Source file 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: zoneToString(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
  }
  

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