github.com/mattn/go@v0.0.0-20171011075504-07f7db3ea99f/src/net/tcpsock_posix.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows

package net

import (
	"context"
	"io"
	"os"
	"syscall"
)

func sockaddrToTCP(sa syscall.Sockaddr) Addr {
	switch sa := sa.(type) {
	case *syscall.SockaddrInet4:
		return &TCPAddr{IP: sa.Addr[0:], Port: sa.Port}
	case *syscall.SockaddrInet6:
		return &TCPAddr{IP: sa.Addr[0:], Port: sa.Port, Zone: zoneCache.name(int(sa.ZoneId))}
	}
	return nil
}

func (a *TCPAddr) family() int {
	if a == nil || len(a.IP) <= IPv4len {
		return syscall.AF_INET
	}
	if a.IP.To4() != nil {
		return syscall.AF_INET
	}
	return syscall.AF_INET6
}

func (a *TCPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
	if a == nil {
		return nil, nil
	}
	return ipToSockaddr(family, a.IP, a.Port, a.Zone)
}

func (a *TCPAddr) toLocal(net string) sockaddr {
	return &TCPAddr{loopbackIP(net), a.Port, a.Zone}
}

func (c *TCPConn) readFrom(r io.Reader) (int64, error) {
	if n, err, handled := sendFile(c.fd, r); handled {
		return n, err
	}
	return genericReadFrom(c, r)
}

func dialTCP(ctx context.Context, net string, laddr, raddr *TCPAddr) (*TCPConn, error) {
	if testHookDialTCP != nil {
		return testHookDialTCP(ctx, net, laddr, raddr)
	}
	return doDialTCP(ctx, net, laddr, raddr)
}

func doDialTCP(ctx context.Context, net string, laddr, raddr *TCPAddr) (*TCPConn, error) {
	fd, err := internetSocket(ctx, net, laddr, raddr, syscall.SOCK_STREAM, 0, "dial")

	// TCP has a rarely used mechanism called a 'simultaneous connection' in
	// which Dial("tcp", addr1, addr2) run on the machine at addr1 can
	// connect to a simultaneous Dial("tcp", addr2, addr1) run on the machine
	// at addr2, without either machine executing Listen. If laddr == nil,
	// it means we want the kernel to pick an appropriate originating local
	// address. Some Linux kernels cycle blindly through a fixed range of
	// local ports, regardless of destination port. If a kernel happens to
	// pick local port 50001 as the source for a Dial("tcp", "", "localhost:50001"),
	// then the Dial will succeed, having simultaneously connected to itself.
	// This can only happen when we are letting the kernel pick a port (laddr == nil)
	// and when there is no listener for the destination address.
	// It's hard to argue this is anything other than a kernel bug. If we
	// see this happen, rather than expose the buggy effect to users, we
	// close the fd and try again. If it happens twice more, we relent and
	// use the result. See also:
	//	https://golang.org/issue/2690
	//	http://stackoverflow.com/questions/4949858/
	//
	// The opposite can also happen: if we ask the kernel to pick an appropriate
	// originating local address, sometimes it picks one that is already in use.
	// So if the error is EADDRNOTAVAIL, we have to try again too, just for
	// a different reason.
	//
	// The kernel socket code is no doubt enjoying watching us squirm.
	for i := 0; i < 2 && (laddr == nil || laddr.Port == 0) && (selfConnect(fd, err) || spuriousENOTAVAIL(err)); i++ {
		if err == nil {
			fd.Close()
		}
		fd, err = internetSocket(ctx, net, laddr, raddr, syscall.SOCK_STREAM, 0, "dial")
	}

	if err != nil {
		return nil, err
	}
	return newTCPConn(fd), nil
}

func selfConnect(fd *netFD, err error) bool {
	// If the connect failed, we clearly didn't connect to ourselves.
	if err != nil {
		return false
	}

	// The socket constructor can return an fd with raddr nil under certain
	// unknown conditions. The errors in the calls there to Getpeername
	// are discarded, but we can't catch the problem there because those
	// calls are sometimes legally erroneous with a "socket not connected".
	// Since this code (selfConnect) is already trying to work around
	// a problem, we make sure if this happens we recognize trouble and
	// ask the DialTCP routine to try again.
	// TODO: try to understand what's really going on.
	if fd.laddr == nil || fd.raddr == nil {
		return true
	}
	l := fd.laddr.(*TCPAddr)
	r := fd.raddr.(*TCPAddr)
	return l.Port == r.Port && l.IP.Equal(r.IP)
}

func spuriousENOTAVAIL(err error) bool {
	if op, ok := err.(*OpError); ok {
		err = op.Err
	}
	if sys, ok := err.(*os.SyscallError); ok {
		err = sys.Err
	}
	return err == syscall.EADDRNOTAVAIL
}

func (ln *TCPListener) ok() bool { return ln != nil && ln.fd != nil }

func (ln *TCPListener) accept() (*TCPConn, error) {
	fd, err := ln.fd.accept()
	if err != nil {
		return nil, err
	}
	return newTCPConn(fd), nil
}

func (ln *TCPListener) close() error {
	return ln.fd.Close()
}

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

func listenTCP(ctx context.Context, network string, laddr *TCPAddr) (*TCPListener, error) {
	fd, err := internetSocket(ctx, network, laddr, nil, syscall.SOCK_STREAM, 0, "listen")
	if err != nil {
		return nil, err
	}
	return &TCPListener{fd}, nil
}