55 lines
1.1 KiB
Go
55 lines
1.1 KiB
Go
package discovery
|
|
|
|
import (
|
|
"context"
|
|
"fmt"
|
|
"net"
|
|
"strings"
|
|
"time"
|
|
)
|
|
|
|
const requestMagic = "SPEKTR_DISCOVER"
|
|
const responsePrefix = "SPEKTR|"
|
|
|
|
func Discover(ctx context.Context, port int) (string, error) {
|
|
conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
|
|
if err != nil {
|
|
return "", err
|
|
}
|
|
defer conn.Close()
|
|
|
|
target := &net.UDPAddr{IP: net.IPv4bcast, Port: port}
|
|
if _, err := conn.WriteToUDP([]byte(requestMagic), target); err != nil {
|
|
return "", err
|
|
}
|
|
|
|
if err := conn.SetReadDeadline(time.Now().Add(2 * time.Second)); err != nil {
|
|
return "", err
|
|
}
|
|
|
|
buf := make([]byte, 256)
|
|
for {
|
|
select {
|
|
case <-ctx.Done():
|
|
return "", ctx.Err()
|
|
default:
|
|
}
|
|
|
|
n, _, err := conn.ReadFromUDP(buf)
|
|
if err != nil {
|
|
if ne, ok := err.(net.Error); ok && ne.Timeout() {
|
|
return "", fmt.Errorf("discovery timeout")
|
|
}
|
|
return "", err
|
|
}
|
|
|
|
resp := strings.TrimSpace(string(buf[:n]))
|
|
if strings.HasPrefix(resp, responsePrefix) {
|
|
addr := strings.TrimSpace(strings.TrimPrefix(resp, responsePrefix))
|
|
if addr != "" {
|
|
return addr, nil
|
|
}
|
|
}
|
|
}
|
|
}
|