deflate: Fix no_context_takeover parameter handling and implement context_takeover.

[keesverruijt]

I ran into issue #49 as well.

Analysis

The existing code did not implement context takeover, so it should always send client_no_context_takeover and server_no_context_takeover in the Sec-WebSocket-Extensions header, but it didn't.

Further investigation showed that my use-case (lots of small messages) would really benefit from context takeover, increasing the compression ratio up to ten fold.

Fix

• Keep the decoder and encoder objects alive, and allow context takeover by default.
• Add an option to disable either client or server context takeover in memory constrained situations.
• Reset the decoder and encoder when no_context_takeover is active.

[alula]

I ran into similar issue and just submitted a PR without seeing that someone outran me :)

I have one request though, could you add max decompressed payload size (to limit potential decompression bomb attacks) parameter like my PR does?

[keesverruijt]

Hi @alula , I reviewed your PR and I will update mine with your improvements.

[keesverruijt]

I think we can still improve the handling by returning better errors to the client, but this will do for now (it's no worse than it was.)