[v2] Add support for AssetsHandler (#1325)

* [website] Fix devserver default value doc

* [v2] Add support for AssetsHandler

AssetsHandler is a http.Handler delegate, which gets called
as a fallback for all Non-GET requests and for GET requests
for which the Assets didn’t find the file.

Known Limitations on Linux:
- All requests are GET requests
- No request headers
- No request body
- No response status code, only StatusOK will be returned
- No response headers

Known Limitations on Windows:
-  Request body is leaking memory. Seems to be a bug in
    WebView2, investigation angoing.

Most of these limitations on Linux will be fixed in the future with
adding support for Webkit2Gtk 2.36.0+.

* [v2, linux] Add response streaming support

The complete response won’t be held anymore in memory and will
be streamed to WebKit2.

Co-authored-by: Lea Anthony <lea.anthony@gmail.com>

v2/internal/appng/app_dev.go

@@ -9,6 +9,7 @@ import (
 	"flag"
 	"fmt"
 	iofs "io/fs"
+	"net/url"
 	"os"
 	"path/filepath"
 
@@ -114,7 +115,13 @@ func CreateApp(appoptions *options.App) (*App, error) {
 		if devServer == "" {
 			return nil, fmt.Errorf("Unable to use FrontendDevServerUrl without a DevServer address")
 		}
-		ctx = context.WithValue(ctx, "starturl", "http://"+devServer)
+
+		startURL, err := url.Parse("http://" + devServer)
+		if err != nil {
+			return nil, err
+		}
+
+		ctx = context.WithValue(ctx, "starturl", startURL)
 		ctx = context.WithValue(ctx, "frontenddevserverurl", frontendDevServerURL)
 
 		myLogger.Info("Serving assets from frontend DevServer URL: %s", frontendDevServerURL)

v2/internal/frontend/assetserver/assethandler.go

@@ -1,8 +1,11 @@
 package assetserver
 
 import (
+	"bytes"
 	"context"
 	_ "embed"
+	"fmt"
+	"io"
 	iofs "io/fs"
 	"net/http"
 	"os"
@@ -18,8 +21,13 @@ import (
 //go:embed defaultindex.html
 var defaultHTML []byte
 
+const (
+	indexHTML = "index.html"
+)
+
 type assetHandler struct {
-	fs iofs.FS
+	fs      iofs.FS
+	handler http.Handler
 
 	logger *logger.Logger
 
@@ -33,7 +41,7 @@ func NewAsssetHandler(ctx context.Context, options *options.App) (http.Handler,
 			return nil, err
 		}
 
-		subDir, err := fs.FindPathToFile(vfs, "index.html")
+		subDir, err := fs.FindPathToFile(vfs, indexHTML)
 		if err != nil {
 			return nil, err
 		}
@@ -45,7 +53,8 @@ func NewAsssetHandler(ctx context.Context, options *options.App) (http.Handler,
 	}
 
 	result := &assetHandler{
-		fs: vfs,
+		fs:      vfs,
+		handler: options.AssetsHandler,
 
 		// Check if we have been given a directory to serve assets from.
 		// If so, this means we are in dev mode and are serving assets off disk.
@@ -62,63 +71,96 @@ func NewAsssetHandler(ctx context.Context, options *options.App) (http.Handler,
 }
 
 func (d *assetHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
-	if d.fs == nil {
-		rw.WriteHeader(http.StatusNotFound)
-		return
-	}
-
-	filename := strings.TrimPrefix(req.URL.Path, "/")
-	if d.logger != nil {
-		d.logger.Debug("[AssetHandler] Loading file '%s'", filename)
-	}
-
-	var content []byte
-	var err error
-	switch filename {
-	case "", "index.html":
-		content, err = d.loadFile("index.html")
-		if err != nil {
-			err = nil
-			content = defaultHTML
+	handler := d.handler
+	if strings.EqualFold(req.Method, http.MethodGet) {
+		filename := strings.TrimPrefix(req.URL.Path, "/")
+		if filename == "" {
+			filename = indexHTML
 		}
 
-	default:
-		content, err = d.loadFile(filename)
+		d.logDebug("[AssetHandler] Loading file '%s'", filename)
+		if err := d.serveFSFile(rw, filename); err != nil {
+			if os.IsNotExist(err) {
+				if handler != nil {
+					d.logDebug("[AssetHandler] File '%s' not found, serving '%s' by AssetHandler", filename, req.URL)
+					handler.ServeHTTP(rw, req)
+				} else {
+					rw.WriteHeader(http.StatusNotFound)
+				}
+			} else {
+				d.logError("[AssetHandler] Unable to load file '%s': %s", filename, err)
+				http.Error(rw, err.Error(), http.StatusInternalServerError)
+			}
+		}
+	} else if handler != nil {
+		d.logDebug("[AssetHandler] No GET request, serving '%s' by AssetHandler", req.URL)
+		handler.ServeHTTP(rw, req)
+	} else {
+		rw.WriteHeader(http.StatusMethodNotAllowed)
+	}
+}
+
+// serveFile will try to load the file from the fs.FS and write it to the response
+func (d *assetHandler) serveFSFile(rw http.ResponseWriter, filename string) error {
+	if d.fs == nil {
+		return os.ErrNotExist
 	}
 
-	if os.IsNotExist(err) {
-		rw.WriteHeader(http.StatusNotFound)
-		return
-	}
-
-	if err == nil {
-		mimeType := GetMimetype(filename, content)
-		rw.Header().Set(HeaderContentType, mimeType)
-		rw.WriteHeader(http.StatusOK)
-		_, err = rw.Write(content)
+	file, err := d.fs.Open(filename)
+	if err != nil && d.servingFromDisk {
+		for tries := 0; tries < 50; tries++ {
+			file, err = d.fs.Open(filename)
+			if err != nil {
+				time.Sleep(100 * time.Millisecond)
+			}
+		}
 	}
 
 	if err != nil {
-		rw.WriteHeader(http.StatusInternalServerError)
-		if d.logger != nil {
-			d.logger.Error("[AssetHandler] Unable to load file '%s': %s", filename, err)
+		if filename == indexHTML && os.IsNotExist(err) {
+			return serveFile(rw, filename, defaultHTML)
 		}
+		return err
+	}
+	defer file.Close()
+
+	statInfo, err := file.Stat()
+	if err != nil {
+		return err
+	}
+
+	rw.Header().Set(HeaderContentLength, fmt.Sprintf("%d", statInfo.Size()))
+
+	var buf [512]byte
+	n, err := file.Read(buf[:])
+	if err != nil && err != io.EOF {
+		return err
+	}
+
+	// Detect MimeType by sniffing the first 512 bytes
+	if contentType := GetMimetype(filename, buf[:n]); contentType != "" {
+		rw.Header().Set(HeaderContentType, contentType)
+	}
+
+	// Write the first bytes
+	_, err = io.Copy(rw, bytes.NewReader(buf[:n]))
+	if err != nil {
+		return err
+	}
+
+	// Copy the remaining content of the file
+	_, err = io.Copy(rw, file)
+	return err
+}
+
+func (d *assetHandler) logDebug(message string, args ...interface{}) {
+	if d.logger != nil {
+		d.logger.Debug("[AssetHandler] "+message, args...)
 	}
 }
 
