tcpsock_posix.go

     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  //go:build unix || (js && wasm) || wasip1 || 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 := splice(c.fd, r); handled {
    49  		return n, err
    50  	}
    51  	if n, err, handled := sendFile(c.fd, r); handled {
    52  		return n, err
    53  	}
    54  	return genericReadFrom(c, r)
    55  }
    56  
    57  func (sd *sysDialer) dialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
    58  	if h := sd.testHookDialTCP; h != nil {
    59  		return h(ctx, sd.network, laddr, raddr)
    60  	}
    61  	if h := testHookDialTCP; h != nil {
    62  		return h(ctx, sd.network, laddr, raddr)
    63  	}
    64  	return sd.doDialTCP(ctx, laddr, raddr)
    65  }
    66  
    67  func (sd *sysDialer) doDialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
    68  	return sd.doDialTCPProto(ctx, laddr, raddr, 0)
    69  }
    70  
    71  func (sd *sysDialer) doDialTCPProto(ctx context.Context, laddr, raddr *TCPAddr, proto int) (*TCPConn, error) {
    72  	ctrlCtxFn := sd.Dialer.ControlContext
    73  	if ctrlCtxFn == nil && sd.Dialer.Control != nil {
    74  		ctrlCtxFn = func(cxt context.Context, network, address string, c syscall.RawConn) error {
    75  			return sd.Dialer.Control(network, address, c)
    76  		}
    77  	}
    78  	fd, err := internetSocket(ctx, sd.network, laddr, raddr, syscall.SOCK_STREAM, proto, "dial", ctrlCtxFn)
    79  
    80  	// TCP has a rarely used mechanism called a 'simultaneous connection' in
    81  	// which Dial("tcp", addr1, addr2) run on the machine at addr1 can
    82  	// connect to a simultaneous Dial("tcp", addr2, addr1) run on the machine
    83  	// at addr2, without either machine executing Listen. If laddr == nil,
    84  	// it means we want the kernel to pick an appropriate originating local
    85  	// address. Some Linux kernels cycle blindly through a fixed range of
    86  	// local ports, regardless of destination port. If a kernel happens to
    87  	// pick local port 50001 as the source for a Dial("tcp", "", "localhost:50001"),
    88  	// then the Dial will succeed, having simultaneously connected to itself.
    89  	// This can only happen when we are letting the kernel pick a port (laddr == nil)
    90  	// and when there is no listener for the destination address.
    91  	// It's hard to argue this is anything other than a kernel bug. If we
    92  	// see this happen, rather than expose the buggy effect to users, we
    93  	// close the fd and try again. If it happens twice more, we relent and
    94  	// use the result. See also:
    95  	//	https://golang.org/issue/2690
    96  	//	https://stackoverflow.com/questions/4949858/
    97  	//
    98  	// The opposite can also happen: if we ask the kernel to pick an appropriate
    99  	// originating local address, sometimes it picks one that is already in use.
   100  	// So if the error is EADDRNOTAVAIL, we have to try again too, just for
   101  	// a different reason.
   102  	//
   103  	// The kernel socket code is no doubt enjoying watching us squirm.
   104  	for i := 0; i < 2 && (laddr == nil || laddr.Port == 0) && (selfConnect(fd, err) || spuriousENOTAVAIL(err)); i++ {
   105  		if err == nil {
   106  			fd.Close()
   107  		}
   108  		fd, err = internetSocket(ctx, sd.network, laddr, raddr, syscall.SOCK_STREAM, proto, "dial", ctrlCtxFn)
   109  	}
   110  
   111  	if err != nil {
   112  		return nil, err
   113  	}
   114  	return newTCPConn(fd, sd.Dialer.KeepAlive, testHookSetKeepAlive), nil
   115  }
   116  
   117  func selfConnect(fd *netFD, err error) bool {
   118  	// If the connect failed, we clearly didn't connect to ourselves.
   119  	if err != nil {
   120  		return false
   121  	}
   122  
   123  	// The socket constructor can return an fd with raddr nil under certain
   124  	// unknown conditions. The errors in the calls there to Getpeername
   125  	// are discarded, but we can't catch the problem there because those
   126  	// calls are sometimes legally erroneous with a "socket not connected".
   127  	// Since this code (selfConnect) is already trying to work around
   128  	// a problem, we make sure if this happens we recognize trouble and
   129  	// ask the DialTCP routine to try again.
   130  	// TODO: try to understand what's really going on.
   131  	if fd.laddr == nil || fd.raddr == nil {
   132  		return true
   133  	}
   134  	l := fd.laddr.(*TCPAddr)
   135  	r := fd.raddr.(*TCPAddr)
   136  	return l.Port == r.Port && l.IP.Equal(r.IP)
   137  }
   138  
   139  func spuriousENOTAVAIL(err error) bool {
   140  	if op, ok := err.(*OpError); ok {
   141  		err = op.Err
   142  	}
   143  	if sys, ok := err.(*os.SyscallError); ok {
   144  		err = sys.Err
   145  	}
   146  	return err == syscall.EADDRNOTAVAIL
   147  }
   148  
   149  func (ln *TCPListener) ok() bool { return ln != nil && ln.fd != nil }
   150  
   151  func (ln *TCPListener) accept() (*TCPConn, error) {
   152  	fd, err := ln.fd.accept()
   153  	if err != nil {
   154  		return nil, err
   155  	}
   156  	return newTCPConn(fd, ln.lc.KeepAlive, nil), nil
   157  }
   158  
   159  func (ln *TCPListener) close() error {
   160  	return ln.fd.Close()
   161  }
   162  
   163  func (ln *TCPListener) file() (*os.File, error) {
   164  	f, err := ln.fd.dup()
   165  	if err != nil {
   166  		return nil, err
   167  	}
   168  	return f, nil
   169  }
   170  
   171  func (sl *sysListener) listenTCP(ctx context.Context, laddr *TCPAddr) (*TCPListener, error) {
   172  	return sl.listenTCPProto(ctx, laddr, 0)
   173  }
   174  
   175  func (sl *sysListener) listenTCPProto(ctx context.Context, laddr *TCPAddr, proto int) (*TCPListener, error) {
   176  	var ctrlCtxFn func(cxt context.Context, network, address string, c syscall.RawConn) error
   177  	if sl.ListenConfig.Control != nil {
   178  		ctrlCtxFn = func(cxt context.Context, network, address string, c syscall.RawConn) error {
   179  			return sl.ListenConfig.Control(network, address, c)
   180  		}
   181  	}
   182  	fd, err := internetSocket(ctx, sl.network, laddr, nil, syscall.SOCK_STREAM, proto, "listen", ctrlCtxFn)
   183  	if err != nil {
   184  		return nil, err
   185  	}
   186  	return &TCPListener{fd: fd, lc: sl.ListenConfig}, nil
   187  }
   188
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