hgext/lfs/blobstore.py

lfs: import the Facebook git-lfs client extension

The purpose of this is the same as the built-in largefiles extension- to handle
huge files outside of the normal storage system, generally to keep the amount of
data cloned to a lower amount.  There are several benefits of implementing the
git-lfs protocol, instead of using the largefiles extension:

  - Bitbucket and Github support (and probably wider support in 3rd party
    hosting sites in general). [1][2]

  - The number of hg internals monkey patched are several orders of magnitude
    lower, so it will be easier to reason about and maintain.  Future commands
    will likely just work, without requiring various wrappers.

  - The "standin" files are only written to the filelog, not the disk.  That
    should avoid weird edge cases where the largefile and standin files get out
    of sync. [3]  It also avoids the occasional printing of the "hidden" standin
    file in various messages.

  - Filesets like size() will work, even if the file isn't present.  (It always
    says 41 bytes for largefiles, whether present or not.)

The only place that I see where largefiles comes out on top is that it works
with `hg serve` for simple sharing, without external infrastructure.  Getting
lfs-test-server working was a hassle, and took awhile to figure out.  Maybe we
can do something to make it work in the future.

Long term, I expect that this will be highly preferred over largefiles.  But if
we are to recommend this to largefile users, there are some UI issues to
bikeshed.  Until they are resolved, I've marked this experimental, and am not
putting a pointer to this in the largefiles help.  The (non exhaustive) list of
issues I've seen so far are:

  - It isn't sufficient to just enable the largefiles extension- you have to
    explicitly add a file with --large before it will pay attention to the
    configured sizes and patterns on future adds.  The justification being that
    once you use it, you're stuck with it.  I've seen people confused by this,
    and haven't liked it myself.  But it's also saved me a few times.  Should we
    do something like have a specific enabling config setting that must be set
    in the local repo config, so that enabling this extension in the user or
    system hgrc doesn't silently start storing lfs files?

  - The largefiles extension adds a repo requirement when the first largefile is
    committed, so that the extension must always be enabled in the future.  This
    extension is not doing that, and since I only enabled it locally to avoid
    infecting other repos, I got a cryptic error about missing flag processors
    when I cloned.  Is there no repo requirement due to shallow/narrow clone
    considerations (or other future advanced things)?

  - In the (small amount of) reading I've done about the git implementation, it
    seems that the files and sizes are stored in a tracked .gitattributes file.
    I think a tracked file for this would be extremely useful for consistency
    across developers, but this kind of touches on the tracked hgrc file
    proposal a few months back.

  - The git client can specify file patterns, not just sizes.

  - The largefiles extension has a cache directory in the local repo, but also a
    system wide one.  We should probably implement a system wide cache too, so
    that multiple clones don't have to refetch the files from the server.

  - Jun mentioned other missing features, like SSH authentication, gc, etc.

The code corresponds to c0492b73c7ef in hg-experimental. [4]  The only tweaks
are to load the extension in the tests with 'lfs=' instead of
'lfs=$TESTDIR/../hgext3rd/lfs', change the import in the *.py test to hgext
(from hgext3rd), add the 'testedwith' declaration, and mark it experimental for
now.  The infinite-push, p4fastimport, and remotefilelog tests were left behind.

The devel-warnings for unregistered config options are not corrected yet, nor
are the import check warnings.

[1] https://www.mercurial-scm.org/pipermail/mercurial/2017-November/050699.html
[2] https://bitbucket.org/site/master/issues/3843/largefiles-support-bb-3903
[3] https://bz.mercurial-scm.org/show_bug.cgi?id=5738
[4] https://bitbucket.org/facebook/hg-experimental

# blobstore.py - local and remote (speaking Git-LFS protocol) blob storages
#
# Copyright 2017 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.

from __future__ import absolute_import

import json
import os
import re

from mercurial import (
    error,
    url as urlmod,
    util,
    vfs as vfsmod,
)
from mercurial.i18n import _

# 64 bytes for SHA256
_lfsre = re.compile(r'\A[a-f0-9]{64}\Z')

class lfsvfs(vfsmod.vfs):
    def join(self, path):
        """split the path at first two characters, like: XX/XXXXX..."""
        if not _lfsre.match(path):
            raise error.ProgrammingError('unexpected lfs path: %s' % path)
        return super(lfsvfs, self).join(path[0:2], path[2:])

class filewithprogress(object):
    """a file-like object that supports __len__ and read.

    Useful to provide progress information for how many bytes are read.
    """

    def __init__(self, fp, callback):
        self._fp = fp
        self._callback = callback # func(readsize)
        fp.seek(0, os.SEEK_END)
        self._len = fp.tell()
        fp.seek(0)

    def __len__(self):
        return self._len

    def read(self, size):
        if self._fp is None:
            return b''
        data = self._fp.read(size)
        if data:
            if self._callback:
                self._callback(len(data))
        else:
            self._fp.close()
            self._fp = None
        return data

class local(object):
    """Local blobstore for large file contents.

