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Source file src/net/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	// +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: zoneToString(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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