HTTP2 headers are sent in (potentially) many frames, but all must be
sent sequentially with no traffic intervening.
This was not clear when I wrote the HPACK parser, and still indeed quite
contentious on the HTTP2 mailing lists.
Now that matter is well settled (years ago!) take advantage of the fact
by delaying parsing until all bytes are available.
A future change will leverage this to avoid having to store and verify
partial parse state, completely eliminating indirect calls within the
parser.
This is a fairly low effort migration of the current codebase into a C++ class, instead of free standing C code.
It builds upon #26657 as a necessary first step.
I've tried to minimize any changes to semantics or logic in this change, except where required to get a minimal amount of encapsulation - which is the major aim of this change.
A future change in this series will buffer slices until all HPACK headers are in memory for a stream prior to decoding -- it's important to have an encapsulated API to the parser before doing so however (hence this CL).
The next change after that will be an almost complete rewrite of the parsing functionality -- since we'll have the total set of header bytes, we'll no longer need to support suspending decoding at arbitrary points. This will allow us to move to a simple recursive descent parser, eliminate a bunch of indirection in this code, and end up in a much more malleable place for when we start doing metadata API changes.
(we likely also end up with some good performance wins!)
The urgent argument is a platform-specific flag that leaked into the (ideally) platform-independent HTTP/2 transport layer. In an effort to clean up the cross-platform API surface, it would be helpful if we can remove this argument from the TCP Read api without losing the performance optimization that was introduced along with it (see #18240).
- The HEADER frame should get the END_STREAM flag per the HTTP/2 spec;
the old code put END_STREAM on the last CONTINUATION frame.
- Removing deprecated parameter, is_last_in_stream, from finish_frame();
it has been superseded by the is_end_of_stream member of the framer_state
struct.
- Adding some gRPC frame validation tests to hpack_encoder_test.cc,
and explicting checking that the END_STREAM flag is not on the
CONTINUATION frame.
fixes#21436
on_hdr() checks if a void-return function pointer is null before jumping to it.
If it is null, it returns an error; else it executes that function and returns
success.
This change converts the void-returning function to one that returns a
grpc_error* and thus saves a branch in on_hdr() (since we're branching once by
following the function pointer anyways, we're effectively coalescing these two
branches).
Several asserts in grpc_chttp2_stream_map_find() can be converted to debug
asserts. This PR also templatizes the internal find() method to have it be
strict in the delete case (which saves some branches).