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Message-ID: <20181029225957.GR5150@brightrain.aerifal.cx>
Date: Mon, 29 Oct 2018 18:59:57 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Cc: Robert Högberg <robert.hogberg@...il.com>
Subject: Re: Unexpected regex behaviour
On Mon, Oct 29, 2018 at 11:26:19PM +0100, Robert Högberg wrote:
> Hi,
>
> I've noticed that the musl regex implementation behaves slightly
> differently than the glibc implementation. I'm attaching a short program
> showing the behaviour.
>
> The difference makes yate (http://yate.null.ro) misbehave when running with
> musl (reported here: https://github.com/openwrt/telephony/issues/378).
>
> Yate uses a regexp like this:
> "^\\([[:alpha:]][[:alnum:]]\\+:\\)\\?/\\?/\\?\\([^[:space:][:cntrl:]@]\\+@\\)\\?\\([[:alnum:]._+-]\\+\\|[[][[:xdigit:].:]\\+[]]\\)\\(:[0-9]\\+\\)\\?"
>
> ... to parse strings like:
> "sip:012345678@...111.11.111:5060;user=phone"
>
> ... and the matches produced by musl are:
> Match 0: 0 - 32 sip:012345678@...111.11.111:5060
> Match 1: -1 - -1
> Match 2: 0 - 14 sip:012345678@
> Match 3: 14 - 27 11.111.11.111
> Match 4: 27 - 32 :5060
>
> ... while glibc produces:
> Match 0: 0 - 32 sip:012345678@...111.11.111:5060
> Match 1: 0 - 4 sip:
> Match 2: 4 - 14 012345678@
> Match 3: 14 - 27 11.111.11.111
> Match 4: 27 - 32 :5060
>
> What do you think?
>
> I've only tested musl 1.1.19. Sorry if this is not valid for later
> releases. I skimmed the 1.1.20 release notes and didn't find anything regex
> related.
I haven't checked which of the extensions you're using are supported
in musl, but the above is not a conforming POSIX BRE. It would be a
lot more readable and portable to use POSIX ERE (REG_EXTENDED) which
has the +, ?, and | operators as standard features. This looks like it
should work:
"^([[:alpha:]][[:alnum:]]+:)?/?/?([^[:space:][:cntrl:]@]+@)?([[:alnum:]._+-]+|[[][[:xdigit:].:]+[]])(:[0-9]+)?"
The only reason to use POSIX BRE is if you need backreferences, which
are not regular and explicitly not supported in ERE.
Rich
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