/
udpping1.go
103 lines (84 loc) · 2.31 KB
/
udpping1.go
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//
// UDP ping command
// Model 1, does UDP work inline
//
// this doesn't use ZeroMQ at all
package main
import (
"fmt"
"log"
"syscall"
"time"
)
const (
PING_PORT_NUMBER = 9999
PING_MSG_SIZE = 1
PING_INTERVAL = 1000 * time.Millisecond // Once per second
)
func main() {
log.SetFlags(log.Lshortfile)
// Create UDP socket
fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, syscall.IPPROTO_UDP)
if err != nil {
log.Fatalln(err)
}
// Ask operating system to let us do broadcasts from socket
if err := syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1); err != nil {
log.Fatalln(err)
}
// Bind UDP socket to local port so we can receive pings
if err := syscall.Bind(fd, &syscall.SockaddrInet4{Port: PING_PORT_NUMBER, Addr: [4]byte{0, 0, 0, 0}}); err != nil {
log.Fatalln(err)
}
buffer := make([]byte, PING_MSG_SIZE)
// We use syscall.Select to wait for activity on the UDP socket.
// We send a beacon once a second, and we collect and report
// beacons that come in from other nodes:
rfds := &syscall.FdSet{}
timeout := &syscall.Timeval{}
// Send first ping right away
ping_at := time.Now()
bcast := &syscall.SockaddrInet4{Port: PING_PORT_NUMBER, Addr: [4]byte{255, 255, 255, 255}}
for {
dur := int64(ping_at.Sub(time.Now()) / time.Microsecond)
if dur < 0 {
dur = 0
}
timeout.Sec, timeout.Usec = dur/1000000, dur%1000000
FD_ZERO(rfds)
FD_SET(rfds, fd)
_, err := syscall.Select(fd+1, rfds, nil, nil, timeout)
if err != nil {
log.Fatalln(err)
}
// Someone answered our ping
if FD_ISSET(rfds, fd) {
_, addr, err := syscall.Recvfrom(fd, buffer, 0)
if err != nil {
log.Fatalln(err)
}
a := addr.(*syscall.SockaddrInet4)
fmt.Printf("Found peer %v.%v.%v.%v:%v\n", a.Addr[0], a.Addr[1], a.Addr[2], a.Addr[3], a.Port)
}
if time.Now().After(ping_at) {
// Broadcast our beacon
fmt.Println("Pinging peers...")
buffer[0] = '!'
if err := syscall.Sendto(fd, buffer, 0, bcast); err != nil {
log.Fatalln(err)
}
ping_at = time.Now().Add(PING_INTERVAL)
}
}
}
func FD_SET(p *syscall.FdSet, i int) {
p.Bits[i/64] |= 1 << uint(i) % 64
}
func FD_ISSET(p *syscall.FdSet, i int) bool {
return (p.Bits[i/64] & (1 << uint(i) % 64)) != 0
}
func FD_ZERO(p *syscall.FdSet) {
for i := range p.Bits {
p.Bits[i] = 0
}
}