-// loadFile will try to load the file from disk. If there is an error
-// it will retry until eventually it will give up and error.
-func (d *assetHandler) loadFile(filename string) ([]byte, error) {
-	if !d.servingFromDisk {
-		return iofs.ReadFile(d.fs, filename)
+func (d *assetHandler) logError(message string, args ...interface{}) {
+	if d.logger != nil {
+		d.logger.Error("[AssetHandler] "+message, args...)
 	}
-	var result []byte
-	var err error
-	for tries := 0; tries < 50; tries++ {
-		result, err = iofs.ReadFile(d.fs, filename)
-		if err != nil {
-			time.Sleep(100 * time.Millisecond)
-		}
-	}
-	return result, err
 }

v2/internal/frontend/assetserver/assetserver.go

@@ -6,7 +6,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
-	"strings"
+	"strconv"
 
 	"github.com/wailsapp/wails/v2/internal/frontend/runtime"
 	"github.com/wailsapp/wails/v2/internal/logger"
@@ -106,26 +106,45 @@ func (d *AssetServer) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	}
 }
 
-func (d *AssetServer) Load(filename string) ([]byte, string, error) {
-	// This will be removed as soon as AssetsHandler have been fully introduced.
-	if !strings.HasPrefix(filename, "/") {
-		filename = "/" + filename
-	}
+// ProcessHTTPRequest processes the HTTP Request by faking a golang HTTP Server.
+// The request will be finished with a StatusNotImplemented code if no handler has written to the response.
+func (d *AssetServer) ProcessHTTPRequest(logInfo string, rw http.ResponseWriter, reqGetter func() (*http.Request, error)) {
+	rw = &contentTypeSniffer{rw: rw} // Make sure we have a Content-Type sniffer
 
-	req, err := http.NewRequest(http.MethodGet, "wails://wails"+filename, nil)
+	req, err := reqGetter()
 	if err != nil {
-		return nil, "", err
+		d.logError("Error processing request '%s': %s (HttpResponse=500)", logInfo, err)
+
+		http.Error(rw, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	if req.Body == nil {
+		req.Body = http.NoBody
+	}
+	defer req.Body.Close()
+
+	if req.RemoteAddr == "" {
+		// 192.0.2.0/24 is "TEST-NET" in RFC 5737
+		req.RemoteAddr = "192.0.2.1:1234"
+	}
+
+	if req.RequestURI == "" && req.URL != nil {
+		req.RequestURI = req.URL.String()
+	}
+
+	if req.ContentLength == 0 {
+		req.ContentLength, _ = strconv.ParseInt(req.Header.Get(HeaderContentLength), 10, 64)
+	} else {
+		req.Header.Set(HeaderContentLength, fmt.Sprintf("%d", req.ContentLength))
+	}
+
+	if host := req.Header.Get(HeaderHost); host != "" {
+		req.Host = host
 	}
 
-	rw := httptest.NewRecorder()
 	d.ServeHTTP(rw, req)
-
-	content := rw.Body.Bytes()
-	mimeType := rw.HeaderMap.Get(HeaderContentType)
-	if mimeType == "" {
-		mimeType = GetMimetype(filename, content)
-	}
-	return content, mimeType, nil
+	rw.WriteHeader(http.StatusNotImplemented) // This is a NOP when a handler has already written and set the status
 }
 
 func (d *AssetServer) processIndexHTML(indexHTML []byte) ([]byte, error) {
@@ -158,15 +177,8 @@ func (d *AssetServer) processIndexHTML(indexHTML []byte) ([]byte, error) {
 }
 
 func (d *AssetServer) writeBlob(rw http.ResponseWriter, filename string, blob []byte) {
-	header := rw.Header()
-	header.Set(HeaderContentLength, fmt.Sprintf("%d", len(blob)))
-	if mimeType := header.Get(HeaderContentType); mimeType == "" {
-		mimeType = GetMimetype(filename, blob)
-		header.Set(HeaderContentType, mimeType)
-	}
-
-	rw.WriteHeader(http.StatusOK)
-	if _, err := rw.Write(blob); err != nil {
+	err := serveFile(rw, filename, blob)
+	if err != nil {
 		d.serveError(rw, err, "Unable to write content %s", filename)
 	}
 }

v2/internal/frontend/assetserver/common.go

@@ -3,11 +3,15 @@ package assetserver
 import (
 	"bytes"
 	"errors"
+	"fmt"
+	"io"
+	"net/http"
 
 	"golang.org/x/net/html"
 )
 
 const (
+	HeaderHost          = "Host"
 	HeaderContentType   = "Content-Type"
 	HeaderContentLength = "Content-Length"
 	HeaderUserAgent     = "User-Agent"
@@ -16,6 +20,19 @@ const (
 	WailsUserAgentValue = "wails.io"
 )
 
+func serveFile(rw http.ResponseWriter, filename string, blob []byte) error {
+	header := rw.Header()
+	header.Set(HeaderContentLength, fmt.Sprintf("%d", len(blob)))
+	if mimeType := header.Get(HeaderContentType); mimeType == "" {
+		mimeType = GetMimetype(filename, blob)
+		header.Set(HeaderContentType, mimeType)
+	}
+
+	rw.WriteHeader(http.StatusOK)
+	_, err := io.Copy(rw, bytes.NewReader(blob))
+	return err
+}
+
 func createScriptNode(scriptName string) *html.Node {
 	return &html.Node{
 		Type: html.ElementNode,

v2/internal/frontend/assetserver/content_type_sniffer.go

@@ -0,0 +1,42 @@
+package assetserver
+
+import (
+	"net/http"
+)
+
+type contentTypeSniffer struct {
+	rw http.ResponseWriter
+
+	wroteHeader bool
+}
+
+func (rw *contentTypeSniffer) Header() http.Header {
+	return rw.rw.Header()
+}
+
+func (rw *contentTypeSniffer) Write(buf []byte) (int, error) {
+	rw.writeHeader(buf)
+	return rw.rw.Write(buf)
+}
+
+func (rw *contentTypeSniffer) WriteHeader(code int) {
+	if rw.wroteHeader {
+		return
+	}
+
+	rw.rw.WriteHeader(code)
+	rw.wroteHeader = true
+}
+
+func (rw *contentTypeSniffer) writeHeader(b []byte) {
+	if rw.wroteHeader {
+		return
+	}
+
+	m := rw.rw.Header()
+	if _, hasType := m[HeaderContentType]; !hasType {
+		m.Set(HeaderContentType, http.DetectContentType(b))
+	}
+
+	rw.WriteHeader(http.StatusOK)
+}

