On 12/14/2014 07:09 PM, Tom Lane wrote:
Amit Kapila <amit.kapil...@gmail.com> writes:
On Sat, Dec 13, 2014 at 10:48 PM, Tom Lane <t...@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
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