CURLOPT_IPRESOLVE difference between 8.19.0 and 8.20.0

Hi all, 

I've noticed a different behaviour between 8.19.0 and 8.20.0 regarding CURLOPT_IPRESOLVE
With a local sample that only listening on "::1" (IPv6 localhost), using --ipv4 / CURL_IPRESOLVE_V4 :

- Error with 8.19.0:

$ curl-8.19.0/bin/curl --ipv4 -v 'http://[::1]:8004/hello'
* Could not resolve host: ::1
* Store negative name resolve for ::1:8004
* shutting down connection #0

- OK with 8.20.0:

$ curl-8.20.0/bin/curl --ipv4 -v 'http://[::1]:8004/hello'
*   Trying [::1]:8004...
* Established connection to ::1 (::1 port 8004) from ::1 port 54551 
* using HTTP/1.x
> GET /hello HTTP/1.1
> Host: [::1]:8004
> User-Agent: curl/8.20.0
> Accept: */*
> 
* Request completely sent off
< HTTP/1.1 200 OK
< Content-Length: 12
< Content-Type: text/html; charset=utf-8
< Date: Sun, 03 May 2026 08:51:56 GMT
< Server: Flask Server
< Via: waitress
< 
* Connection #0 to host ::1:8004 left intact
Hello World!%       

I wonder if this change is intentional or not, the behaviour of curl previous versions seems reasonable to me (error with only-IPv6 addresses when using --ipv4).
Tests have been made on macOS and ArchLinux.

Thanks, 

Jean-Christophe









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