Transcode via Brotli

Brotli offers 20% better compression than gzip.

transcoder/zip.go

@@ -0,0 +1,63 @@
+package transcoder
+
+import (
+	"compress/gzip"
+	"github.com/barnacs/compy/proxy"
+	brotlienc "gopkg.in/kothar/brotli-go.v0/enc"
+	"net/http"
+	"strings"
+)
+
+type Zip struct {
+	proxy.Transcoder
+	BrotliCompressionLevel int
+	GzipCompressionLevel   int
+	SkipGzipped            bool
+}
+
+func (t *Zip) Transcode(w *proxy.ResponseWriter, r *proxy.ResponseReader, headers http.Header) error {
+	shouldBrotli := false
+	shouldGzip := false
+	for _, v := range strings.Split(headers.Get("Accept-Encoding"), ", ") {
+		switch strings.SplitN(v, ";", 2)[0] {
+		case "br":
+			shouldBrotli = true
+		case "gzip":
+			shouldGzip = true
+		}
+	}
+
+	// always gunzip if the client supports Brotli
+	if r.Header().Get("Content-Encoding") == "gzip" && (shouldBrotli || !t.SkipGzipped) {
+		gzr, err := gzip.NewReader(r.Reader)
+		if err != nil {
+			return err
+		}
+		defer gzr.Close()
+		r.Reader = gzr
+		r.Header().Del("Content-Encoding")
+		w.Header().Del("Content-Encoding")
+	}
+
+	if shouldBrotli && compress(r) {
+		params := brotlienc.NewBrotliParams()
+		params.SetQuality(t.BrotliCompressionLevel)
+		brw := brotlienc.NewBrotliWriter(params, w.Writer)
+		defer brw.Close()
+		w.Writer = brw
+		w.Header().Set("Content-Encoding", "br")
+	} else if shouldGzip && compress(r) {
+		gzw, err := gzip.NewWriterLevel(w.Writer, t.GzipCompressionLevel)
+		if err != nil {
+			return err
+		}
+		defer gzw.Close()
+		w.Writer = gzw
+		w.Header().Set("Content-Encoding", "gzip")
+	}
+	return t.Transcoder.Transcode(w, r, headers)
+}
+
+func compress(r *proxy.ResponseReader) bool {
+	return r.Header().Get("Content-Encoding") == ""
+}