[Box Backup] Irregular Expressions

[Chris Wilson]

Hi all,

Ben rightly pointed out that my assumptions Box Backup's support for 
regular expressions were wrong. The current state is that we use POSIX 
regular expressions where available (all POSIX Unix platforms) and 
Perl-compatible regular expressions through PCRE on Windows.

This situation is not ideal for three reasons: anyone who uses or supports 
both platforms has to remember that the regular expression styles are 
different; we can't use the much more powerful Perl-compatible regular 
expressions on Unix; and it's possible (but unlikely) that someone with a 
weirdly broken Unix system might end up with a Box Backup build that 
supports PCRE instead of POSIX, confusing the hell out of us all.

There are several options for how to fix this, none of them ideal, and I 
wanted to see what opinions people (users, developers and packagers) had 
about them.

1. Do nothing. The worst option (in my view) except that it takes no time.

2. Use PCRE everywhere and add it as a dependency. People with platforms 
with no native PCRE package, and embedded system developers, might hate us 
for this (Solaris? AIX?) but you could still build Box with no regular 
expression support at all.

3. Use PCRE everywhere and bundle it with Box Backup. Bloats the source by 
about 1MB compressed, 3MB uncompressed.

4. Use PCRE in preference to POSIX regular expressions if available. Some 
platforms would still only have POSIX regular expressions, but I think 
they would be few and rare. We would probably have to add a command-line 
switch to bbackupd to report what kind of regular expression support it 
had been built with. Still risks confusing everyone, but in most cases 
better than the current situation IMHO, because most people would have the 
more powerful PCRE support.

5. Provide a configure-time switch to choose between POSIX and PCRE 
expressions. Packagers could then provide both versions of the packages 
for platforms where it made sense to do so. Still risks confusing users, 
but at least they would hopefully know which version of the package they 
had installed, and we could also add the command-line switch described in 
(4).

I'm also considering whether it's really worth providing the option to 
build Box Backup with NO regular expression support. The only case where I 
think this might actually be useful is for embedded systems. But, I don't 
know if anybody actually does this or plans to do it. And it's more likely 
that such devices would run bbstored rather than bbackupd, so we could 
choose only to build bbstored in that case.

Any other options? Opinions about any of these? Let us know.

Cheers, Chris.
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