bundle2: safely read unpack data from part header
We use the same approach that the other unpack, as function is given the struct
format and his both responsible for reading the right amount of data from the
header and unpack the struct.
This give use flexibility if we decide to change the size of something in the
format before the release.
# bundle2.py - generic container format to transmit arbitrary data.
#
# Copyright 2013 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.
"""Handling of the new bundle2 format
The goal of bundle2 is to act as an atomically packet to transmit a set of
payloads in an application agnostic way. It consist in a sequence of "parts"
that will be handed to and processed by the application layer.
General format architecture
===========================
The format is architectured as follow
- magic string
- stream level parameters
- payload parts (any number)
- end of stream marker.
the Binary format
============================
All numbers are unsigned and big endian.
stream level parameters
------------------------
Binary format is as follow
:params size: (16 bits integer)
The total number of Bytes used by the parameters
:params value: arbitrary number of Bytes
A blob of `params size` containing the serialized version of all stream level
parameters.
The blob contains a space separated list of parameters. parameter with value
are stored in the form `<name>=<value>`. Both name and value are urlquoted.
Empty name are obviously forbidden.
Name MUST start with a letter. If this first letter is lower case, the
parameter is advisory and can be safefly ignored. However when the first
letter is capital, the parameter is mandatory and the bundling process MUST
stop if he is not able to proceed it.
Stream parameters use a simple textual format for two main reasons:
- Stream level parameters should remains simple and we want to discourage any
crazy usage.
- Textual data allow easy human inspection of a the bundle2 header in case of
troubles.
Any Applicative level options MUST go into a bundle2 part instead.
Payload part
------------------------
Binary format is as follow
:header size: (16 bits inter)
The total number of Bytes used by the part headers. When the header is empty
(size = 0) this is interpreted as the end of stream marker.
:header:
The header defines how to interpret the part. It contains two piece of
data: the part type, and the part parameters.
The part type is used to route an application level handler, that can
interpret payload.
Part parameters are passed to the application level handler. They are
meant to convey information that will help the application level object to
interpret the part payload.
The binary format of the header is has follow
:typesize: (one byte)
:typename: alphanumerical part name
:parameters:
Part's parameter may have arbitraty content, the binary structure is::
<mandatory-count><advisory-count><param-sizes><param-data>
:mandatory-count: 1 byte, number of mandatory parameters
:advisory-count: 1 byte, number of advisory parameters
:param-sizes:
N couple of bytes, where N is the total number of parameters. Each
couple contains (<size-of-key>, <size-of-value) for one parameter.
:param-data:
A blob of bytes from which each parameter key and value can be
retrieved using the list of size couples stored in the previous
field.
Mandatory parameters comes first, then the advisory ones.
:payload:
payload is a series of `<chunksize><chunkdata>`.
`chunksize` is a 32 bits integer, `chunkdata` are plain bytes (as much as
`chunksize` says)` The payload part is concluded by a zero size chunk.
The current implementation always produces either zero or one chunk.
This is an implementation limitation that will ultimatly be lifted.
"""
import util
import struct
import urllib
import string
import changegroup
from i18n import _
_pack = struct.pack
_unpack = struct.unpack
_magicstring = 'HG20'
_fstreamparamsize = '>H'
_fpartheadersize = '>H'
_fparttypesize = '>B'
_fpayloadsize = '>I'
_fpartparamcount = '>BB'
def _makefpartparamsizes(nbparams):
"""return a struct format to read part parameter sizes
The number parameters is variable so we need to build that format
dynamically.
"""
return '>'+('BB'*nbparams)
class bundle20(object):
"""represent an outgoing bundle2 container
Use the `addparam` method to add stream level parameter. and `addpart` to
populate it. Then call `getchunks` to retrieve all the binary chunks of
datathat compose the bundle2 container."""
def __init__(self, ui):
self.ui = ui
self._params = []
self._parts = []
def addparam(self, name, value=None):
"""add a stream level parameter"""
if not name:
raise ValueError('empty parameter name')
if name[0] not in string.letters:
raise ValueError('non letter first character: %r' % name)
self._params.append((name, value))
def addpart(self, part):
"""add a new part to the bundle2 container
Parts contains the actuall applicative payload."""