v2/internal/frontend/desktop/common/process_request.go

@@ -1,55 +0,0 @@
-package common
-
-import (
-	"fmt"
-	"net/http"
-	"os"
-	"strings"
-
-	"github.com/wailsapp/wails/v2/internal/frontend/assetserver"
-)
-
-type RequestRespone struct {
-	Body       []byte
-	MimeType   string
-	StatusCode int
-}
-
-func (r RequestRespone) StatusText() string {
-	return http.StatusText(r.StatusCode)
-}
-
-func (r RequestRespone) String() string {
-	return fmt.Sprintf("Body: '%s', StatusCode: %d", string(r.Body), r.StatusCode)
-}
-
-func ProcessRequest(uri string, assets *assetserver.AssetServer, expectedScheme string, expectedHosts ...string) (RequestRespone, error) {
-	// Translate URI to file
-	file, err := translateUriToFile(uri, expectedScheme, expectedHosts...)
-	if err != nil {
-		if err == ErrUnexpectedHost {
-			body := fmt.Sprintf("expected host one of \"%s\"", strings.Join(expectedHosts, ","))
-			return textResponse(body, http.StatusInternalServerError), err
-		}
-
-		return RequestRespone{StatusCode: http.StatusInternalServerError}, err
-	}
-
-	content, mimeType, err := assets.Load(file)
-	if err != nil {
-		statusCode := http.StatusInternalServerError
-		if os.IsNotExist(err) {
-			statusCode = http.StatusNotFound
-		}
-		return RequestRespone{StatusCode: statusCode}, err
-	}
-
-	return RequestRespone{Body: content, MimeType: mimeType, StatusCode: http.StatusOK}, nil
-}
-
-func textResponse(body string, statusCode int) RequestRespone {
-	if body == "" {
-		return RequestRespone{StatusCode: statusCode}
-	}
-	return RequestRespone{Body: []byte(body), MimeType: "text/plain;charset=UTF-8", StatusCode: statusCode}
-}

v2/internal/frontend/desktop/common/uri_translate.go

@@ -1,34 +0,0 @@
-package common
-
-import (
-	"fmt"
-	"net/url"
-)
-
-var ErrUnexpectedScheme = fmt.Errorf("unexpected scheme")
-var ErrUnexpectedHost = fmt.Errorf("unexpected host")
-
-func translateUriToFile(uri string, expectedScheme string, expectedHosts ...string) (file string, err error) {
-	url, err := url.Parse(uri)
-	if err != nil {
-		return "", err
-	}
-
-	if url.Scheme != expectedScheme {
-		return "", ErrUnexpectedScheme
-	}
-
-	for _, expectedHost := range expectedHosts {
-		if url.Host != expectedHost {
-			continue
-		}
-
-		filePath := url.Path
-		if filePath == "" {
-			filePath = "/"
-		}
-		return filePath, nil
-	}
-
-	return "", ErrUnexpectedHost
-}

v2/internal/frontend/desktop/darwin/Application.h

@@ -42,7 +42,7 @@ void Quit(void*);
 const char* GetSize(void *ctx);
 const char* GetPosition(void *ctx);
 
-void ProcessURLResponse(void *inctx, const char *url, int statusCode, const char *contentType, void* data, int datalength);
+void ProcessURLResponse(void *inctx, const char *url, int statusCode, void *headersString, int headersStringLength, void* data, int datalength);
 
 /* Dialogs */
 

v2/internal/frontend/desktop/darwin/Application.m

@@ -51,15 +51,16 @@ WailsContext* Create(const char* title, int width, int height, int frameless, in
     return result;
 }
 
-void ProcessURLResponse(void *inctx, const char *url, int statusCode, const char *contentType, void* data, int datalength) {
+void ProcessURLResponse(void *inctx, const char *url, int statusCode, void *headersString, int headersStringLength, void* data, int datalength) {
     WailsContext *ctx = (__bridge WailsContext*) inctx;
     NSString *nsurl = safeInit(url);
-    NSString *nsContentType = safeInit(contentType);
+    NSData *nsHeadersJSON = [NSData dataWithBytes:headersString length:headersStringLength];
     NSData *nsdata = [NSData dataWithBytes:data length:datalength];
     
-    [ctx processURLResponse:nsurl :statusCode :nsContentType :nsdata];
+    [ctx processURLResponse:nsurl :statusCode :nsHeadersJSON :nsdata];
 
     [nsdata release];
+    [nsHeadersJSON release];
 }
 
 void ExecJS(void* inctx, const char *script) {

v2/internal/frontend/desktop/darwin/WailsContext.h

@@ -81,7 +81,7 @@
 - (void) SaveFileDialog :(NSString*)title :(NSString*)defaultFilename :(NSString*)defaultDirectory :(bool)canCreateDirectories :(bool)treatPackagesAsDirectories :(bool)showHiddenFiles :(NSString*)filters;
 
 - (void) loadRequest:(NSString*)url;
-- (void) processURLResponse:(NSString *)url :(int)statusCode :(NSString *)contentType :(NSData*)data;
+- (void) processURLResponse:(NSString *)url :(int)statusCode :(NSData *)headersString :(NSData*)data;
 - (void) ExecJS:(NSString*)script;
 - (NSScreen*) getCurrentScreen;
 

v2/internal/frontend/desktop/darwin/WailsContext.m

@@ -376,26 +376,44 @@
    [self.webview evaluateJavaScript:script completionHandler:nil];
 }
 
-- (void) processURLResponse:(NSString *)url :(int)statusCode :(NSString *)contentType :(NSData *)data {
+- (void) processURLResponse:(NSString *)url :(int)statusCode :(NSData *)headersJSON :(NSData *)data {
     id<WKURLSchemeTask> urlSchemeTask = self.urlRequests[url];
     NSURL *nsurl = [NSURL URLWithString:url];
-    NSMutableDictionary *headerFields = [NSMutableDictionary new];
-    if ( ![contentType isEqualToString:@""] ) {
-        headerFields[@"content-type"] = contentType;
-    }
+    NSDictionary *headerFields = [NSJSONSerialization JSONObjectWithData: headersJSON options: NSJSONReadingMutableContainers error: nil];
     NSHTTPURLResponse *response = [[NSHTTPURLResponse new] initWithURL:nsurl statusCode:statusCode HTTPVersion:@"HTTP/1.1" headerFields:headerFields];
     [urlSchemeTask didReceiveResponse:response];
     [urlSchemeTask didReceiveData:data];
     [urlSchemeTask didFinish];
     [self.urlRequests removeObjectForKey:url];
     [response release];
-    [headerFields release];
+    if (headerFields != nil) {
+        [headerFields release];
+    }
 }
 
 - (void)webView:(nonnull WKWebView *)webView startURLSchemeTask:(nonnull id<WKURLSchemeTask>)urlSchemeTask {
-    // Do something
+    // This callback is run with an autorelease pool
     self.urlRequests[urlSchemeTask.request.URL.absoluteString] = urlSchemeTask;
-    processURLRequest(self, [urlSchemeTask.request.URL.absoluteString UTF8String]);
+    const char *url = [urlSchemeTask.request.URL.absoluteString UTF8String];
+    const char *method = [urlSchemeTask.request.HTTPMethod UTF8String];
+    const char *headerJSON = "";
+    const void *body;
+    int bodyLen;
+
+    NSData *headers = [NSJSONSerialization dataWithJSONObject: urlSchemeTask.request.allHTTPHeaderFields options:0 error: nil];
+    if (headers) {
+        NSString* headerString = [[[NSString alloc] initWithData:headers encoding:NSUTF8StringEncoding] autorelease];
+        headerJSON = [headerString UTF8String];
+    }
+
+    if (urlSchemeTask.request.HTTPBody) {
+        body = urlSchemeTask.request.HTTPBody.bytes;
+        bodyLen = urlSchemeTask.request.HTTPBody.length;
+    } else {
+        // TODO handle HTTPBodyStream
+    }
+
+    processURLRequest(self, url, method, headerJSON, body, bodyLen);
 }
 
