Correctly sending a JSON message over WebSocket in C#

Question

`I'm trying to send a JSON message over a WebSocket connection using C#. The message I'm trying to send is a serialized object that needs to be nested inside a JSON array.

The class structure for my message is:

public class BulkSubscribeMessage
{
    [JsonProperty("_event")]
    public string Event { get; set; }
    [JsonProperty("tzID")]
    public int TimeZoneId { get; set; }
    public string Message { get; set; }
}

I've serialized an instance of BulkSubscribeMessage and attempted to nest it within a JSON array to send over WebSocket. I'm using JsonConvert.SerializeObject to do this. My code is as follows:

public async Task Subscribe(List<EconomicEvent> events)
{
    StringBuilder sb = new StringBuilder();
    sb.Append("pid-eu-177:%%pid-eu-172:%%pid-eu-8826:%%pid-eu-1175153:%%pid-eu-169:%%pid-eu-8827:%%pid-eu-956731:%%");

    foreach (var eEvent in events)
    {
        sb.Append($"event-eu-{eEvent.Id}:%%");
    }

    // Removing the last two '%%'
    if (sb.Length > 2) sb.Length -= 2;

    BulkSubscribeMessage message = new BulkSubscribeMessage()
    {
        Event = "bulk-subscribe",
        TimeZoneId = 16,
        Message = sb.ToString()
    };

    // Create a list with one element: the serialized message
    var messageList = new List<string>
    {
        JsonConvert.SerializeObject(message)
    };

    // Serialize the list of messages
    string jsonString = JsonConvert.SerializeObject(messageList);

    var buffer = Encoding.UTF8.GetBytes(jsonString);
    await _client.SendAsync(new ArraySegment<byte>(buffer), WebSocketMessageType.Text, true, CancellationToken.None);
}

When I send this message, I don't get a response from the server. When I inspect the WebSocket traffic in the Chrome developer console, the expected message format is:

[
    "{\"_event\":\"bulk-subscribe\",\"tzID\":16,\"message\":\"pid-eu-177:%%pid-eu-172:%%pid-eu-8826:%%pid-eu-1175153:%%pid-eu-169:%%pid-eu-8827:%%pid-eu-956731:%%event-eu-1:%%event-eu-2:...\"}"
]

However, when I print out the jsonString in my code, the format looks correct, but I am not getting any response from the server.

How can I correctly send this JSON message over the WebSocket connection? Are there any issues with my serialization or the WebSocket message sending process? I am using the System.Net.WebSockets.ClientWebSocket for the WebSocket connection.

WebSocket URL: wss://streaming.forexpros.com/echo/321/dgwckgeo/websocket

I tried to serialize my command in an array, aiming to get the same format as the correct command sent by web browser client, but with no success. I still didn't manage to get the quotation marks.

The JSON string is wrong. That's an array of strings, not objects. You can replace all the string manipulation code with just `var buffer = JsonSerializer.SerializeToUtf8Bytes(events);`. This avoids errors, is much faster and uses a lot less memory than manual serialization — Panagiotis Kanavos, Jun 20 '23 at 14:28
Or, if you want to compose events and messages, `var message = new BulkSubscribeMessage(){..., Message = events};` and then `JsonSerialize....(message);`. *Don't* convert `events` to a string. You may have to change `Message` to a generic class. As far as JSON is concerned, a string value is nothing more than an opaque string value — Panagiotis Kanavos, Jun 20 '23 at 14:30
@PanagiotisKanavos my concern is that the server is not receiving the expected message in the correct format. even hardcoding the message: string jsonString = JsonConvert.SerializeObject(new[] { "{\"_event\":\"bulk-subscribe\",\"tzID\":16,\"message\":\"pid-eu-177:%%pid-eu-172:%%pid-eu-8826:%%pid-eu-1175153:%%pid-eu-169:%%pid-eu-8827:%%pid-eu-956731:%%event-eu-1:%%event-eu-2:...\"}" }); _client.Send(jsonString); doesn't produce any response from the server. the same exact message works if sent by an online websocket tester. — Mattia, Jun 20 '23 at 14:35

Serge · Answer 1 · 2023-06-20T18:26:39.503

you are serializing twice. try to replace

var messageList = new List<string>
    {
        JsonConvert.SerializeObject(message)
    };

    // Serialize the list of messages
    string jsonString = JsonConvert.SerializeObject(messageList);

with

 string jsonString = JsonConvert.SerializeObject( 
                                    new BulkSubscribeMessage[] { message });
// or more simple
 string jsonString = "[" + JsonConvert.SerializeObject(message) + "]";

Correctly sending a JSON message over WebSocket in C#

1 Answers1