Azure app service websocket buffer buffer size limits?

Question

I have run into a problem where my websocket connection is functioning as expected locally, but not when deployed to azure app service. (.NET Core 3.0)

I am able to receive messages of any size locally, but the messages cap out at 4088 byte when deploying to azure.

Code example:

await Receive(socket, async (result, buffer) =>
{
    Console.WriteLine("Message size: " + result.Count);
    message = Encoding.UTF8.GetString(buffer, 0, result.Count);
});

private async Task Receive(WebSocket socket, Action<WebSocketReceiveResult, byte[]> handleMessage)
{
    try
    {
        var buffer = new byte[1024 * 16];
        while (socket.State == WebSocketState.Open)
        {
            WebSocketReceiveResult result = null; 
            using (var cts = new CancellationTokenSource(1200000))
            {
                result = await socket.ReceiveAsync(
                    buffer: new ArraySegment<byte>(buffer),
                    cancellationToken: cts.Token
                    );
            }
            handleMessage(result, buffer);
        }
    }
    catch (Exception ex)
    {
        Log.Error(ex, "Exception occured when receiving message async");
    }
}

Is there any kind of limit that can be changed in the app service?

I have already tried to set up a remote client sending messages both to azure app service and my local environment. This is only an issue with azure app service.

eirikjor · Accepted Answer · 2020-11-16 14:05:29Z

Fixed with:

private async Task Receive(WebSocket webSocket, Action<string> handleMessage)
{
    try
    {
        while (webSocket.State == WebSocketState.Open)
        {
            var compoundBuffer = new List<byte>();
            WebSocketReceiveResult messageReceiveResult = null;
            byte[] buffer = new byte[4 * 1024];

            do
            {
                using (var cts = new CancellationTokenSource(1200000))
                {
                    messageReceiveResult = await webSocket.ReceiveAsync(
                    new ArraySegment<byte>(buffer),
                    cts.Token
                    );
                }

                if (messageReceiveResult.MessageType == WebSocketMessageType.Text)
                {
                    byte[] readBytes = new byte[messageReceiveResult.Count];
                    Array.Copy(buffer, readBytes, messageReceiveResult.Count);
                    compoundBuffer.AddRange(readBytes);
                }
            } while (!messageReceiveResult.EndOfMessage);

            string message = Encoding.UTF8.GetString(compoundBuffer.ToArray());
            handleMessage(message);
        }
    }
    catch (Exception ex)
    {
        Log.Error(ex, "Exception occured when receiving message async");
    }
}

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