mac resolution

engine/mac_resolver.go

@@ -0,0 +1,145 @@
+package engine
+
+import (
+	"bufio"
+	"net"
+	"os"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	ifaceCacheTTL = 30 * time.Second
+	arpCacheTTL   = 10 * time.Second
+)
+
+type sourceMACResolver struct {
+	mu sync.RWMutex
+
+	lastIfaceRefresh time.Time
+	ifaceByIP        map[string]net.HardwareAddr
+
+	lastARPRefresh time.Time
+	arpByIP        map[string]net.HardwareAddr
+}
+
+func newSourceMACResolver() *sourceMACResolver {
+	return &sourceMACResolver{
+		ifaceByIP: make(map[string]net.HardwareAddr),
+		arpByIP:   make(map[string]net.HardwareAddr),
+	}
+}
+
+func (r *sourceMACResolver) Resolve(ip net.IP) net.HardwareAddr {
+	if ip == nil {
+		return nil
+	}
+	ipKey := ip.String()
+	if ipKey == "" {
+		return nil
+	}
+
+	now := time.Now()
+	r.mu.RLock()
+	ifaceRefreshDue := now.Sub(r.lastIfaceRefresh) > ifaceCacheTTL
+	arpRefreshDue := now.Sub(r.lastARPRefresh) > arpCacheTTL
+	if mac := r.ifaceByIP[ipKey]; len(mac) != 0 {
+		out := append(net.HardwareAddr(nil), mac...)
+		r.mu.RUnlock()
+		return out
+	}
+	if mac := r.arpByIP[ipKey]; len(mac) != 0 && !arpRefreshDue {
+		out := append(net.HardwareAddr(nil), mac...)
+		r.mu.RUnlock()
+		return out
+	}
+	r.mu.RUnlock()
+
+	if ifaceRefreshDue {
+		r.refreshIfaceCache(now)
+	}
+	if arpRefreshDue {
+		r.refreshARPCache(now)
+	}
+
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	if mac := r.ifaceByIP[ipKey]; len(mac) != 0 {
+		return append(net.HardwareAddr(nil), mac...)
+	}
+	if mac := r.arpByIP[ipKey]; len(mac) != 0 {
+		return append(net.HardwareAddr(nil), mac...)
+	}
+	return nil
+}
+
+func (r *sourceMACResolver) refreshIfaceCache(now time.Time) {
+	interfaces, err := net.Interfaces()
+	if err != nil {
+		return
+	}
+
+	m := make(map[string]net.HardwareAddr)
+	for _, iface := range interfaces {
+		if len(iface.HardwareAddr) == 0 {
+			continue
+		}
+		addrs, err := iface.Addrs()
+		if err != nil {
+			continue
+		}
+		for _, addr := range addrs {
+			ipNet, ok := addr.(*net.IPNet)
+			if !ok || ipNet.IP == nil {
+				continue
+			}
+			m[ipNet.IP.String()] = append(net.HardwareAddr(nil), iface.HardwareAddr...)
+		}
+	}
+
+	r.mu.Lock()
+	r.ifaceByIP = m
+	r.lastIfaceRefresh = now
+	r.mu.Unlock()
+}
+
+func (r *sourceMACResolver) refreshARPCache(now time.Time) {
+	f, err := os.Open("/proc/net/arp")
+	if err != nil {
+		return
+	}
+	defer f.Close()
+
+	m := make(map[string]net.HardwareAddr)
+	scanner := bufio.NewScanner(f)
+	lineNo := 0
+	for scanner.Scan() {
+		lineNo++
+		if lineNo == 1 {
+			continue // header
+		}
+		fields := strings.Fields(scanner.Text())
+		if len(fields) < 4 {
+			continue
+		}
+		ipStr := fields[0]
+		hwAddr := fields[3]
+		if hwAddr == "00:00:00:00:00:00" {
+			continue
+		}
+		mac, err := net.ParseMAC(hwAddr)
+		if err != nil {
+			continue
+		}
+		m[ipStr] = append(net.HardwareAddr(nil), mac...)
+	}
+	if err := scanner.Err(); err != nil {
+		return
+	}
+
+	r.mu.Lock()
+	r.arpByIP = m
+	r.lastARPRefresh = now
+	r.mu.Unlock()
+}