added the details of listening tcp port, the original file comes from https://github.com/prometheus/node_exporter/blob/master/collector/tcpstat_linux.go

gistfile1.txt

// Copyright 2015 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// +build !notcpstat

package collector

import (
    "bufio"
    "fmt"
    "io"
    "os"
    "strconv"
    "strings"

    "github.com/prometheus/client_golang/prometheus"
)

type TCPConnectionState int

type tcpStatCollector struct {
    state  *prometheus.Desc
    listen *prometheus.Desc
}

const (
    TCP_ESTABLISHED TCPConnectionState = iota + 1
    TCP_SYN_SENT
    TCP_SYN_RECV
    TCP_FIN_WAIT1
    TCP_FIN_WAIT2
    TCP_TIME_WAIT
    TCP_CLOSE
    TCP_CLOSE_WAIT
    TCP_LAST_ACK
    TCP_LISTEN
    TCP_CLOSING
)

func init() {
    Factories["tcpstat"] = NewTCPStatCollector
}

// NewTCPStatCollector takes a returns
// a new Collector exposing network stats.
func NewTCPStatCollector() (Collector, error) {
    return &tcpStatCollector{
        state: prometheus.NewDesc(
            prometheus.BuildFQName(Namespace, "", "tcp_state"),
            "Number of connection states.",
            []string{"state"}, nil,
        ),
        listen: prometheus.NewDesc(
            prometheus.BuildFQName(Namespace, "", "tcp_listen_state"),
            "tcp listen states.",
            []string{"port"}, nil,
        ),
    }, nil
}

func (c *tcpStatCollector) Update(ch chan<- prometheus.Metric) (err error) {
    tcpStats, ports, err := getTCPStats(procFilePath("net/tcp"))
    if err != nil {
        return fmt.Errorf("couldn't get tcpstats: %s", err)
    }

    // if enabled ipv6 system
    tcp6File := procFilePath("net/tcp6")
    if _, hasIPv6 := os.Stat(tcp6File); hasIPv6 == nil {
        tcp6Stats, tcp6ports, err := getTCPStats(tcp6File)
        if err != nil {
            return fmt.Errorf("couldn't get tcp6stats: %s", err)
        }

        for st, value := range tcp6Stats {
            tcpStats[st] += value
        }
        for st, _ := range tcp6ports {
            ports[st] = 1
        }
    }

    for st, value := range tcpStats {
        name := st.String()
        ch <- prometheus.MustNewConstMetric(c.state, prometheus.GaugeValue, value, name)
    }
    for st, value := range ports {
        name := strconv.FormatInt(st, 10)
        ch <- prometheus.MustNewConstMetric(c.listen, prometheus.GaugeValue, float64(value), name)
    }
    return err
}

func getTCPStats(statsFile string) (map[TCPConnectionState]float64, map[int64]int, error) {
    file, err := os.Open(statsFile)
    if err != nil {
        return nil, nil, err
    }
    defer file.Close()

    return parseTCPStats(file)
}

func parseTCPStats(r io.Reader) (map[TCPConnectionState]float64, map[int64]int, error) {
    var (
        tcpStats = map[TCPConnectionState]float64{}
        scanner  = bufio.NewScanner(r)
        ports    = make(map[int64]int)
    )

    for scanner.Scan() {
        parts := strings.Fields(scanner.Text())
        if len(parts) == 0 {
            continue
        }
        if strings.HasPrefix(parts[0], "sl") {
            continue
        }
        st, err := strconv.ParseInt(parts[3], 16, 8)
        if err != nil {
            return nil, nil, err
        }
        if st == 10 {
            part := strings.Split(parts[1], ":")
            pt, _ := strconv.ParseInt(part[1], 16, 16)
            ports[pt] = 1
        }

        tcpStats[TCPConnectionState(st)]++
    }

    return tcpStats, ports, nil
}

func (st TCPConnectionState) String() string {
    switch st {
    case TCP_ESTABLISHED:
        return "established"
    case TCP_SYN_SENT:
        return "syn_sent"
    case TCP_SYN_RECV:
        return "syn_recv"
    case TCP_FIN_WAIT1:
        return "fin_wait1"
    case TCP_FIN_WAIT2:
        return "fin_wait2"
    case TCP_TIME_WAIT:
        return "time_wait"
    case TCP_CLOSE:
        return "close"
    case TCP_CLOSE_WAIT:
        return "close_wait"
    case TCP_LAST_ACK:
        return "last_ack"
    case TCP_LISTEN:
        return "listen"
    case TCP_CLOSING:
        return "closing"
    default:
        return "unknown"
    }
}