Add gauges for allocated memory for queued UDP and TCP packages (#1503)

* Two new states will be added to the tcpstat collector called rx_queued_bytes and tx_queued_bytes.

For UDP datagrams an additional collector 'udp_queues' can be used to expose the total lengths of the tx_queue and rx_queue.
@SuperQ and @discordianfish this changes gives us the option to check for overloaded UDP + TCP processing.
The names of the new TCP states and the UDP metric can be discussed.
The current reasons are just:

I don't want to add another collector for the same exposed file, so I just added the new states to the tcpstat collector.
I chose the name 'udp_queue' instead of 'udpstat' as UDP has no state.


Signed-off-by: Peter Bueschel <peter.bueschel@logmein.com>

collector/tcpstat_linux.go

@@ -52,6 +52,10 @@ const (
 	tcpListen
 	// TCP_CLOSING
 	tcpClosing
+	// TCP_RX_BUFFER
+	tcpRxQueuedBytes
+	// TCP_TX_BUFFER
+	tcpTxQueuedBytes
 )
 
 type tcpStatCollector struct {
@@ -122,16 +126,34 @@ func parseTCPStats(r io.Reader) (map[tcpConnectionState]float64, error) {
 		if len(parts) == 0 {
 			continue
 		}
-		if len(parts) < 4 {
+		if len(parts) < 5 {
 			return nil, fmt.Errorf("invalid TCP stats line: %q", line)
 		}
 
+		qu := strings.Split(parts[4], ":")
+		if len(qu) < 2 {
+			return nil, fmt.Errorf("cannot parse tx_queues and rx_queues: %q", line)
+		}
+
+		tx, err := strconv.ParseUint(qu[0], 16, 64)
+		if err != nil {
+			return nil, err
+		}
+		tcpStats[tcpConnectionState(tcpTxQueuedBytes)] += float64(tx)
+
+		rx, err := strconv.ParseUint(qu[1], 16, 64)
+		if err != nil {
+			return nil, err
+		}
+		tcpStats[tcpConnectionState(tcpRxQueuedBytes)] += float64(rx)
+
 		st, err := strconv.ParseInt(parts[3], 16, 8)
 		if err != nil {
 			return nil, err
 		}
 
 		tcpStats[tcpConnectionState(st)]++
+
 	}
 
 	return tcpStats, nil
@@ -161,6 +183,10 @@ func (st tcpConnectionState) String() string {
 		return "listen"
 	case tcpClosing:
 		return "closing"
+	case tcpRxQueuedBytes:
+		return "rx_queued_bytes"
+	case tcpTxQueuedBytes:
+		return "tx_queued_bytes"
 	default:
 		return "unknown"
 	}