1from ..i18n import _ 2from .. import error 3 4 5def get_checker(ui, revlog_name=b'changelog'): 6 """Get a function that checks file handle position is as expected. 7 8 This is used to ensure that files haven't been modified outside of our 9 knowledge (such as on a networked filesystem, if `hg debuglocks` was used, 10 or writes to .hg that ignored locks happened). 11 12 Due to revlogs supporting a concept of buffered, delayed, or diverted 13 writes, we're allowing the files to be shorter than expected (the data may 14 not have been written yet), but they can't be longer. 15 16 Please note that this check is not perfect; it can't detect all cases (there 17 may be false-negatives/false-OKs), but it should never claim there's an 18 issue when there isn't (false-positives/false-failures). 19 """ 20 21 vpos = ui.config(b'debug', b'revlog.verifyposition.' + revlog_name) 22 # Avoid any `fh.tell` cost if this isn't enabled. 23 if not vpos or vpos not in [b'log', b'warn', b'fail']: 24 return None 25 26 def _checker(fh, fn, expected): 27 if fh.tell() <= expected: 28 return 29 30 msg = _(b'%s: file cursor at position %d, expected %d') 31 # Always log if we're going to warn or fail. 32 ui.log(b'debug', msg + b'\n', fn, fh.tell(), expected) 33 if vpos == b'warn': 34 ui.warn((msg + b'\n') % (fn, fh.tell(), expected)) 35 elif vpos == b'fail': 36 raise error.RevlogError(msg % (fn, fh.tell(), expected)) 37 38 return _checker 39