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
# changelog.py - changelog class for mercurial
#
# Copyright 2005-2007 Matt Mackall <mpm@selenic.com>
#
# 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 .i18n import _
from .node import (
bin,
hex,
nullid,
)
from .thirdparty import (
attr,
)
from . import (
encoding,
error,
pycompat,
revlog,
)
from .utils import (
dateutil,
stringutil,
)
_defaultextra = {'branch': 'default'}
def _string_escape(text):
"""
>>> from .pycompat import bytechr as chr
>>> d = {b'nl': chr(10), b'bs': chr(92), b'cr': chr(13), b'nul': chr(0)}
>>> s = b"ab%(nl)scd%(bs)s%(bs)sn%(nul)sab%(cr)scd%(bs)s%(nl)s" % d
>>> s
'ab\\ncd\\\\\\\\n\\x00ab\\rcd\\\\\\n'
>>> res = _string_escape(s)
>>> s == stringutil.unescapestr(res)
True
"""
# subset of the string_escape codec
text = text.replace('\\', '\\\\').replace('\n', '\\n').replace('\r', '\\r')
return text.replace('\0', '\\0')
def decodeextra(text):
"""
>>> from .pycompat import bytechr as chr
>>> sorted(decodeextra(encodeextra({b'foo': b'bar', b'baz': chr(0) + b'2'})
... ).items())
[('baz', '\\x002'), ('branch', 'default'), ('foo', 'bar')]
>>> sorted(decodeextra(encodeextra({b'foo': b'bar',
... b'baz': chr(92) + chr(0) + b'2'})
... ).items())
[('baz', '\\\\\\x002'), ('branch', 'default'), ('foo', 'bar')]
"""
extra = _defaultextra.copy()
for l in text.split('\0'):
if l:
if '\\0' in l:
# fix up \0 without getting into trouble with \\0
l = l.replace('\\\\', '\\\\\n')
l = l.replace('\\0', '\0')
l = l.replace('\n', '')
k, v = stringutil.unescapestr(l).split(':', 1)
extra[k] = v
return extra
def encodeextra(d):
# keys must be sorted to produce a deterministic changelog entry
items = [_string_escape('%s:%s' % (k, d[k])) for k in sorted(d)]
return "\0".join(items)
def stripdesc(desc):
"""strip trailing whitespace and leading and trailing empty lines"""
return '\n'.join([l.rstrip() for l in desc.splitlines()]).strip('\n')
class appender(object):
'''the changelog index must be updated last on disk, so we use this class
to delay writes to it'''
def __init__(self, vfs, name, mode, buf):
self.data = buf
fp = vfs(name, mode)
self.fp = fp
self.offset = fp.tell()
self.size = vfs.fstat(fp).st_size
self._end = self.size
def end(self):
return self._end
def tell(self):
return self.offset
def flush(self):
pass
@property
def closed(self):
return self.fp.closed
def close(self):
self.fp.close()
def seek(self, offset, whence=0):
'''virtual file offset spans real file and data'''
if whence == 0:
self.offset = offset
elif whence == 1:
self.offset += offset
elif whence == 2:
self.offset = self.end() + offset
if self.offset < self.size:
self.fp.seek(self.offset)
def read(self, count=-1):
'''only trick here is reads that span real file and data'''
ret = ""
if self.offset < self.size:
s = self.fp.read(count)
ret = s
self.offset += len(s)
if count > 0:
count -= len(s)
if count != 0:
doff = self.offset - self.size
self.data.insert(0, "".join(self.data))
del self.data[1:]
s = self.data[0][doff:doff + count]
self.offset += len(s)
ret += s
return ret
def write(self, s):
self.data.append(bytes(s))
self.offset += len(s)
self._end += len(s)
def __enter__(self):
self.fp.__enter__()
return self
def __exit__(self, *args):
return self.fp.__exit__(*args)
def _divertopener(opener, target):
"""build an opener that writes in 'target.a' instead of 'target'"""
def _divert(name, mode='r', checkambig=False):
if name != target:
return opener(name, mode)
return opener(name + ".a", mode)
return _divert
def _delayopener(opener, target, buf):
"""build an opener that stores chunks in 'buf' instead of 'target'"""
def _delay(name, mode='r', checkambig=False):
if name != target:
return opener(name, mode)
return appender(opener, name, mode, buf)
return _delay
@attr.s
class _changelogrevision(object):
# Extensions might modify _defaultextra, so let the constructor below pass
# it in
extra = attr.ib()
manifest = attr.ib(default=nullid)
user = attr.ib(default='')
date = attr.ib(default=(0, 0))
files = attr.ib(default=attr.Factory(list))
description = attr.ib(default='')
class changelogrevision(object):
"""Holds results of a parsed changelog revision.
Changelog revisions consist of multiple pieces of data, including
the manifest node, user, and date. This object exposes a view into
the parsed object.
