view mercurial/revlogutils/concurrency_checker.py @ 51182:a93e52f0b6ff

changelog: disallow delayed write on inline changesets

Since this will never happens, we can make the situation invalid and to stop to
handling the associated the case.

This simplify the random access file reading too.

from ..i18n import _
from .. import error


def get_checker(ui, revlog_name=b'changelog'):
    """Get a function that checks file handle position is as expected.

    This is used to ensure that files haven't been modified outside of our
    knowledge (such as on a networked filesystem, if `hg debuglocks` was used,
    or writes to .hg that ignored locks happened).

    Due to revlogs supporting a concept of buffered, delayed, or diverted
    writes, we're allowing the files to be shorter than expected (the data may
    not have been written yet), but they can't be longer.

    Please note that this check is not perfect; it can't detect all cases (there
    may be false-negatives/false-OKs), but it should never claim there's an
    issue when there isn't (false-positives/false-failures).
    """

    vpos = ui.config(b'debug', b'revlog.verifyposition.' + revlog_name)
    # Avoid any `fh.tell` cost if this isn't enabled.
    if not vpos or vpos not in [b'log', b'warn', b'fail']:
        return None

    def _checker(fh, fn, expected):
        if fh.tell() <= expected:
            return

        msg = _(b'%s: file cursor at position %d, expected %d')
        # Always log if we're going to warn or fail.
        ui.log(b'debug', msg + b'\n', fn, fh.tell(), expected)
        if vpos == b'warn':
            ui.warn((msg + b'\n') % (fn, fh.tell(), expected))
        elif vpos == b'fail':
            raise error.RevlogError(msg % (fn, fh.tell(), expected))

    return _checker