contrib/fuzz/README.rst

wireprotov2: define and use stream encoders

Now that we have basic support for defining stream encoding, it is
time to start doing something with it.

We define various classes implementing stream encoders/decoders for
the defined encoding profiles. This is relatively straightforward.

We teach the inputstream and outputstream classes how to encode,
decode, and flush data.

We then teach the clientreactor how to filter received data through
the inputstream decoder.

One of the features of the framing format is that streams can span
requests. This is a differentiating feature from say HTTP/2, which
associates streams with requests. By allowing streams to span requests,
we can reuse compression context data across requests/responses. But
in order to do this, we need a mechanism to "flush" the encoder at
logical boundaries so that receivers receive all data where it is
expected. And a "flush" event is distinct from a "finish" event from
the perspective of certain compressors because a "flush" will retain
compression context state whereas a "finish" operation will not. This
is why encoders have both a flush() and a finish() and each uses
specific flushing semantics on the underlying compressor.

The added tests verify various behavior of decoders via clientreactor.
These tests do test some compression behavior via use of outputstream.
But for all intents and purposes, server reactor support for encoding
is not yet implemented.

Differential Revision: https://phab.mercurial-scm.org/D4921

How to add fuzzers (partially cribbed from oss-fuzz[0]):

  1) git clone https://github.com/google/oss-fuzz
  2) cd oss-fuzz
  3) python infra/helper.py build_image mercurial
  4) docker run --cap-add=SYS_PTRACE -it -v $HG_REPO_PATH:/hg-new \
         gcr.io/oss-fuzz/mercurial bash
  5) cd /src
  6) rm -r mercurial
  7) ln -s /hg-new mercurial
  8) cd mercurial
  9) compile
  10) ls $OUT

Step 9 is literally running the command "compile", which is part of
the docker container. Once you have that working, you can build the
fuzzers like this (in the oss-fuzz repo):

python infra/helper.py build_fuzzers --sanitizer address mercurial $HG_REPO_PATH

(you can also say "memory", "undefined" or "coverage" for
sanitizer). Then run the built fuzzers like this:

python infra/helper.py run_fuzzer mercurial -- $FUZZER

0: https://github.com/google/oss-fuzz/blob/master/docs/new_project_guide.md