in websocket.Conn

This permits the websocket handler to inspect http headers and such.

Fixes #1726.

R=ukai, bradfitz, bradfitzgo
CC=golang-dev
https://golang.org/cl/4439069

src/pkg/websocket/server.go

@@ -150,6 +150,7 @@ func (f Handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 	ws := newConn(origin, location, protocol, buf, rwc)
+	ws.Request = req
 	f(ws)
 }
 

src/pkg/websocket/websocket.go

@@ -13,6 +13,7 @@ import (
 	"bufio"
 	"crypto/md5"
 	"encoding/binary"
+	"http"
 	"io"
 	"net"
 	"os"
@@ -43,6 +44,8 @@ type Conn struct {
 	Location string
 	// The subprotocol for the Web Socket.
 	Protocol string
+	// The initial http Request (for the Server side only).
+	Request *http.Request
 
 	buf *bufio.ReadWriter
 	rwc io.ReadWriteCloser