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

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