gzhttp: Canonicalize ETag header (#1139)

This ensures the fast-path is hit in the net/http header functions for a
minor speed improvement.

Author: justinmayhew

gzhttp/compress.go

@@ -64,7 +64,7 @@ const (
 	acceptRanges    = "Accept-Ranges"
 	contentType     = "Content-Type"
 	contentLength   = "Content-Length"
-	eTag            = "ETag"
+	eTag            = "Etag"
 )
 
 type codings map[string]float64

gzhttp/compress_test.go

@@ -230,7 +230,7 @@ func TestGzipHandlerSuffixETag(t *testing.T) {
 
 	handlerWithETag := wrapper(
 		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			w.Header().Set("ETag", `W/"1234"`)
+			w.Header().Set("Etag", `W/"1234"`)
 			w.WriteHeader(http.StatusOK)
 			w.Write([]byte(testBody))
 		}))
@@ -251,7 +251,7 @@ func TestGzipHandlerSuffixETag(t *testing.T) {
 	resWithEtag := respWithEtag.Result()
 	assertEqual(t, 200, resWithEtag.StatusCode)
 	assertEqual(t, "gzip", resWithEtag.Header.Get("Content-Encoding"))
-	assertEqual(t, `W/"1234-gzip"`, resWithEtag.Header.Get("ETag"))
+	assertEqual(t, `W/"1234-gzip"`, resWithEtag.Header.Get("Etag"))
 	zr, err := gzip.NewReader(resWithEtag.Body)
 	assertNil(t, err)
 	got, err := io.ReadAll(zr)
@@ -261,7 +261,7 @@ func TestGzipHandlerSuffixETag(t *testing.T) {
 	resWithoutEtag := respWithoutEtag.Result()
 	assertEqual(t, 200, resWithoutEtag.StatusCode)
 	assertEqual(t, "gzip", resWithoutEtag.Header.Get("Content-Encoding"))
-	assertEqual(t, "", resWithoutEtag.Header.Get("ETag"))
+	assertEqual(t, "", resWithoutEtag.Header.Get("Etag"))
 	zr, err = gzip.NewReader(resWithoutEtag.Body)
 	assertNil(t, err)
 	got, err = io.ReadAll(zr)
@@ -275,13 +275,13 @@ func TestGzipHandlerDropETag(t *testing.T) {
 
 	handlerCompressed := wrapper(
 		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			w.Header().Set("ETag", `W/"1234"`)
+			w.Header().Set("Etag", `W/"1234"`)
 			w.WriteHeader(http.StatusOK)
 			w.Write([]byte(testBody))
 		}))
 	handlerUncompressed := wrapper(
 		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			w.Header().Set("ETag", `W/"1234"`)
+			w.Header().Set("Etag", `W/"1234"`)
 			w.Header().Set(HeaderNoCompression, "true")
 			w.WriteHeader(http.StatusOK)
 			w.Write([]byte(testBody))
@@ -298,7 +298,7 @@ func TestGzipHandlerDropETag(t *testing.T) {
 	resCompressed := respCompressed.Result()
 	assertEqual(t, 200, resCompressed.StatusCode)
 	assertEqual(t, "gzip", resCompressed.Header.Get("Content-Encoding"))
-	assertEqual(t, "", resCompressed.Header.Get("ETag"))
+	assertEqual(t, "", resCompressed.Header.Get("Etag"))
 	zr, err := gzip.NewReader(resCompressed.Body)
 	assertNil(t, err)
 	got, err := io.ReadAll(zr)
@@ -308,7 +308,7 @@ func TestGzipHandlerDropETag(t *testing.T) {
 	resUncompressed := respUncompressed.Result()
 	assertEqual(t, 200, resUncompressed.StatusCode)
 	assertEqual(t, "", resUncompressed.Header.Get("Content-Encoding"))
-	assertEqual(t, `W/"1234"`, resUncompressed.Header.Get("ETag"))
+	assertEqual(t, `W/"1234"`, resUncompressed.Header.Get("Etag"))
 	got, err = io.ReadAll(resUncompressed.Body)
 	assertNil(t, err)
 	assertEqual(t, testBody, got)
@@ -333,7 +333,7 @@ func TestSuffixETagEncodingSpecific(t *testing.T) {
 			assertNil(t, err)
 
 			handler := wrapper(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-				w.Header().Set("ETag", `W/"1234"`)
+				w.Header().Set("Etag", `W/"1234"`)
 				w.Write(testBody)
 			}))
 
@@ -343,7 +343,7 @@ func TestSuffixETagEncodingSpecific(t *testing.T) {
 			handler.ServeHTTP(resp, req)
 
 			res := resp.Result()
-			assertEqual(t, tt.wantETag, res.Header.Get("ETag"))
+			assertEqual(t, tt.wantETag, res.Header.Get("Etag"))
 		})
 	}
 }