self._parts.append(part)
def getchunks(self):
self.ui.debug('start emission of %s stream\n' % _magicstring)
yield _magicstring
param = self._paramchunk()
self.ui.debug('bundle parameter: %s\n' % param)
yield _pack(_fstreamparamsize, len(param))
if param:
yield param
self.ui.debug('start of parts\n')
for part in self._parts:
self.ui.debug('bundle part: "%s"\n' % part.type)
for chunk in part.getchunks():
yield chunk
self.ui.debug('end of bundle\n')
yield '\0\0'
def _paramchunk(self):
"""return a encoded version of all stream parameters"""
blocks = []
for par, value in self._params:
par = urllib.quote(par)
if value is not None:
value = urllib.quote(value)
par = '%s=%s' % (par, value)
blocks.append(par)
return ' '.join(blocks)
class unbundle20(object):
"""interpret a bundle2 stream
(this will eventually yield parts)"""
def __init__(self, ui, fp):
self.ui = ui
self._fp = fp
header = self._readexact(4)
magic, version = header[0:2], header[2:4]
if magic != 'HG':
raise util.Abort(_('not a Mercurial bundle'))
if version != '20':
raise util.Abort(_('unknown bundle version %s') % version)
self.ui.debug('start processing of %s stream\n' % header)
def _unpack(self, format):
"""unpack this struct format from the stream"""
data = self._readexact(struct.calcsize(format))
return _unpack(format, data)
def _readexact(self, size):
"""read exactly <size> bytes from the stream"""
return changegroup.readexactly(self._fp, size)
@util.propertycache
def params(self):
"""dictionnary of stream level parameters"""
self.ui.debug('reading bundle2 stream parameters\n')
params = {}
paramssize = self._unpack(_fstreamparamsize)[0]
if paramssize:
for p in self._readexact(paramssize).split(' '):
p = p.split('=', 1)
p = [urllib.unquote(i) for i in p]
if len(p) < 2:
p.append(None)
self._processparam(*p)
params[p[0]] = p[1]
return params
def _processparam(self, name, value):
"""process a parameter, applying its effect if needed
Parameter starting with a lower case letter are advisory and will be
ignored when unknown. Those starting with an upper case letter are
mandatory and will this function will raise a KeyError when unknown.
Note: no option are currently supported. Any input will be either
ignored or failing.
"""
if not name:
raise ValueError('empty parameter name')
if name[0] not in string.letters:
raise ValueError('non letter first character: %r' % name)
# Some logic will be later added here to try to process the option for
# a dict of known parameter.
if name[0].islower():
self.ui.debug("ignoring unknown parameter %r\n" % name)
else:
raise KeyError(name)
def __iter__(self):
"""yield all parts contained in the stream"""
# make sure param have been loaded
self.params
self.ui.debug('start extraction of bundle2 parts\n')
part = self._readpart()
while part is not None:
yield part
part = self._readpart()
self.ui.debug('end of bundle2 stream\n')
def _readpart(self):
"""return None when an end of stream markers is reach"""
headersize = self._unpack(_fpartheadersize)[0]
self.ui.debug('part header size: %i\n' % headersize)
if not headersize:
return None
headerblock = self._readexact(headersize)
# some utility to help reading from the header block
self._offset = 0 # layer violation to have something easy to understand
def fromheader(size):
"""return the next <size> byte from the header"""
offset = self._offset
data = headerblock[offset:(offset + size)]
self._offset = offset + size
return data
def unpackheader(format):
"""read given format from header
This automatically compute the size of the format to read."""
data = fromheader(struct.calcsize(format))
return _unpack(format, data)
typesize = unpackheader(_fparttypesize)[0]
parttype = fromheader(typesize)
self.ui.debug('part type: "%s"\n' % parttype)
## reading parameters
# param count
mancount, advcount = unpackheader(_fpartparamcount)
self.ui.debug('part parameters: %i\n' % (mancount + advcount))
# param size
paramsizes = unpackheader(_makefpartparamsizes(mancount + advcount))
# make it a list of couple again
paramsizes = zip(paramsizes[::2], paramsizes[1::2])
# split mandatory from advisory
mansizes = paramsizes[:mancount]
advsizes = paramsizes[mancount:]
# retrive param value
manparams = []
for key, value in mansizes:
manparams.append((fromheader(key), fromheader(value)))
advparams = []
for key, value in advsizes:
advparams.append((fromheader(key), fromheader(value)))
del self._offset # clean up layer, nobody saw anything.
## part payload
payload = []
payloadsize = self._unpack(_fpayloadsize)[0]
self.ui.debug('payload chunk size: %i\n' % payloadsize)
while payloadsize:
payload.append(self._readexact(payloadsize))
payloadsize = self._unpack(_fpayloadsize)[0]
self.ui.debug('payload chunk size: %i\n' % payloadsize)
payload = ''.join(payload)
current = part(parttype, manparams, advparams, data=payload)
return current
class part(object):
"""A bundle2 part contains application level payload
The part `type` is used to route the part to the application level
handler.
"""
def __init__(self, parttype, mandatoryparams=(), advisoryparams=(),
data=''):
self.type = parttype
self.data = data
self.mandatoryparams = mandatoryparams
self.advisoryparams = advisoryparams
def getchunks(self):
#### header
## parttype
header = [_pack(_fparttypesize, len(self.type)),
self.type,
]
## parameters
# count
manpar = self.mandatoryparams
advpar = self.advisoryparams
header.append(_pack(_fpartparamcount, len(manpar), len(advpar)))
# size
parsizes = []
for key, value in manpar:
parsizes.append(len(key))
parsizes.append(len(value))
for key, value in advpar:
parsizes.append(len(key))
parsizes.append(len(value))
paramsizes = _pack(_makefpartparamsizes(len(parsizes) / 2), *parsizes)
header.append(paramsizes)
# key, value
for key, value in manpar:
header.append(key)
header.append(value)
for key, value in advpar:
header.append(key)
header.append(value)
## finalize header
headerchunk = ''.join(header)
yield _pack(_fpartheadersize, len(headerchunk))
yield headerchunk
## payload
# we only support fixed size data now.
# This will be improved in the future.
if len(self.data):
yield _pack(_fpayloadsize, len(self.data))
yield self.data
# end of payload
yield _pack(_fpayloadsize, 0)