MM-25095: Handles static JS and CSS using Brotli encoding. (#14524)

* MM-25095: Handles static JS and CSS files using Brotli.

* MM-25095: Linting fix.

* MM-25095: Adds missing license.

* MM-25095: Moves initialization of slice.

* MM-25095: Moves initialization of slice.

web/static_test.go

@@ -0,0 +1,58 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package web
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+var tests = []struct {
+	requestURL            string
+	requestContentType    string
+	requestAcceptEncoding []string
+	expectBrotli          bool
+}{
+	{"http://test.com/foo.js", "application/javascript", []string{"br"}, true},
+	{"http://test.com/foo.css", "text/css", []string{"br"}, true},
+	{"http://test.com/foo.jss", "text/plain; charset=utf-8", []string{"gzip"}, false},
+	{"http://test.com/foo.css", "text/plain; charset=utf-8", []string{"gzip"}, false},
+	{"http://test.com/foo.jsx", "text/plain; charset=utf-8", []string{"br"}, false},
+	{"http://test.com/foo.xcss", "text/plain; charset=utf-8", []string{"gzip"}, false},
+}
+
+type mockHandler struct{}
+
+func (mh mockHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintf(w, "hello")
+}
+
+func TestBrotliFilesHandler(t *testing.T) {
+	for _, tt := range tests {
+		t.Run(fmt.Sprintf("%v", tt), func(t *testing.T) {
+
+			req := httptest.NewRequest("GET", tt.requestURL, nil)
+			req.Header.Set("Accept-Encoding", strings.Join(tt.requestAcceptEncoding, ", "))
+			w := httptest.NewRecorder()
+
+			handler := brotliFilesHandler(mockHandler{})
+			handler.ServeHTTP(w, req)
+
+			resp := w.Result()
+
+			require.Equal(t, tt.expectBrotli, resp.Header.Get("Content-Encoding") == "br")
+			if tt.expectBrotli {
+				require.Equal(t, tt.requestURL+".br", req.URL.String())
+			} else {
+				require.Equal(t, tt.requestURL, req.URL.String())
+			}
+			require.Equal(t, tt.requestContentType, resp.Header.Get("Content-Type"))
+		})
+	}
+}