go/src/net/ipsock_posix.go

// probe probes IPv4, IPv6 and IPv4-mapped IPv6 communication
// capabilities which are controlled by the IPV6_V6ONLY socket option
// and kernel configuration.
//
// Should we try to use the IPv4 socket interface if we're only
// dealing with IPv4 sockets? As long as the host system understands
// IPv4-mapped IPv6, it's okay to pass IPv4-mapped IPv6 addresses to
// the IPv6 interface. That simplifies our code and is most
// general. Unfortunately, we need to run on kernels built without
// IPv6 support too. So probe the kernel to figure it out.
func (p *ipStackCapabilities) probe() { … }

// favoriteAddrFamily returns the appropriate address family for the
// given network, laddr, raddr and mode.
//
// If mode indicates "listen" and laddr is a wildcard, we assume that
// the user wants to make a passive-open connection with a wildcard
// address family, both AF_INET and AF_INET6, and a wildcard address
// like the following:
//
//   - A listen for a wildcard communication domain, "tcp" or
//     "udp", with a wildcard address: If the platform supports
//     both IPv6 and IPv4-mapped IPv6 communication capabilities,
//     or does not support IPv4, we use a dual stack, AF_INET6 and
//     IPV6_V6ONLY=0, wildcard address listen. The dual stack
//     wildcard address listen may fall back to an IPv6-only,
//     AF_INET6 and IPV6_V6ONLY=1, wildcard address listen.
//     Otherwise we prefer an IPv4-only, AF_INET, wildcard address
//     listen.
//
//   - A listen for a wildcard communication domain, "tcp" or
//     "udp", with an IPv4 wildcard address: same as above.
//
//   - A listen for a wildcard communication domain, "tcp" or
//     "udp", with an IPv6 wildcard address: same as above.
//
//   - A listen for an IPv4 communication domain, "tcp4" or "udp4",
//     with an IPv4 wildcard address: We use an IPv4-only, AF_INET,
//     wildcard address listen.
//
//   - A listen for an IPv6 communication domain, "tcp6" or "udp6",
//     with an IPv6 wildcard address: We use an IPv6-only, AF_INET6
//     and IPV6_V6ONLY=1, wildcard address listen.
//
// Otherwise guess: If the addresses are IPv4 then returns AF_INET,
// or else returns AF_INET6. It also returns a boolean value what
// designates IPV6_V6ONLY option.
//
// Note that the latest DragonFly BSD and OpenBSD kernels allow
// neither "net.inet6.ip6.v6only=1" change nor IPPROTO_IPV6 level
// IPV6_V6ONLY socket option setting.
//
// favoriteAddrFamily should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/database64128/tfo-go/v2
//   - github.com/metacubex/tfo-go
//   - github.com/sagernet/tfo-go
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:linkname favoriteAddrFamily
func favoriteAddrFamily(network string, laddr, raddr sockaddr, mode string) (family int, ipv6only bool) { … }

func internetSocket(ctx context.Context, net string, laddr, raddr sockaddr, sotype, proto int, mode string, ctrlCtxFn func(context.Context, string, string, syscall.RawConn) error) (fd *netFD, err error) { … }

func ipToSockaddrInet4(ip IP, port int) (syscall.SockaddrInet4, error) { … }

func ipToSockaddrInet6(ip IP, port int, zone string) (syscall.SockaddrInet6, error) { … }

// ipToSockaddr should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/database64128/tfo-go/v2
//   - github.com/metacubex/tfo-go
//   - github.com/sagernet/tfo-go
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:linkname ipToSockaddr
func ipToSockaddr(family int, ip IP, port int, zone string) (syscall.Sockaddr, error) { … }

func addrPortToSockaddrInet4(ap netip.AddrPort) (syscall.SockaddrInet4, error) { … }

func addrPortToSockaddrInet6(ap netip.AddrPort) (syscall.SockaddrInet6, error) { … }