From e5056553385dc84354b6640d5132642319b295e2 Mon Sep 17 00:00:00 2001
From: Andrew Gaul <andrew@gaul.org>
Date: Thu, 19 Jan 2017 11:38:48 -0800
Subject: [PATCH] Add GIF to WebP transcoding

---
 compy_test.go     | 15 +++++++++++++++
 transcoder/gif.go | 15 +++++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/compy_test.go b/compy_test.go
index 887d890..8a25180 100644
--- a/compy_test.go
+++ b/compy_test.go
@@ -134,6 +134,21 @@ func (s *CompyTest) TestGif(c *C) {
 	c.Assert(uncompressedLength > compressedLength, Equals, true)
 }
 
+func (s *CompyTest) TestGifToWebP(c *C) {
+	req, err := http.NewRequest("GET", s.server.URL+"/image/gif", nil)
+	c.Assert(err, IsNil)
+	req.Header.Add("Accept", "image/webp")
+
+	resp, err := s.client.Do(req)
+	c.Assert(err, IsNil)
+	defer resp.Body.Close()
+	c.Assert(resp.StatusCode, Equals, 200)
+	c.Assert(resp.Header.Get("Content-Type"), Equals, "image/webp")
+
+	_, err = webp.Decode(resp.Body)
+	c.Assert(err, IsNil)
+}
+
 func (s *CompyTest) TestJpeg(c *C) {
 	resp, err := s.client.Get(s.server.URL + "/image/jpeg")
 	c.Assert(err, IsNil)
diff --git a/transcoder/gif.go b/transcoder/gif.go
index eb0392d..a4901b6 100644
--- a/transcoder/gif.go
+++ b/transcoder/gif.go
@@ -2,6 +2,7 @@ package transcoder
 
 import (
 	"github.com/barnacs/compy/proxy"
+	"github.com/chai2010/webp"
 	"image/gif"
 	"net/http"
 )
@@ -13,8 +14,18 @@ func (t *Gif) Transcode(w *proxy.ResponseWriter, r *proxy.ResponseReader, header
 	if err != nil {
 		return err
 	}
-	if err = gif.Encode(w, img, nil); err != nil {
-		return err
+	if SupportsWebP(headers) {
+		w.Header().Set("Content-Type", "image/webp")
+		options := webp.Options{
+			Lossless: true,
+		}
+		if err = webp.Encode(w, img, &options); err != nil {
+			return err
+		}
+	} else {
+		if err = gif.Encode(w, img, nil); err != nil {
+			return err
+		}
 	}
 	return nil
 }