Re: How Handle DNS timeout cases from Application

On Mon, 8 Jun 2020, Jayashankara DM via curl-library wrote:

> When DNS resolution is not possible for some reason (like DNS server is down
> or can be any other reason) our application is crashing.

That sounds like an application error. Why does it crash because of this? A
failed resolve should make libcurl simply return an error and that should not
make your application crash.

I think you should dig into this crash and figure out more about why this
happens.

> Can please let me know how to handle this case in our application

Check the return code?

> We tried setting CURLOPT_NOSIGNAL = 1 which solves this problem, But leads
> to some other issues like not handling dynamic server down issues.

If setting this option this solves the problem, something was wrong to begin
with. CURLOPT_NOSIGNAL is not a very good band aid for crashes.

> Can you please suggest how to handle the DNS resolution issues ( May be
> timeout or DNS server is wrong or DNS server is not configured ) from
> application point of view to avoid the crash ?

You can set a timeout with CURLOPT_CONNECTTIMEOUT. But again, your application
should never crash because of a timeout, with or without using this option.

> Please also let me know "curl-7.63.0" is by default support "threaded
> resolver" or from which curl version onward "threaded resolver " is
> supported by default ?

It does yes, but you can also see that at the end of the configure run and
with curl -V and curl_version_info() if you're not sure. (They shold show
asynchdns as a feature while *not* mentioning c-ares being used.)

> One basic question: We have a board with curl 7.49.1 and Client application
> is built with curl-7.63.0 (libcurl.so dynamic library) .

You can only use one libcurl version, so you *either* use 7.49.1 or 7.63.0.

I would recommend the latter.

-- 
  / daniel.haxx.se | Commercial curl support up to 24x7 is available!
                   | Private help, bug fixes, support, ports, new features
                   | https://www.wolfssl.com/contact/
-------------------------------------------------------------------
Unsubscribe: https://cool.haxx.se/list/listinfo/curl-library
Etiquette:   https://curl.haxx.se/mail/etiquette.html