[assetserver] Add support for serving the index.html file when requesting a directory (#2110)

* [assets] Improve error message if no `index.html` could be found in the assets

* [assetoptions] Valide options that at least one property has been set

* [assetserver] Move defaultHTML handling for 404 from assethandler to assetserver

* [assetserver] Add support for serving the index.html file when requesting a directory

* [docs] Update changelog

v2/internal/app/app_dev.go

@@ -91,7 +91,10 @@ func CreateApp(appoptions *options.App) (*App, error) {
 		}
 	}
 
-	assetConfig := assetserver.BuildAssetServerConfig(appoptions)
+	assetConfig, err := assetserver.BuildAssetServerConfig(appoptions)
+	if err != nil {
+		return nil, err
+	}
 
 	if assetConfig.Assets == nil && frontendDevServerURL != "" {
 		myLogger.Warning("No AssetServer.Assets has been defined but a frontend DevServer, the frontend DevServer will not be used.")
@@ -118,7 +121,7 @@ func CreateApp(appoptions *options.App) (*App, error) {
 			// If no assetdir has been defined, let's try to infer it from the project root and the asset FS.
 			assetdir, err = tryInferAssetDirFromFS(assetConfig.Assets)
 			if err != nil {
-				return nil, err
+				return nil, fmt.Errorf("unable to infer the AssetDir from your Assets fs.FS: %w", err)
 			}
 		}
 

v2/internal/frontend/assetserver/assethandler.go

@@ -3,7 +3,8 @@ package assetserver
 import (
 	"bytes"
 	"context"
-	_ "embed"
+	"embed"
+	"errors"
 	"fmt"
 	"io"
 	iofs "io/fs"
@@ -47,6 +48,16 @@ func NewAssetHandler(ctx context.Context, options assetserver.Options) (http.Han
 
 		subDir, err := fs.FindPathToFile(vfs, indexHTML)
 		if err != nil {
+			if errors.Is(err, os.ErrNotExist) {
+				msg := "no `index.html` could be found in your Assets fs.FS"
+				if embedFs, isEmbedFs := vfs.(embed.FS); isEmbedFs {
+					rootFolder, _ := fs.FindEmbedRootPath(embedFs)
+					msg += fmt.Sprintf(", please make sure the embedded directory '%s' is correct and contains your assets", rootFolder)
+				}
+
+				return nil, fmt.Errorf(msg)
+			}
+
 			return nil, err
 		}
 
@@ -70,22 +81,18 @@ func NewAssetHandler(ctx context.Context, options assetserver.Options) (http.Han
 }
 
 func (d *assetHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	url := req.URL.Path
 	handler := d.handler
 	if strings.EqualFold(req.Method, http.MethodGet) {
-		filename := strings.TrimPrefix(req.URL.Path, "/")
+		filename := path.Clean(strings.TrimPrefix(url, "/"))
-		if filename == "" {
-			filename = indexHTML
-		}
 
-		d.logDebug("Loading file '%s'", filename)
+		d.logDebug("Handling request '%s' (file='%s')", url, filename)
 		if err := d.serveFSFile(rw, req, filename); err != nil {
 			if os.IsNotExist(err) {
 				if handler != nil {
-					d.logDebug("File '%s' not found, serving '%s' by AssetHandler", filename, req.URL)
+					d.logDebug("File '%s' not found, serving '%s' by AssetHandler", filename, url)
 					handler.ServeHTTP(rw, req)
 					err = nil
-				} else if filename == indexHTML {
-					err = serveFile(rw, filename, defaultHTML)
 				} else {
 					rw.WriteHeader(http.StatusNotFound)
 					err = nil
@@ -98,7 +105,7 @@ func (d *assetHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 			}
 		}
 	} else if handler != nil {
-		d.logDebug("No GET request, serving '%s' by AssetHandler", req.URL)
+		d.logDebug("No GET request, serving '%s' by AssetHandler", url)
 		handler.ServeHTTP(rw, req)
 	} else {
 		rw.WriteHeader(http.StatusMethodNotAllowed)
@@ -122,6 +129,29 @@ func (d *assetHandler) serveFSFile(rw http.ResponseWriter, req *http.Request, fi
 		return err
 	}
 
