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// Copyright 2013 The Gorilla Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package handlers
import (
"compress/flate"
"compress/gzip"
"io"
"net/http"
"strings"
"github.com/felixge/httpsnoop"
)
const acceptEncoding string = "Accept-Encoding"
type compressResponseWriter struct {
compressor io.Writer
w http.ResponseWriter
}
func (cw *compressResponseWriter) WriteHeader(c int) {
cw.w.Header().Del("Content-Length")
cw.w.WriteHeader(c)
}
func (cw *compressResponseWriter) Write(b []byte) (int, error) {
h := cw.w.Header()
if h.Get("Content-Type") == "" {
h.Set("Content-Type", http.DetectContentType(b))
}
h.Del("Content-Length")
return cw.compressor.Write(b)
}
func (cw *compressResponseWriter) ReadFrom(r io.Reader) (int64, error) {
return io.Copy(cw.compressor, r)
}
type flusher interface {
Flush() error
}
func (w *compressResponseWriter) Flush() {
// Flush compressed data if compressor supports it.
if f, ok := w.compressor.(flusher); ok {
f.Flush()
}
// Flush HTTP response.
if f, ok := w.w.(http.Flusher); ok {
f.Flush()
}
}
// CompressHandler gzip compresses HTTP responses for clients that support it
// via the 'Accept-Encoding' header.
//
// Compressing TLS traffic may leak the page contents to an attacker if the
// page contains user input: http://security.stackexchange.com/a/102015/12208
func CompressHandler(h http.Handler) http.Handler {
return CompressHandlerLevel(h, gzip.DefaultCompression)
}
// CompressHandlerLevel gzip compresses HTTP responses with specified compression level
// for clients that support it via the 'Accept-Encoding' header.
//
// The compression level should be gzip.DefaultCompression, gzip.NoCompression,
// or any integer value between gzip.BestSpeed and gzip.BestCompression inclusive.
// gzip.DefaultCompression is used in case of invalid compression level.
func CompressHandlerLevel(h http.Handler, level int) http.Handler {
if level < gzip.DefaultCompression || level > gzip.BestCompression {
level = gzip.DefaultCompression
}
const (
gzipEncoding = "gzip"
flateEncoding = "deflate"
)
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// detect what encoding to use
var encoding string
for _, curEnc := range strings.Split(r.Header.Get(acceptEncoding), ",") {
curEnc = strings.TrimSpace(curEnc)
if curEnc == gzipEncoding || curEnc == flateEncoding {
encoding = curEnc
break
}
}
// always add Accept-Encoding to Vary to prevent intermediate caches corruption
w.Header().Add("Vary", acceptEncoding)
// if we weren't able to identify an encoding we're familiar with, pass on the
// request to the handler and return
if encoding == "" {
h.ServeHTTP(w, r)
return
}
if r.Header.Get("Upgrade") != "" {
h.ServeHTTP(w, r)
return
}
// wrap the ResponseWriter with the writer for the chosen encoding
var encWriter io.WriteCloser
if encoding == gzipEncoding {
encWriter, _ = gzip.NewWriterLevel(w, level)
} else if encoding == flateEncoding {
encWriter, _ = flate.NewWriter(w, level)
}
defer encWriter.Close()
w.Header().Set("Content-Encoding", encoding)
r.Header.Del(acceptEncoding)
cw := &compressResponseWriter{
w: w,
compressor: encWriter,
}
w = httpsnoop.Wrap(w, httpsnoop.Hooks{
Write: func(httpsnoop.WriteFunc) httpsnoop.WriteFunc {
return cw.Write
},
WriteHeader: func(httpsnoop.WriteHeaderFunc) httpsnoop.WriteHeaderFunc {
return cw.WriteHeader
},
Flush: func(httpsnoop.FlushFunc) httpsnoop.FlushFunc {
return cw.Flush
},
ReadFrom: func(rff httpsnoop.ReadFromFunc) httpsnoop.ReadFromFunc {
return cw.ReadFrom
},
})
h.ServeHTTP(w, r)
})
}
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