hgext/automv.py

lfs: add basic routing for the server side wire protocol processing

The recent hgweb refactoring yielded a clean point to wrap a function that could
handle this, so I moved the routing for this out of the core.  While not an hg
wire protocol, this seems logically close enough.  For now, these handlers do
nothing other than check permissions.

The protocol requires support for PUT requests, so that has been added to the
core, and funnels into the same handler as GET and POST.  The permission
checking code was assuming that anything not checking 'pull' or None ops should
be using POST.  But that breaks the upload check if it checks 'push'.  So I
invented a new 'upload' permission, and used it to avoid the mandate to POST.  A
function wrap point could be added, but security code should probably stay
grouped together.  Given that anything not 'pull' or None was requiring POST,
the comment on hgweb.common.permhooks is probably wrong- there is no 'read'.

The rationale for the URIs is that the spec for the Batch API[1] defines the URL
as the LFS server url + '/objects/batch'.  The default git URLs are:

    Git remote: https://git-server.com/foo/bar
    LFS server: https://git-server.com/foo/bar.git/info/lfs
    Batch API: https://git-server.com/foo/bar.git/info/lfs/objects/batch

'.git/' seems like it's not something a user would normally track.  If we adhere
to how git defines the URLs, then the hg-git extension should be able to talk to
a git based server without any additional work.

The URI for the transfer requests starts with '.hg/' to ensure that there are no
conflicts with tracked files.  Since these are handed out by the Batch API, we
can change this at any point in the future.  (Specifically, it might be a good
idea to use something under the proposed /api/ namespace.)  In any case, no
files are stored at these locations in the repository directory.

I started a new module for this because it seems like a good idea to keep all of
the security sensitive server side code together.  There's also an issue with
`hg verify` in that it will want to download *all* blobs in order to run.
Sadly, there's no way in the protocol to ask the server to verify the content of
a blob it may have.  (The verify action is for storing files on a 3rd party
server, and then informing the LFS server when that completes.)  So we may end
up implementing a custom transfer adapter that simply indicates if the blobs are
valid, and fall back to basic transfers for non-hg servers.  In other words,
this code is likely to get bigger before this is made non-experimental.

[1] https://github.com/git-lfs/git-lfs/blob/master/docs/api/batch.md

# automv.py
#
# Copyright 2013-2016 Facebook, Inc.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
"""check for unrecorded moves at commit time (EXPERIMENTAL)

This extension checks at commit/amend time if any of the committed files
comes from an unrecorded mv.

The threshold at which a file is considered a move can be set with the
``automv.similarity`` config option. This option takes a percentage between 0
(disabled) and 100 (files must be identical), the default is 95.

"""

# Using 95 as a default similarity is based on an analysis of the mercurial
# repositories of the cpython, mozilla-central & mercurial repositories, as
# well as 2 very large facebook repositories. At 95 50% of all potential
# missed moves would be caught, as well as correspond with 87% of all
# explicitly marked moves.  Together, 80% of moved files are 95% similar or
# more.
#
# See http://markmail.org/thread/5pxnljesvufvom57 for context.

from __future__ import absolute_import

from mercurial.i18n import _
from mercurial import (
    commands,
    copies,
    error,
    extensions,
    pycompat,
    registrar,
    scmutil,
    similar
)

configtable = {}
configitem = registrar.configitem(configtable)

configitem('automv', 'similarity',
    default=95,
)

def extsetup(ui):
    entry = extensions.wrapcommand(
        commands.table, 'commit', mvcheck)
    entry[1].append(
        ('', 'no-automv', None,
         _('disable automatic file move detection')))

def mvcheck(orig, ui, repo, *pats, **opts):
    """Hook to check for moves at commit time"""
    opts = pycompat.byteskwargs(opts)
    renames = None
    disabled = opts.pop('no_automv', False)
    if not disabled:
        threshold = ui.configint('automv', 'similarity')
        if not 0 <= threshold <= 100:
            raise error.Abort(_('automv.similarity must be between 0 and 100'))
        if threshold > 0:
            match = scmutil.match(repo[None], pats, opts)
            added, removed = _interestingfiles(repo, match)
            renames = _findrenames(repo, match, added, removed,
                                   threshold / 100.0)

    with repo.wlock():
        if renames is not None:
            scmutil._markchanges(repo, (), (), renames)
        return orig(ui, repo, *pats, **pycompat.strkwargs(opts))

def _interestingfiles(repo, matcher):
    """Find what files were added or removed in this commit.

    Returns a tuple of two lists: (added, removed). Only files not *already*
    marked as moved are included in the added list.

    """
    stat = repo.status(match=matcher)
    added = stat[1]
    removed = stat[2]

    copy = copies._forwardcopies(repo['.'], repo[None], matcher)
    # remove the copy files for which we already have copy info
    added = [f for f in added if f not in copy]

    return added, removed

def _findrenames(repo, matcher, added, removed, similarity):
    """Find what files in added are really moved files.

    Any file named in removed that is at least similarity% similar to a file
    in added is seen as a rename.

    """
    renames = {}
    if similarity > 0:
        for src, dst, score in similar.findrenames(
                repo, added, removed, similarity):
            if repo.ui.verbose:
                repo.ui.status(
                    _('detected move of %s as %s (%d%% similar)\n') % (
                        matcher.rel(src), matcher.rel(dst), score * 100))
            renames[dst] = src
    if renames:
        repo.ui.status(_('detected move of %d files\n') % len(renames))
    return renames