refactor: use interval as write deadline instead of separate parameter

Simplify the ghost connection fix by reusing the existing interval
duration as the write deadline. This removes the need for a separate
-write_deadline_ms flag while maintaining the same protection against
goroutine leaks from dead connections.

client/client.go

@@ -41,16 +41,15 @@ func randStringBytes(n int64) []byte {
 }
 
 type Client struct {
-	conn          net.Conn
-	next          time.Time
-	start         time.Time
-	last          time.Time
-	interval      time.Duration
-	writeDeadline time.Duration
-	bytesSent     int
+	conn      net.Conn
+	next      time.Time
+	start     time.Time
+	last      time.Time
+	interval  time.Duration
+	bytesSent int
 }
 
-func NewClient(conn net.Conn, interval time.Duration, maxClients int64, writeDeadline time.Duration) *Client {
+func NewClient(conn net.Conn, interval time.Duration, maxClients int64) *Client {
 	for numCurrentClients >= maxClients {
 		time.Sleep(interval)
 	}
@@ -63,13 +62,12 @@ func NewClient(conn net.Conn, interval time.Duration, maxClients int64, writeDea
 	addr := conn.RemoteAddr().(*net.TCPAddr)
 	glog.V(1).Infof("ACCEPT host=%v port=%v n=%v/%v\n", addr.IP, addr.Port, numCurrentClients, maxClients)
 	return &Client{
-		conn:          conn,
-		next:          time.Now().Add(interval),
-		start:         time.Now(),
-		last:          time.Now(),
-		interval:      interval,
-		writeDeadline: writeDeadline,
-		bytesSent:     0,
+		conn:      conn,
+		next:      time.Now().Add(interval),
+		start:     time.Now(),
+		last:      time.Now(),
+		interval:  interval,
+		bytesSent: 0,
 	}
 }
 
@@ -90,9 +88,7 @@ func (c *Client) Send(bannerMaxLength int64) (int, error) {
 	// Set a write deadline to detect dead connections where the kernel
 	// buffers data but the remote peer is gone. Without this, Write()
 	// can succeed indefinitely on dead connections, causing goroutine leaks.
-	if c.writeDeadline > 0 {
-		c.conn.SetWriteDeadline(time.Now().Add(c.writeDeadline))
-	}
+	c.conn.SetWriteDeadline(time.Now().Add(c.interval))
 	bytesSent, err := c.conn.Write(randStringBytes(length))
 	if err != nil {
 		return 0, err

main.go

@@ -76,7 +76,7 @@ func startSending(maxClients int64, bannerMaxLength int64, records chan<- metric
 	return clients
 }
 
-func startAccepting(maxClients int64, connType, connHost, connPort string, interval time.Duration, writeDeadline time.Duration, clients chan<- *client.Client, records chan<- metrics.RecordEntry, proxyProtocolEnabled bool, proxyProtocolReadHeaderTimeout int) {
+func startAccepting(maxClients int64, connType, connHost, connPort string, interval time.Duration, clients chan<- *client.Client, records chan<- metrics.RecordEntry, proxyProtocolEnabled bool, proxyProtocolReadHeaderTimeout int) {
 	go func() {
 		connPortInt, err := strconv.Atoi(connPort)
 		if err != nil {
@@ -109,7 +109,7 @@ func startAccepting(maxClients int64, connType, connHost, connPort string, inter
 				glog.Errorf("Error accepting connection from port %v: %v", connPort, err)
 				os.Exit(1)
 			}
-			c := client.NewClient(conn, interval, maxClients, writeDeadline)
+			c := client.NewClient(conn, interval, maxClients)
 			remoteIpAddr := c.RemoteIpAddr()
 			records <- metrics.RecordEntry{
 				RecordType: metrics.RecordEntryTypeStart,
@@ -150,7 +150,6 @@ func main() {
 	prometheusCleanUnseenSeconds := flag.Int("prometheus_clean_unseen_seconds", 0, "Remove series if the IP is not seen for the given time. Set to 0 to disable. (default 0)")
 	geoipSupplier := flag.String("geoip_supplier", "off", "Supplier to obtain Geohash of IPs. Possible values are \"off\", \"ip-api\", \"max-mind-db\"")
 	maxMindDbFileName := flag.String("max_mind_db", "", "Path to the MaxMind DB file.")
-	writeDeadlineMs := flag.Int("write_deadline_ms", 30000, "Write deadline in milliseconds for sending tarpit data. Detects dead connections where the kernel buffers data but the remote peer is gone. Set to 0 to disable. (default 30000)")
 	proxyProtocolEnabled := flag.Bool("proxy_protocol_enabled", false, "Enable PROXY protocol support. This causes the server to expect PROXY protocol headers on incoming connections.")
 	proxyProtocolReadHeaderTimeout := flag.Int("proxy_protocol_read_header_timeout_ms", 200, "Timeout for reading the PROXY protocol header in milliseconds. If the connection does not send a valid PROXY protocol header in this time, the header is ignored.")
 
@@ -175,7 +174,6 @@ func main() {
 	clients := startSending(*maxClients, *bannerMaxLength, records)
 
 	interval := time.Duration(*intervalMs) * time.Millisecond
-	writeDeadline := time.Duration(*writeDeadlineMs) * time.Millisecond
 	// Listen for incoming connections.
 	if *connType == "tcp6" && *connHost == "0.0.0.0" {
 		*connHost = "[::]"
@@ -184,7 +182,7 @@ func main() {
 		connPorts = append(connPorts, defaultPort)
 	}
 	for _, connPort := range connPorts {
-		startAccepting(*maxClients, *connType, *connHost, connPort, interval, writeDeadline, clients, records, *proxyProtocolEnabled, *proxyProtocolReadHeaderTimeout)
+		startAccepting(*maxClients, *connType, *connHost, connPort, interval, clients, records, *proxyProtocolEnabled, *proxyProtocolReadHeaderTimeout)
 	}
 	for {
 		if *prometheusCleanUnseenSeconds <= 0 {