Add DNSBL querying in conditions

utils/decaymap.go

@@ -0,0 +1,73 @@
+package utils
+
+import (
+	"sync"
+	"time"
+)
+
+func zilch[T any]() T {
+	var zero T
+	return zero
+}
+
+type DecayMap[K, V comparable] struct {
+	data map[K]DecayMapEntry[V]
+	lock sync.RWMutex
+}
+
+type DecayMapEntry[V comparable] struct {
+	Value  V
+	expiry time.Time
+}
+
+func NewDecayMap[K, V comparable]() *DecayMap[K, V] {
+	return &DecayMap[K, V]{
+		data: make(map[K]DecayMapEntry[V]),
+	}
+}
+
+func (m *DecayMap[K, V]) Get(key K) (V, bool) {
+	m.lock.RLock()
+	value, ok := m.data[key]
+	m.lock.RUnlock()
+
+	if !ok {
+		return zilch[V](), false
+	}
+
+	if time.Now().After(value.expiry) {
+		m.lock.Lock()
+		// Since previously reading m.data[key], the value may have been updated.
+		// Delete the entry only if the expiry time is still the same.
+		if m.data[key].expiry == value.expiry {
+			delete(m.data, key)
+		}
+		m.lock.Unlock()
+
+		return zilch[V](), false
+	}
+
+	return value.Value, true
+}
+
+func (m *DecayMap[K, V]) Set(key K, value V, ttl time.Duration) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+
+	m.data[key] = DecayMapEntry[V]{
+		Value:  value,
+		expiry: time.Now().Add(ttl),
+	}
+}
+
+func (m *DecayMap[K, V]) Decay() {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+
+	now := time.Now()
+	for key, entry := range m.data {
+		if now.After(entry.expiry) {
+			delete(m.data, key)
+		}
+	}
+}