Rework some things into packages (#489)

firewall/cache.go

@@ -0,0 +1,59 @@
+package firewall
+
+import (
+	"sync/atomic"
+	"time"
+
+	"github.com/sirupsen/logrus"
+)
+
+// ConntrackCache is used as a local routine cache to know if a given flow
+// has been seen in the conntrack table.
+type ConntrackCache map[Packet]struct{}
+
+type ConntrackCacheTicker struct {
+	cacheV    uint64
+	cacheTick uint64
+
+	cache ConntrackCache
+}
+
+func NewConntrackCacheTicker(d time.Duration) *ConntrackCacheTicker {
+	if d == 0 {
+		return nil
+	}
+
+	c := &ConntrackCacheTicker{
+		cache: ConntrackCache{},
+	}
+
+	go c.tick(d)
+
+	return c
+}
+
+func (c *ConntrackCacheTicker) tick(d time.Duration) {
+	for {
+		time.Sleep(d)
+		atomic.AddUint64(&c.cacheTick, 1)
+	}
+}
+
+// Get checks if the cache ticker has moved to the next version before returning
+// the map. If it has moved, we reset the map.
+func (c *ConntrackCacheTicker) Get(l *logrus.Logger) ConntrackCache {
+	if c == nil {
+		return nil
+	}
+	if tick := atomic.LoadUint64(&c.cacheTick); tick != c.cacheV {
+		c.cacheV = tick
+		if ll := len(c.cache); ll > 0 {
+			if l.Level == logrus.DebugLevel {
+				l.WithField("len", ll).Debug("resetting conntrack cache")
+			}
+			c.cache = make(ConntrackCache, ll)
+		}
+	}
+
+	return c.cache
+}