gzip_handler.go

package main

import (
	"compress/gzip"
	"encoding/json"
	"io"
	"net/http"
)

type GzipHandler struct {
	http.Handler
}

func (g *GzipHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Header.Get("Accept-Encoding") == "gzip" {
		gw := gzip.NewWriter(w)
		defer gw.Close()

		w = CompressedWriter{w, gw}
		w.Header().Set("Content-Encoding", "gzip")
		w.Header().Set("Vary", "Accept-Encoding")
	}

	g.Handler.ServeHTTP(w, r)
}

type CompressedWriter struct {
	http.ResponseWriter
	w io.Writer
}

func (c CompressedWriter) Write(b []byte) (int, error) {
	return c.w.Write(b)
}

type Example struct {
	Message string
}

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		example := Example{Message: "compression example"}
		json.NewEncoder(w).Encode(example)
	})

	http.ListenAndServe(":5000", &GzipHandler{http.DefaultServeMux})
}