Rsync lets user corrupt dest by applying non-inplace batch in inplace mode

[Matt McCutchen]

Wayne,

I noticed that rsync will let me apply a non-inplace batch file in
inplace mode.  This corrupts the destination file if the batch file
copies any data forward (from earlier offsets to later ones).  Of
course, the post-transfer checksum detects the corruption and gives the
"ERROR: <file> failed verification" message, but rsync doesn't give the
user a clue why the corruption occurred.

I think rsync should at least warn the user and possibly refuse outright
to apply a non-inplace batch in inplace mode.  However, existing batch
files don't indicate which mode they were written in, and it would be
nice to let a user apply a non-inplace batch if it happened not to use
any forward copies.  Thus, the best thing to do might be to issue an
error like this the first time a forward copy is seen for each file
(followed, of course, by the post-transfer checksum failure):

rsync: error: batch file delta for <file> contains a forward copy, which
cannot be performed in --inplace mode (probably the batch file was
written without --inplace); the update will probably be corrupted

Matt