// 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. //go:build unix || js || wasip1 || 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: zoneCache.name(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 := spliceFrom(c.fd, r); handled { return n, err } if n, err, handled := sendFile(c.fd, r); handled { return n, err } return genericReadFrom(c, r) } func (c *TCPConn) writeTo(w io.Writer) (int64, error) { if n, err, handled := spliceTo(w, c.fd); handled { return n, err } return genericWriteTo(c, w) } func (sd *sysDialer) dialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) { if h := sd.testHookDialTCP; h != nil { return h(ctx, sd.network, laddr, raddr) } if h := testHookDialTCP; h != nil { return h(ctx, sd.network, laddr, raddr) } return sd.doDialTCP(ctx, laddr, raddr) } func (sd *sysDialer) doDialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) { return sd.doDialTCPProto(ctx, laddr, raddr, 0) } func (sd *sysDialer) doDialTCPProto(ctx context.Context, laddr, raddr *TCPAddr, proto int) (*TCPConn, error) { ctrlCtxFn := sd.Dialer.ControlContext if ctrlCtxFn == nil && sd.Dialer.Control != nil { ctrlCtxFn = func(cxt context.Context, network, address string, c syscall.RawConn) error { return sd.Dialer.Control(network, address, c) } } fd, err := internetSocket(ctx, sd.network, laddr, raddr, syscall.SOCK_STREAM, proto, "dial", ctrlCtxFn) // 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 // https://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, sd.network, laddr, raddr, syscall.SOCK_STREAM, proto, "dial", ctrlCtxFn) } if err != nil { return nil, err } return newTCPConn(fd, sd.Dialer.KeepAlive, testHookSetKeepAlive), 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, ln.lc.KeepAlive, nil), 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 (sl *sysListener) listenTCP(ctx context.Context, laddr *TCPAddr) (*TCPListener, error) { return sl.listenTCPProto(ctx, laddr, 0) } func (sl *sysListener) listenTCPProto(ctx context.Context, laddr *TCPAddr, proto int) (*TCPListener, error) { var ctrlCtxFn func(cxt context.Context, network, address string, c syscall.RawConn) error if sl.ListenConfig.Control != nil { ctrlCtxFn = func(cxt context.Context, network, address string, c syscall.RawConn) error { return sl.ListenConfig.Control(network, address, c) } } fd, err := internetSocket(ctx, sl.network, laddr, nil, syscall.SOCK_STREAM, proto, "listen", ctrlCtxFn) if err != nil { return nil, err } return &TCPListener{fd: fd, lc: sl.ListenConfig}, nil }