Improve caching, move mutex to the cache implementation

adapters/inmemorycache/cache.go

@@ -1,11 +1,42 @@
 package inmemorycache
 
-type Cache map[uint64][]string
+import (
+	"sync"
+)
 
-func (c Cache) Get(id uint64) []string {
-	return c[id]
+func NewCache() *Cache {
+	return &Cache{cache: map[uint64][]string{}}
 }
 
-func (c Cache) Append(id uint64, ip string) {
-	c[id] = append(c[id], ip)
+type Cache struct {
+	cache map[uint64][]string
+	mu    sync.RWMutex
+}
+
+func (c *Cache) Get(id uint64) []string {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+
+	return c.cache[id]
+}
+
+func (c *Cache) Append(id uint64, ip string) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if ips := c.cache[id]; len(ips) == 0 {
+		c.cache[id] = append(c.cache[id], ip)
+
+		return
+	}
+
+	for _, s := range c.cache[id] {
+		if s == ip {
+			return
+		}
+	}
+
+	c.cache[id] = append(c.cache[id], ip)
+
+	return
 }