tests/test-exchange-obsmarkers-case-B3.t

wireprotov2: move response handling out of httppeer

And fix some bugs while we're here.

The code for processing response data from the unified framing
protocol is mostly peer agnostic. The peer-specific bits are the
configuration of the client reactor and how I/O is performed. I
initially implemented things in httppeer for expediency.

This commit establishes a module for holding the peer API level
code for the framing based protocol. Inside this module we have
a class to help coordinate higher-level activities, such as managing
response object.

The client handler bits could be rolled into clientreactor. However,
I want clientreactor to be sans I/O and I want it to only be
concerned with protocol-level details, not higher-level concepts
like how protocol events are converted into peer API concepts. I
want clientreactor to receive a frame and then tell the caller what
should probably be done about it. If we start putting things like
future resolution into clientreactor, we'll constrain how the protocol
can be used (e.g. by requiring futures).

The new code is loosely based on what was in httppeer before. I
changed things a bit around response handling. We now buffer the
entire response "body" and then handle it as one atomic unit. This
fixed a bug around decoding CBOR data that spanned multiple frames.
I also fixed an off-by-one bug where we failed to read a single byte
CBOR value at the end of the stream. That's why tests have changed.

The new state of httppeer is much cleaner. It is largely agnostic
about framing protocol implementation details. That's how it should
be: the framing protocol is designed to be largely transport
agnostic. We want peers merely putting bytes on the wire and telling
the framing protocol where to read response data from.

There's still a bit of work to be done here, especially for
representing responses. But at least we're a step closer to having a
higher-level peer interface that can be plugged into the SSH peer
someday.

I initially added this class to wireprotoframing. However, we'll
eventually need version 2 specific functions to convert CBOR responses
into data structures expected by the code calling commands. This
needs to live somewhere. Since that code would be shared across peers,
we need a common module. We have wireprotov1peer for the equivalent
version 1 code. So I decided to establish wireprotov2peer.

Differential Revision: https://phab.mercurial-scm.org/D3379

============================================
Testing obsolescence markers push: Cases B.3
============================================

Mercurial pushes obsolescences markers relevant to the "pushed-set", the set of
all changesets that requested to be "in sync" after the push (even if they are
already on both side).

This test belongs to a series of tests checking such set is properly computed
and applied. This does not tests "obsmarkers" discovery capabilities.

Category B: pruning case
TestCase 3: Pruned changeset on non-pushed part of the history

B.3 Pruned changeset on non-pushed part of the history
======================================================

.. {{{
..   ⊗ C
..   |
..   ○ B
..   | ◔ A
..   |/
..   ● O
.. }}}
..
.. Marker exists from:
..
..  * C (prune)
..
.. Commands run:
..
..  * hg push -r A
..
.. Expected exchange:
..
..  * ø
..
.. Expected exclude:
..
..  * chain from B

Setup
-----

  $ . $TESTDIR/testlib/exchange-obsmarker-util.sh

initial

  $ setuprepos B.3
  creating test repo for test case B.3
  - pulldest
  - main
  - pushdest
  cd into `main` and proceed with env setup
  $ cd main
  $ mkcommit A
  $ hg up --quiet 0
  $ mkcommit B
  created new head
  $ mkcommit C
  $ hg prune -qd '0 0' .
  $ hg log -G --hidden
  x  e56289ab6378 (draft): C
  |
  @  35b183996678 (draft): B
  |
  | o  f5bc6836db60 (draft): A
  |/
  o  a9bdc8b26820 (public): O
  
  $ inspect_obsmarkers
  obsstore content
  ================
  e56289ab6378dc752fd7965f8bf66b58bda740bd 0 {35b1839966785d5703a01607229eea932db42f87} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  $ cd ..
  $ cd ..

Actual Test
-----------------------------------

  $ dotest B.3 A
  ## Running testcase B.3
  # testing echange of "A" (f5bc6836db60)
  ## initial state
  # obstore: main
  e56289ab6378dc752fd7965f8bf66b58bda740bd 0 {35b1839966785d5703a01607229eea932db42f87} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  # obstore: pushdest
  # obstore: pulldest
  ## pushing "A" from main to pushdest
  pushing to pushdest
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files
  ## post push state
  # obstore: main
  e56289ab6378dc752fd7965f8bf66b58bda740bd 0 {35b1839966785d5703a01607229eea932db42f87} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  # obstore: pushdest
  # obstore: pulldest
  ## pulling "f5bc6836db60" from main into pulldest
  pulling from main
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets f5bc6836db60
  (run 'hg update' to get a working copy)
  ## post pull state
  # obstore: main
  e56289ab6378dc752fd7965f8bf66b58bda740bd 0 {35b1839966785d5703a01607229eea932db42f87} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  # obstore: pushdest
  # obstore: pulldest