exchangev2: start to implement pull with wire protocol v2

Wire protocol version 2 will take a substantially different
approach to exchange than version 1 (at least as far as pulling
is concerned).

This commit establishes a new exchangev2 module for holding
code related to exchange using wire protocol v2. I could have
added things to the existing exchange module. But it is already
quite big. And doing things inline isn't in question because
the existing code is already littered with conditional code
for various states of support for the existing wire protocol
as it evolved over 10+ years. A new module gives us a chance
to make a clean break.

This approach does mean we'll end up writing some duplicate
code. And there's a significant chance we'll miss functionality
as code is ported. The plan is to eventually add #testcase's
to existing tests so the new wire protocol is tested side-by-side
with the existing one. This will hopefully tease out any
features that weren't ported properly. But before we get there,
we need to build up support for the new exchange methods.

Our journey towards implementing a new exchange begins with pulling.
And pulling begins with discovery.

The discovery code added to exchangev2 is heavily drawn from
the following functions:

* exchange._pulldiscoverychangegroup
* discovery.findcommonincoming

For now, we build on top of existing discovery mechanisms. The
new wire protocol should be capable of doing things more efficiently.
But I'd rather defer on this problem.

To foster the transition, we invent a fake capability on the HTTPv2
peer and have the main pull code in exchange.py call into exchangev2
when the new wire protocol is being used.

Differential Revision: https://phab.mercurial-scm.org/D4480

mercurial/exchangev2.py

@@ -0,0 +1,55
+# exchangev2.py - repository exchange for wire protocol version 2
+#
+# Copyright 2018 Gregory Szorc <[e-mail]>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+from .node import (
+    nullid,
+)
+from . import (
+    setdiscovery,
+)
+
+def pull(pullop):
+    """Pull using wire protocol version 2."""
+    repo = pullop.repo
+    remote = pullop.remote
+
+    # Figure out what needs to be fetched.
+    common, fetch, remoteheads = _pullchangesetdiscovery(
+        repo, remote, pullop.heads, abortwhenunrelated=pullop.force)
+
+def _pullchangesetdiscovery(repo, remote, heads, abortwhenunrelated=True):
+    """Determine which changesets need to be pulled."""
+
+    if heads:
+        knownnode = repo.changelog.hasnode
+        if all(knownnode(head) for head in heads):
+            return heads, False, heads
+
+    # TODO wire protocol version 2 is capable of more efficient discovery
+    # than setdiscovery. Consider implementing something better.
+    common, fetch, remoteheads = setdiscovery.findcommonheads(
+        repo.ui, repo, remote, abortwhenunrelated=abortwhenunrelated)
+
+    common = set(common)
+    remoteheads = set(remoteheads)
+
+    # If a remote head is filtered locally, put it back in the common set.
+    # See the comment in exchange._pulldiscoverychangegroup() for more.
+
+    if fetch and remoteheads:
+        nodemap = repo.unfiltered().changelog.nodemap
+
+        common |= {head for head in remoteheads if head in nodemap}
+
+        if set(remoteheads).issubset(common):
+            fetch = []
+
+    common.discard(nullid)
+
+    return common, fetch, remoteheads

tests/test-wireproto-exchangev2.t

@@ -0,0 +1,53
+Tests for wire protocol version 2 exchange.
+Tests in this file should be folded into existing tests once protocol
+v2 has enough features that it can be enabled via #testcase in existing
+tests.
+
+  $ . $TESTDIR/wireprotohelpers.sh
+  $ enablehttpv2client
+
+  $ hg init server-simple
+  $ enablehttpv2 server-simple
+  $ cd server-simple
+  $ cat >> .hg/hgrc << EOF
+  > [phases]
+  > publish = false
+  > EOF
+  $ echo a0 > a
+  $ echo b0 > b
+  $ hg -q commit -A -m 'commit 0'
+
+  $ echo a1 > a
+  $ hg commit -m 'commit 1'
+  $ hg phase --public -r .
+  $ echo a2 > a
+  $ hg commit -m 'commit 2'
+
+  $ hg -q up -r 0
+  $ echo b1 > b
+  $ hg -q commit -m 'head 2 commit 1'
+  $ echo b2 > b
+  $ hg -q commit -m 'head 2 commit 2'
+
+  $ hg serve -p $HGPORT -d --pid-file hg.pid -E error.log
+  $ cat hg.pid > $DAEMON_PIDS
+
+  $ cd ..
+
+Test basic clone
+
+  $ hg --debug clone -U http://localhost:$HGPORT client-simple
+  using http://localhost:$HGPORT/
+  sending capabilities command
+  query 1; heads
+  sending 2 commands
+  sending command heads: {}
+  sending command known: {
+    'nodes': []
+  }
+  received frame(size=11; request=1; stream=2; streamflags=stream-begin; type=command-response; flags=continuation)
+  received frame(size=43; request=1; stream=2; streamflags=; type=command-response; flags=continuation)
+  received frame(size=0; request=1; stream=2; streamflags=; type=command-response; flags=eos)
+  received frame(size=11; request=3; stream=2; streamflags=; type=command-response; flags=continuation)
+  received frame(size=1; request=3; stream=2; streamflags=; type=command-response; flags=continuation)
+  received frame(size=0; request=3; stream=2; streamflags=; type=command-response; flags=eos)

mercurial/exchange.py

@@ -26,6 +26,7 from . import (
     changegroup,
     discovery,
     error,
+    exchangev2,
     lock as lockmod,
     logexchange,
     narrowspec,
@@ -1506,6 +1507,10 def pull(repo, remote, heads=None, force
 
     pullop.trmanager = transactionmanager(repo, 'pull', remote.url())
     with repo.wlock(), repo.lock(), pullop.trmanager:
+        # Use the modern wire protocol, if available.
+        if remote.capable('exchangev2'):
+            exchangev2.pull(pullop)
+        else:
         # This should ideally be in _pullbundle2(). However, it needs to run
         # before discovery to avoid extra work.
         _maybeapplyclonebundle(pullop)

mercurial/httppeer.py

@@ -802,7 +802,8 class httpv2peer(object):
             return True
 
         # Other concepts.
-        if name in ('bundle2',):
+        # TODO remove exchangev2 once we have a command implemented.
+        if name in ('bundle2', 'exchangev2'):
             return True
 
         # Alias command-* to presence of command of that name.

tests/wireprotohelpers.sh

@@ -56,3 +56,10 web.apiserver = true
 web.api.http-v2 = true
 EOF
 }
+
+enablehttpv2client() {
+  cat >> $HGRCPATH << EOF
+[experimental]
+httppeer.advertise-v2 = true
+EOF
+}