XICMP finalmask: Refine seq (#5652)

Example: https://github.com/XTLS/Xray-core/pull/5633#issue-3881559866

transport/internet/finalmask/xicmp/client.go

@@ -20,6 +20,7 @@ const (
 	maxPollDelay        = 10 * time.Second
 	pollDelayMultiplier = 2.0
 	pollLimit           = 16
+	windowSize          = 1000
 )
 
 type packet struct {
@@ -30,7 +31,6 @@ type packet struct {
 type seqStatus struct {
 	needSeqByte bool
 	seqByte     byte
-	received    bool
 }
 
 type xicmpConnClient struct {
@@ -129,12 +129,14 @@ func (c *xicmpConnClient) encode(p []byte) ([]byte, error) {
 	c.seqStatus[c.seq] = &seqStatus{
 		needSeqByte: needSeqByte,
 		seqByte:     seqByte,
-		received:    false,
 	}
 
+	delete(c.seqStatus, int(uint16(c.seq-windowSize)))
+
 	c.seq++
 
 	if c.seq == 65536 {
+		delete(c.seqStatus, int(uint16(c.seq-windowSize)))
 		c.seq = 1
 	}
 
@@ -168,16 +170,14 @@ func (c *xicmpConnClient) recvLoop() {
 			continue
 		}
 
+		c.mutex.Lock()
 		seqStatus, ok := c.seqStatus[echo.Seq]
+		c.mutex.Unlock()
 
 		if !ok {
 			continue
 		}
 
-		if seqStatus.received {
-			continue
-		}
-
 		if seqStatus.needSeqByte {
 			if len(echo.Data) <= 1 {
 				continue
@@ -189,7 +189,9 @@ func (c *xicmpConnClient) recvLoop() {
 		}
 
 		if len(echo.Data) > 0 {
-			seqStatus.received = true
+			c.mutex.Lock()
+			delete(c.seqStatus, echo.Seq)
+			c.mutex.Unlock()
 
 			buf := make([]byte, len(echo.Data))
 			copy(buf, echo.Data)