+	if statInfo.IsDir() {
+		url := req.URL.Path
+		if url != "" && url[len(url)-1] != '/' {
+			// If the URL doesn't end in a slash normally a http.redirect should be done, but that currently doesn't work on
+			// WebKit WebVies (macOS/Linux).
+			// So we handle this as a file that could not be found.
+			return os.ErrNotExist
+		}
+
+		filename = path.Join(filename, indexHTML)
+
+		file, err = d.fs.Open(filename)
+		if err != nil {
+			return err
+		}
+		defer file.Close()
+
+		statInfo, err = file.Stat()
+		if err != nil {
+			return err
+		}
+	}
+
 	var buf [512]byte
 	n, err := file.Read(buf[:])
 	if err != nil && err != io.EOF {

v2/internal/frontend/assetserver/assetserver.go

@@ -34,7 +34,11 @@ type AssetServer struct {
 }
 
 func NewAssetServerMainPage(ctx context.Context, bindingsJSON string, options *options.App) (*AssetServer, error) {
-	return NewAssetServer(ctx, bindingsJSON, BuildAssetServerConfig(options))
+	assetOptions, err := BuildAssetServerConfig(options)
+	if err != nil {
+		return nil, err
+	}
+	return NewAssetServer(ctx, bindingsJSON, assetOptions)
 }
 
 func NewAssetServer(ctx context.Context, bindingsJSON string, options assetserver.Options) (*AssetServer, error) {
@@ -96,19 +100,23 @@ func (d *AssetServer) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 			header[k] = v
 		}
 
-		if recorder.Code != http.StatusOK {
+		switch recorder.Code {
+		case http.StatusOK:
+			content, err := d.processIndexHTML(recorder.Body.Bytes())
+			if err != nil {
+				d.serveError(rw, err, "Unable to processIndexHTML")
+				return
+			}
+			d.writeBlob(rw, indexHTML, content)
+
+		case http.StatusNotFound:
+			d.writeBlob(rw, indexHTML, defaultHTML)
+
+		default:
 			rw.WriteHeader(recorder.Code)
-			return
-		}
 
-		content, err := d.processIndexHTML(recorder.Body.Bytes())
-		if err != nil {
-			d.serveError(rw, err, "Unable to processIndexHTML")
-			return
 		}
 
-		d.writeBlob(rw, "/index.html", content)
-
 	case runtimeJSPath:
 		d.writeBlob(rw, path, d.runtimeJS)
 

v2/internal/frontend/assetserver/common.go

@@ -13,19 +13,22 @@ import (
 	"golang.org/x/net/html"
 )
 
-func BuildAssetServerConfig(options *options.App) assetserver.Options {
+func BuildAssetServerConfig(appOptions *options.App) (assetserver.Options, error) {
-	if opts := options.AssetServer; opts != nil {
+	var options assetserver.Options
-		if options.Assets != nil || options.AssetsHandler != nil {
+	if opt := appOptions.AssetServer; opt != nil {
+		if appOptions.Assets != nil || appOptions.AssetsHandler != nil {
 			panic("It's not possible to use the deprecated Assets and AssetsHandler options and the new AssetServer option at the same time. Please migrate all your Assets options to the AssetServer option.")
 		}
 
-		return *opts
+		options = *opt
+	} else {
+		options = assetserver.Options{
+			Assets:  appOptions.Assets,
+			Handler: appOptions.AssetsHandler,
+		}
 	}
 
-	return assetserver.Options{
+	return options, options.Validate()
-		Assets:  options.Assets,
-		Handler: options.AssetsHandler,
-	}
 }
 
 const (

v2/internal/frontend/devserver/devserver.go

@@ -54,7 +54,10 @@ func (d *DevWebServer) Run(ctx context.Context) error {
 	d.server.GET("/wails/reload", d.handleReload)
 	d.server.GET("/wails/ipc", d.handleIPCWebSocket)
 
