mercurial/txnutil.py

internals: refactor wire protocol documentation

Upcoming work will introduce a new version of the HTTP and SSH
transports. The differences will be significant enough to consider
them new transports. So, we now attach a version number to each
transport.

In addition, having the handshake documented after the transport
and in a single shared section made it harder to follow the flow
of the connection. The handshake documentation is now moved to the
protocol section it describes. We now have a generic section about
the purpose of the handshake, which was rewritten significantly.

Differential Revision: https://phab.mercurial-scm.org/D2060

# 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)