I was hit by this problem in gnupg, which uses libcurl to download keys from keyserver. But this is perfectly reproducable by curl command line tool itself.

My first idea was whether or not this is a problem of libcurl not being thread safe. The requests are done in parallel, possibly overwriting each others memory, no?

Any hints on how to debug this?

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** [bugs:#1346] resolver error**
**Status:** open
**Labels:** dns 
**Created:** Mon Mar 17, 2014 03:40 PM UTC by Christian Hesse
**Last Updated:** Mon Mar 17, 2014 03:59 PM UTC
**Owner:** Daniel Stenberg
libcurl has a resolver bug that requires some conditions to trigger:
* libcurl tries to resolv A and AAAA records
* DNS response is too long to fit into a UDP packet
What happens:
* libcurl sends two DNS UDP requests, one for A record, one for AAAA record
* libcurl receives one truncated UDP response
* libcurl sends TCP request
* libcurl receives TCP response
* libcurl sends TCP reset, ignoring the response
Everything works just fine when querying only A record (give option -4).
A capture demonstrating the problem is attached.
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