-	assetServerConfig := assetserver.BuildAssetServerConfig(d.appoptions)
+	assetServerConfig, err := assetserver.BuildAssetServerConfig(d.appoptions)
+	if err != nil {
+		return err
+	}
 
 	var assetHandler http.Handler
 	var wsHandler http.Handler

v2/internal/fs/fs.go

@@ -2,6 +2,7 @@ package fs
 
 import (
 	"crypto/md5"
+	"embed"
 	"fmt"
 	"io"
 	"io/fs"
@@ -376,7 +377,7 @@ func FindPathToFile(fsys fs.FS, file string) (string, error) {
 		path, _ := filepath.Split(indexFiles.AsSlice()[0])
 		return path, nil
 	}
-	return "", fmt.Errorf("no index.html found")
+	return "", fmt.Errorf("%s: %w", file, os.ErrNotExist)
 }
 
 // FindFileInParents searches for a file in the current directory and all parent directories.
@@ -402,3 +403,32 @@ func FindFileInParents(path string, filename string) string {
 	}
 	return pathToFile
 }
+
+// FindEmbedRootPath finds the root path in the embed FS. It's the directory which contains all the files.
+func FindEmbedRootPath(fsys embed.FS) (string, error) {
+	stopErr := fmt.Errorf("files or multiple dirs found")
+
+	fPath := ""
+	err := fs.WalkDir(fsys, ".", func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if d.IsDir() {
+			fPath = path
+			if entries, dErr := fs.ReadDir(fsys, path); dErr != nil {
+				return dErr
+			} else if len(entries) <= 1 {
+				return nil
+			}
+		}
+
+		return stopErr
+	})
+
+	if err != nil && err != stopErr {
+		return "", err
+	}
+
+	return fPath, nil
+}

v2/pkg/options/assetserver/options.go

@@ -1,6 +1,7 @@
 package assetserver
 
 import (
+	"fmt"
 	"io/fs"
 	"net/http"
 )
@@ -33,3 +34,12 @@ type Options struct {
 	//   ChainMiddleware(middleware ...Middleware) Middleware
 	Middleware Middleware
 }
+
+// Validate the options
+func (o Options) Validate() error {
+	if o.Assets == nil && o.Handler == nil && o.Middleware == nil {
+		return fmt.Errorf("AssetServer options invalid: either Assets, Handler or Middleware must be set")
+	}
+
+	return nil
+}

website/src/pages/changelog.mdx

@@ -20,12 +20,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - The [AssetServer](/docs/reference/options#assetserver) now supports handling range-requests if the [Assets](/docs/reference/options/#assets-1) `fs.FS` provides an `io.ReadSeeker`. Added by @stffabi in [PR](https://github.com/wailsapp/wails/pull/2091)
 - Add new property for the `wails.json` config file - `bindings`. More information on the new property can be found in the updated [schema](/schemas/config.v2.json). Properties `prefix` and `suffix` allow you to control the generated TypeScript entity name in the `model.ts` file. Added by @OlegGulevskyy in [PR](https://github.com/wailsapp/wails/pull/2101)
 - The `WindowSetAlwaysOnTop` method is now exposed in the JS runtime. Fixed by @gotid in [PR](https://github.com/wailsapp/wails/pull/2128)
+- The [AssetServer](/docs/reference/options#assetserver) now supports serving the index.html file when requesting a directory. Added by @stffabi in [PR](https://github.com/wailsapp/wails/pull/2110)
 
 ### Fixed
 - The `noreload` flag in wails dev wasn't applied. Fixed by @stffabi in this [PR](https://github.com/wailsapp/wails/pull/2081)
 - `build/bin` folder was duplicating itself on each reload in `wails dev` mode. Fixed by @OlegGulevskyy in this [PR](https://github.com/wailsapp/wails/pull/2103)
 - Prevent a thin white line at the bottom of a frameless window on Windows. Fixed by @stffabi in this [PR](https://github.com/wailsapp/wails/pull/2111)
 
+### Changed
+- Improve error message if no `index.html` could be found in the assets and validate assetserver options. Changed by @stffabi in this [PR](https://github.com/wailsapp/wails/pull/2110)
+
 ## v2.2.0 - 2022-11-09
 
 ### Added