Source: sock_posix.go in package net

+build aix darwin dragonfly freebsd linux netbsd openbsd solaris windows


package net

import (
	"context"
	"internal/poll"
	"os"
	"syscall"
)

socket returns a network file descriptor that is ready for asynchronous I/O using the network poller.

func socket(ctx context.Context, net string, family, sotype, proto int, ipv6only bool, laddr, raddr sockaddr, ctrlFn func(string, string, syscall.RawConn) error) (fd *netFD, err error) {
	s, err := sysSocket(family, sotype, proto)
	if err != nil {
		return nil, err
	}
	if err = setDefaultSockopts(s, family, sotype, ipv6only); err != nil {
		poll.CloseFunc(s)
		return nil, err
	}
	if fd, err = newFD(s, family, sotype, net); err != nil {
		poll.CloseFunc(s)
		return nil, err
	}

This function makes a network file descriptor for the following applications: - An endpoint holder that opens a passive stream connection, known as a stream listener - An endpoint holder that opens a destination-unspecific datagram connection, known as a datagram listener - An endpoint holder that opens an active stream or a destination-specific datagram connection, known as a dialer - An endpoint holder that opens the other connection, such as talking to the protocol stack inside the kernel For stream and datagram listeners, they will only require named sockets, so we can assume that it's just a request from stream or datagram listeners when laddr is not nil but raddr is nil. Otherwise we assume it's just for dialers or the other connection holders.


	if laddr != nil && raddr == nil {
		switch sotype {
		case syscall.SOCK_STREAM, syscall.SOCK_SEQPACKET:
			if err := fd.listenStream(laddr, listenerBacklog(), ctrlFn); err != nil {
				fd.Close()
				return nil, err
			}
			return fd, nil
		case syscall.SOCK_DGRAM:
			if err := fd.listenDatagram(laddr, ctrlFn); err != nil {
				fd.Close()
				return nil, err
			}
			return fd, nil
		}
	}
	if err := fd.dial(ctx, laddr, raddr, ctrlFn); err != nil {
		fd.Close()
		return nil, err
	}
	return fd, nil
}

func (fd *netFD) ctrlNetwork() string {
	switch fd.net {
	case "unix", "unixgram", "unixpacket":
		return fd.net
	}
	switch fd.net[len(fd.net)-1] {
	case '4', '6':
		return fd.net
	}
	if fd.family == syscall.AF_INET {
		return fd.net + "4"
	}
	return fd.net + "6"
}

func (fd *netFD) addrFunc() func(syscall.Sockaddr) Addr {
	switch fd.family {
	case syscall.AF_INET, syscall.AF_INET6:
		switch fd.sotype {
		case syscall.SOCK_STREAM:
			return sockaddrToTCP
		case syscall.SOCK_DGRAM:
			return sockaddrToUDP
		case syscall.SOCK_RAW:
			return sockaddrToIP
		}
	case syscall.AF_UNIX:
		switch fd.sotype {
		case syscall.SOCK_STREAM:
			return sockaddrToUnix
		case syscall.SOCK_DGRAM:
			return sockaddrToUnixgram
		case syscall.SOCK_SEQPACKET:
			return sockaddrToUnixpacket
		}
	}
	return func(syscall.Sockaddr) Addr { return nil }
}

func (fd *netFD) dial(ctx context.Context, laddr, raddr sockaddr, ctrlFn func(string, string, syscall.RawConn) error) error {
	if ctrlFn != nil {
		c, err := newRawConn(fd)
		if err != nil {
			return err
		}
		var ctrlAddr string
		if raddr != nil {
			ctrlAddr = raddr.String()
		} else if laddr != nil {
			ctrlAddr = laddr.String()
		}
		if err := ctrlFn(fd.ctrlNetwork(), ctrlAddr, c); err != nil {
			return err
		}
	}
	var err error
	var lsa syscall.Sockaddr
	if laddr != nil {
		if lsa, err = laddr.sockaddr(fd.family); err != nil {
			return err
		} else if lsa != nil {
			if err = syscall.Bind(fd.pfd.Sysfd, lsa); err != nil {
				return os.NewSyscallError("bind", err)
			}
		}
	}
	var rsa syscall.Sockaddr  // remote address from the user
	var crsa syscall.Sockaddr // remote address we actually connected to
	if raddr != nil {
		if rsa, err = raddr.sockaddr(fd.family); err != nil {
			return err
		}
		if crsa, err = fd.connect(ctx, lsa, rsa); err != nil {
			return err
		}
		fd.isConnected = true
	} else {
		if err := fd.init(); err != nil {
			return err
		}

