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
"""This unit test primarily tests parsers.parse_index2().
It also checks certain aspects of the parsers module as a whole.
"""
from __future__ import absolute_import, print_function
import struct
import subprocess
import sys
import unittest
from mercurial.node import (
nullid,
nullrev,
)
from mercurial import (
node as nodemod,
policy,
pycompat,
)
parsers = policy.importmod(r'parsers')
# original python implementation
def gettype(q):
return int(q & 0xFFFF)
def offset_type(offset, type):
return int(int(offset) << 16 | type)
indexformatng = ">Qiiiiii20s12x"
def py_parseindex(data, inline) :
s = 64
cache = None
index = []
nodemap = {nullid: nullrev}
n = off = 0
l = len(data) - s
append = index.append
if inline:
cache = (0, data)
while off <= l:
e = struct.unpack(indexformatng, data[off:off + s])
nodemap[e[7]] = n
append(e)
n += 1
if e[1] < 0:
break
off += e[1] + s
else:
while off <= l:
e = struct.unpack(indexformatng, data[off:off + s])
nodemap[e[7]] = n
append(e)
n += 1
off += s
e = list(index[0])
type = gettype(e[0])
e[0] = offset_type(0, type)
index[0] = tuple(e)
return index, cache
data_inlined = (
b'\x00\x01\x00\x01\x00\x00\x00\x00\x00\x00\x01\x8c'
b'\x00\x00\x04\x07\x00\x00\x00\x00\x00\x00\x15\x15\xff\xff\xff'
b'\xff\xff\xff\xff\xff\xebG\x97\xb7\x1fB\x04\xcf\x13V\x81\tw\x1b'
b'w\xdduR\xda\xc6\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
b'x\x9c\x9d\x93?O\xc30\x10\xc5\xf7|\x8a\xdb\x9a\xa8m\x06\xd8*\x95'
b'\x81B\xa1\xa2\xa2R\xcb\x86Pd\x9a\x0b5$vd_\x04\xfd\xf6\x9c\xff@'
b'\x11!\x0b\xd9\xec\xf7\xbbw\xe7gG6\xad6\x04\xdaN\xc0\x92\xa0$)'
b'\xb1\x82\xa2\xd1%\x16\xa4\x8b7\xa9\xca\xd4-\xb2Y\x02\xfc\xc9'
b'\xcaS\xf9\xaeX\xed\xb6\xd77Q\x02\x83\xd4\x19\xf5--Y\xea\xe1W'
b'\xab\xed\x10\xceR\x0f_\xdf\xdf\r\xe1,\xf5\xf0\xcb\xf5 \xceR\x0f'
b'_\xdc\x0e\x0e\xc3R\x0f_\xae\x96\x9b!\x9e\xa5\x1e\xbf\xdb,\x06'
b'\xc7q\x9a/\x88\x82\xc3B\xea\xb5\xb4TJ\x93\xb6\x82\x0e\xe16\xe6'
b'KQ\xdb\xaf\xecG\xa3\xd1 \x01\xd3\x0b_^\xe8\xaa\xa0\xae\xad\xd1'
b'&\xbef\x1bz\x08\xb0|\xc9Xz\x06\xf6Z\x91\x90J\xaa\x17\x90\xaa'
b'\xd2\xa6\x11$5C\xcf\xba#\xa0\x03\x02*2\x92-\xfc\xb1\x94\xdf\xe2'
b'\xae\xb8\'m\x8ey0^\x85\xd3\x82\xb4\xf0`:\x9c\x00\x8a\xfd\x01'
b'\xb0\xc6\x86\x8b\xdd\xae\x80\xf3\xa9\x9fd\x16\n\x00R%\x1a\x06'
b'\xe9\xd8b\x98\x1d\xf4\xf3+\x9bf\x01\xd8p\x1b\xf3.\xed\x9f^g\xc3'
b'^\xd9W81T\xdb\xd5\x04sx|\xf2\xeb\xd6`%?x\xed"\x831\xbf\xf3\xdc'
b'b\xeb%gaY\xe1\xad\x9f\xb9f\'1w\xa9\xa5a\x83s\x82J\xb98\xbc4\x8b'
b'\x83\x00\x9f$z\xb8#\xa5\xb1\xdf\x98\xd9\xec\x1b\x89O\xe3Ts\x9a4'
b'\x17m\x8b\xfc\x8f\xa5\x95\x9a\xfc\xfa\xed,\xe5|\xa1\xfe\x15\xb9'
b'\xbc\xb2\x93\x1f\xf2\x95\xff\xdf,\x1a\xc5\xe7\x17*\x93Oz:>\x0e'
)
data_non_inlined = (
b'\x00\x00\x00\x01\x00\x00\x00\x00\x00\x01D\x19'
b'\x00\x07e\x12\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff\xff\xff'
b'\xff\xff\xff\xff\xd1\xf4\xbb\xb0\xbe\xfc\x13\xbd\x8c\xd3\x9d'
b'\x0f\xcd\xd9;\x8c\x07\x8cJ/\x00\x00\x00\x00\x00\x00\x00\x00\x00'
b'\x00\x00\x00\x00\x00\x00\x01D\x19\x00\x00\x00\x00\x00\xdf\x00'
b'\x00\x01q\x00\x00\x00\x01\x00\x00\x00\x01\x00\x00\x00\x00\xff'
b'\xff\xff\xff\xc1\x12\xb9\x04\x96\xa4Z1t\x91\xdfsJ\x90\xf0\x9bh'
b'\x07l&\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
b'\x00\x01D\xf8\x00\x00\x00\x00\x01\x1b\x00\x00\x01\xb8\x00\x00'
b'\x00\x01\x00\x00\x00\x02\x00\x00\x00\x01\xff\xff\xff\xff\x02\n'
b'\x0e\xc6&\xa1\x92\xae6\x0b\x02i\xfe-\xe5\xbao\x05\xd1\xe7\x00'
b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01F'
b'\x13\x00\x00\x00\x00\x01\xec\x00\x00\x03\x06\x00\x00\x00\x01'
b'\x00\x00\x00\x03\x00\x00\x00\x02\xff\xff\xff\xff\x12\xcb\xeby1'
b'\xb6\r\x98B\xcb\x07\xbd`\x8f\x92\xd9\xc4\x84\xbdK\x00\x00\x00'
b'\x00\x00\x00\x00\x00\x00\x00\x00\x00'
)
def parse_index2(data, inline):
index, chunkcache = parsers.parse_index2(data, inline)
return list(index), chunkcache
def importparsers(hexversion):
"""Import mercurial.parsers with the given sys.hexversion."""