    This blobstore is used both as a cache and as a staging area for large blobs
    to be uploaded to the remote blobstore.
    """

    def __init__(self, repo):
        fullpath = repo.svfs.join('lfs/objects')
        self.vfs = lfsvfs(fullpath)

    def write(self, oid, data):
        """Write blob to local blobstore."""
        with self.vfs(oid, 'wb', atomictemp=True) as fp:
            fp.write(data)

    def read(self, oid):
        """Read blob from local blobstore."""
        return self.vfs.read(oid)

    def has(self, oid):
        """Returns True if the local blobstore contains the requested blob,
        False otherwise."""
        return self.vfs.exists(oid)

class _gitlfsremote(object):

    def __init__(self, repo, url):
        ui = repo.ui
        self.ui = ui
        baseurl, authinfo = url.authinfo()
        self.baseurl = baseurl.rstrip('/')
        self.urlopener = urlmod.opener(ui, authinfo)
        self.retry = ui.configint('lfs', 'retry', 5)

    def writebatch(self, pointers, fromstore):
        """Batch upload from local to remote blobstore."""
        self._batch(pointers, fromstore, 'upload')

    def readbatch(self, pointers, tostore):
        """Batch download from remote to local blostore."""
        self._batch(pointers, tostore, 'download')

    def _batchrequest(self, pointers, action):
        """Get metadata about objects pointed by pointers for given action

        Return decoded JSON object like {'objects': [{'oid': '', 'size': 1}]}
        See https://github.com/git-lfs/git-lfs/blob/master/docs/api/batch.md
        """
        objects = [{'oid': p.oid(), 'size': p.size()} for p in pointers]
        requestdata = json.dumps({
            'objects': objects,
            'operation': action,
        })
        batchreq = util.urlreq.request('%s/objects/batch' % self.baseurl,
                                       data=requestdata)
        batchreq.add_header('Accept', 'application/vnd.git-lfs+json')
        batchreq.add_header('Content-Type', 'application/vnd.git-lfs+json')
        try:
            rawjson = self.urlopener.open(batchreq).read()
        except util.urlerr.httperror as ex:
            raise LfsRemoteError(_('LFS HTTP error: %s (action=%s)')
                                 % (ex, action))
        try:
            response = json.loads(rawjson)
        except ValueError:
            raise LfsRemoteError(_('LFS server returns invalid JSON: %s')
                                 % rawjson)
        return response

    def _checkforservererror(self, pointers, responses):
        """Scans errors from objects

        Returns LfsRemoteError if any objects has an error"""
        for response in responses:
            error = response.get('error')
            if error:
                ptrmap = {p.oid(): p for p in pointers}
                p = ptrmap.get(response['oid'], None)
                if error['code'] == 404 and p:
                    filename = getattr(p, 'filename', 'unknown')
                    raise LfsRemoteError(
                        _(('LFS server error. Remote object '
                          'for file %s not found: %r')) % (filename, response))
                raise LfsRemoteError(_('LFS server error: %r') % response)

    def _extractobjects(self, response, pointers, action):
        """extract objects from response of the batch API

        response: parsed JSON object returned by batch API
        return response['objects'] filtered by action
        raise if any object has an error
        """
        # Scan errors from objects - fail early
        objects = response.get('objects', [])
        self._checkforservererror(pointers, objects)

        # Filter objects with given action. Practically, this skips uploading
        # objects which exist in the server.
        filteredobjects = [o for o in objects if action in o.get('actions', [])]
        # But for downloading, we want all objects. Therefore missing objects
        # should be considered an error.
        if action == 'download':
            if len(filteredobjects) < len(objects):
                missing = [o.get('oid', '?')
                           for o in objects
                           if action not in o.get('actions', [])]
                raise LfsRemoteError(
                    _('LFS server claims required objects do not exist:\n%s')
                    % '\n'.join(missing))

        return filteredobjects

    def _basictransfer(self, obj, action, localstore, progress=None):
        """Download or upload a single object using basic transfer protocol

        obj: dict, an object description returned by batch API
        action: string, one of ['upload', 'download']
        localstore: blobstore.local