"""
__slots__ = (
u'_offsets',
u'_text',
)
def __new__(cls, text):
if not text:
return _changelogrevision(extra=_defaultextra)
self = super(changelogrevision, cls).__new__(cls)
# We could return here and implement the following as an __init__.
# But doing it here is equivalent and saves an extra function call.
# format used:
# nodeid\n : manifest node in ascii
# user\n : user, no \n or \r allowed
# time tz extra\n : date (time is int or float, timezone is int)
# : extra is metadata, encoded and separated by '\0'
# : older versions ignore it
# files\n\n : files modified by the cset, no \n or \r allowed
# (.*) : comment (free text, ideally utf-8)
#
# changelog v0 doesn't use extra
nl1 = text.index('\n')
nl2 = text.index('\n', nl1 + 1)
nl3 = text.index('\n', nl2 + 1)
# The list of files may be empty. Which means nl3 is the first of the
# double newline that precedes the description.
if text[nl3 + 1:nl3 + 2] == '\n':
doublenl = nl3
else:
doublenl = text.index('\n\n', nl3 + 1)
self._offsets = (nl1, nl2, nl3, doublenl)
self._text = text
return self
@property
def manifest(self):
return bin(self._text[0:self._offsets[0]])
@property
def user(self):
off = self._offsets
return encoding.tolocal(self._text[off[0] + 1:off[1]])
@property
def _rawdate(self):
off = self._offsets
dateextra = self._text[off[1] + 1:off[2]]
return dateextra.split(' ', 2)[0:2]
@property
def _rawextra(self):
off = self._offsets
dateextra = self._text[off[1] + 1:off[2]]
fields = dateextra.split(' ', 2)
if len(fields) != 3:
return None
return fields[2]
@property
def date(self):
raw = self._rawdate
time = float(raw[0])
# Various tools did silly things with the timezone.
try:
timezone = int(raw[1])
except ValueError:
timezone = 0
return time, timezone
@property
def extra(self):
raw = self._rawextra
if raw is None:
return _defaultextra
return decodeextra(raw)
@property
def files(self):
off = self._offsets
if off[2] == off[3]:
return []
return self._text[off[2] + 1:off[3]].split('\n')
@property
def description(self):
return encoding.tolocal(self._text[self._offsets[3] + 2:])
class changelog(revlog.revlog):
def __init__(self, opener, trypending=False):
"""Load a changelog revlog using an opener.
If ``trypending`` is true, we attempt to load the index from a
``00changelog.i.a`` file instead of the default ``00changelog.i``.
The ``00changelog.i.a`` file contains index (and possibly inline
revision) data for a transaction that hasn't been finalized yet.
It exists in a separate file to facilitate readers (such as
hooks processes) accessing data before a transaction is finalized.
"""
if trypending and opener.exists('00changelog.i.a'):
indexfile = '00changelog.i.a'
else:
indexfile = '00changelog.i'
datafile = '00changelog.d'
revlog.revlog.__init__(self, opener, indexfile, datafile=datafile,
checkambig=True, mmaplargeindex=True)
if self._initempty:
# changelogs don't benefit from generaldelta
self.version &= ~revlog.FLAG_GENERALDELTA
self._generaldelta = False
# Delta chains for changelogs tend to be very small because entries
# tend to be small and don't delta well with each. So disable delta
# chains.
self._storedeltachains = False
self._realopener = opener
self._delayed = False
self._delaybuf = None
self._divert = False
self.filteredrevs = frozenset()
def tiprev(self):
for i in pycompat.xrange(len(self) -1, -2, -1):
if i not in self.filteredrevs:
return i
def tip(self):
"""filtered version of revlog.tip"""
return self.node(self.tiprev())
def __contains__(self, rev):
"""filtered version of revlog.__contains__"""
return (0 <= rev < len(self)
and rev not in self.filteredrevs)
def __iter__(self):
"""filtered version of revlog.__iter__"""
if len(self.filteredrevs) == 0:
return revlog.revlog.__iter__(self)
def filterediter():
for i in pycompat.xrange(len(self)):
if i not in self.filteredrevs:
yield i
return filterediter()
def revs(self, start=0, stop=None):
"""filtered version of revlog.revs"""
for i in super(changelog, self).revs(start, stop):
if i not in self.filteredrevs:
yield i
def reachableroots(self, minroot, heads, roots, includepath=False):
return self.index.reachableroots2(minroot, heads, roots, includepath)
def headrevs(self):
if self.filteredrevs:
try:
return self.index.headrevsfiltered(self.filteredrevs)
# AttributeError covers non-c-extension environments and
# old c extensions without filter handling.
except AttributeError:
return self._headrevs()
return super(changelog, self).headrevs()
def strip(self, *args, **kwargs):
