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1 // Copyright 2009 The Go Authors. All rights reserved. | 1 // Copyright 2009 The Go Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style | 2 // Use of this source code is governed by a BSD-style |
3 // license that can be found in the LICENSE file. | 3 // license that can be found in the LICENSE file. |
4 | 4 |
5 // +build darwin freebsd linux netbsd openbsd windows | 5 // +build darwin freebsd linux netbsd openbsd windows |
6 | 6 |
7 // TCP sockets | 7 // TCP sockets |
8 | 8 |
9 package net | 9 package net |
10 | 10 |
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220 // Closing c does not affect f, and closing f does not affect c. | 220 // Closing c does not affect f, and closing f does not affect c. |
221 func (c *TCPConn) File() (f *os.File, err error) { return c.fd.dup() } | 221 func (c *TCPConn) File() (f *os.File, err error) { return c.fd.dup() } |
222 | 222 |
223 // DialTCP connects to the remote address raddr on the network net, | 223 // DialTCP connects to the remote address raddr on the network net, |
224 // which must be "tcp", "tcp4", or "tcp6". If laddr is not nil, it is used | 224 // which must be "tcp", "tcp4", or "tcp6". If laddr is not nil, it is used |
225 // as the local address for the connection. | 225 // as the local address for the connection. |
226 func DialTCP(net string, laddr, raddr *TCPAddr) (*TCPConn, error) { | 226 func DialTCP(net string, laddr, raddr *TCPAddr) (*TCPConn, error) { |
227 if raddr == nil { | 227 if raddr == nil { |
228 return nil, &OpError{"dial", net, nil, errMissingAddress} | 228 return nil, &OpError{"dial", net, nil, errMissingAddress} |
229 } | 229 } |
| 230 |
230 fd, err := internetSocket(net, laddr.toAddr(), raddr.toAddr(), syscall.S
OCK_STREAM, 0, "dial", sockaddrToTCP) | 231 fd, err := internetSocket(net, laddr.toAddr(), raddr.toAddr(), syscall.S
OCK_STREAM, 0, "dial", sockaddrToTCP) |
| 232 |
| 233 // TCP has a rarely used mechanism called a 'simultaneous connection' in |
| 234 // which Dial("tcp", addr1, addr2) run on the machine at addr1 can |
| 235 // connect to a simultaneous Dial("tcp", addr2, addr1) run on the machin
e |
| 236 // at addr2, without either machine executing Listen. If laddr == nil, |
| 237 // it means we want the kernel to pick an appropriate originating local |
| 238 // address. Some Linux kernels cycle blindly through a fixed range of |
| 239 // local ports, regardless of destination port. If a kernel happens to |
| 240 // pick local port 50001 as the source for a Dial("tcp", "", "localhost:
50001"), |
| 241 // then the Dial will succeed, having simultaneously connected to itself
. |
| 242 // This can only happen when we are letting the kernel pick a port (ladd
r == nil) |
| 243 // and when there is no listener for the destination address. |
| 244 // It's hard to argue this is anything other than a kernel bug. If we |
| 245 // see this happen, rather than expose the buggy effect to users, we |
| 246 // close the fd and try again. If it happens twice more, we relent and |
| 247 // use the result. See also: |
| 248 // http://golang.org/issue/2690 |
| 249 // http://stackoverflow.com/questions/4949858/ |
| 250 for i := 0; i < 2 && err == nil && laddr == nil && selfConnect(fd); i++
{ |
| 251 fd.Close() |
| 252 fd, err = internetSocket(net, laddr.toAddr(), raddr.toAddr(), sy
scall.SOCK_STREAM, 0, "dial", sockaddrToTCP) |
| 253 } |
| 254 |
231 if err != nil { | 255 if err != nil { |
232 return nil, err | 256 return nil, err |
233 } | 257 } |
234 return newTCPConn(fd), nil | 258 return newTCPConn(fd), nil |
| 259 } |
| 260 |
| 261 func selfConnect(fd *netFD) bool { |
| 262 l := fd.laddr.(*TCPAddr) |
| 263 r := fd.raddr.(*TCPAddr) |
| 264 return l.Port == r.Port && l.IP.Equal(r.IP) |
235 } | 265 } |
236 | 266 |
237 // TCPListener is a TCP network listener. | 267 // TCPListener is a TCP network listener. |
238 // Clients should typically use variables of type Listener | 268 // Clients should typically use variables of type Listener |
239 // instead of assuming TCP. | 269 // instead of assuming TCP. |
240 type TCPListener struct { | 270 type TCPListener struct { |
241 fd *netFD | 271 fd *netFD |
242 } | 272 } |
243 | 273 |
244 // ListenTCP announces on the TCP address laddr and returns a TCP listener. | 274 // ListenTCP announces on the TCP address laddr and returns a TCP listener. |
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301 if l == nil || l.fd == nil { | 331 if l == nil || l.fd == nil { |
302 return os.EINVAL | 332 return os.EINVAL |
303 } | 333 } |
304 return setDeadline(l.fd, t) | 334 return setDeadline(l.fd, t) |
305 } | 335 } |
306 | 336 |
307 // File returns a copy of the underlying os.File, set to blocking mode. | 337 // File returns a copy of the underlying os.File, set to blocking mode. |
308 // It is the caller's responsibility to close f when finished. | 338 // It is the caller's responsibility to close f when finished. |
309 // Closing c does not affect f, and closing f does not affect c. | 339 // Closing c does not affect f, and closing f does not affect c. |
310 func (l *TCPListener) File() (f *os.File, err error) { return l.fd.dup() } | 340 func (l *TCPListener) File() (f *os.File, err error) { return l.fd.dup() } |
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