 - (void)webView:(nonnull WKWebView *)webView stopURLSchemeTask:(nonnull id<WKURLSchemeTask>)urlSchemeTask {

v2/internal/frontend/desktop/darwin/frontend.go

@@ -14,26 +14,26 @@ package darwin
 */
 import "C"
 import (
+	"bytes"
 	"context"
 	"encoding/json"
+	"fmt"
 	"html/template"
+	"io"
 	"log"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
 	"strconv"
 	"unsafe"
 
 	"github.com/wailsapp/wails/v2/internal/binding"
 	"github.com/wailsapp/wails/v2/internal/frontend"
 	"github.com/wailsapp/wails/v2/internal/frontend/assetserver"
-	"github.com/wailsapp/wails/v2/internal/frontend/desktop/common"
 	"github.com/wailsapp/wails/v2/internal/logger"
 	"github.com/wailsapp/wails/v2/pkg/options"
 )
 
-type request struct {
-	url *C.char
-	ctx unsafe.Pointer
-}
-
 var messageBuffer = make(chan string, 100)
 var requestBuffer = make(chan *request, 100)
 var callbackBuffer = make(chan uint, 10)
@@ -49,39 +49,27 @@ type Frontend struct {
 
 	// Assets
 	assets   *assetserver.AssetServer
-	startURL string
+	startURL *url.URL
 
 	// main window handle
-	mainWindow      *Window
-	bindings        *binding.Bindings
-	dispatcher      frontend.Dispatcher
-	servingFromDisk bool
+	mainWindow *Window
+	bindings   *binding.Bindings
+	dispatcher frontend.Dispatcher
 }
 
 func NewFrontend(ctx context.Context, appoptions *options.App, myLogger *logger.Logger, appBindings *binding.Bindings, dispatcher frontend.Dispatcher) *Frontend {
-
 	result := &Frontend{
 		frontendOptions: appoptions,
 		logger:          myLogger,
 		bindings:        appBindings,
 		dispatcher:      dispatcher,
 		ctx:             ctx,
-		startURL:        "wails://wails/",
 	}
+	result.startURL, _ = url.Parse("wails://wails/")
 
-	_starturl, _ := ctx.Value("starturl").(string)
-	if _starturl != "" {
+	if _starturl, _ := ctx.Value("starturl").(*url.URL); _starturl != nil {
 		result.startURL = _starturl
 	} else {
-		// Check if we have been given a directory to serve assets from.
-		// If so, this means we are in dev mode and are serving assets off disk.
-		// We indicate this through the `servingFromDisk` flag to ensure requests
-		// aren't cached by WebView2 in dev mode
-		_assetdir := ctx.Value("assetdir")
-		if _assetdir != nil {
-			result.servingFromDisk = true
-		}
-
 		bindingsJSON, err := appBindings.ToJSON()
 		if err != nil {
 			log.Fatal(err)
@@ -155,7 +143,7 @@ func (f *Frontend) Run(ctx context.Context) error {
 			f.frontendOptions.OnStartup(f.ctx)
 		}
 	}()
-	mainWindow.Run(f.startURL)
+	mainWindow.Run(f.startURL.String())
 	return nil
 }
 
@@ -299,21 +287,48 @@ func (f *Frontend) ExecJS(js string) {
 func (f *Frontend) processRequest(r *request) {
 	uri := C.GoString(r.url)
 
-	res, err := common.ProcessRequest(uri, f.assets, "wails", "wails")
-	if err != nil {
-		f.logger.Error("Error processing request '%s': %s (HttpResponse=%s)", uri, err, res)
+	rw := httptest.NewRecorder()
+	f.assets.ProcessHTTPRequest(
+		uri,
+		rw,
+		func() (*http.Request, error) {
+			req, err := r.GetHttpRequest()
+			if err != nil {
+				return nil, err
+			}
+
+			if req.URL.Host != f.startURL.Host {
+				if req.Body != nil {
+					req.Body.Close()
+				}
+
+				return nil, fmt.Errorf("Expected host '%d' in request, but was '%s'", f.startURL.Host, req.URL.Host)
+			}
+			return req, nil
+		},
+	)
+
+	header := map[string]string{}
+	for k := range rw.Header() {
+		header[k] = rw.Header().Get(k)
 	}
+	headerData, _ := json.Marshal(header)
 
 	var content unsafe.Pointer
 	var contentLen int
-	if _contents := res.Body; _contents != nil {
+	if _contents := rw.Body.Bytes(); _contents != nil {
 		content = unsafe.Pointer(&_contents[0])
 		contentLen = len(_contents)
 	}
-	mimetype := C.CString(res.MimeType)
-	defer C.free(unsafe.Pointer(mimetype))
 
-	C.ProcessURLResponse(r.ctx, r.url, C.int(res.StatusCode), mimetype, content, C.int(contentLen))
+	var headers unsafe.Pointer
+	var headersLen int
+	if len(headerData) != 0 {
+		headers = unsafe.Pointer(&headerData[0])
+		headersLen = len(headerData)
+	}
+
+	C.ProcessURLResponse(r.ctx, r.url, C.int(rw.Code), headers, C.int(headersLen), content, C.int(contentLen))
 }
 
 //func (f *Frontend) processSystemEvent(message string) {
@@ -332,6 +347,40 @@ func (f *Frontend) processRequest(r *request) {
 //	}
 //}
 
+type request struct {
+	url     *C.char
+	method  string
+	headers string
+	body    []byte
+
+	ctx unsafe.Pointer
+}
+
+func (r *request) GetHttpRequest() (*http.Request, error) {
+	var body io.Reader
+	if len(r.body) != 0 {
+		body = bytes.NewReader(r.body)
+	}
+
+	req, err := http.NewRequest(r.method, C.GoString(r.url), body)
+	if err != nil {
+		return nil, err
+	}
+
+	if r.headers != "" {
+		var h map[string]string
+		if err := json.Unmarshal([]byte(r.headers), &h); err != nil {
+			return nil, fmt.Errorf("Unable to unmarshal request headers: %s", err)
+		}
+
+		for k, v := range h {
+			req.Header.Add(k, v)
+		}
+	}
+
+	return req, nil
+}
+
 //export processMessage
 func processMessage(message *C.char) {
 	goMessage := C.GoString(message)
@@ -339,10 +388,18 @@ func processMessage(message *C.char) {
 }
 
 //export processURLRequest
-func processURLRequest(ctx unsafe.Pointer, url *C.char) {
+func processURLRequest(ctx unsafe.Pointer, url *C.char, method *C.char, headers *C.char, body unsafe.Pointer, bodyLen C.int) {
+	var goBody []byte
+	if bodyLen != 0 {
+		goBody = C.GoBytes(body, bodyLen)
+	}
+
 	requestBuffer <- &request{
-		url: url,
-		ctx: ctx,
+		url:     url,
+		method:  C.GoString(method),
+		headers: C.GoString(headers),
+		body:    goBody,
+		ctx:     ctx,
 	}
 }
 

v2/internal/frontend/desktop/darwin/main.m

@@ -29,11 +29,11 @@ void processCallback(int callbackID) {
     NSLog(@"Process callback %d", callbackID);
 }
 
