add cdn node

internal/simulation/cdnnode.go

@@ -0,0 +1,89 @@
+package simulation
+
+import (
+	"math/rand"
+)
+
+type CDNNode struct {
+	ID              string
+	Label           string
+	TTL             int
+	GeoReplication  string
+	CachingStrategy string
+	Compression     string
+	HTTP2           string
+	CacheHitRate    float64             // % of requests served from edge cache
+	CurrentLoad     int                 // optional: can track active queue length
+	Queue           []*Request          // incoming request queue
+	EdgeNodes       map[string]*CDNNode // future expansion: simulate geographic edge clusters
+	Alive           bool
+	Targets         []string
+	output          []*Request // cache HIT responses
+	missQueue       []*Request // cache MISSes to forward
+}
+
+func (n *CDNNode) GetID() string          { return n.ID }
+func (n *CDNNode) Type() string           { return "cdn" }
+func (n *CDNNode) IsAlive() bool          { return n.Alive }
+func (n *CDNNode) QueueState() []*Request { return n.Queue }
+
+func (n *CDNNode) Tick(tick int) {
+	if len(n.Queue) == 0 {
+		return
+	}
+
+	maxProcessPerTick := 10
+	processCount := min(len(n.Queue), maxProcessPerTick)
+
+	// Avoid slice leak by reusing a cleared slice
+	queue := n.Queue
+	n.Queue = n.Queue[:0]
+
+	for i := 0; i < processCount; i++ {
+		req := queue[i]
+
+		// Simulate cache hit or miss
+		hitRate := n.CacheHitRate
+		if hitRate == 0 {
+			hitRate = 0.8 // default if unset
+		}
+
+		if rand.Float64() < hitRate {
+			// Cache HIT
+			req.LatencyMS += 5
+			req.Path = append(req.Path, n.ID)
+			n.output = append(n.output, req)
+		} else {
+			// Cache MISS
+			req.LatencyMS += 10
+			req.Path = append(req.Path, n.ID+"(miss)")
+			n.missQueue = append(n.missQueue, req)
+		}
+	}
+
+	// Optionally simulate cache expiration every 100 ticks
+	if tick%100 == 0 {
+		// e.g., simulate reduced hit rate or TTL expiration
+	}
+}
+
+func (n *CDNNode) Receive(req *Request) {
+	if req == nil {
+		return
+	}
+
+	geoLatency := rand.Intn(20) + 5 // 5–25ms routing delay
+	req.LatencyMS += geoLatency
+
+	n.Queue = append(n.Queue, req)
+}
+
+func (n *CDNNode) Emit() []*Request {
+	out := append(n.output, n.missQueue...)
+
+	// Clear for next tick
+	n.output = n.output[:0]
+	n.missQueue = n.missQueue[:0]
+
+	return out
+}