exchange: support sorting URLs by client-side preferences
Not all bundles are appropriate for all clients. For example, someone
with a slow Internet connection may want to prefer bz2 bundles over gzip
bundles because they are smaller and don't take as long to transfer.
This is information that a server cannot know on its own. So, we invent
a mechanism for "preferring" server-advertised URLs based on their
attributes.
We could invent a negotiation between client and server where the client
sends its preferences and the sorting/filtering is done server-side.
However, this feels complex. We can avoid complicating the wire protocol
and exposing ourselves to backwards compatible concerns by performing
the sorting locally.
This patch defines a new config option for expressing preferred
attributes in server-advertised bundles.
At Mozilla, we leverage this feature so clients in fast data centers
prefer uncompressed bundles. (We advertise gzip bundles first because
that is a reasonable default.)
I consider this an advanced feature. I'm on the fence as to whether it
should be documented in `hg help config`.
# extension to emulate invoking 'dirstate.write()' at the time
# specified by '[fakedirstatewritetime] fakenow', only when
# 'dirstate.write()' is invoked via functions below:
#
# - 'workingctx._checklookup()' (= 'repo.status()')
# - 'committablectx.markcommitted()'
from mercurial import context, dirstate, extensions, parsers, util
def pack_dirstate(fakenow, orig, dmap, copymap, pl, now):
# execute what original parsers.pack_dirstate should do actually
# for consistency
actualnow = int(now)
for f, e in dmap.iteritems():
if e[0] == 'n' and e[3] == actualnow:
e = parsers.dirstatetuple(e[0], e[1], e[2], -1)
dmap[f] = e
return orig(dmap, copymap, pl, fakenow)
def fakewrite(ui, func):
# fake "now" of 'pack_dirstate' only if it is invoked while 'func'
fakenow = ui.config('fakedirstatewritetime', 'fakenow')
if not fakenow:
# Execute original one, if fakenow isn't configured. This is
# useful to prevent subrepos from executing replaced one,
# because replacing 'parsers.pack_dirstate' is also effective
# in subrepos.
return func()
# parsing 'fakenow' in YYYYmmddHHMM format makes comparison between
# 'fakenow' value and 'touch -t YYYYmmddHHMM' argument easy
fakenow = util.parsedate(fakenow, ['%Y%m%d%H%M'])[0]
orig_pack_dirstate = parsers.pack_dirstate
orig_dirstate_getfsnow = dirstate._getfsnow
wrapper = lambda *args: pack_dirstate(fakenow, orig_pack_dirstate, *args)
parsers.pack_dirstate = wrapper
dirstate._getfsnow = lambda *args: fakenow
try:
return func()
finally:
parsers.pack_dirstate = orig_pack_dirstate
dirstate._getfsnow = orig_dirstate_getfsnow
def _checklookup(orig, workingctx, files):
ui = workingctx.repo().ui
return fakewrite(ui, lambda : orig(workingctx, files))
def markcommitted(orig, committablectx, node):
ui = committablectx.repo().ui
return fakewrite(ui, lambda : orig(committablectx, node))
def extsetup(ui):
extensions.wrapfunction(context.workingctx, '_checklookup',
_checklookup)
extensions.wrapfunction(context.committablectx, 'markcommitted',
markcommitted)