-void processURLRequest(void *ctx, const char* url) {
+void processURLRequest(void *ctx, const char* url const char *method, const char *headers, const void *body, int bodyLen) {
     NSLog(@"processURLRequest called");
     const char myByteArray[] = { 0x3c,0x68,0x31,0x3e,0x48,0x65,0x6c,0x6c,0x6f,0x20,0x57,0x6f,0x72,0x6c,0x64,0x21,0x3c,0x2f,0x68,0x31,0x3e };
-    // void *inctx, const char *url, int statusCode, const char *contentType, void* data, int datalength
-    ProcessURLResponse(ctx, url, 200, "text/html", (void*)myByteArray, 21);
+    // void *inctx, const char *url, int statusCode, const char *headers, void* data, int datalength
+    ProcessURLResponse(ctx, url, 200, "{\"Content-Type\": \"text/html\"}", (void*)myByteArray, 21);
 }
 
 unsigned char _Users_username_Pictures_SaltBae_png[] = {

v2/internal/frontend/desktop/darwin/message.h

@@ -15,7 +15,7 @@ extern "C"
 #endif
 
 void processMessage(const char *);
-void processURLRequest(void*, const char *);
+void processURLRequest(void*, const char *, const char *, const char *, const void *, int);
 void processMessageDialogResponse(int);
 void processOpenFileDialogResponse(const char*);
 void processSaveFileDialogResponse(const char*);

v2/internal/frontend/desktop/linux/frontend.go

@@ -14,8 +14,10 @@ import "C"
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"log"
 	"net/http"
+	"net/url"
 	"os"
 	"runtime"
 	"strconv"
@@ -25,7 +27,6 @@ import (
 	"github.com/wailsapp/wails/v2/internal/binding"
 	"github.com/wailsapp/wails/v2/internal/frontend"
 	"github.com/wailsapp/wails/v2/internal/frontend/assetserver"
-	"github.com/wailsapp/wails/v2/internal/frontend/desktop/common"
 	"github.com/wailsapp/wails/v2/internal/logger"
 	"github.com/wailsapp/wails/v2/pkg/options"
 )
@@ -41,13 +42,12 @@ type Frontend struct {
 
 	// Assets
 	assets   *assetserver.AssetServer
-	startURL string
+	startURL *url.URL
 
 	// main window handle
-	mainWindow      *Window
-	bindings        *binding.Bindings
-	dispatcher      frontend.Dispatcher
-	servingFromDisk bool
+	mainWindow *Window
+	bindings   *binding.Bindings
+	dispatcher frontend.Dispatcher
 }
 
 func init() {
@@ -65,23 +65,12 @@ func NewFrontend(ctx context.Context, appoptions *options.App, myLogger *logger.
 		bindings:        appBindings,
 		dispatcher:      dispatcher,
 		ctx:             ctx,
-		startURL:        "wails://wails/",
 	}
+	result.startURL, _ = url.Parse("wails://wails/")
 
-	_starturl, _ := ctx.Value("starturl").(string)
-	if _starturl != "" {
+	if _starturl, _ := ctx.Value("starturl").(*url.URL); _starturl != nil {
 		result.startURL = _starturl
 	} else {
-		// Check if we have been given a directory to serve assets from.
-		// If so, this means we are in dev mode and are serving assets off disk.
-		// We indicate this through the `servingFromDisk` flag to ensure requests
-		// aren't cached by webkit.
-
-		_assetdir := ctx.Value("assetdir")
-		if _assetdir != nil {
-			result.servingFromDisk = true
-		}
-
 		bindingsJSON, err := appBindings.ToJSON()
 		if err != nil {
 			log.Fatal(err)
@@ -93,7 +82,10 @@ func NewFrontend(ctx context.Context, appoptions *options.App, myLogger *logger.
 		}
 		result.assets = assets
 
-		go result.startRequestProcessor()
+		// Start 10 processors to handle requests in parallel
+		for i := 0; i < 10; i++ {
+			go result.startRequestProcessor()
+		}
 	}
 
 	go result.startMessageProcessor()
@@ -141,7 +133,7 @@ func (f *Frontend) Run(ctx context.Context) error {
 		}
 	}()
 
-	f.mainWindow.Run(f.startURL)
+	f.mainWindow.Run(f.startURL.String())
 
 	return nil
 }
@@ -300,11 +292,15 @@ var requestBuffer = make(chan unsafe.Pointer, 100)
 func (f *Frontend) startRequestProcessor() {
 	for request := range requestBuffer {
 		f.processRequest(request)
+		C.g_object_unref(C.gpointer(request))
 	}
 }
 
 //export processURLRequest
 func processURLRequest(request unsafe.Pointer) {
+	// Increment reference counter to allow async processing, will be decremented after the processing
+	// has been finished by a worker.
+	C.g_object_ref(C.gpointer(request))
 	requestBuffer <- request
 }
 
@@ -313,38 +309,29 @@ func (f *Frontend) processRequest(request unsafe.Pointer) {
 	uri := C.webkit_uri_scheme_request_get_uri(req)
 	goURI := C.GoString(uri)
 
-	res, err := common.ProcessRequest(goURI, f.assets, "wails", "wails")
-	if err != nil {
-		f.logger.Error("Error processing request '%s': %s (HttpResponse=%s)", goURI, err, res)
-	}
+	// WebKitGTK stable < 2.36 API does not support request method, request headers and request.
+	// Apart from request bodies, this is only available beginning with 2.36: https://webkitgtk.org/reference/webkit2gtk/stable/WebKitURISchemeResponse.html
+	rw := &webKitResponseWriter{req: req}
+	defer rw.Close()
 
-	if code := res.StatusCode; code != http.StatusOK {
-		message := C.CString(res.StatusText())
-		gerr := C.g_error_new_literal(C.g_quark_from_string(message), C.int(code), message)
-		C.webkit_uri_scheme_request_finish_error(req, gerr)
-		C.g_error_free(gerr)
-		C.free(unsafe.Pointer(message))
-		return
-	}
+	f.assets.ProcessHTTPRequest(
+		goURI,
+		rw,
+		func() (*http.Request, error) {
+			req, err := http.NewRequest(http.MethodGet, goURI, nil)
+			if err != nil {
+				return nil, err
+			}
 
-	var cContent unsafe.Pointer
-	bodyLen := len(res.Body)
-	var cLen C.long
-	if bodyLen > 0 {
-		cContent = C.malloc(C.ulong(bodyLen))
-		if cContent != nil {
-			C.memcpy(cContent, unsafe.Pointer(&res.Body[0]), C.size_t(bodyLen))
-			cLen = C.long(bodyLen)
-		}
-	}
+			if req.URL.Host != f.startURL.Host {
+				if req.Body != nil {
+					req.Body.Close()
+				}
 
