Initial commit

core/lan.go

@@ -0,0 +1,94 @@
+package core
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+
+	"log/slog"
+)
+
+type LanEntry struct {
+	Motd string
+	Port int
+}
+
+func LanDiscoverService(ctx context.Context, entryList []LanEntry, logger *slog.Logger) {
+	mcastAddrs := []string{
+		"224.0.2.60:4445",
+		"[ff75:230::60]:4445",
+	}
+
+	var fdList []*net.UDPConn
+	for _, addrStr := range mcastAddrs {
+		addr, err := net.ResolveUDPAddr("udp", addrStr)
+		if err != nil {
+			logger.With(slog.String("error", err.Error())).Error("failed to resolve udp address")
+			continue
+		}
+		fd, err := net.DialUDP("udp", nil, addr)
+		if err != nil {
+			logger.With(slog.String("error", err.Error())).Error("failed to dial udp server")
+			continue
+		}
+		fdList = append(fdList, fd)
+	}
+
+	if len(fdList) == 0 {
+		// init fail
+		logger.Warn("all multicast binding failed, service discovery is disabled")
+		return
+	}
+
+	for _, entry := range entryList {
+		// debug log to print entry detail
+		logger.With(
+			slog.Int("port", entry.Port),
+			slog.String("motd", entry.Motd),
+		).Debug("discover service: %s on %d", entry.Motd, entry.Port)
+	}
+
+	ticker := time.NewTicker(1500 * time.Millisecond)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			logger.Debug("shutting down lan discovery service")
+			for _, fd := range fdList {
+				fd.Close()
+			}
+			return
+		case <-ticker.C:
+			for _, e := range entryList {
+				msg := fmt.Sprintf("[MOTD]%s[/MOTD][AD]%d[/AD]", e.Motd, e.Port)
+				for _, c := range fdList {
+					_, err := c.Write([]byte(msg))
+					if err != nil {
+						logger.With(slog.String("error", err.Error())).Error("failed to write to udp server")
+						return
+					}
+				}
+			}
+		}
+	}
+}
+
+func RunLanDiscoverService(ctx context.Context, rules map[string][]ConnectRule, logger *slog.Logger) {
+	var lanEntries []LanEntry
+	for tag, rs := range rules {
+		for _, rule := range rs {
+			if !rule.LANEnabled() {
+				continue
+			}
+			motd := rule.LANMotdOr(tag)
+			lanEntries = append(lanEntries, LanEntry{
+				Motd: motd,
+				Port: rule.LocalPort,
+			})
+		}
+	}
+
+	go LanDiscoverService(ctx, lanEntries, logger)
+}