/usr/share/gocode/src/github.com/docker/libnetwork/cmd/proxy/udp_proxy.go is in golang-github-docker-libnetwork-dev 0.8.0-dev.2+git20170202.599.45b4086-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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import (
"encoding/binary"
"log"
"net"
"strings"
"sync"
"syscall"
"time"
)
const (
// UDPConnTrackTimeout is the timeout used for UDP connection tracking
UDPConnTrackTimeout = 90 * time.Second
// UDPBufSize is the buffer size for the UDP proxy
UDPBufSize = 65507
)
// A net.Addr where the IP is split into two fields so you can use it as a key
// in a map:
type connTrackKey struct {
IPHigh uint64
IPLow uint64
Port int
}
func newConnTrackKey(addr *net.UDPAddr) *connTrackKey {
if len(addr.IP) == net.IPv4len {
return &connTrackKey{
IPHigh: 0,
IPLow: uint64(binary.BigEndian.Uint32(addr.IP)),
Port: addr.Port,
}
}
return &connTrackKey{
IPHigh: binary.BigEndian.Uint64(addr.IP[:8]),
IPLow: binary.BigEndian.Uint64(addr.IP[8:]),
Port: addr.Port,
}
}
type connTrackMap map[connTrackKey]*net.UDPConn
// UDPProxy is proxy for which handles UDP datagrams. It implements the Proxy
// interface to handle UDP traffic forwarding between the frontend and backend
// addresses.
type UDPProxy struct {
listener *net.UDPConn
frontendAddr *net.UDPAddr
backendAddr *net.UDPAddr
connTrackTable connTrackMap
connTrackLock sync.Mutex
}
// NewUDPProxy creates a new UDPProxy.
func NewUDPProxy(frontendAddr, backendAddr *net.UDPAddr) (*UDPProxy, error) {
listener, err := net.ListenUDP("udp", frontendAddr)
if err != nil {
return nil, err
}
return &UDPProxy{
listener: listener,
frontendAddr: listener.LocalAddr().(*net.UDPAddr),
backendAddr: backendAddr,
connTrackTable: make(connTrackMap),
}, nil
}
func (proxy *UDPProxy) replyLoop(proxyConn *net.UDPConn, clientAddr *net.UDPAddr, clientKey *connTrackKey) {
defer func() {
proxy.connTrackLock.Lock()
delete(proxy.connTrackTable, *clientKey)
proxy.connTrackLock.Unlock()
proxyConn.Close()
}()
readBuf := make([]byte, UDPBufSize)
for {
proxyConn.SetReadDeadline(time.Now().Add(UDPConnTrackTimeout))
again:
read, err := proxyConn.Read(readBuf)
if err != nil {
if err, ok := err.(*net.OpError); ok && err.Err == syscall.ECONNREFUSED {
// This will happen if the last write failed
// (e.g: nothing is actually listening on the
// proxied port on the container), ignore it
// and continue until UDPConnTrackTimeout
// expires:
goto again
}
return
}
for i := 0; i != read; {
written, err := proxy.listener.WriteToUDP(readBuf[i:read], clientAddr)
if err != nil {
return
}
i += written
}
}
}
// Run starts forwarding the traffic using UDP.
func (proxy *UDPProxy) Run() {
readBuf := make([]byte, UDPBufSize)
for {
read, from, err := proxy.listener.ReadFromUDP(readBuf)
if err != nil {
// NOTE: Apparently ReadFrom doesn't return
// ECONNREFUSED like Read do (see comment in
// UDPProxy.replyLoop)
if !isClosedError(err) {
log.Printf("Stopping proxy on udp/%v for udp/%v (%s)", proxy.frontendAddr, proxy.backendAddr, err)
}
break
}
fromKey := newConnTrackKey(from)
proxy.connTrackLock.Lock()
proxyConn, hit := proxy.connTrackTable[*fromKey]
if !hit {
proxyConn, err = net.DialUDP("udp", nil, proxy.backendAddr)
if err != nil {
log.Printf("Can't proxy a datagram to udp/%s: %s\n", proxy.backendAddr, err)
proxy.connTrackLock.Unlock()
continue
}
proxy.connTrackTable[*fromKey] = proxyConn
go proxy.replyLoop(proxyConn, from, fromKey)
}
proxy.connTrackLock.Unlock()
for i := 0; i != read; {
written, err := proxyConn.Write(readBuf[i:read])
if err != nil {
log.Printf("Can't proxy a datagram to udp/%s: %s\n", proxy.backendAddr, err)
break
}
i += written
}
}
}
// Close stops forwarding the traffic.
func (proxy *UDPProxy) Close() {
proxy.listener.Close()
proxy.connTrackLock.Lock()
defer proxy.connTrackLock.Unlock()
for _, conn := range proxy.connTrackTable {
conn.Close()
}
}
// FrontendAddr returns the UDP address on which the proxy is listening.
func (proxy *UDPProxy) FrontendAddr() net.Addr { return proxy.frontendAddr }
// BackendAddr returns the proxied UDP address.
func (proxy *UDPProxy) BackendAddr() net.Addr { return proxy.backendAddr }
func isClosedError(err error) bool {
/* This comparison is ugly, but unfortunately, net.go doesn't export errClosing.
* See:
* http://golang.org/src/pkg/net/net.go
* https://code.google.com/p/go/issues/detail?id=4337
* https://groups.google.com/forum/#!msg/golang-nuts/0_aaCvBmOcM/SptmDyX1XJMJ
*/
return strings.HasSuffix(err.Error(), "use of closed network connection")
}
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