-	cMimeType := C.CString(res.MimeType)
-	defer C.free(unsafe.Pointer(cMimeType))
+				return nil, fmt.Errorf("Expected host '%d' in request, but was '%s'", f.startURL.Host, req.URL.Host)
+			}
+
+			return req, nil
+		})
 
-	stream := C.g_memory_input_stream_new_from_data(
-		cContent,
-		cLen,
-		(*[0]byte)(C.free))
-	C.webkit_uri_scheme_request_finish(req, stream, cLen, cMimeType)
-	C.g_object_unref(C.gpointer(stream))
 }

v2/internal/frontend/desktop/linux/responsewriter.go

@@ -0,0 +1,119 @@
+//go:build linux
+// +build linux
+
+package linux
+
+/*
+#cgo linux pkg-config: gtk+-3.0 webkit2gtk-4.0 gio-unix-2.0
+
+#include "gtk/gtk.h"
+#include "webkit2/webkit2.h"
+#include "gio/gunixinputstream.h"
+
+*/
+import "C"
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"strconv"
+	"syscall"
+	"unsafe"
+
+	"github.com/wailsapp/wails/v2/internal/frontend/assetserver"
+)
+
+type webKitResponseWriter struct {
+	req *C.WebKitURISchemeRequest
+
+	header      http.Header
+	wroteHeader bool
+
+	w    io.WriteCloser
+	wErr error
+}
+
+func (rw *webKitResponseWriter) Header() http.Header {
+	if rw.header == nil {
+		rw.header = http.Header{}
+	}
+	return rw.header
+}
+
+func (rw *webKitResponseWriter) Write(buf []byte) (int, error) {
+	rw.WriteHeader(http.StatusOK)
+	if rw.wErr != nil {
+		return 0, rw.wErr
+	}
+	return rw.w.Write(buf)
+}
+
+func (rw *webKitResponseWriter) WriteHeader(code int) {
+	if rw.wroteHeader {
+		return
+	}
+	rw.wroteHeader = true
+
+	if code != http.StatusOK {
+		// WebKitGTK stable < 2.36 API does not support response headers and response statuscodes
+		rw.w = &nopCloser{io.Discard}
+		rw.finishWithError(http.StatusText(code), code)
+		return
+	}
+
+	// We can't use os.Pipe here, because that returns files with a finalizer for closing the FD. But the control over the
+	// read FD is given to the InputStream and will be closed there.
+	// Furthermore we especially don't want to have the FD_CLOEXEC
+	rFD, w, err := pipe()
+	if err != nil {
+		rw.wErr = fmt.Errorf("Unable opening pipe: %s", err)
+		rw.finishWithError(rw.wErr.Error(), http.StatusInternalServerError)
+		return
+	}
+	rw.w = w
+
+	cMimeType := C.CString(rw.Header().Get(assetserver.HeaderContentType))
+	defer C.free(unsafe.Pointer(cMimeType))
+
+	contentLength := int64(-1)
+	if sLen := rw.Header().Get(assetserver.HeaderContentLength); sLen != "" {
+		if pLen, _ := strconv.ParseInt(sLen, 10, 64); pLen > 0 {
+			contentLength = pLen
+		}
+	}
+
+	stream := C.g_unix_input_stream_new(C.int(rFD), gtkBool(true))
+	C.webkit_uri_scheme_request_finish(rw.req, stream, C.long(contentLength), cMimeType)
+	C.g_object_unref(C.gpointer(stream))
+}
+
+func (rw *webKitResponseWriter) Close() {
+	if rw.w != nil {
+		rw.w.Close()
+	}
+}
+
+func (rw *webKitResponseWriter) finishWithError(message string, code int) {
+	msg := C.CString(http.StatusText(code))
+	gerr := C.g_error_new_literal(C.g_quark_from_string(msg), C.int(code), msg)
+	C.webkit_uri_scheme_request_finish_error(rw.req, gerr)
+	C.g_error_free(gerr)
+	C.free(unsafe.Pointer(msg))
+}
+
+type nopCloser struct {
+	io.Writer
+}
+
+func (nopCloser) Close() error { return nil }
+
+func pipe() (r int, w *os.File, err error) {
+	var p [2]int
+	e := syscall.Pipe2(p[0:], 0)
+	if e != nil {
+		return 0, nil, fmt.Errorf("pipe2: %s", e)
+	}
+
+	return p[0], os.NewFile(uintptr(p[1]), "|1"), nil
+}

v2/internal/frontend/desktop/windows/frontend.go

@@ -7,7 +7,11 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
 	"log"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
 	"runtime"
 	"strconv"
 	"strings"
@@ -16,7 +20,6 @@ import (
 	"github.com/wailsapp/wails/v2/internal/binding"
 	"github.com/wailsapp/wails/v2/internal/frontend"
 	"github.com/wailsapp/wails/v2/internal/frontend/assetserver"
-	"github.com/wailsapp/wails/v2/internal/frontend/desktop/common"
 	"github.com/wailsapp/wails/v2/internal/frontend/desktop/windows/go-webview2/pkg/edge"
 	"github.com/wailsapp/wails/v2/internal/frontend/desktop/windows/winc"
 	"github.com/wailsapp/wails/v2/internal/frontend/desktop/windows/winc/w32"
@@ -38,13 +41,12 @@ type Frontend struct {
 
 	// Assets
 	assets   *assetserver.AssetServer
-	startURL string
+	startURL *url.URL
 
 	// main window handle
-	mainWindow      *Window
-	bindings        *binding.Bindings
-	dispatcher      frontend.Dispatcher
-	servingFromDisk bool
+	mainWindow *Window
+	bindings   *binding.Bindings
+	dispatcher frontend.Dispatcher
 
 	hasStarted bool
 
@@ -63,26 +65,17 @@ func NewFrontend(ctx context.Context, appoptions *options.App, myLogger *logger.
 		bindings:        appBindings,
 		dispatcher:      dispatcher,
 		ctx:             ctx,
-		startURL:        "http://wails.localhost/",
 		versionInfo:     versionInfo,
 	}
 
-	_starturl, _ := ctx.Value("starturl").(string)
-	if _starturl != "" {
+	// We currently can't use wails://wails/ as other platforms do, therefore we map the assets sever onto the following url.
+	result.startURL, _ = url.Parse("http://wails.localhost/")
+
+	if _starturl, _ := ctx.Value("starturl").(*url.URL); _starturl != nil {
 		result.startURL = _starturl
 		return result
 	}
 
-	// Check if we have been given a directory to serve assets from.
-	// If so, this means we are in dev mode and are serving assets off disk.
-	// We indicate this through the `servingFromDisk` flag to ensure requests
-	// aren't cached by WebView2 in dev mode
-
-	_assetdir := ctx.Value("assetdir")
-	if _assetdir != nil {
-		result.servingFromDisk = true
-	}
-
 	bindingsJSON, err := appBindings.ToJSON()
 	if err != nil {
 		log.Fatal(err)
@@ -372,7 +365,7 @@ func (f *Frontend) setupChromium() {
 
 	chromium.SetGlobalPermission(edge.CoreWebView2PermissionStateAllow)
 	chromium.AddWebResourceRequestedFilter("*", edge.COREWEBVIEW2_WEB_RESOURCE_CONTEXT_ALL)
-	chromium.Navigate(f.startURL)
+	chromium.Navigate(f.startURL.String())
 }
 
 type EventNotify struct {
@@ -403,34 +396,39 @@ func (f *Frontend) processRequest(req *edge.ICoreWebView2WebResourceRequest, arg
 		reqHeaders.Release()
 	}
 
