[v3] AssetServer options update comments

v3/pkg/application/application.go

@@ -45,7 +45,12 @@ func New(appOptions Options) *App {
 
 	result.Events = NewCustomEventProcessor(result.dispatchEventToWindows)
 
-	opts := assetserveroptions.Options{Assets: appOptions.Assets.FS, Handler: appOptions.Assets.Handler, Middleware: appOptions.Assets.Middleware}
+	opts := assetserveroptions.Options{
+		Assets:     appOptions.Assets.FS,
+		Handler:    appOptions.Assets.Handler,
+		Middleware: assetserveroptions.Middleware(appOptions.Assets.Middleware),
+	}
+
 	// TODO ServingFrom disk?
 	srv, err := assetserver.NewAssetServer("", opts, false, nil, wailsruntime.RuntimeAssetsBundle)
 	if err != nil {

v3/pkg/application/options_application.go

@@ -20,11 +20,46 @@ type Options struct {
 	Assets AssetOptions
 }
 
+// AssetOptions defines the configuration of the AssetServer.
 type AssetOptions struct {
-	// FS to use for loading assets from
+	// FS defines the static assets to be used. A GET request is first tried to be served from this FS. If the FS returns
+	// `os.ErrNotExist` for that file, the request handling will fallback to the Handler and tries to serve the GET
+	// request from it.
+	//
+	// If set to nil, all GET requests will be forwarded to Handler.
 	FS fs.FS
-	// Handler is a custom handler to use for serving assets. If this is set, the `URL` and `FS` fields are ignored.
+
+	// Handler will be called for every GET request that can't be served from FS, due to `os.ErrNotExist`. Furthermore all
+	// non GET requests will always be served from this Handler.
+	//
+	// If not defined, the result is the following in cases where the Handler would have been called:
+	//   GET request:   `http.StatusNotFound`
+	//   Other request: `http.StatusMethodNotAllowed`
 	Handler http.Handler
-	// Middleware is a custom middleware to use for serving assets. If this is set, the `URL` and `FS` fields are ignored.
-	Middleware func(http.Handler) http.Handler
+
+	// Middleware is a HTTP Middleware which allows to hook into the AssetServer request chain. It allows to skip the default
+	// request handler dynamically, e.g. implement specialized Routing etc.
+	// The Middleware is called to build a new `http.Handler` used by the AssetSever and it also receives the default
+	// handler used by the AssetServer as an argument.
+	//
+	// If not defined, the default AssetServer request chain is executed.
+	//
+	// Multiple Middlewares can be chained together with:
+	//   ChainMiddleware(middleware ...Middleware) Middleware
+	Middleware Middleware
+}
+
+// Middleware defines a HTTP middleware that can be applied to the AssetServer.
+// The handler passed as next is the next handler in the chain. One can decide to call the next handler
+// or implement a specialized handling.
+type Middleware func(next http.Handler) http.Handler
+
+// ChainMiddleware allows chaining multiple middlewares to one middleware.
+func ChainMiddleware(middleware ...Middleware) Middleware {
+	return func(h http.Handler) http.Handler {
+		for i := len(middleware) - 1; i >= 0; i-- {
+			h = middleware[i](h)
+		}
+		return h
+	}
 }