mercurial/bundle2.py

bundle2: introduce a `parthandler` decorator

Simple syntax sugar to register an handler for a new part type.

# 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)

parthandlermapping = {}

def parthandler(parttype):
    """decorator that register a function as a bundle2 part handler

    eg::

        @parthandler('myparttype')
        def myparttypehandler(...):
            '''process a part of type "my part".'''
            ...
    """
    def _decorator(func):
        assert parttype not in parthandlermapping
        parthandlermapping[parttype] = func
        return func
    return _decorator

def processbundle(repo, stream):
    """This function process a bundle, apply effect to/from a repo

    Currently it:
    - parse a stream into an unbundle20 object
    - iterate over each parts then search and use the proper handling code to
      process the part.

    Parts are processes in order.

    This is very early version of this function that will be strongly reworked
    before final usage.

    All unknown parts are currently ignored (Mandatory parts logic will comes
    later).
    """
    ui = repo.ui
    # Extraction of the unbundler object will most likely change. It may be
    # done outside of this function, the unbundler would be passed as argument.
    # in all case the unbundler will eventually be created by a
    # `changegroup.readbundle` style function.
    unbundler = unbundle20(ui, stream)
    # todo:
    # - replace this is a init function soon.
    # - exception catching
    unbundler.params
    for part in unbundler:
        parttype = part.type
        # part key are matched lower case
        key = parttype.lower()
        try:
            handler = parthandlermapping[key]
            ui.debug('found an handler for part %r\n' % parttype)
        except KeyError:
            ui.debug('ignoring unknown advisory part %r\n' % key)
            # todo: consume the part (once we use streamed parts)
            continue
        handler(repo, part)

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)