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Re: [Bug-wget] Anyone want to add libcares support to wget?


From: Ángel González
Subject: Re: [Bug-wget] Anyone want to add libcares support to wget?
Date: Wed, 16 Mar 2016 02:40:24 +0100
User-agent: Thunderbird

On 15/03/16 17:03, Ben Greear wrote:
I want to use wget on multi-homed machines, and I use routing rules to route pkts
out specific interfaces based on the source IP.

So, I need to be able to bind to a local IP address, including for the resolver logic,
which is why I want to use libcares.

To test, I think it would be sufficient to put two IPs on a port (1.1.1.1, 1.1.1.2), and then use cmd-line args to choose one or the other. Sniff and watch for proper source address.

For DNS servers, have 1.1.1.3 and 1.1.1.4 be specified. Sniff and watch to see that the resolver destination IP is as specified. This should be completely independent of whatever
is in /etc/resolv.conf, etc.

I (and others) have patched libcares and curl in the past to handle all of this, so I know libcares can do it. I think the main work is to handle new cmd-line arguments, pass appropriate info to libcares, and make wget use libcares for it's
resolve logic.

Thanks,
Ben

I think it's ok to add a --bind parameter to wget to choose the interface for download, but I don't think it should use a different resolver just for this.

You _could_ change the libc nameservers from the application by changing _res.nsaddr_list after res_init(). It may be a bit fragile, but should work fine. And even better than changing each application, I would recommend you to create a simple LD_PRELOAD library that overrides res_init() & friends, and allows you to specify the target dns server with an environment variable. It's a pity there's no RESOLV_CONF var similar to RESOLV_HOST_CONF, for using a separate /etc/resolv.conf.

Best regards





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