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Fwd: Duplicate DNS Requests using cURL and C-ARES

From: Josh Russell <josh_at_the-root.co.uk>
Date: Thu, 27 Nov 2014 12:01:24 +0000

Hi All,

I'm working on an application which uses a combination of libcurl 7.36.0
and c-ares 1.10.1 (c-ares for async DSN lookup). The application is cross
compiled for various platforms but is closely POSIX like.

I'm using curl_easy_init & curl_easy_setopt to set up my curl handles.
Those handles are then processed using curl_multi but I'm also using
curl_share with CURL_LOCK_DATA_COOKIE and CURL_LOCK_DATA_SSL_SESSION.

What I'm finding is that when I make a few requests to various URLs on the
same domain multiple DNS requests are made for the same domain. Once the
first DNS response returned its cached I don't see any more requests for
that domain - as expected.

The problem is, if I make enough requests to the same domain before the
first DNS response returns, I can my client banned by the DNS server if I
make too many requests.

Is there any way to de-duplicate concurrent requests for the same DNS
address?

Cheers

Josh

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Received on 2014-11-27