Record the local and remote addresses from the actual socket. Get the local address by calling Getsockname. For the remote address, use 1) the one returned by the connect method, if any; or 2) the one from Getpeername, if it succeeds; or 3) the one passed to us as the raddr parameter.

	lsa, _ = syscall.Getsockname(fd.pfd.Sysfd)
	if crsa != nil {
		fd.setAddr(fd.addrFunc()(lsa), fd.addrFunc()(crsa))
	} else if rsa, _ = syscall.Getpeername(fd.pfd.Sysfd); rsa != nil {
		fd.setAddr(fd.addrFunc()(lsa), fd.addrFunc()(rsa))
	} else {
		fd.setAddr(fd.addrFunc()(lsa), raddr)
	}
	return nil
}

func (fd *netFD) listenStream(laddr sockaddr, backlog int, ctrlFn func(string, string, syscall.RawConn) error) error {
	var err error
	if err = setDefaultListenerSockopts(fd.pfd.Sysfd); err != nil {
		return err
	}
	var lsa syscall.Sockaddr
	if lsa, err = laddr.sockaddr(fd.family); err != nil {
		return err
	}
	if ctrlFn != nil {
		c, err := newRawConn(fd)
		if err != nil {
			return err
		}
		if err := ctrlFn(fd.ctrlNetwork(), laddr.String(), c); err != nil {
			return err
		}
	}
	if err = syscall.Bind(fd.pfd.Sysfd, lsa); err != nil {
		return os.NewSyscallError("bind", err)
	}
	if err = listenFunc(fd.pfd.Sysfd, backlog); err != nil {
		return os.NewSyscallError("listen", err)
	}
	if err = fd.init(); err != nil {
		return err
	}
	lsa, _ = syscall.Getsockname(fd.pfd.Sysfd)
	fd.setAddr(fd.addrFunc()(lsa), nil)
	return nil
}

func (fd *netFD) listenDatagram(laddr sockaddr, ctrlFn func(string, string, syscall.RawConn) error) error {
	switch addr := laddr.(type) {

We provide a socket that listens to a wildcard address with reusable UDP port when the given laddr is an appropriate UDP multicast address prefix. This makes it possible for a single UDP listener to join multiple different group addresses, for multiple UDP listeners that listen on the same UDP port to join the same group address.

		if addr.IP != nil && addr.IP.IsMulticast() {
			if err := setDefaultMulticastSockopts(fd.pfd.Sysfd); err != nil {
				return err
			}
			addr := *addr
			switch fd.family {
			case syscall.AF_INET:
				addr.IP = IPv4zero
			case syscall.AF_INET6:
				addr.IP = IPv6unspecified
			}
			laddr = &addr
		}
	}
	var err error
	var lsa syscall.Sockaddr
	if lsa, err = laddr.sockaddr(fd.family); err != nil {
		return err
	}
	if ctrlFn != nil {
		c, err := newRawConn(fd)
		if err != nil {
			return err
		}
		if err := ctrlFn(fd.ctrlNetwork(), laddr.String(), c); err != nil {
			return err
		}
	}
	if err = syscall.Bind(fd.pfd.Sysfd, lsa); err != nil {
		return os.NewSyscallError("bind", err)
	}
	if err = fd.init(); err != nil {
		return err
	}
	lsa, _ = syscall.Getsockname(fd.pfd.Sysfd)
	fd.setAddr(fd.addrFunc()(lsa), nil)
	return nil