mercurial/dirstateguard.py

wireprotoserver: add context manager mechanism for redirecting stdio

Today, proto.redirect() sets up redirecting stdio and proto.restore()
undoes that. The API is a bit wonky because restore() is only
implemented on the HTTP protocol. Furthermore, not all calls to
redirect() are obviously paired with calls to restore(). For
example, the call to restore() for "unbundle" requests is handled
by the response handler for the HTTP protocol.

This commit introduces a new method on the protocol handler interface
to maybe capture stdio. It emits a file object or None depending on
whether stdio capture is used by the transport.

To prove it works, the "pushkey" wire protocol command has been
updated to use the new API.

I'm not convinced this is the best mechanism to capture stdio. I may
need to come up with something better once the new wire protocol
emerges into existence. But it is strictly better than before because
it removes variance in the wire protocol handler interface. It
therefore gets us closer to a unified interface between the SSH and
HTTP transports.

Differential Revision: https://phab.mercurial-scm.org/D2081

# dirstateguard.py - class to allow restoring dirstate after failure
#
# Copyright 2005-2007 Matt Mackall <[e-mail]>
#
# 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

from .i18n import _

from . import (
    error,
    util,
)

class dirstateguard(util.transactional):
    '''Restore dirstate at unexpected failure.

    At the construction, this class does:

    - write current ``repo.dirstate`` out, and
    - save ``.hg/dirstate`` into the backup file

    This restores ``.hg/dirstate`` from backup file, if ``release()``
    is invoked before ``close()``.

    This just removes the backup file at ``close()`` before ``release()``.
    '''

    def __init__(self, repo, name):
        self._repo = repo
        self._active = False
        self._closed = False
        self._backupname = 'dirstate.backup.%s.%d' % (name, id(self))
        repo.dirstate.savebackup(repo.currenttransaction(), self._backupname)
        self._active = True

    def __del__(self):
        if self._active: # still active
            # this may occur, even if this class is used correctly:
            # for example, releasing other resources like transaction
            # may raise exception before ``dirstateguard.release`` in
            # ``release(tr, ....)``.
            self._abort()

    def close(self):
        if not self._active: # already inactivated
            msg = (_("can't close already inactivated backup: %s")
                   % self._backupname)
            raise error.Abort(msg)

        self._repo.dirstate.clearbackup(self._repo.currenttransaction(),
                                         self._backupname)
        self._active = False
        self._closed = True

    def _abort(self):
        self._repo.dirstate.restorebackup(self._repo.currenttransaction(),
                                           self._backupname)
        self._active = False

    def release(self):
        if not self._closed:
            if not self._active: # already inactivated
                msg = (_("can't release already inactivated backup: %s")
                       % self._backupname)
                raise error.Abort(msg)
            self._abort()