mercurial/txnutil.py

wireprototypes: move wire protocol response types to new module

We'll be introducing more types as part of wire protocol version 2.
These types are shared between the command handling code (in
wireproto.py) and the protocol/transport code in wireprotoserver.py.
So they need to go in a new module to prevent a cycle.

The types are aliased into the wireproto module, so API compatibility
is preserved.

Differential Revision: https://phab.mercurial-scm.org/D2088

# txnutil.py - transaction related utilities
#
#  Copyright FUJIWARA Katsunori <[e-mail]> and others
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import errno

from . import (
    encoding,
)

def mayhavepending(root):
    '''return whether 'root' may have pending changes, which are
    visible to this process.
    '''
    return root == encoding.environ.get('HG_PENDING')

def trypending(root, vfs, filename, **kwargs):
    '''Open  file to be read according to HG_PENDING environment variable

    This opens '.pending' of specified 'filename' only when HG_PENDING
    is equal to 'root'.

    This returns '(fp, is_pending_opened)' tuple.
    '''
    if mayhavepending(root):
        try:
            return (vfs('%s.pending' % filename, **kwargs), True)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
    return (vfs(filename, **kwargs), False)