switched to SSE transport, seems to work

src/server.go

@@ -29,6 +29,7 @@ type ChatMessage struct {
 
 var global_msg_id uint64 = 0 /* track global message ID */
 var message_transport chan ChatMessage  /* global message channel */
+var sse_transports []chan string /* SSE output channels */
 var bro webview.WebView /* global browser instance handle */
 
 /* escape HTML entities in JS parameters */
@@ -50,12 +51,20 @@ func appendChatMessages() {
     global_msg_id += 1
     msg.Id = global_msg_id
 
-    /* directly call the append function on the JS side */
+    /* TODO any additional message logging should be done at this point! */
-    fmt_str := "gooseAppendMessage('%d', '%s', '%s', '%s', '%s', '%s');"
-    js := fmt.Sprintf(fmt_str, msg.Id, esc(msg.Type), esc(msg.Timestamp), esc(msg.Username), esc(msg.Text), esc(msg.Icon))
-    log.Printf("Evaluating JS: %s", js)
-    bro.Eval(js)
     
+    /* serialize the message and send it to the SSE channel */
+    json_msg, err := json.Marshal(msg)
+    if err != nil {
+      log.Println("Error serializing the message:", err)
+    }
+
+    /* broadcast the message across the clients */
+    for _, transport := range sse_transports {
+      if transport != nil {
+        transport <- string(json_msg)
+      }
+    }
   }
 }
 
@@ -73,6 +82,40 @@ func msgAddHandler(w http.ResponseWriter, r *http.Request) {
   w.Write([]byte("{\"status\": 1}")) /* respond with a status */
 }
 
+/* GET /sse handler */
+func sseHandler(w http.ResponseWriter, r *http.Request) {
+  /* prepare the headers */
+  w.Header().Set("Content-Type", "text/event-stream")
+  w.Header().Set("Cache-Control", "no-cache")
+  w.Header().Set("Connection", "keep-alive")
+  w.Header().Set("Access-Control-Allow-Origin", "*")
+
+  /* create the channel */
+  transport := make(chan string)
+  /* append it to the broadcast list */
+  sse_transports = append(sse_transports, transport)
+
+  /* close the channel after exiting the function */
+  defer func() {
+    close(transport)
+    transport = nil
+  }()
+
+  /* use HTTP response flusher */
+  flusher, _ := w.(http.Flusher)
+
+  /* message loop */
+  for {
+    select {
+      case message := <-transport:
+        fmt.Fprintf(w, "data: %s\n\n", message)
+        flusher.Flush()
+      case <-r.Context().Done(): /* handle disconnects */
+        return
+    }
+  }
+}
+
 /* entry point */
 func main() {
   config_path := "config.json"
@@ -100,6 +143,8 @@ func main() {
   go func() { /* start the server thread */
     /* serve the POST /new */
     http.HandleFunc("/new", msgAddHandler)
+    /* serve the GET /sse */
+    http.HandleFunc("/sse", sseHandler)
     /* serve the webroot directory */
     fs := http.FileServer(http.Dir("./webroot"))
     http.Handle("/", fs)

webroot/script.js

@@ -57,3 +57,12 @@ function gooseAppendMessage(id, type, timestamp, username, text, icon) {
   /* autoscroll to the end */
   window.scrollTo(0, document.body.scrollHeight)
 }
+
+/* entry point, set up an event source */
+window.addEventListener('DOMContentLoaded', function() {
+  var msgSource = new EventSource('/sse')
+  msgSource.onmessage = e => {
+    var msg = JSON.parse(e.data)
+    gooseAppendMessage(msg.id, msg.type, msg.timestamp, msg.username, msg.text, msg.icon)
+  }
+}, false)