Re: pg_basebackup vs. Windows and tablespaces

On 12/14/2014 07:09 PM, Tom Lane wrote:
> Amit Kapila <amit.kapila16@gmail.com> writes:
>>> On Sat, Dec 13, 2014 at 10:48 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>>> 1. The patch is completely naive about what might be in the symlink
>>>> path string; eg embedded spaces in the path would break it.  On at
>>>> least some platforms, newlines could be in the path as well.  I'm not
>>>> sure about how to guard against this while maintaining human readability
>>>> of the file.
>> One way to deal with this could be to append a delimiter(which is not
>> allowed
>> in tablespace path like quote (\')) at the end of tablespace path while
>> writing the same to symlink label file and then use that as end marker while
>> reading it from file.
> What makes you think quote isn't allowed in tablespace paths?  Even if we
> were to disallow it at the SQL level, there'd be nothing stopping a DBA
> from changing the path after the fact by redefining the symlink outside
> SQL --- something I believe we specifically meant to allow, considering
> we went to the trouble of getting rid of the pg_tablespace.spclocation
> column.
>
> Pretty much the only character we can be entirely certain is not in a
> symlink's value is \0.  As Alvaro mentioned, using that in the file
> is a possible alternative, although it could easily confuse some users
> and/or text editors.  The only other alternatives I can see are:
>
> * Go over to a byte-count-then-value format.  Also possible, also rather
>    unfriendly from a user's standpoint.
>
> * Establish an escaping convention, eg backslash before any funny
>    characters.  Unfortunately backslash wouldn't be too nice from the
>    viewpoint of Windows users.
>
> * Make pg_basebackup check for and fail on symlinks containing characters
>    it can't handle.  Pretty icky, though I suppose there's some argument
>    that things like newlines wouldn't be in any rational tablespace path.
>    But I doubt you can make that argument for spaces, quotes, or backslashes.
>
>             


Using an escaping convention makes by far the most sense to me. It's 
what occurred to me earlier today even before I read the above. We could 
adopt the URL convention of %xx for escapable characters - that would 
avoid \ nastiness.

cheers

andrew