tcpsock_posix.go

Documentation: net

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
     6  
     7  package net
     8  
     9  import (
    10  	"context"
    11  	"io"
    12  	"os"
    13  	"syscall"
    14  )
    15  
    16  func sockaddrToTCP(sa syscall.Sockaddr) Addr {
    17  	switch sa := sa.(type) {
    18  	case *syscall.SockaddrInet4:
    19  		return &TCPAddr{IP: sa.Addr[0:], Port: sa.Port}
    20  	case *syscall.SockaddrInet6:
    21  		return &TCPAddr{IP: sa.Addr[0:], Port: sa.Port, Zone: zoneCache.name(int(sa.ZoneId))}
    22  	}
    23  	return nil
    24  }
    25  
    26  func (a *TCPAddr) family() int {
    27  	if a == nil || len(a.IP) <= IPv4len {
    28  		return syscall.AF_INET
    29  	}
    30  	if a.IP.To4() != nil {
    31  		return syscall.AF_INET
    32  	}
    33  	return syscall.AF_INET6
    34  }
    35  
    36  func (a *TCPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
    37  	if a == nil {
    38  		return nil, nil
    39  	}
    40  	return ipToSockaddr(family, a.IP, a.Port, a.Zone)
    41  }
    42  
    43  func (a *TCPAddr) toLocal(net string) sockaddr {
    44  	return &TCPAddr{loopbackIP(net), a.Port, a.Zone}
    45  }
    46  
    47  func (c *TCPConn) readFrom(r io.Reader) (int64, error) {
    48  	if n, err, handled := sendFile(c.fd, r); handled {
    49  		return n, err
    50  	}
    51  	return genericReadFrom(c, r)
    52  }
    53  
    54  func dialTCP(ctx context.Context, net string, laddr, raddr *TCPAddr) (*TCPConn, error) {
    55  	if testHookDialTCP != nil {
    56  		return testHookDialTCP(ctx, net, laddr, raddr)
    57  	}
    58  	return doDialTCP(ctx, net, laddr, raddr)
    59  }
    60  
    61  func doDialTCP(ctx context.Context, net string, laddr, raddr *TCPAddr) (*TCPConn, error) {
    62  	fd, err := internetSocket(ctx, net, laddr, raddr, syscall.SOCK_STREAM, 0, "dial")
    63  
    64  	// TCP has a rarely used mechanism called a 'simultaneous connection' in
    65  	// which Dial("tcp", addr1, addr2) run on the machine at addr1 can
    66  	// connect to a simultaneous Dial("tcp", addr2, addr1) run on the machine
    67  	// at addr2, without either machine executing Listen. If laddr == nil,
    68  	// it means we want the kernel to pick an appropriate originating local
    69  	// address. Some Linux kernels cycle blindly through a fixed range of
    70  	// local ports, regardless of destination port. If a kernel happens to
    71  	// pick local port 50001 as the source for a Dial("tcp", "", "localhost:50001"),
    72  	// then the Dial will succeed, having simultaneously connected to itself.
    73  	// This can only happen when we are letting the kernel pick a port (laddr == nil)
    74  	// and when there is no listener for the destination address.
    75  	// It's hard to argue this is anything other than a kernel bug. If we
    76  	// see this happen, rather than expose the buggy effect to users, we
    77  	// close the fd and try again. If it happens twice more, we relent and
    78  	// use the result. See also:
    79  	//	https://golang.org/issue/2690
    80  	//	http://stackoverflow.com/questions/4949858/
    81  	//
    82  	// The opposite can also happen: if we ask the kernel to pick an appropriate
    83  	// originating local address, sometimes it picks one that is already in use.
    84  	// So if the error is EADDRNOTAVAIL, we have to try again too, just for
    85  	// a different reason.
    86  	//
    87  	// The kernel socket code is no doubt enjoying watching us squirm.
    88  	for i := 0; i < 2 && (laddr == nil || laddr.Port == 0) && (selfConnect(fd, err) || spuriousENOTAVAIL(err)); i++ {
    89  		if err == nil {
    90  			fd.Close()
    91  		}
    92  		fd, err = internetSocket(ctx, net, laddr, raddr, syscall.SOCK_STREAM, 0, "dial")
    93  	}
    94  
    95  	if err != nil {
    96  		return nil, err
    97  	}
    98  	return newTCPConn(fd), nil
    99  }
   100  
   101  func selfConnect(fd *netFD, err error) bool {
   102  	// If the connect failed, we clearly didn't connect to ourselves.
   103  	if err != nil {
   104  		return false
   105  	}
   106  
   107  	// The socket constructor can return an fd with raddr nil under certain
   108  	// unknown conditions. The errors in the calls there to Getpeername
   109  	// are discarded, but we can't catch the problem there because those
   110  	// calls are sometimes legally erroneous with a "socket not connected".
   111  	// Since this code (selfConnect) is already trying to work around
   112  	// a problem, we make sure if this happens we recognize trouble and
   113  	// ask the DialTCP routine to try again.
   114  	// TODO: try to understand what's really going on.
   115  	if fd.laddr == nil || fd.raddr == nil {
   116  		return true
   117  	}
   118  	l := fd.laddr.(*TCPAddr)
   119  	r := fd.raddr.(*TCPAddr)
   120  	return l.Port == r.Port && l.IP.Equal(r.IP)
   121  }
   122  
   123  func spuriousENOTAVAIL(err error) bool {
   124  	if op, ok := err.(*OpError); ok {
   125  		err = op.Err
   126  	}
   127  	if sys, ok := err.(*os.SyscallError); ok {
   128  		err = sys.Err
   129  	}
   130  	return err == syscall.EADDRNOTAVAIL
   131  }
   132  
   133  func (ln *TCPListener) ok() bool { return ln != nil && ln.fd != nil }
   134  
   135  func (ln *TCPListener) accept() (*TCPConn, error) {
   136  	fd, err := ln.fd.accept()
   137  	if err != nil {
   138  		return nil, err
   139  	}
   140  	return newTCPConn(fd), nil
   141  }
   142  
   143  func (ln *TCPListener) close() error {
   144  	return ln.fd.Close()
   145  }
   146  
   147  func (ln *TCPListener) file() (*os.File, error) {
   148  	f, err := ln.fd.dup()
   149  	if err != nil {
   150  		return nil, err
   151  	}
   152  	return f, nil
   153  }
   154  
   155  func listenTCP(ctx context.Context, network string, laddr *TCPAddr) (*TCPListener, error) {
   156  	fd, err := internetSocket(ctx, network, laddr, nil, syscall.SOCK_STREAM, 0, "listen")
   157  	if err != nil {
   158  		return nil, err
   159  	}
   160  	return &TCPListener{fd}, nil
   161  }
   162
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