IPV6 support on tcp_client.h

[Simon-Janos]

Hi,

I have noticed in connect() of tcp_client.h (and of tcp_client-windows.h as well) that it is tied to IPv4, could it be changed AF_UNSPEC for ipv6 support?
hints.ai_family = AF_INET; // IPv4

https://github.com/gabime/spdlog/blob/v1.x/include/spdlog/details/tcp_client.h#L61
https://github.com/gabime/spdlog/blob/v1.x/include/spdlog/details/tcp_client-windows.h#L86

Sincerely,
Janis

[tt4g]

That structure is a hint, and AF_INET specifies IPv4, so if you pass a hostname to getaddrinfo(), IPv4 will be returned.
However, it is only a hint. If you pass an IPv6 string to the host argument, it should connect to IPv6.

See: https://learn.microsoft.com/en-us/windows/win32/api/ws2tcpip/nf-ws2tcpip-getaddrinfo

[Simon-Janos]

So on my ipv6 rocky8/redhat environments I get "::getaddrinfo failed: Name or service not known" error. Which clearly does exist and sure enough no problem on ipv4. If I try with the service ip address (IPv6) I got "address family not supported" whiles it does work with a proper ipv4 address.

[tt4g]

Are you saying that passing an IPv6 string will not work? If so, it may have to be AF_INET6 or AF_UNSPEC to work.

[Simon-Janos]

So on some linux/c version - at least - they are incompatible. AF_UNSPEC is a better approach or at least we are better making it configurable.

[gabime]

@Simon-Janos PR is welcome.

[gabime]

Implemented in #2790