[pocketbase#661] serve css files with text/css content-type

Currently, css files are served as text/plain by the server. It is not
trivial to detect css file types similar to the issue with svg files.

When the css files are served as text/plain instead of
text/css they become unusable as stylesheets in the browser when served
via the api.

In this commit we generalize the svg detection to also detect css files
and serve specific extensions with their respective mimetypes.

tools/filesystem/filesystem.go

@@ -196,6 +196,12 @@ var inlineServeContentTypes = []string{
 	"application/pdf", "application/x-pdf",
 }
 
+// manualExtensionContentTypes is a map of file extensions to content types.
+var manualExtensionContentTypes = map[string]string{
+	".svg": "image/svg+xml", // (see https://github.com/whatwg/mimesniff/issues/7)
+	".css": "text/css",      // (see https://github.com/gabriel-vasile/mimetype/pull/113)
+}
+
 // Serve serves the file at fileKey location to an HTTP response.
 func (s *System) Serve(response http.ResponseWriter, fileKey string, name string) error {
 	r, readErr := s.bucket.NewReader(s.ctx, fileKey, nil)
@@ -210,12 +216,11 @@ func (s *System) Serve(response http.ResponseWriter, fileKey string, name string
 		disposition = "inline"
 	}
 
-	// make an exception for svg and force a custom content type
-	// to send in the response so that it can be loaded in an img tag
-	// (see https://github.com/whatwg/mimesniff/issues/7)
+	// make an exception for specific content types and force a
+	// custom content type to send in the response so that it can be loaded directly.
 	extContentType := realContentType
-	if extContentType != "image/svg+xml" && filepath.Ext(name) == ".svg" {
-		extContentType = "image/svg+xml"
+	if ct, found := manualExtensionContentTypes[filepath.Ext(name)]; found && extContentType != ct {
+		extContentType = ct
 	}
 
 	response.Header().Set("Content-Disposition", disposition+"; filename="+name)

tools/filesystem/filesystem_test.go

@@ -207,6 +207,18 @@ func TestFileSystemServe(t *testing.T) {
 				"Content-Security-Policy": "default-src 'none'; style-src 'unsafe-inline'; sandbox",
 			},
 		},
+		{
+			// css exception
+			"style.css",
+			"test_name.css",
+			false,
+			map[string]string{
+				"Content-Disposition":     "attachment; filename=test_name.css",
+				"Content-Type":            "text/css",
+				"Content-Length":          "0",
+				"Content-Security-Policy": "default-src 'none'; style-src 'unsafe-inline'; sandbox",
+			},
+		},
 	}
 
 	for _, scenario := range scenarios {
@@ -216,7 +228,7 @@ func TestFileSystemServe(t *testing.T) {
 		hasErr := err != nil
 
 		if hasErr != scenario.expectError {
-			t.Errorf("(%s) Expected hasError %v, got %v", scenario.path, scenario.expectError, hasErr)
+			t.Errorf("(%s) Expected hasError %v, got %v (%v)", scenario.path, scenario.expectError, hasErr, err)
 			continue
 		}
 
@@ -321,5 +333,11 @@ func createTestDir(t *testing.T) string {
 	}
 	file4.Close()
 
+	file5, err := os.OpenFile(filepath.Join(dir, "style.css"), os.O_WRONLY|os.O_CREATE, 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+	file5.Close()
+
 	return dir
 }