CODEWITHSUNDEEP
websocket
ElkeAusBerlin
ElkeAusBerlin

Reputation: 575

Websocket: what is the purpose text/binary frame indicator

I am implementing a WebSocket server in C and was wondering what's the purpose of the text/binary frame indicators (opcode 1 and 2). Why they are there? In the end in both cases the payload contains bits. And when there is a protocol using websocket or so then I know what expect in the data. Is it because when it's a text message I can be sure that payload only contains UTF-8 valid data?

Upvotes: 2

Views: 1952

Answers (1)

Myst
Myst

Reputation: 19221

I will start my answer by pointing out that WebSockets are often implemented with a Javascript client in mind (i.e., a browser).

When you're using C, the different opcode might be used in different ways, but when using Javascript, this difference controls the type of the data in the event (Blob vs. String).

As you point out in the question, a string is always a valid UTF-8 stream of bytes, whereas a blob isn't.

This affects some data transport schemes (such as JSON parsing, which requires a UTF-8 valid stream).

Obviously, in C, this opcode could be used in different ways, but it would be better to use the opcode in the same manner as a potential javascript client.

P.S.

There are a number of Websocket C libraries and frameworks out there (I'm the author of facil.io).

Unless this is a study project, I would consider using one of the established frameworks / libraries.

Upvotes: 3

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