caddy/middleware/gzip.go

package middleware

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

func Gzip(p parser) Middleware {
	return func(next http.HandlerFunc) http.HandlerFunc {
		return func(w http.ResponseWriter, r *http.Request) {
			if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
				next(w, r)
				return
			}
			w.Header().Set("Content-Encoding", "gzip")
			gzipWriter := gzip.NewWriter(w)
			defer gzipWriter.Close()
			gz := gzipResponseWriter{Writer: gzipWriter, ResponseWriter: w}
			next(gz, r)
		}
	}
}

// gzipResponeWriter wraps the underlying Write method
// with a gzip.Writer to compress the output.
type gzipResponseWriter struct {
	io.Writer
	http.ResponseWriter
}

// Write wraps the underlying Write method to do compression.
func (w gzipResponseWriter) Write(b []byte) (int, error) {
	if w.Header().Get("Content-Type") == "" {
		w.Header().Set("Content-Type", http.DetectContentType(b))
	}
	n, err := w.Writer.Write(b)
	return n, err
}