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// Copyright 2013 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package httputil
import (
"io"
"net/http"
"strings"
"github.com/klauspost/compress/gzip"
"github.com/klauspost/compress/zlib"
)
const (
acceptEncodingHeader = "Accept-Encoding"
contentEncodingHeader = "Content-Encoding"
gzipEncoding = "gzip"
deflateEncoding = "deflate"
)
// Wrapper around http.Handler which adds suitable response compression based
// on the client's Accept-Encoding headers.
type compressedResponseWriter struct {
http.ResponseWriter
writer io.Writer
}
// Writes HTTP response content data.
func (c *compressedResponseWriter) Write(p []byte) (int, error) {
return c.writer.Write(p)
}
// Closes the compressedResponseWriter and ensures to flush all data before.
func (c *compressedResponseWriter) Close() {
if zlibWriter, ok := c.writer.(*zlib.Writer); ok {
zlibWriter.Flush()
}
if gzipWriter, ok := c.writer.(*gzip.Writer); ok {
gzipWriter.Flush()
}
if closer, ok := c.writer.(io.Closer); ok {
defer closer.Close()
}
}
// Constructs a new compressedResponseWriter based on client request headers.
func newCompressedResponseWriter(writer http.ResponseWriter, req *http.Request) *compressedResponseWriter {
encodings := strings.Split(req.Header.Get(acceptEncodingHeader), ",")
for _, encoding := range encodings {
switch strings.TrimSpace(encoding) {
case gzipEncoding:
writer.Header().Set(contentEncodingHeader, gzipEncoding)
return &compressedResponseWriter{
ResponseWriter: writer,
writer: gzip.NewWriter(writer),
}
case deflateEncoding:
writer.Header().Set(contentEncodingHeader, deflateEncoding)
return &compressedResponseWriter{
ResponseWriter: writer,
writer: zlib.NewWriter(writer),
}
}
}
return &compressedResponseWriter{
ResponseWriter: writer,
writer: writer,
}
}
// CompressionHandler is a wrapper around http.Handler which adds suitable
// response compression based on the client's Accept-Encoding headers.
type CompressionHandler struct {
Handler http.Handler
}
// ServeHTTP adds compression to the original http.Handler's ServeHTTP() method.
func (c CompressionHandler) ServeHTTP(writer http.ResponseWriter, req *http.Request) {
compWriter := newCompressedResponseWriter(writer, req)
c.Handler.ServeHTTP(compWriter, req)
compWriter.Close()
}
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