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Re: Callback for socket options in curl + c-ares

From: Francisco Sedano Crippa (fsedanoc) <>
Date: Wed, 14 Feb 2018 15:19:59 +0000

Hi folks,
I went ahead and created a patch to provide a new libcurl CB, that will be called just before a new resolver is called, and the resolver data (channel in case of cares) is passed. This solves the problem perfectly for my use case.
Initially I thought about just adding a new easy_getinfo option to retrieve it, but since libcurl can create easy_handles on it's own, I feel this callback approach is a safer option.

Are you guys OK with that approach? If that's ok I can send the pull request for review.


. .:|:.:|:. Francisco Sedano | CCIE 14859, Tech Lead Software Engineering | CSG Enterprise Access and Services Group (EASG)
On 14.02.18, 00:54, "curl-library on behalf of Francisco Sedano Crippa (fsedanoc)" < on behalf of> wrote:

    Hello Daniel,
    I feel it would be useful in some other cases - for example dealing with multi-vrf sockets, currently you can bind the libcurl socket to any vrf you want, but no way to do that with the underlying c-ares.
    Wouldn't be enough to provide access to the c-ares channel (which is in curl_easy->state.resolver if I'm not wrong)? Once I create my easy socket and the c-ares channel is created, I could just use ares_set_socket_configure_callback on the channel and I'd be done. Anything else I'm missing?
    . .:|:.:|:. Francisco Sedano | CCIE 14859, Tech Lead Software Engineering | CSG Enterprise Access and Services Group (EASG)
    On 13.02.18, 23:49, "curl-library on behalf of Daniel Stenberg" < on behalf of> wrote:
        On Tue, 13 Feb 2018, Francisco Sedano Crippa (fsedanoc) wrote:
> Ideally I’d like to setup a callback with
> ares_set_socket_configure_callback(), but in order to do so, I need access
> to internal libcurl c-ares channel, which is embedded in the Curl_easy
> structure.
> Is there any way to access such c-ares channel so I can properly intercept
> c-ares socket usage, like we can do with CURLOPT_OPENSOCKETFUNCTION in
> libcurl?
        No, that's something we've not felt the need for before... I can't think of
        any other way to offer such a feature than to add a special and dedicated "set
        socket options" callback for c-ares or perhaps rather for "the resolver
        back-end". (There's work ongoing in making the resolver back-end totally
        pluggable which then possibly also appreciate such an ability.)

Received on 2018-02-14