        See https://github.com/git-lfs/git-lfs/blob/master/docs/api/\
        basic-transfers.md
        """
        oid = str(obj['oid'])

        href = str(obj['actions'][action].get('href'))
        headers = obj['actions'][action].get('header', {}).items()

        request = util.urlreq.request(href)
        if action == 'upload':
            # If uploading blobs, read data from local blobstore.
            request.data = filewithprogress(localstore.vfs(oid), progress)
            request.get_method = lambda: 'PUT'

        for k, v in headers:
            request.add_header(k, v)

        response = b''
        try:
            req = self.urlopener.open(request)
            while True:
                data = req.read(1048576)
                if not data:
                    break
                if action == 'download' and progress:
                    progress(len(data))
                response += data
        except util.urlerr.httperror as ex:
            raise LfsRemoteError(_('HTTP error: %s (oid=%s, action=%s)')
                                 % (ex, oid, action))

        if action == 'download':
            # If downloading blobs, store downloaded data to local blobstore
            localstore.write(oid, response)

    def _batch(self, pointers, localstore, action):
        if action not in ['upload', 'download']:
            raise error.ProgrammingError('invalid Git-LFS action: %s' % action)

        response = self._batchrequest(pointers, action)
        prunningsize = [0]
        objects = self._extractobjects(response, pointers, action)
        total = sum(x.get('size', 0) for x in objects)
        topic = {'upload': _('lfs uploading'),
                 'download': _('lfs downloading')}[action]
        if self.ui.verbose and len(objects) > 1:
            self.ui.write(_('lfs: need to transfer %d objects (%s)\n')
                          % (len(objects), util.bytecount(total)))
        self.ui.progress(topic, 0, total=total)
        def progress(size):
            # advance progress bar by "size" bytes
            prunningsize[0] += size
            self.ui.progress(topic, prunningsize[0], total=total)
        for obj in sorted(objects, key=lambda o: o.get('oid')):
            objsize = obj.get('size', 0)
            if self.ui.verbose:
                if action == 'download':
                    msg = _('lfs: downloading %s (%s)\n')
                elif action == 'upload':
                    msg = _('lfs: uploading %s (%s)\n')
                self.ui.write(msg % (obj.get('oid'), util.bytecount(objsize)))
            origrunningsize = prunningsize[0]
            retry = self.retry
            while True:
                prunningsize[0] = origrunningsize
                try:
                    self._basictransfer(obj, action, localstore,
                                        progress=progress)
                    break
                except Exception as ex:
                    if retry > 0:
                        if self.ui.verbose:
                            self.ui.write(
                                _('lfs: failed: %r (remaining retry %d)\n')
                                % (ex, retry))
                        retry -= 1
                        continue
                    raise

        self.ui.progress(topic, pos=None, total=total)

    def __del__(self):
        # copied from mercurial/httppeer.py
        urlopener = getattr(self, 'urlopener', None)
        if urlopener:
            for h in urlopener.handlers:
                h.close()
                getattr(h, "close_all", lambda : None)()

class _dummyremote(object):
    """Dummy store storing blobs to temp directory."""

    def __init__(self, repo, url):
        fullpath = repo.vfs.join('lfs', url.path)
        self.vfs = lfsvfs(fullpath)

    def writebatch(self, pointers, fromstore):
        for p in pointers:
            content = fromstore.read(p.oid())
            with self.vfs(p.oid(), 'wb', atomictemp=True) as fp:
                fp.write(content)

    def readbatch(self, pointers, tostore):
        for p in pointers:
            content = self.vfs.read(p.oid())
            tostore.write(p.oid(), content)

class _nullremote(object):
    """Null store storing blobs to /dev/null."""

    def __init__(self, repo, url):
        pass

    def writebatch(self, pointers, fromstore):
        pass

    def readbatch(self, pointers, tostore):
        pass

class _promptremote(object):
    """Prompt user to set lfs.url when accessed."""

    def __init__(self, repo, url):
        pass

    def writebatch(self, pointers, fromstore, ui=None):
        self._prompt()

    def readbatch(self, pointers, tostore, ui=None):
        self._prompt()

    def _prompt(self):
        raise error.Abort(_('lfs.url needs to be configured'))

_storemap = {
    'https': _gitlfsremote,
    'http': _gitlfsremote,
    'file': _dummyremote,
    'null': _nullremote,
    None: _promptremote,
}

def remote(repo):
    """remotestore factory. return a store in _storemap depending on config"""
    defaulturl = ''

    # convert deprecated configs to the new url. TODO: remove this if other
    # places are migrated to the new url config.
    # deprecated config: lfs.remotestore
    deprecatedstore = repo.ui.config('lfs', 'remotestore')
    if deprecatedstore == 'dummy':
        # deprecated config: lfs.remotepath
        defaulturl = 'file://' + repo.ui.config('lfs', 'remotepath')
    elif deprecatedstore == 'git-lfs':
        # deprecated config: lfs.remoteurl
        defaulturl = repo.ui.config('lfs', 'remoteurl')
    elif deprecatedstore == 'null':
        defaulturl = 'null://'

    url = util.url(repo.ui.config('lfs', 'url', defaulturl))
    scheme = url.scheme
    if scheme not in _storemap:
        raise error.Abort(_('lfs: unknown url scheme: %s') % scheme)
    return _storemap[scheme](repo, url)

class LfsRemoteError(error.RevlogError):
    pass