Handle abnormal WebSocket close on client (fixes #114)

[MaxMaeder]

Modified the WebSocket Stream to insert the control frame closed: 1006 when a client tries to read from a stream after it's been abnormally closed by the server.

In my implementation, 'abnormally closed' means the underlying TCP stream was closed without the WebSocket-level closing handshake (we get an io.EOF). I admit I am newer to working with WebSockets on this low of a level, so there may be other cases we need to check.

Previously, tests (and presumably library users) would expect to receive this io.EOF error from methods like nextFrame() after the connection was abnormally closed, so I maintain this behavior while also returning the aforementioned control frame.

I've also added tests to check correct client behavior on abnormal server close for both synchronous and asynchronous stream methods.

Separately, I recently applied for Talos’s backend internship position. If this is a helpful fix maybe you can look at my application :) It should be under Maxim Maeder / [email protected]

[sergiu128]

Thanks for the PR! The change looks good and is correct! I've left some comments - once resolved we can merge and release a new version. About your application - I've flagged it with the team!

[MaxMaeder]

Thanks for the review, glad to hear my changes were correct for the most part!

I've addressed the requested changes:

• Cleaned up how I'm constructing the Frame, thanks for pointing out how Go automatically coerces types!
• Added check to make sure WebSocket is StateActive before starting the test
• Replaced t.Fail and assertState in my tests with assert.* methods
• Updated srv.Accept to accept an optional callback called on port assignment by making it a variadic function
  • Let me know if this is bad practice, it kind of seems like a 'hack' to get around Go's lack of function overloading
  • Also updated my tests to use this callback so the server port is not hard-coded

Happy to knock out #66 too if how I implemented dynamic port assignment in my tests looks good, although it looks like port assignments are hardcoded in tests other than stream_test as well, so I'd likely need to make other changes too.

[sergiu128]

This all looks really good! Thank you! I made some notes in #66 , let's continue the discussion there.