"""

changegroup.py - Mercurial changegroup manipulation functions

 Copyright 2006 Matt Mackall <mpm@selenic.com>

This software may be used and distributed according to the terms

of the GNU General Public License, incorporated herein by reference.

"""

import struct

from demandload import *

demandload(globals(), "util")

def getchunk(source):

    """get a chunk from a changegroup"""

    d = source.read(4)

    if not d:

        return ""

    l = struct.unpack(">l", d)[0]

    if l <= 4:

        return ""

    d = source.read(l - 4)

    if len(d) < l - 4:

        raise util.Abort(_("premature EOF reading chunk"

                           " (got %d bytes, expected %d)")

                          % (len(d), l - 4))

    return d

def chunkiter(source):

    """iterate through the chunks in source"""

    while 1:

        c = getchunk(source)

        if not c:

            break

        yield c

def genchunk(data):

    """build a changegroup chunk"""

    header = struct.pack(">l", len(data)+ 4)

    return "%s%s" % (header, data)

def closechunk():

    return struct.pack(">l", 0)