+	if f.assets == nil {
+		// We are using the devServer let the WebView2 handle the request with its default handler
+		return
+	}
+
 	//Get the request
 	uri, _ := req.GetUri()
-
-	res, err := common.ProcessRequest(uri, f.assets, "http", "wails.localhost")
-	if err == common.ErrUnexpectedScheme {
-		// In this case we should let the WebView2 handle the request with its default handler
+	reqUri, err := url.ParseRequestURI(uri)
+	if err != nil {
+		f.logger.Error("Unable to parse equest uri %s: %s", uri, err)
 		return
-	} else if err == common.ErrUnexpectedHost {
-		// This means file:// to something other than wails, should we prevent this?
-		// Maybe we should introduce an AllowList for explicitly allowing schemes and hosts, this could also be interesting
-		// for all other platforms to improve security.
-		return // Let WebView2 handle the request with its default handler
-	} else if err != nil {
-		path := strings.Replace(uri, "http://wails.localhost", "", 1)
-		f.logger.Error("Error processing request '%s': %s (HttpResponse=%s)", path, err, res)
 	}
 
+	if reqUri.Scheme != f.startURL.Scheme {
+		// Let the WebView2 handle the request with its default handler
+		return
+	} else if reqUri.Host != f.startURL.Host {
+		// Let the WebView2 handle the request with its default handler
+		return
+	}
+
+	logInfo := strings.Replace(uri, f.startURL.String(), "", 1)
+
+	rw := httptest.NewRecorder()
+	f.assets.ProcessHTTPRequest(logInfo, rw, coreWebview2RequestToHttpRequest(req))
+
 	headers := []string{}
-	if mimeType := res.MimeType; mimeType != "" {
-		headers = append(headers, "Content-Type: "+mimeType)
-	}
-	content := res.Body
-	if content != nil && f.servingFromDisk {
-		headers = append(headers, "Pragma: no-cache")
+	for k, v := range rw.Header() {
+		headers = append(headers, fmt.Sprintf("%s: %s", k, strings.Join(v, ",")))
 	}
 
 	env := f.chromium.Environment()
-	response, err := env.CreateWebResourceResponse(content, res.StatusCode, res.StatusText(), strings.Join(headers, "\n"))
+	response, err := env.CreateWebResourceResponse(rw.Body.Bytes(), rw.Code, http.StatusText(rw.Code), strings.Join(headers, "\n"))
 	if err != nil {
 		f.logger.Error("CreateWebResourceResponse Error: %s", err)
 		return
@@ -596,3 +594,87 @@ func (f *Frontend) ShowWindow() {
 func (f *Frontend) onFocus(arg *winc.Event) {
 	f.chromium.Focus()
 }
+
+func coreWebview2RequestToHttpRequest(coreReq *edge.ICoreWebView2WebResourceRequest) func() (*http.Request, error) {
+	return func() (r *http.Request, err error) {
+		header := http.Header{}
+		headers, err := coreReq.GetHeaders()
+		if err != nil {
+			return nil, fmt.Errorf("GetHeaders Error: %s", err)
+		}
+		defer headers.Release()
+
+		headersIt, err := headers.GetIterator()
+		if err != nil {
+			return nil, fmt.Errorf("GetIterator Error: %s", err)
+		}
+		defer headersIt.Release()
+
+		for {
+			has, err := headersIt.HasCurrentHeader()
+			if err != nil {
+				return nil, fmt.Errorf("HasCurrentHeader Error: %s", err)
+			}
+			if !has {
+				break
+			}
+
+			name, value, err := headersIt.GetCurrentHeader()
+			if err != nil {
+				return nil, fmt.Errorf("GetCurrentHeader Error: %s", err)
+			}
+
+			header.Set(name, value)
+			if _, err := headersIt.MoveNext(); err != nil {
+				return nil, fmt.Errorf("MoveNext Error: %s", err)
+			}
+		}
+
+		method, err := coreReq.GetMethod()
+		if err != nil {
+			return nil, fmt.Errorf("GetMethod Error: %s", err)
+		}
+
+		uri, err := coreReq.GetUri()
+		if err != nil {
+			return nil, fmt.Errorf("GetUri Error: %s", err)
+		}
+
+		var body io.ReadCloser
+		if content, err := coreReq.GetContent(); err != nil {
+			return nil, fmt.Errorf("GetContent Error: %s", err)
+		} else if content != nil {
+			body = &iStreamReleaseCloser{stream: content}
+		}
+
+		req, err := http.NewRequest(method, uri, body)
+		if err != nil {
+			if body != nil {
+				body.Close()
+			}
+			return nil, err
+		}
+		req.Header = header
+		return req, nil
+	}
+}
+
+type iStreamReleaseCloser struct {
+	stream *edge.IStream
+	closed bool
+}
+
+func (i *iStreamReleaseCloser) Read(p []byte) (int, error) {
+	if i.closed {
+		return 0, io.ErrClosedPipe
+	}
+	return i.stream.Read(p)
+}
+
+func (i *iStreamReleaseCloser) Close() error {
+	if i.closed {
+		return nil
+	}
+	i.closed = true
+	return i.stream.Release()
+}

v2/internal/frontend/devserver/devserver.go

@@ -12,7 +12,6 @@ import (
 	"log"
 	"net"
 	"net/http"
-	"net/http/httputil"
 	"net/url"
 	"strings"
 	"sync"
@@ -84,12 +83,16 @@ func (d *DevWebServer) Run(ctx context.Context) error {
 			return err
 		}
 
+		if externalURL.Host == "" {
+			return fmt.Errorf("Invalid frontend:dev:serverUrl missing protocol scheme?")
+		}
+
 		waitCb := func() { d.LogDebug("Waiting for frontend DevServer '%s' to be ready", externalURL) }
 		if !checkPortIsOpen(externalURL.Host, time.Minute, waitCb) {
 			d.logger.Error("Timeout waiting for frontend DevServer")
 		}
 
-		assetHandler = httputil.NewSingleHostReverseProxy(externalURL)
+		assetHandler = newExternalDevServerAssetHandler(d.logger, externalURL, d.appoptions.AssetsHandler)
 	}
 
 	// Setup internal dev server
@@ -103,7 +106,7 @@ func (d *DevWebServer) Run(ctx context.Context) error {
 		log.Fatal(err)
 	}
 