# The file parsers.c inspects sys.hexversion to determine the version
# of the currently-running Python interpreter, so we monkey-patch
# sys.hexversion to simulate using different versions.
code = ("import sys; sys.hexversion=%s; "
"import mercurial.cext.parsers" % hexversion)
cmd = "python -c \"%s\"" % code
# We need to do these tests inside a subprocess because parser.c's
# version-checking code happens inside the module init function, and
# when using reload() to reimport an extension module, "The init function
# of extension modules is not called a second time"
# (from http://docs.python.org/2/library/functions.html?#reload).
p = subprocess.Popen(cmd, shell=True,
stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
return p.communicate() # returns stdout, stderr
def hexfailmsg(testnumber, hexversion, stdout, expected):
try:
hexstring = hex(hexversion)
except TypeError:
hexstring = None
return ("FAILED: version test #%s with Python %s and patched "
"sys.hexversion %r (%r):\n Expected %s but got:\n-->'%s'\n" %
(testnumber, sys.version_info, hexversion, hexstring, expected,
stdout))
def makehex(major, minor, micro):
return int("%x%02x%02x00" % (major, minor, micro), 16)
class parseindex2tests(unittest.TestCase):
def assertversionokay(self, testnumber, hexversion):
stdout, stderr = importparsers(hexversion)
self.assertFalse(
stdout, hexfailmsg(testnumber, hexversion, stdout, 'no stdout'))
def assertversionfail(self, testnumber, hexversion):
stdout, stderr = importparsers(hexversion)
# We include versionerrortext to distinguish from other ImportErrors.
errtext = b"ImportError: %s" % pycompat.sysbytes(
parsers.versionerrortext)
self.assertIn(errtext, stdout,
hexfailmsg(testnumber, hexversion, stdout,
expected="stdout to contain %r" % errtext))
def testversiondetection(self):
"""Check the version-detection logic when importing parsers."""
# Only test the version-detection logic if it is present.
try:
parsers.versionerrortext
except AttributeError:
return
info = sys.version_info
major, minor, micro = info[0], info[1], info[2]
# Test same major-minor versions.
self.assertversionokay(1, makehex(major, minor, micro))
self.assertversionokay(2, makehex(major, minor, micro + 1))
# Test different major-minor versions.
self.assertversionfail(3, makehex(major + 1, minor, micro))
self.assertversionfail(4, makehex(major, minor + 1, micro))
self.assertversionfail(5, "'foo'")
def testbadargs(self):
# Check that parse_index2() raises TypeError on bad arguments.
with self.assertRaises(TypeError):
parse_index2(0, True)
def testparseindexfile(self):
# Check parsers.parse_index2() on an index file against the
# original Python implementation of parseindex, both with and
# without inlined data.
want = py_parseindex(data_inlined, True)
got = parse_index2(data_inlined, True)
self.assertEqual(want, got) # inline data
want = py_parseindex(data_non_inlined, False)
got = parse_index2(data_non_inlined, False)
self.assertEqual(want, got) # no inline data
ix = parsers.parse_index2(data_inlined, True)[0]
for i, r in enumerate(ix):
if r[7] == nullid:
i = -1
try:
self.assertEqual(
ix[r[7]], i,
'Reverse lookup inconsistent for %r' % nodemod.hex(r[7]))
except TypeError:
# pure version doesn't support this
break
def testminusone(self):
want = (0, 0, 0, -1, -1, -1, -1, nullid)
index, junk = parsers.parse_index2(data_inlined, True)
got = index[-1]
self.assertEqual(want, got) # inline data
index, junk = parsers.parse_index2(data_non_inlined, False)
got = index[-1]
self.assertEqual(want, got) # no inline data
if __name__ == '__main__':
import silenttestrunner
silenttestrunner.main(__name__)