Hello,

Error

An error curl: (45) bind failed with errno 22: Invalid argument occurs whenever we specify IPv4 from local interface as a source address trying to connect to a site which have both IPv4 and IPv6.

Steps to reproduce

Pick up a domain which resolves both to IPv4 and IPv6:

# host canhazip.com
canhazip.com has address 104.16.222.38
canhazip.com has address 104.16.223.38
canhazip.com has IPv6 address 2606:4700::6810:de26
canhazip.com has IPv6 address 2606:4700::6810:df26

The request:

# curl --interface 1.2.3.4 https://canhazip.com/
curl: (45) bind failed with errno 22: Invalid argument

can be fixed with -4 flag:

# curl --interface 1.2.3.4 -4 https://canhazip.com/
1.2.3.4 

OS

Tested with CentOS 7:

• default version cURL: curl-7.29.0-51.el7.x86_64
• and from a git repository: curl 7.65.1-DEV (x86_64-unknown-linux-gnu) libcurl/7.65.1-DEV OpenSSL/1.0.2k-fips zlib/1.2.7

Results are the same.

Expected behavior:

Whenever a source IPv4 is specified cURL should auto add -4 flag, i.e.:

curl_easy_setopt(easyhandle, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);

The same with IPv6, whenever a source IPv6 is specified cURL should auto add -6 flag, i.e.

curl_easy_setopt(easyhandle, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V6);

Regards,
Alex.