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gzip.go
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gzip.go
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// Package gzip provides a simple middleware layer that performs
// gzip compression on the response.
package gzip
import (
"compress/gzip"
"fmt"
"io"
"net/http"
"strings"
"github.com/mholt/caddy/middleware"
)
// Gzip is a middleware type which gzips HTTP responses. It is
// imperative that any handler which writes to a gzipped response
// specifies the Content-Type, otherwise some clients will assume
// application/x-gzip and try to download a file.
type Gzip struct {
Next middleware.Handler
}
// ServeHTTP serves a gzipped response if the client supports it.
func (g Gzip) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
return g.Next.ServeHTTP(w, r)
}
// Delete this header so gzipping isn't repeated later in the chain
r.Header.Del("Accept-Encoding")
w.Header().Set("Content-Encoding", "gzip")
gzipWriter := gzip.NewWriter(w)
defer gzipWriter.Close()
gz := gzipResponseWriter{Writer: gzipWriter, ResponseWriter: w}
// Any response in forward middleware will now be compressed
status, err := g.Next.ServeHTTP(gz, r)
// If there was an error that remained unhandled, we need
// to send something back before gzipWriter gets closed at
// the return of this method!
if status >= 400 {
gz.Header().Set("Content-Type", "text/plain") // very necessary
gz.WriteHeader(status)
fmt.Fprintf(gz, "%d %s", status, http.StatusText(status))
return 0, err
} else {
return status, err
}
}
// gzipResponeWriter wraps the underlying Write method
// with a gzip.Writer to compress the output.
type gzipResponseWriter struct {
io.Writer
http.ResponseWriter
}
// WriteHeader wraps the underlying WriteHeader method to prevent
// problems with conflicting headers from proxied backends. For
// example, a backend system that calculates Content-Length would
// be wrong because it doesn't know it's being gzipped.
func (w gzipResponseWriter) WriteHeader(code int) {
w.Header().Del("Content-Length")
w.ResponseWriter.WriteHeader(code)
}
// 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
}