Can one add WebSocket handler after Server.begin?

[cniedzi]

Hi,

For some reason, I have to add a WebSocket handler after starting AsyncWebServer with Server.begin():

AsyncWebServer Server(80);
AsyncWebSocket ws("/ws");

void setup() {
   Server.on("/", HTTP_GET, [](AsyncWebServerRequest *request.....);
   Server.begin();
   ...
   ws.onEvent(onWebSocketEvent);
   Server.addHandler(&ws);   
}

Looks like it works, but is this a proper approach?

[mathieucarbou]

yes, that's possible. there is a handler list that can be updated at runtime, and once a request comes in, the handler list is iterated to find the right handler.

the only thing you need to pay attention to is concurrency across cores: it can crash if you concurrently update the list while iterating to find the right handler. So make sure the code that does the update runs on the same core than the async_tcp task.

[cniedzi]

Thank @mathieucarbou for quick reply!

Assuming the client got connected and server returned a web page just after Server.begin, but before adding a handler:

Server.begin();
...............................................................
    >>> client got connected & web page was displayed
...............................................................
ws.onEvent(onWebSocketEvent);
Server.addHandler(&ws); 

when the first event WS_EVT_CONNECT is fired?

[mathieucarbou]

No this won’t work. If you do not add the handler you won’t get any event.

I think you are trying to solve a use case / need by using a wrong direction. Handlers are better set at once before begin. You then have several mechanisms to decide whether you want to activate them or not.

maybe if you explain what you want to achieve I could help you go in the right direction

[cniedzi]

No this won’t work. If you do not add the handler you won’t get any event.

I think you are trying to solve a use case / need by using a wrong direction. Handlers are better set at once before begin. You then have several mechanisms to decide whether you want to activate them or not.

maybe if you explain what you want to achieve I could help you go in the right direction

I’m building an Internet radio using the ESP32-S3. I use AsyncWebServer to provide two functionalities:
a) importing playlists from the Internet to flash memory, and
b) serving the radio user interface.

The playlist import page is activated under certain conditions in the setup routine, right after calling server.begin(). After that (or if the import page wasn’t requested), the next step in the setup function is to load the playlists from flash into RAM and perform some additional initialization.

Only after successfully loading the playlists into ESP32 memory should the playlist-related information be pushed to the web interface via WebSocket. I use WS_EVT_CONNECT to publish (using ws.textAll) playlist information to the web interface after loading a page or refreshing it — for example, details about the previous, current, and next playlist or station.

My goal is to avoid an edge case during setup: the server is started, the playlists are not yet loaded into memory, and meanwhile a client requests the web interface, causing WS_EVT_CONNECT to fire too early. In such a case, invalid or empty data might be sent.

Here’s my current algorithm which works, but I thought I could simplified it:

void onWebSocketEvent(AsyncWebSocket *server, AsyncWebSocketClient *client, AwsEventType type, void *arg, uint8_t *data, size_t len) {
  if (type == WS_EVT_CONNECT && g_isPlaylistsDataReady) { // required when user refreshes the web page
    ws.textAll("PLAYLIST:" + currentPlaylistName);
    ...
  }
}

void setup {
    g_isPlaylistsDataReady = false;
    // WebSocket
    ws.onEvent(onWebSocketEvent);
    Server.addHandler(&ws);
    // WebServer
    Server.on("/", HTTP_GET, [](AsyncWebServerRequest *request.....);
    Server.begin();  

   // start Playlists import from Internet into flash if requested using dedicated web page
   
  // load playlists from flash to RAM

  g_isPlaylistsDataReady = true;
 
  ws.textAll("PLAYLIST:" + currentPlaylistName); // push info to radio web interface
}

[mathieucarbou]

No this won’t work. If you do not add the handler you won’t get any event.
I think you are trying to solve a use case / need by using a wrong direction. Handlers are better set at once before begin. You then have several mechanisms to decide whether you want to activate them or not.
maybe if you explain what you want to achieve I could help you go in the right direction

I’m building an Internet radio using the ESP32-S3. I use AsyncWebServer to provide two functionalities: a) importing playlists from the Internet to flash memory, and b) serving the radio user interface.

The playlist import page is activated under certain conditions in the setup routine, right after calling server.begin(). After that (or if the import page wasn’t requested), the next step in the setup function is to load the playlists from flash into RAM and perform some additional initialization.

Only after successfully loading the playlists into ESP32 memory should the playlist-related information be pushed to the web interface via WebSocket. I use WS_EVT_CONNECT to publish (using ws.textAll) playlist information to the web interface after loading a page or refreshing it — for example, details about the previous, current, and next playlist or station.

My goal is to avoid an edge case during setup: the server is started, the playlists are not yet loaded into memory, and meanwhile a client requests the web interface, causing WS_EVT_CONNECT to fire too early. In such a case, invalid or empty data might be sent.

Here’s my current algorithm which works, but I thought I could simplified it:

void onWebSocketEvent(AsyncWebSocket *server, AsyncWebSocketClient *client, AwsEventType type, void *arg, uint8_t *data, size_t len) {
  if (type == WS_EVT_CONNECT && g_isPlaylistsDataReady) { // required when user refreshes the web page
    ws.textAll("PLAYLIST:" + currentPlaylistName);
    ...
  }
}

void setup {
   g_isPlaylistsDataReady = false;
   // WebSocket
   ws.onEvent(onWebSocketEvent);
   Server.addHandler(&ws);
   // WebServer
   Server.on("/", HTTP_GET, [](AsyncWebServerRequest *request.....);
   Server.begin();  

  // start Playlists import from Internet into flash if requested using dedicated web page
  
 // load playlists from flash to RAM

 g_isPlaylistsDataReady = true;

 ws.textAll("PLAYLIST:" + currentPlaylistName); // push info to radio web interface
}

This can be solved by the setFilter function available on handlers which can allow or deny the execution of a handler based on some global application states.

look at the examples in the project.

[cniedzi]

Thanks!