Remove HTTP/2 Push Promise support since Plug is deprecating it

[mtrudel]

See elixir-plug/plug@cd258e7

@moogle19 you've had a lot of eyes here lately; care to give this a once over?

[moogle19]

Can't we get rid of the PushPromise frame altogether and just handle it as an Unknown frame?

Alternatively if you want to keep the frame, it can be an empty struct since the fields aren't used anyway (as far as I can see). If we want to ignore invalid PushPromise frames (zero stream_id and invalid padding length) the deserialization can also be skipped and Frame.deserialize/2 can return the empty PushPromise struct directly.

WDYT?

Edit: And the Stream.stream_id_is_valid_server/1 is reported as unused by the compiler.

[mtrudel]

Can't we get rid of the PushPromise frame altogether and just handle it as an Unknown frame?

Sadly we cannot, since a number of tests in h2spec require us to handle push frames in a specific way (even if we don't support them). We can drop the deserialization down to a single error clause though, since all of the failure cases in the spec resolve down to the same error (protocol error, close connection).

We will need to keep the deserialize function around, but no longer need to have a struct definition for PushPromise.

Edit: And the Stream.stream_id_is_valid_server/1 is reported as unused by the compiler.

✅ thanks!

[mtrudel]

Updated

[moogle19]

Just one little thing.
Otherwise it looks good!

[moogle19]

Can we remove these cases all together (and ignore invalid enable_push values)?
h2spec seems fine with it.

Otherwise group the valid cases to {:ok, {0x02, val}}, {:ok, acc} when val in [0x00, 0x01] ->?

[mtrudel]

I'd like to keep the handling, even if h2spec doesn't complain. No sense in walking back strict conformance.

Updated to use a when clause, as suggested

[moogle19]

Or maybe use {:ok, {0x02, value}}, {:ok, _acc} when value not in [0x00, 0x01] on the error case and drop the noop case?