Compress Handler

compress.go

package main

import (
	"compress/gzip"
	"io"
	"net/http"
	"strings"
)

type GzipResponseWriter struct {
	*gzip.Writer
	http.ResponseWriter
}

func NewGzipResponseWriter(w http.ResponseWriter) http.ResponseWriter {
	return &GzipResponseWriter{
		Writer:         gzip.NewWriter(w),
		ResponseWriter: w,
	}
}

func (w *GzipResponseWriter) Header() http.Header {
	return w.ResponseWriter.Header()
}

func (w *GzipResponseWriter) Write(b []byte) (int, error) {
	h := w.ResponseWriter.Header()
	if h.Get("Content-Type") == "" {
		h.Set("Content-Type", http.DetectContentType(b))
	}

	return w.Writer.Write(b)
}

func CompressHandler(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	L:
		for _, enc := range strings.Split(r.Header.Get("Accept-Encoding"), ",") {
			switch enc {
			case "gzip":
				w.Header().Set("Content-Encoding", "gzip")
				w.Header().Add("Vary", "Accept-Encoding")

				cw := NewGzipResponseWriter(w)
				switch x := cw.(type) {
				case io.Closer:
					defer x.Close()
				}
				w = cw
				break L
			}
		}

		h.ServeHTTP(w, r)
	})
}

func main() {
	http.Handle("/", CompressHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		for i := 0; i < 32; i++ {
			io.WriteString(w, "Hello, gzip!\n")
		}
	})))
	http.ListenAndServe(":8080", nil)
}