websocket onMessage data type

[Srabutdotcom]

Dear All,

So far i use websocket to send string from client to server is fine,
And recently, I just try send data from Client with data type other than string i.e. ArrayBuffer, Blob, TypedArray and DataView.
However, when i check in data received in server (Deno websocket) was only ArrayBuffer or its having different type from Client, except ArrayBuffer its self.

My question is, whether it is the default of Deno.websocket if the data type received from Client is only String and ArrayBuffer instead any data type?

[agammann]

Yes. A WebSocket message is a text or binary frame; it does not preserve the JavaScript class passed to send(). I tested this with Deno 2.9.7: a string arrived as a string, while an ArrayBuffer, Uint8Array, Blob, and DataView each arrived as an ArrayBuffer with the receiving socket's default binaryType (arraybuffer).

If you prefer Blob for binary messages, set socket.binaryType = 'blob' on the receiving socket before messages arrive; I tested that too, and all four binary sends then arrived as Blob. If the original typed-array or view kind matters, encode that information in your application message. See the WebSocket API reference.

[Icaro0310]

The WebSocket wire format doesn't carry any JS type info. On the client, a TypedArray, DataView or Blob all get flattened to raw bytes before going on the wire, so the server just sees a binary frame. That's why everything arrives as ArrayBuffer regardless of what you sent.

If you need the original type back, you have to tag it yourself. I usually prepend a single byte header, or send a small JSON text message describing the next binary frame.

You can also set socket.binaryType = "blob" on the server if you'd rather get a Blob than an ArrayBuffer, but the TypedArray/DataView distinction is gone either way since those are just views over the same bytes.

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Related work of mine: github.com/Icaro0310 · Website: icaro0310.github.io