cborutil: implement sans I/O decoder
The vendored CBOR package decodes by calling read(n) on an object.
There are a number of disadvantages to this:
* Uses blocking I/O. If sufficient data is not available, the decoder
will hang until it is.
* No support for partial reads. If the read(n) returns less data than
requested, the decoder raises an error.
* Requires the use of a file like object. If the original data is in
say a buffer, we need to "cast" it to e.g. a BytesIO to appease the
decoder.
In addition, the vendored CBOR decoder doesn't provide flexibility
that we desire. Specifically:
* It buffers indefinite length bytestrings instead of streaming them.
* It doesn't allow limiting the set of types that can be decoded. This
property is useful when implementing a "hardened" decoder that is
less susceptible to abusive input.
* It doesn't provide sufficient "hook points" and introspection to
institute checks around behavior. These are useful for implementing
a "hardened" decoder.
This all adds up to a reasonable set of justifications for writing our
own decoder.
So, this commit implements our own CBOR decoder.
At the heart of the decoder is a function that decodes a single "item"
from a buffer. This item can be a complete simple value or a special
value, such as "start of array." Using this function, we can build a
decoder that effectively iterates over the stream of decoded items and
builds up higher-level values, such as arrays, maps, sets, and indefinite
length bytestrings. And we can do this without performing I/O in the
decoder itself.
The core of the sans I/O decoder will probably not be used directly.
Instead, it is expected that we'll build utility functions for invoking
the decoder given specific input types. This will allow extreme
flexibility in how data is delivered to the decoder.
I'm pretty happy with the state of the decoder modulo the TODO items
to track wanted features to help with a "hardened" decoder. The one
thing I could be convinced to change is the handling of semantic tags.
Since we only support a single semantic tag (sets), I thought it would
be easier to handle them inline in decodeitem(). This is simpler now.
But if we add support for other semantic tags, it will likely be easier
to move semantic tag handling outside of decodeitem(). But, properly
supporting semantic tags opens up a whole can of worms, as many
semantic tags imply new types. I'm optimistic we won't need these in
Mercurial. But who knows.
I'm also pretty happy with the test coverage. Writing comprehensive
tests for partial decoding did flush out a handful of bugs. One
general improvement to testing would be fuzz testing for partial
decoding. I may implement that later. I also anticipate switching the
wire protocol code to this new decoder will flush out any lingering
bugs.
Differential Revision: https://phab.mercurial-scm.org/D4414
# fetch.py - pull and merge remote changes
#
# Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
'''pull, update and merge in one command (DEPRECATED)'''
from __future__ import absolute_import
from mercurial.i18n import _
from mercurial.node import (
short,
)
from mercurial import (
cmdutil,
error,
exchange,
hg,
lock,
pycompat,
registrar,
util,
)
from mercurial.utils import dateutil
release = lock.release
cmdtable = {}
command = registrar.command(cmdtable)
# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
# be specifying the version(s) of Mercurial they are tested with, or
# leave the attribute unspecified.
testedwith = 'ships-with-hg-core'
@command('fetch',
[('r', 'rev', [],
_('a specific revision you would like to pull'), _('REV')),
('', 'edit', None, _('invoke editor on commit messages')),
('', 'force-editor', None, _('edit commit message (DEPRECATED)')),
('', 'switch-parent', None, _('switch parents when merging')),
] + cmdutil.commitopts + cmdutil.commitopts2 + cmdutil.remoteopts,
_('hg fetch [SOURCE]'))
def fetch(ui, repo, source='default', **opts):
'''pull changes from a remote repository, merge new changes if needed.
This finds all changes from the repository at the specified path
or URL and adds them to the local repository.
If the pulled changes add a new branch head, the head is
automatically merged, and the result of the merge is committed.
Otherwise, the working directory is updated to include the new
changes.
When a merge is needed, the working directory is first updated to
the newly pulled changes. Local changes are then merged into the
pulled changes. To switch the merge order, use --switch-parent.
See :hg:`help dates` for a list of formats valid for -d/--date.
Returns 0 on success.
'''
opts = pycompat.byteskwargs(opts)
date = opts.get('date')
if date:
opts['date'] = dateutil.parsedate(date)
parent, _p2 = repo.dirstate.parents()
branch = repo.dirstate.branch()
try:
branchnode = repo.branchtip(branch)
except error.RepoLookupError:
branchnode = None
if parent != branchnode:
raise error.Abort(_('working directory not at branch tip'),
hint=_("use 'hg update' to check out branch tip"))
wlock = lock = None
try:
wlock = repo.wlock()
lock = repo.lock()
cmdutil.bailifchanged(repo)
bheads = repo.branchheads(branch)
bheads = [head for head in bheads if len(repo[head].children()) == 0]
if len(bheads) > 1:
raise error.Abort(_('multiple heads in this branch '
'(use "hg heads ." and "hg merge" to merge)'))
other = hg.peer(repo, opts, ui.expandpath(source))
ui.status(_('pulling from %s\n') %
util.hidepassword(ui.expandpath(source)))
revs = None
if opts['rev']:
try:
revs = [other.lookup(rev) for rev in opts['rev']]
except error.CapabilityError:
err = _("other repository doesn't support revision lookup, "
"so a rev cannot be specified.")
raise error.Abort(err)
# Are there any changes at all?
modheads = exchange.pull(repo, other, heads=revs).cgresult
if modheads == 0:
return 0
# Is this a simple fast-forward along the current branch?
newheads = repo.branchheads(branch)
newchildren = repo.changelog.nodesbetween([parent], newheads)[2]
if len(newheads) == 1 and len(newchildren):
if newchildren[0] != parent:
return hg.update(repo, newchildren[0])
else:
return 0
# Are there more than one additional branch heads?
newchildren = [n for n in newchildren if n != parent]
newparent = parent
if newchildren:
newparent = newchildren[0]
hg.clean(repo, newparent)
newheads = [n for n in newheads if n != newparent]
if len(newheads) > 1:
ui.status(_('not merging with %d other new branch heads '
'(use "hg heads ." and "hg merge" to merge them)\n') %
(len(newheads) - 1))
return 1
if not newheads:
return 0
# Otherwise, let's merge.
err = False
if newheads:
# By default, we consider the repository we're pulling
# *from* as authoritative, so we merge our changes into
# theirs.
if opts['switch_parent']:
firstparent, secondparent = newparent, newheads[0]
else:
firstparent, secondparent = newheads[0], newparent
ui.status(_('updating to %d:%s\n') %
(repo.changelog.rev(firstparent),
short(firstparent)))
hg.clean(repo, firstparent)
ui.status(_('merging with %d:%s\n') %
(repo.changelog.rev(secondparent), short(secondparent)))
err = hg.merge(repo, secondparent, remind=False)
if not err:
# we don't translate commit messages
message = (cmdutil.logmessage(ui, opts) or
('Automated merge with %s' %
util.removeauth(other.url())))
editopt = opts.get('edit') or opts.get('force_editor')
editor = cmdutil.getcommiteditor(edit=editopt, editform='fetch')
n = repo.commit(message, opts['user'], opts['date'], editor=editor)
ui.status(_('new changeset %d:%s merges remote changes '
'with local\n') % (repo.changelog.rev(n),
short(n)))
return err
finally:
release(lock, wlock)