feat: implement real ping RTT calculation instead of hardcoded 50ms

internal/client/packet.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"encoding/binary"
 	"log"
+	"math"
+	"time"
 
 	"go-ts/pkg/protocol"
 )
@@ -114,8 +116,59 @@ func (c *Client) handlePacket(pkt *protocol.Packet) error {
 
 		c.Conn.SendPacket(pong)
 	case protocol.PacketTypePong:
-		// Server acknowledged our Ping
-		log.Printf("Received Pong for sequence %d", pkt.Header.PacketID)
+		// Server acknowledged our Ping - calculate RTT
+		receivedAt := time.Now()
+
+		// Decrypt Pong body if needed to get the PingID it's acknowledging
+		var pongData []byte
+		if pkt.Header.FlagUnencrypted() {
+			pongData = pkt.Data
+		} else if c.Handshake != nil && c.Handshake.Step >= 6 && len(c.Handshake.SharedIV) > 0 {
+			crypto := &protocol.CryptoState{
+				SharedIV:     c.Handshake.SharedIV,
+				SharedMac:    c.Handshake.SharedMac,
+				GenerationID: 0,
+			}
+			key, nonce := crypto.GenerateKeyNonce(&pkt.Header, false) // Server->Client
+			meta := make([]byte, 3)
+			binary.BigEndian.PutUint16(meta[0:2], pkt.Header.PacketID)
+			meta[2] = pkt.Header.Type
+			decrypted, err := protocol.DecryptEAX(key, nonce, meta, pkt.Data, pkt.Header.MAC[:])
+			if err == nil {
+				pongData = decrypted
+			}
+		}
+
+		// Extract PingID from Pong body
+		var pingID uint16
+		if len(pongData) >= 2 {
+			pingID = binary.BigEndian.Uint16(pongData[0:2])
+		} else {
+			pingID = pkt.Header.PacketID // fallback
+		}
+
+		// Calculate RTT if we have the send time
+		if sentTime, ok := c.PingSentTimes[pingID]; ok {
+			rtt := receivedAt.Sub(sentTime).Seconds() * 1000 // RTT in ms
+			delete(c.PingSentTimes, pingID)
+
+			// Update rolling average using Welford's algorithm
+			c.PingSampleCount++
+			if c.PingSampleCount == 1 {
+				c.PingRTT = rtt
+				c.PingDeviation = 0
+			} else {
+				oldMean := c.PingRTT
+				c.PingRTT = oldMean + (rtt-oldMean)/float64(c.PingSampleCount)
+				// Rolling deviation: exponential smoothing
+				c.PingDeviation = c.PingDeviation*0.9 + math.Abs(rtt-c.PingRTT)*0.1
+			}
+
+			log.Printf("Received Pong for Ping %d: RTT=%.2fms, AvgRTT=%.2fms, Dev=%.2fms",
+				pingID, rtt, c.PingRTT, c.PingDeviation)
+		} else {
+			log.Printf("Received Pong for unknown Ping %d", pingID)
+		}
 	case protocol.PacketTypeAck:
 		// Server acknowledged our packet
 		var data []byte