Consider supporting buffer types other than Vec<u8> for binary Messages

[chuigda]

I personally want to get a somewhat more aligned buffer for received binary messages somehow, in order to do some in-place dirty dirty things. and I guess there should be some real world use cases. I wonder if such feature can be added, or if there could be some workarounds.

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An alternative option, as far as I've considered, is to utilize the allocator_api but it's still unstable.

[daniel-abramov]

It seems like it's having a broad overlap with #96 and the corresponding PR, i.e. we thought about changing the underlying type for the Message to not enforce owned data when calling write_message(). This won't quite work with any data type that you've mentioned ("in place dirty dirty things" 😉 ).

Or, to be more precise, there have been discussions around splitting the sans I/O part of the library into tungstenite-core that is generic over the data (read accepts a buffer, write accepts a buffer also, no I/O on streams) and then make tungstenite and tokio-tungstenite wrappers around it. But we have not come up with a plan (though PRs or changes in this direction are welcome).