main.go

package main

import (
	"fmt"
	"log"
	"os"
	"time"

	"github.com/google/gopacket"
	"github.com/google/gopacket/pcap"
	"github.com/urfave/cli"
)

var (
	snapshot_len int32 = 1024
	promiscuous  bool  = false
	err          error
	timeout      time.Duration = 100 * time.Millisecond
	handle       *pcap.Handle
)

func findDevice(c *cli.Context) string {
	if c.String("interface") != "" {
		return c.String("interface")
	}
	devices, err := pcap.FindAllDevs()
	if err != nil {
		panic(err)
	}

	return devices[0].Name
}

func createHandle(c *cli.Context) (*pcap.Handle, error) {
	fileName := c.String("read")
	if fileName != "" {
		return pcap.OpenOffline(fileName)
	} else {
		device := findDevice(c)
		return pcap.OpenLive(device, snapshot_len, promiscuous, timeout)

	}
}

func findSource(c *cli.Context) (*gopacket.PacketSource, func()) {
	handle, err := createHandle(c)
	if err != nil {
		log.Fatal(err)
	}

	if c.String("filter") != "" {
		err := handle.SetBPFFilter(c.String("filter"))
		if err != nil {
			log.Fatal(err)
		}
	}

	return gopacket.NewPacketSource(handle, handle.LinkType()), handle.Close
}

func main() {
	app := cli.NewApp()
	app.Name = "tcpterm"
	app.Usage = "tcpdump for human"
	app.Version = "0.0.1"

	app.Flags = []cli.Flag{
		cli.StringFlag{
			Name:  "interface, i",
			Usage: "If unspecified, use lowest numbered interface.",
		},
		cli.StringFlag{
			Name:  "read, r",
			Usage: "Read packets from pcap file.",
		},
		cli.StringFlag{
			Name:  "filter, f",
			Usage: "BPF Filter",
		},
		cli.BoolFlag{
			Name:  "debug",
			Usage: "debug mode.",
		},
	}

	app.Action = func(c *cli.Context) error {
		packetSource, close := findSource(c)
		defer close()

		tcpterm := NewTcpterm(packetSource, c.Bool("debug"))
		tcpterm.Run()
		return nil
	}

	if err := app.Run(os.Args); err != nil {
		fmt.Fprintln(os.Stderr, "Error:", err)
		os.Exit(1)
	}
}