Motivation:
Quote from issue 4914:
"Http2MultiplexCodec currently does two things: mapping the existing h2 API to frames and managing the child channels.
It would be better if the two parts were separated. This would allow less-coupled development of the HTTP/2 handlers (flow control could be its own handler, for instance) and allow applications to insert themselves between all streams and the codec, which permits custom logic and could be used, in part, to implement custom frame types.
It would also greatly ease testing, as the child channel could be tested by itself without dealing with how frames are encoded on the wire."
Modifications:
- Split the Http2MultiplexCodec into Http2FrameCodec and Http2MultiplexCodec. The Http2FrameCodec interacts with the existing HTTP/2 callback-based API, while the Http2MulitplexCodec is completely independent of it and simply multiplexes Http2StreamFrames to the child channels. Additionally, the Http2Codec handler is introduced, which is a convenience class that simply sets up the Http2FrameCodec and Http2MultiplexCodec in the channel pipeline and removes itself.
- Improved test coverage quite a bit.
Result:
- The original Http2MultiplexCodec is split into Http2FrameCodec and Http2MultiplexCodec.
- More tests for higher confidence in the code.
Related: #4333#4421#5128
Motivation:
slice(), duplicate() and readSlice() currently create a non-recyclable
derived buffer instance. Under heavy load, an application that creates a
lot of derived buffers can put the garbage collector under pressure.
Modifications:
- Add the following methods which creates a non-recyclable derived buffer
- retainedSlice()
- retainedDuplicate()
- readRetainedSlice()
- Add the new recyclable derived buffer implementations, which has its
own reference count value
- Add ByteBufHolder.retainedDuplicate()
- Add ByteBufHolder.replace(ByteBuf) so that..
- a user can replace the content of the holder in a consistent way
- copy/duplicate/retainedDuplicate() can delegate the holder
construction to replace(ByteBuf)
- Use retainedDuplicate() and retainedSlice() wherever possible
- Miscellaneous:
- Rename DuplicateByteBufTest to DuplicatedByteBufTest (missing 'D')
- Make ReplayingDecoderByteBuf.reject() return an exception instead of
throwing it so that its callers don't need to add dummy return
statement
Result:
Derived buffers are now recycled when created via retainedSlice() and
retainedDuplicate() and derived from a pooled buffer
Motivation:
Some codecs should be considered unstable as these are relative new. For this purpose we should introduce an annotation which these codecs should us to be marked as unstable in terms of API.
Modifications:
- Add UnstableApi annotation and use it on codecs that are not stable
- Move http2.hpack to http2.internal.hpack as it is internal.
Result:
Better document unstable APIs.
Motivation:
This allows using handlers for Streams in normal Netty-style. Frames are
read/written to the channel as messages, not directly as a
callback/method call. Handlers allow mixing and can ease HTTP/1 and
HTTP/2 interoperability by eventually supporting HTTP/1 handlers in
HTTP/2 and vise versa.
Modifications:
New handler Http2MultiplexCodec that converts from the current HTTP/2
API to a message-based API and child channels for streams.
Result:
The basics are done for server-side: new streams trigger creation of new
channels in much the same appearance to how new connections trigger new
channel creation. The basic frames HEADERS and DATA are handled, but
also GOAWAY and RST_STREAM.
Inbound flow control is implemented, but outbound is not. That will be
done later, along with not completing write promises on the child
channel until the write actually completes on the parent.
There is not yet support for outbound priority/weight, push promises,
and many other features.
There is a generic Object that may be set on stream frames. This also
paves the way for client-side support which needs a way to refer to
yet-to-be-created streams (due to how HEADERS allocates a stream id, and
the allocation order must be the same as transmission order).
