Source: unixsock_posix.go in package net

+build aix darwin dragonfly freebsd js,wasm linux netbsd openbsd solaris windows


package net

import (
	"context"
	"errors"
	"os"
	"syscall"
)

func unixSocket(ctx context.Context, net string, laddr, raddr sockaddr, mode string, ctrlFn func(string, string, syscall.RawConn) error) (*netFD, error) {
	var sotype int
	switch net {
	case "unix":
		sotype = syscall.SOCK_STREAM
	case "unixgram":
		sotype = syscall.SOCK_DGRAM
	case "unixpacket":
		sotype = syscall.SOCK_SEQPACKET
	default:
		return nil, UnknownNetworkError(net)
	}

	switch mode {
	case "dial":
		if laddr != nil && laddr.isWildcard() {
			laddr = nil
		}
		if raddr != nil && raddr.isWildcard() {
			raddr = nil
		}
		if raddr == nil && (sotype != syscall.SOCK_DGRAM || laddr == nil) {
			return nil, errMissingAddress
		}
	case "listen":
	default:
		return nil, errors.New("unknown mode: " + mode)
	}

	fd, err := socket(ctx, net, syscall.AF_UNIX, sotype, 0, false, laddr, raddr, ctrlFn)
	if err != nil {
		return nil, err
	}
	return fd, nil
}

func sockaddrToUnix(sa syscall.Sockaddr) Addr {
	if s, ok := sa.(*syscall.SockaddrUnix); ok {
		return &UnixAddr{Name: s.Name, Net: "unix"}
	}
	return nil
}

func sockaddrToUnixgram(sa syscall.Sockaddr) Addr {
	if s, ok := sa.(*syscall.SockaddrUnix); ok {
		return &UnixAddr{Name: s.Name, Net: "unixgram"}
	}
	return nil
}

func sockaddrToUnixpacket(sa syscall.Sockaddr) Addr {
	if s, ok := sa.(*syscall.SockaddrUnix); ok {
		return &UnixAddr{Name: s.Name, Net: "unixpacket"}
	}
	return nil
}

func sotypeToNet(sotype int) string {
	switch sotype {
	case syscall.SOCK_STREAM:
		return "unix"
	case syscall.SOCK_DGRAM:
		return "unixgram"
	case syscall.SOCK_SEQPACKET:
		return "unixpacket"
	default:
		panic("sotypeToNet unknown socket type")
	}
}

func (a *UnixAddr) family() int {
	return syscall.AF_UNIX
}

func (a *UnixAddr) sockaddr(family int) (syscall.Sockaddr, error) {
	if a == nil {
		return nil, nil
	}
	return &syscall.SockaddrUnix{Name: a.Name}, nil
}

func (a *UnixAddr) toLocal(net string) sockaddr {
	return a
}

func (c *UnixConn) readFrom(b []byte) (int, *UnixAddr, error) {
	var addr *UnixAddr
	n, sa, err := c.fd.readFrom(b)
	switch sa := sa.(type) {
	case *syscall.SockaddrUnix:
		if sa.Name != "" {
			addr = &UnixAddr{Name: sa.Name, Net: sotypeToNet(c.fd.sotype)}
		}
	}
	return n, addr, err
}

func (c *UnixConn) readMsg(b, oob []byte) (n, oobn, flags int, addr *UnixAddr, err error) {
	var sa syscall.Sockaddr
	n, oobn, flags, sa, err = c.fd.readMsg(b, oob)
	switch sa := sa.(type) {
	case *syscall.SockaddrUnix:
		if sa.Name != "" {
			addr = &UnixAddr{Name: sa.Name, Net: sotypeToNet(c.fd.sotype)}
		}
	}
	return
}

func (c *UnixConn) writeTo(b []byte, addr *UnixAddr) (int, error) {
	if c.fd.isConnected {
		return 0, ErrWriteToConnected
	}
	if addr == nil {
		return 0, errMissingAddress
	}
	if addr.Net != sotypeToNet(c.fd.sotype) {
		return 0, syscall.EAFNOSUPPORT
	}
	sa := &syscall.SockaddrUnix{Name: addr.Name}
	return c.fd.writeTo(b, sa)
}

func (c *UnixConn) writeMsg(b, oob []byte, addr *UnixAddr) (n, oobn int, err error) {
	if c.fd.sotype == syscall.SOCK_DGRAM && c.fd.isConnected {
		return 0, 0, ErrWriteToConnected
	}
	var sa syscall.Sockaddr
	if addr != nil {
		if addr.Net != sotypeToNet(c.fd.sotype) {
			return 0, 0, syscall.EAFNOSUPPORT
		}
		sa = &syscall.SockaddrUnix{Name: addr.Name}
	}
	return c.fd.writeMsg(b, oob, sa)
}

func (sd *sysDialer) dialUnix(ctx context.Context, laddr, raddr *UnixAddr) (*UnixConn, error) {
	fd, err := unixSocket(ctx, sd.network, laddr, raddr, "dial", sd.Dialer.Control)
	if err != nil {
		return nil, err
	}
	return newUnixConn(fd), nil
}

func (ln *UnixListener) accept() (*UnixConn, error) {
	fd, err := ln.fd.accept()
	if err != nil {
		return nil, err
	}
	return newUnixConn(fd), nil
}

The operating system doesn't clean up the file that announcing created, so we have to clean it up ourselves. There's a race here--we can't know for sure whether someone else has come along and replaced our socket name already-- but this sequence (remove then close) is at least compatible with the auto-remove sequence in ListenUnix. It's only non-Go programs that can mess us up. Even if there are racy calls to Close, we want to unlink only for the first one.

	ln.unlinkOnce.Do(func() {
		if ln.path[0] != '@' && ln.unlink {
			syscall.Unlink(ln.path)
		}
	})
	return ln.fd.Close()
}

func (ln *UnixListener) file() (*os.File, error) {
	f, err := ln.fd.dup()
	if err != nil {
		return nil, err
	}
	return f, nil
}

SetUnlinkOnClose sets whether the underlying socket file should be removed from the file system when the listener is closed. The default behavior is to unlink the socket file only when package net created it. That is, when the listener and the underlying socket file were created by a call to Listen or ListenUnix, then by default closing the listener will remove the socket file. but if the listener was created by a call to FileListener to use an already existing socket file, then by default closing the listener will not remove the socket file.

func (l *UnixListener) SetUnlinkOnClose(unlink bool) {
	l.unlink = unlink
}

func (sl *sysListener) listenUnix(ctx context.Context, laddr *UnixAddr) (*UnixListener, error) {
	fd, err := unixSocket(ctx, sl.network, laddr, nil, "listen", sl.ListenConfig.Control)
	if err != nil {
		return nil, err
	}
	return &UnixListener{fd: fd, path: fd.laddr.String(), unlink: true}, nil
}

func (sl *sysListener) listenUnixgram(ctx context.Context, laddr *UnixAddr) (*UnixConn, error) {
	fd, err := unixSocket(ctx, sl.network, laddr, nil, "listen", sl.ListenConfig.Control)
	if err != nil {
		return nil, err
	}
	return newUnixConn(fd), nil