-	d.server.GET("/*", func(c echo.Context) error {
+	d.server.Any("/*", func(c echo.Context) error {
 		assetServer.ServeHTTP(c.Response(), c.Request())
 		return nil
 	})

v2/internal/frontend/devserver/external.go

@@ -0,0 +1,78 @@
+//go:build dev
+// +build dev
+
+package devserver
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+
+	"github.com/labstack/echo/v4"
+	"github.com/wailsapp/wails/v2/internal/logger"
+)
+
+func newExternalDevServerAssetHandler(logger *logger.Logger, url *url.URL, handler http.Handler) http.Handler {
+	errSkipProxy := fmt.Errorf("skip proxying")
+
+	proxy := httputil.NewSingleHostReverseProxy(url)
+	baseDirector := proxy.Director
+	proxy.Director = func(r *http.Request) {
+		baseDirector(r)
+		if logger != nil {
+			logger.Debug("[ExternalAssetHandler] Loading '%s'", r.URL)
+		}
+	}
+
+	proxy.ModifyResponse = func(res *http.Response) error {
+		if handler == nil {
+			return nil
+		}
+
+		if res.StatusCode == http.StatusSwitchingProtocols {
+			return nil
+		}
+
+		if res.StatusCode == http.StatusNotFound || res.StatusCode == http.StatusMethodNotAllowed {
+			return errSkipProxy
+		}
+
+		return nil
+	}
+
+	proxy.ErrorHandler = func(rw http.ResponseWriter, r *http.Request, err error) {
+		if handler != nil && errors.Is(err, errSkipProxy) {
+			if logger != nil {
+				logger.Debug("[ExternalAssetHandler] Loading '%s' failed, using AssetHandler", r.URL)
+			}
+			handler.ServeHTTP(rw, r)
+		} else {
+			if logger != nil {
+				logger.Error("[ExternalAssetHandler] Proxy error: %v", err)
+			}
+			rw.WriteHeader(http.StatusBadGateway)
+		}
+	}
+
+	e := echo.New()
+	e.Any("/*",
+		func(c echo.Context) error {
+			req := c.Request()
+			rw := c.Response()
+			if c.IsWebSocket() || req.Method == http.MethodGet {
+				proxy.ServeHTTP(rw, req)
+				return nil
+			}
+
+			if handler != nil {
+				handler.ServeHTTP(rw, req)
+				return nil
+			}
+
+			return c.NoContent(http.StatusMethodNotAllowed)
+		})
+
+	return e
+}

v2/pkg/options/options.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"io/fs"
 	"log"
+	"net/http"
 	"runtime"
 
 	"github.com/wailsapp/wails/v2/pkg/options/linux"
@@ -42,6 +43,7 @@ type App struct {
 	AlwaysOnTop       bool
 	RGBA              *RGBA
 	Assets            fs.FS
+	AssetsHandler     http.Handler
 	Menu              *menu.Menu
 	Logger            logger.Logger `json:"-"`
 	LogLevel          logger.LogLevel

website/docs/guides/application-development.mdx

@@ -161,6 +161,15 @@ The second, if given, will be executed in the `frontend` directory to build the
 
 If these 2 keys aren't given, then Wails does absolutely nothing with the frontend. It is only expecting that `embed.FS`.
 
+### AssetsHandler
+
+A Wails v2 app can optionally define a `http.Handler` in the `options.App`, which allows hooking into the AssetServer to
+create files on the fly or process POST/PUT requests.
+GET requests are always first handled by the `assets` FS. If the FS doesn't find the requested file the request will be
+forwarded to the `http.Handler` for serving. Any requests other than GET will be directly processed by the `AssetsHandler`
+if specified.
+It's also possible to only use the `AssetsHandler` by specifiy `nil` as the `Assets` option.
+
 ## Built in Dev Server
 
 Running `wails dev` will start the built in dev server which will start a file watcher in your project directory. By

website/docs/reference/options.mdx

@@ -30,6 +30,7 @@ func main() {
         RGBA:              &options.RGBA{R: 0, G: 0, B: 0, A: 255},
         AlwaysOnTop:       false,
         Assets:            assets,
+        AssetsHandler:     assetsHandler,
         Menu:              app.applicationMenu(),
         Logger:            nil,
         LogLevel:          logger.DEBUG,
@@ -221,6 +222,36 @@ Type: \*embed.FS
 
 The frontend assets to be used by the application. Requires an `index.html` file.
 
+### AssetsHandler
+
+Name: AssetsHandler
+
+Type: \*http.Handler
+
+The assets handler is a generic `http.Handler` which will be called for any non GET request on the assets server
+and for GET requests which can not be served from the `assets` because the file is not found.
+
+| Value                         | Win | Mac | Lin |
+| ----------------------------- | --- | --- | --- |
+| GET                           | ✅  | ✅   | ✅  |
+| POST                          | ✅  | ✅   | ❌  |
+| PUT                           | ✅  | ✅   | ❌  |
+| PATCH                         | ✅  | ✅   | ❌  |
+| DELETE                        | ✅  | ✅   | ❌  |
+| Request Headers               | ✅  | ✅   | ❌  |
+| Request Body                  | ✅  | ✅   | ❌  |
+| Request Body Streaming        | ❌  | ❌   | ❌  |
+| Response StatusCodes          | ✅  | ✅   | ❌  |
+| Response Headers              | ✅  | ✅   | ❌  |
+| Response Body                 | ✅  | ✅   | ✅  |
+| Response Body Streaming       | ❌  | ❌   | ✅  |
+
+NOTE: Linux is currently very limited due to targeting a WebKit2GTK Version < 2.36.0. In the future some features will be
+supported by the introduction of WebKit2GTK 2.36.0+ support.
+
+NOTE: When used in combination with a Frontend DevServer there might be limitations, eg. Vite serves the index.html
+on every path, that does not contain a file extension.
+
 ### Menu
 
 Name: Menu
@@ -316,7 +347,7 @@ Defines how the window should present itself at startup.
 | --------------- | --- | --- | --- |
 | Fullscreen      | ✅  | ✅   | ✅ |
 | Maximised       | ✅  | ✅   | ✅ |
-| Minimised       | ✅  |     | ✅ |
+| Minimised       | ✅  | ❌   | ✅ |
 
 ### Bind
 

website/docs/reference/project-config.mdx

@@ -20,7 +20,7 @@ The project config resides in the `wails.json` file in the project directory. Th
 	"version": "[Project config version]",
 	"outputfilename": "[The name of the binary]",
 	"debounceMS": 100, // The default time the dev server waits to reload when it detects a vhange in assets
-	"devServer": "[Address to bind the wails dev sever to. Default: http://localhost:34115]",
+	"devServer": "[Address to bind the wails dev sever to. Default: localhost:34115]",
 	"appargs": "[Arguments passed to the application in shell style when in dev mode]",
 	"runNonNativeBuildHooks": false, // Defines if build hooks should be run though they are defined for an OS other than the host OS.
 	"postBuildHooks": {

website/i18n/zh-Hans/docusaurus-plugin-content-docs/current/reference/project-config.mdx

@@ -20,7 +20,7 @@ sidebar_position: 5
   "version": "[项目配置版本]",
   "outputfilename": "[二进制文件的名称]",
   "debounceMS": 100, // 在检测到资源更改时，开发服务器等待重新加载的时间
-  "devServer": "[将 wails 开发服务器绑定到的地址。默认：http://localhost:34115]",
+  "devServer": "[将 wails 开发服务器绑定到的地址。默认：localhost:34115]",
   "appargs": "[在dev模式下以shell样式传递给应用程序的参数]",
   "runNonNativeBuildHooks": false, // 定义构建钩子是否应该运行，尽管它们是为主机操作系统以外的操作系统定义的。
   "postBuildHooks": {