try add live reloading

.vscode/settings.json

@@ -1,3 +1,10 @@
 {
-  "cSpell.words": ["apihub", "spahandler"]
+  "cSpell.words": [
+    "apihub",
+    "appender",
+    "livereloader",
+    "onclose",
+    "spahandler",
+    "Upgrader"
+  ]
 }

go.mod

@@ -1,3 +1,5 @@
 module git.apihub24.de/admin/spa-handler
 
 go 1.22.0
+
+require github.com/gorilla/websocket v1.5.3

go.sum

@@ -0,0 +1,2 @@
+github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
+github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=

handler.go

@@ -11,6 +11,8 @@ import (
 type handler struct {
 	staticFS            embed.FS
 	indexPath           string
+	addLiveReloadScript bool
+	clientVersion       string
 }
 
 func (h handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
@@ -28,7 +30,11 @@ func (h handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 		defer indexFile.Close()
+		if h.addLiveReloadScript {
+			tryToDeliverFile(indexFile, h.indexPath, w, r, clientScript(h.clientVersion))
+		} else {
 			tryToDeliverFile(indexFile, h.indexPath, w, r)
+		}
 		return
 	} else if err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
@@ -37,14 +43,34 @@ func (h handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	tryToDeliverFile(f, h.indexPath, w, r)
 }
 
-func HandleFiles(path string, options HandlerOptions) {
+func HandleFiles(path string, options HandlerOptions, mux *http.ServeMux) {
 	if options.AdditionalMimeTypeMapping != nil {
 		for key, value := range options.AdditionalMimeTypeMapping {
 			contentTypeMapping[key] = value
 		}
 	}
+	if mux == nil {
 		http.Handle(path, handler{
 			staticFS:            options.Files,
 			indexPath:           options.IndexPath,
+			addLiveReloadScript: options.ActivateLiveReloading,
+			clientVersion:       options.ClientVersion,
+		})
+		if options.ActivateLiveReloading {
+			mux.Handle("/_livereloader_", reloader{
+				clientVersion: options.ClientVersion,
 			})
 		}
+		return
+	} else {
+		mux.Handle(path, handler{
+			staticFS:  options.Files,
+			indexPath: options.IndexPath,
+		})
+		if options.ActivateLiveReloading {
+			mux.Handle("/_livereloader_", reloader{
+				clientVersion: options.ClientVersion,
+			})
+		}
+	}
+}

helper.go

@@ -1,19 +1,27 @@
 package spa_handler
 
 import (
+	"bytes"
 	"io"
 	"io/fs"
 	"net/http"
 	"strings"
+	"time"
 )
 
-func tryToDeliverFile(file fs.File, path string, w http.ResponseWriter, r *http.Request) {
+func tryToDeliverFile(file fs.File, path string, w http.ResponseWriter, r *http.Request, appender ...string) {
-	fileSeeker, ok := file.(io.ReadSeeker)
+	content, err := io.ReadAll(file)
-	if !ok {
+	if err != nil {
 		file.Close()
-		http.Error(w, "Index file does not implement ReadSeeker", http.StatusInternalServerError)
+		http.Error(w, "can not read file", http.StatusInternalServerError)
 		return
 	}
+	modified := []byte{}
+	for _, a := range appender {
+		modified = append(modified, []byte(a)...)
+	}
+	modified = append(modified, content...)
+
 	stats, statErr := file.Stat()
 	if statErr != nil {
 		http.Error(w, "Cannot stat index file", http.StatusInternalServerError)
@@ -24,8 +32,10 @@ func tryToDeliverFile(file fs.File, path string, w http.ResponseWriter, r *http.
 		contentType = "text/html"
 	}
 	contentType = getContentTypeDetail(contentType, stats)
+
+	fileSeeker := bytes.NewReader(modified)
 	w.Header().Set("Content-Type", contentType)
-	http.ServeContent(w, r, path, stats.ModTime(), fileSeeker)
+	http.ServeContent(w, r, path, time.Now(), fileSeeker)
 }
 
 func detectContentType(file fs.File) (string, error) {

options.go

@@ -5,5 +5,7 @@ import "embed"
 type HandlerOptions struct {
 	Files                     embed.FS
 	IndexPath                 string
+	ClientVersion             string
+	ActivateLiveReloading     bool
 	AdditionalMimeTypeMapping map[string]string
 }

reloader.go

@@ -0,0 +1,74 @@
+package spa_handler
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/gorilla/websocket"
+)
+
+func clientScript(clientVersion string) string {
+	return fmt.Sprintf(`
+<!-- [spa_handler] Live Reloading Script Start -->
+<script type="application/javascript">
+	function spaHandlerLiveReloaderConnect() {
+		const ws = new WebSocket("/_livereloader_");
+		ws.onopen = function() {
+			console.info('[spa_handler]: live reloader connected!');
+		};
+		ws.onmessage = function(event) {
+			try {
+				const message = JSON.parse(event.data);
+				if (message && message.clientVersion && message.clientVersion !== '%s') {
+					console.info('[spa_handler]: receive reload');
+					location.reload(true);
+				}
+			} catch (err) {
+				console.warning('[spa_handler]: something was wrong! ', err)
+			}
+		};
+		ws.onclose = function() {
+			console.info('[spa_handler]: connection closed');
+			setTimeout(function() {
+				console.info('[spa_handler]: try reconnect');
+				spaHandlerLiveReloaderConnect();
+			}, 5000);
+		};
+		ws.onerror = function(err) {
+			console.warning('[spa_handler]: something was wrong with websocket connection! ', err)
+		};
+	}
+	document.onload = function() {
+		spaHandlerLiveReloaderConnect();
+	};
+</script>
+<!-- [spa_handler] Live Reloading Script End -->
+`, clientVersion)
+}
+
+var upgrader = websocket.Upgrader{
+	CheckOrigin: func(r *http.Request) bool {
+		return true
+	},
+}
+
+type reloader struct {
+	clientVersion string
+}
+
+func (rel reloader) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	conn, err := upgrader.Upgrade(w, r, nil)
+	if err != nil {
+		fmt.Println("Error upgrading:", err)
+		return
+	}
+	defer conn.Close()
+	_ = conn.WriteMessage(websocket.TextMessage, []byte(fmt.Sprintf("{\"clientVersion\":\"%s\"}", rel.clientVersion)))
+	for {
+		_, _, err := conn.ReadMessage()
+		if err != nil {
+			fmt.Println("Error reading message:", err)
+			break
+		}
+	}
+}