From adf16b31781325cbd41085c5be901d95b4d1f33d Mon Sep 17 00:00:00 2001
From: Gary Burd <gary@beagledreams.com>
Date: Sat, 31 Dec 2016 20:13:41 -0800
Subject: [PATCH] Add safe maskBytes

Fixes #200.
---
 conn.go      |  6 ++++++
 mask.go      | 12 +++---------
 mask_safe.go | 15 +++++++++++++++
 mask_test.go |  2 +-
 4 files changed, 25 insertions(+), 10 deletions(-)
 create mode 100644 mask_safe.go

diff --git a/conn.go b/conn.go
index 9c3645b..218d8a9 100644
--- a/conn.go
+++ b/conn.go
@@ -10,6 +10,7 @@ import (
 	"errors"
 	"io"
 	"io/ioutil"
+	"math/rand"
 	"net"
 	"strconv"
 	"sync"
@@ -180,6 +181,11 @@ var (
 	errInvalidControlFrame = errors.New("websocket: invalid control frame")
 )
 
+func newMaskKey() [4]byte {
+	n := rand.Uint32()
+	return [4]byte{byte(n), byte(n >> 8), byte(n >> 16), byte(n >> 24)}
+}
+
 func hideTempErr(err error) error {
 	if e, ok := err.(net.Error); ok && e.Temporary() {
 		err = &netError{msg: e.Error(), timeout: e.Timeout()}
diff --git a/mask.go b/mask.go
index 6758a2c..6a88bbc 100644
--- a/mask.go
+++ b/mask.go
@@ -2,20 +2,14 @@
 // this source code is governed by a BSD-style license that can be found in the
 // LICENSE file.
 
+// +build !appengine
+
 package websocket
 
-import (
-	"math/rand"
-	"unsafe"
-)
+import "unsafe"
 
 const wordSize = int(unsafe.Sizeof(uintptr(0)))
 
-func newMaskKey() [4]byte {
-	n := rand.Uint32()
-	return [4]byte{byte(n), byte(n >> 8), byte(n >> 16), byte(n >> 24)}
-}
-
 func maskBytes(key [4]byte, pos int, b []byte) int {
 
 	// Mask one byte at a time for small buffers.
diff --git a/mask_safe.go b/mask_safe.go
new file mode 100644
index 0000000..2aac060
--- /dev/null
+++ b/mask_safe.go
@@ -0,0 +1,15 @@
+// Copyright 2016 The Gorilla WebSocket Authors. All rights reserved.  Use of
+// this source code is governed by a BSD-style license that can be found in the
+// LICENSE file.
+
+// +build appengine
+
+package websocket
+
+func maskBytes(key [4]byte, pos int, b []byte) int {
+	for i := range b {
+		b[i] ^= key[pos&3]
+		pos++
+	}
+	return pos & 3
+}
diff --git a/mask_test.go b/mask_test.go
index de06029..298a1e5 100644
--- a/mask_test.go
+++ b/mask_test.go
@@ -3,7 +3,7 @@
 // LICENSE file.
 
 // Require 1.7 for sub-bencmarks
-// +build go1.7
+// +build go1.7,!appengine
 
 package websocket