serve http: add fallback embedded favicon

Browsers make a request to /favicon.ico when visiting pages generated
by the HTTP server.

Previously, if remotes did not have a /favicon.ico then the server
responded with a 404, causing browsers to show a default icon.

This adds a tiny fallback embedded PNG rclone favicon to help users
identify the rclone browser tab.

cmd/serve/http/http.go

@@ -3,6 +3,7 @@ package http
 
 import (
 	"context"
+	_ "embed"
 	"errors"
 	"fmt"
 	"io"
@@ -57,6 +58,9 @@ var DefaultOpt = Options{
 // Opt is options set by command line flags
 var Opt = DefaultOpt
 
+//go:embed favicon.png
+var faviconData []byte
+
 func init() {
 	fs.RegisterGlobalOptions(fs.OptionsInfo{Name: "http", Opt: &Opt, Options: OptionsInfo})
 }
@@ -201,6 +205,7 @@ func newServer(ctx context.Context, f fs.Fs, opt *Options, vfsOpt *vfscommon.Opt
 		middleware.SetHeader("Accept-Ranges", "bytes"),
 		middleware.SetHeader("Server", "rclone/"+fs.Version),
 	)
+	router.Get("/favicon.ico", s.serveFavicon)
 	router.Get("/*", s.handler)
 	router.Head("/*", s.handler)
 
@@ -225,6 +230,27 @@ func (s *HTTP) Shutdown() error {
 	return s.server.Shutdown()
 }
 
+// serveFavicon serves the remote's favicon.ico if it exists, otherwise
+// the rclone favicon
+func (s *HTTP) serveFavicon(w http.ResponseWriter, r *http.Request) {
+	ctx := r.Context()
+	VFS, err := s.getVFS(ctx)
+	if err == nil {
+		node, err := VFS.Stat("favicon.ico")
+		if err == nil && node.IsFile() {
+			// Remote has favicon.ico, serve it as a regular file
+			s.serveFile(w, r, "favicon.ico")
+			return
+		}
+	}
+	// Serve the embedded rclone favicon
+	w.Header().Set("Content-Type", "image/png")
+	w.Header().Set("Cache-Control", "max-age=86400")
+	if _, err := w.Write(faviconData); err != nil {
+		fs.Debugf(nil, "Failed to write favicon: %v", err)
+	}
+}
+
 // handler reads incoming requests and dispatches them
 func (s *HTTP) handler(w http.ResponseWriter, r *http.Request) {
 	isDir := strings.HasSuffix(r.URL.Path, "/")

cmd/serve/http/http_test.go

@@ -297,6 +297,56 @@ func TestAuthProxy(t *testing.T) {
 	testGET(t, true)
 }
 
+func TestFavicon(t *testing.T) {
+	ctx := context.Background()
+
+	doGet := func(testURL, path string) *http.Response {
+		req, err := http.NewRequest("GET", testURL+path, nil)
+		require.NoError(t, err)
+		req.SetBasicAuth(testUser, testPass)
+		resp, err := http.DefaultClient.Do(req)
+		require.NoError(t, err)
+		return resp
+	}
+
+	t.Run("fallback", func(t *testing.T) {
+		// testdata/files has no favicon.ico, so the embedded fallback is served
+		f, err := fs.NewFs(ctx, "testdata/files")
+		require.NoError(t, err)
+		s, testURL := start(ctx, t, f)
+		defer func() { assert.NoError(t, s.server.Shutdown()) }()
+
+		resp := doGet(testURL, "favicon.ico")
+		defer func() { _ = resp.Body.Close() }()
+		assert.Equal(t, http.StatusOK, resp.StatusCode)
+		assert.Equal(t, "image/png", resp.Header.Get("Content-Type"))
+		assert.Equal(t, "max-age=86400", resp.Header.Get("Cache-Control"))
+		body, err := io.ReadAll(resp.Body)
+		require.NoError(t, err)
+		assert.Equal(t, faviconData, body)
+	})
+
+	t.Run("remote override", func(t *testing.T) {
+		// Start a server on a temp dir that already contains a custom favicon.ico,
+		// so the VFS sees it at init time and serves it instead of the fallback.
+		dir := t.TempDir()
+		customFavicon := []byte("custom favicon data")
+		require.NoError(t, os.WriteFile(filepath.Join(dir, "favicon.ico"), customFavicon, 0666))
+
+		f, err := fs.NewFs(ctx, dir)
+		require.NoError(t, err)
+		s, testURL := start(ctx, t, f)
+		defer func() { assert.NoError(t, s.server.Shutdown()) }()
+
+		resp := doGet(testURL, "favicon.ico")
+		defer func() { _ = resp.Body.Close() }()
+		assert.Equal(t, http.StatusOK, resp.StatusCode)
+		body, err := io.ReadAll(resp.Body)
+		require.NoError(t, err)
+		assert.Equal(t, customFavicon, body)
+	})
+}
+
 func TestRc(t *testing.T) {
 	servetest.TestRc(t, rc.Params{
 		"type":           "http",