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Re: DNS Lookups.

From: Daniel Stenberg <>
Date: Thu, 31 Mar 2011 13:46:15 +0200 (CEST)

On Thu, 31 Mar 2011, Keean Schupke wrote:

> We are using the CURLOPT_OPENSOCKETFUNCTION to open a socket to our
> destination. We need to be able to replace the DNS lookup, as our socket
> connect function takes the host name directly not an IP address.

So you're kind of doing a socks-like thing outside of libcurl? I can see how
one could find a use for such a feature.

> We can get the hostname from curl_easy_getinfo with CURLINFO_EFFECTIVE_URL
> inside the open-socket-function. What we need to do now is suppress the DNS
> lookup, as the hostname will not be a resolvable name. Currently we push the
> name into the DNS cache using CURLOPT_RESOLVE, but this does not work when
> the remote server does a redirect.

The obvious immediate way is of course to not use libcurl's internal redirect
following but to do it yourself (with libcurl's CURLINFO_* variables'

libcurl doesn't have any pluggable way for an application to do the host name
resolving. I wouldn't mind seeing such a way getting introduced, but I think
it'll take some careful condiderations and planning first as it would then
probably be wiser to allow a pluggable completely asynch resolver.

> Any suggestions as to the best way to disable DNS lookup for our non-DNS
> hostnames?

An alternative approach that is transparent to libcurl is to
LD_PRELOAD-replace the resolver functions libcurl uses - when built to use the
synchronous resolver.

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Received on 2011-03-31