On Wed, 19 Aug 2009, Tom Van de Putte wrote:

> It hangs on curl_multi_select() because it can't resolve the hostname.

Note that this function is not libcurl's, it's only provided by the PHP/CURL
exension and is some kind of wrapper on top of select().

> However the CLI of curl works perfectly so I checked the configs (the
> development server is an plain (arch)linux - apache - php installation) but
> they seem clean. If I comment out the direction to our own dns server in
> /etc/resolve.conf the CLI version also stops working so I figure out that
> libcurl/php uses another way to resolve eg. via glibc?

curl uses libcurl for the transfers parts, and PHP/CURL uses libcurl for the
transfer parts. Assuming they both use the SAME libcurl installation (which
they might not) they will use the exact same name resolving method.

The explanation to why one works and the other doesn't is then left to other
details: like SElinux? Other security/rights management stuff that sits in the
way? or whatever. It feels like there's something that makes the http server's
process not able/allowed to do this.

Quite possibly stracing the server and the tool could help to figure out how
the system call sequences differ or similar.

Or perhaps you can just wireshark the traffic and see the DNS resolves (not)
fly by.

> Using the options CURLOPT_DNS_USE_GLOBAL_CACHE and CURLOPT_DNS_CACHE_TIMEOUT
> does not make any differance.

No, they just affect the data after libcurl has received it...

> Even worse: if I run 'host dns.be' it returns the requested dns data. which
> normaly uses the same routines as gethostbyname() (the c function curl uses
> for this).

If curl works from the command line I would expect host to do so too.

> So this could mean this is perhaps not a dns/bind problem and a fault in how
> curl caches dns data or handles ipv4/ipv6 adresses?

Why? curl works you say, and it uses the same way to resolve names that your
PHP/CURL does. So it's not the implementation that's wrong, there's something
else than hinders it from functioning correctly.

-- 
  / daniel.haxx.se