annotate mercurial/changegroup.py @ 2439:e8c4f3d3df8c

extend network protocol to stop clients from locking servers

now all repositories have capabilities slot, tuple with list of names.

if 'unbundle' capability present, repo supports push where client does
not need to lock server.  repository classes that have unbundle capability
also have unbundle method.

implemented for ssh now, will be base for push over http.

unbundle protocol acts this way.  server tells client what heads it
has during normal negotiate step.  client starts unbundle by repeat
server's heads back to it.  if server has new heads, abort immediately.
otherwise, transfer changes to server.  once data transferred, server
locks and checks heads again.  if heads same, changes can be added.
else someone else added heads, and server aborts.

if client wants to force server to add heads, sends special heads list of
'force'.

"""
changegroup.py - Mercurial changegroup manipulation functions

 Copyright 2006 Matt Mackall <[e-mail]>

This software may be used and distributed according to the terms
of the GNU General Public License, incorporated herein by reference.
"""
import struct
from i18n import gettext as _
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)