# XXX make something better than assert
# We can't expect proper strip behavior if we are filtered.
assert not self.filteredrevs
super(changelog, self).strip(*args, **kwargs)
def rev(self, node):
"""filtered version of revlog.rev"""
r = super(changelog, self).rev(node)
if r in self.filteredrevs:
raise error.FilteredLookupError(hex(node), self.indexfile,
_('filtered node'))
return r
def node(self, rev):
"""filtered version of revlog.node"""
if rev in self.filteredrevs:
raise error.FilteredIndexError(rev)
return super(changelog, self).node(rev)
def linkrev(self, rev):
"""filtered version of revlog.linkrev"""
if rev in self.filteredrevs:
raise error.FilteredIndexError(rev)
return super(changelog, self).linkrev(rev)
def parentrevs(self, rev):
"""filtered version of revlog.parentrevs"""
if rev in self.filteredrevs:
raise error.FilteredIndexError(rev)
return super(changelog, self).parentrevs(rev)
def flags(self, rev):
"""filtered version of revlog.flags"""
if rev in self.filteredrevs:
raise error.FilteredIndexError(rev)
return super(changelog, self).flags(rev)
def delayupdate(self, tr):
"delay visibility of index updates to other readers"
if not self._delayed:
if len(self) == 0:
self._divert = True
if self._realopener.exists(self.indexfile + '.a'):
self._realopener.unlink(self.indexfile + '.a')
self.opener = _divertopener(self._realopener, self.indexfile)
else:
self._delaybuf = []
self.opener = _delayopener(self._realopener, self.indexfile,
self._delaybuf)
self._delayed = True
tr.addpending('cl-%i' % id(self), self._writepending)
tr.addfinalize('cl-%i' % id(self), self._finalize)
def _finalize(self, tr):
"finalize index updates"
self._delayed = False
self.opener = self._realopener
# move redirected index data back into place
if self._divert:
assert not self._delaybuf
tmpname = self.indexfile + ".a"
nfile = self.opener.open(tmpname)
nfile.close()
self.opener.rename(tmpname, self.indexfile, checkambig=True)
elif self._delaybuf:
fp = self.opener(self.indexfile, 'a', checkambig=True)
fp.write("".join(self._delaybuf))
fp.close()
self._delaybuf = None
self._divert = False
# split when we're done
self._enforceinlinesize(tr)
def _writepending(self, tr):
"create a file containing the unfinalized state for pretxnchangegroup"
if self._delaybuf:
# make a temporary copy of the index
fp1 = self._realopener(self.indexfile)
pendingfilename = self.indexfile + ".a"
# register as a temp file to ensure cleanup on failure
tr.registertmp(pendingfilename)
# write existing data
fp2 = self._realopener(pendingfilename, "w")
fp2.write(fp1.read())
# add pending data
fp2.write("".join(self._delaybuf))
fp2.close()
# switch modes so finalize can simply rename
self._delaybuf = None
self._divert = True
self.opener = _divertopener(self._realopener, self.indexfile)
if self._divert:
return True
return False
def _enforceinlinesize(self, tr, fp=None):
if not self._delayed:
revlog.revlog._enforceinlinesize(self, tr, fp)
def read(self, node):
"""Obtain data from a parsed changelog revision.
Returns a 6-tuple of:
- manifest node in binary
- author/user as a localstr
- date as a 2-tuple of (time, timezone)
- list of files
- commit message as a localstr
- dict of extra metadata
Unless you need to access all fields, consider calling
``changelogrevision`` instead, as it is faster for partial object
access.
"""
c = changelogrevision(self.revision(node))
return (
c.manifest,
c.user,
c.date,
c.files,
c.description,
c.extra
)
def changelogrevision(self, nodeorrev):
"""Obtain a ``changelogrevision`` for a node or revision."""
return changelogrevision(self.revision(nodeorrev))
def readfiles(self, node):
"""
short version of read that only returns the files modified by the cset
"""
text = self.revision(node)
if not text:
return []
last = text.index("\n\n")
l = text[:last].split('\n')
return l[3:]
def add(self, manifest, files, desc, transaction, p1, p2,
user, date=None, extra=None):
# Convert to UTF-8 encoded bytestrings as the very first
# thing: calling any method on a localstr object will turn it
# into a str object and the cached UTF-8 string is thus lost.
user, desc = encoding.fromlocal(user), encoding.fromlocal(desc)
user = user.strip()
# An empty username or a username with a "\n" will make the
# revision text contain two "\n\n" sequences -> corrupt
# repository since read cannot unpack the revision.
if not user:
raise error.RevlogError(_("empty username"))
if "\n" in user:
raise error.RevlogError(_("username %r contains a newline")
% pycompat.bytestr(user))
desc = stripdesc(desc)
if date:
parseddate = "%d %d" % dateutil.parsedate(date)
else:
parseddate = "%d %d" % dateutil.makedate()
if extra:
branch = extra.get("branch")
if branch in ("default", ""):
del extra["branch"]
elif branch in (".", "null", "tip"):
raise error.RevlogError(_('the name \'%s\' is reserved')
% branch)
if extra:
extra = encodeextra(extra)
parseddate = "%s %s" % (parseddate, extra)
l = [hex(manifest), user, parseddate] + sorted(files) + ["", desc]
text = "\n".join(l)
return self.addrevision(text, transaction, len(self), p1, p2)
def branchinfo(self, rev):
"""return the branch name and open/close state of a revision
This function exists because creating a changectx object
just to access this is costly."""
extra = self.read(rev)[5]
return encoding.tolocal(extra.get("branch")), 'close' in extra