Small enhancements for the cli

Author: shadowy-pycoder

cmd/mshark/cli.go

@@ -6,6 +6,7 @@ import (
 	"net"
 	"os"
 	"strings"
+	"text/tabwriter"
 
 	ms "github.com/shadowy-pycoder/mshark"
 )
@@ -31,15 +32,18 @@ Options:
 `
 
 func displayInterfaces() error {
+	w := new(tabwriter.Writer)
+	w.Init(os.Stdout, 0, 0, 2, ' ', tabwriter.TabIndent)
 	ifaces, err := net.Interfaces()
 	if err != nil {
 		return fmt.Errorf("failed to get network interfaces: %v", err)
 	}
-	fmt.Println("0. any")
+	fmt.Fprintln(w, "Index\tName\tFlags")
+	fmt.Fprintln(w, "0\tany\tUP")
 	for _, iface := range ifaces {
-		fmt.Printf("%d. %s    %s\n", iface.Index, iface.Name, strings.ToUpper(iface.Flags.String()))
+		fmt.Fprintf(w, "%d\t%s\t%s\n", iface.Index, iface.Name, strings.ToUpper(iface.Flags.String()))
 	}
-	return nil
+	return w.Flush()
 }
 
 func root(args []string) error {
@@ -48,19 +52,18 @@ func root(args []string) error {
 	flags := flag.NewFlagSet("mshark", flag.ExitOnError)
 	flags.StringVar(&conf.Iface, "i", "any", "The name of the network interface. Example: eth0")
 	flags.IntVar(&conf.Snaplen, "s", 0, "The maximum length of each packet snapshot. Defaults to 65535.")
-	flags.BoolFunc("p", `Promiscuous mode. This setting is ignored for "any" interface.`, func(flagValue string) error {
+	flags.BoolFunc("p", `Promiscuous mode. This setting is ignored for "any" interface. Defaults to false.`, func(flagValue string) error {
 		conf.Promisc = true
 		return nil
 	})
 	flags.DurationVar(&conf.Timeout, "t", 0, "The maximum duration of the packet capture process. Example: 5s")
 	flags.IntVar(&conf.PacketCount, "c", 0, "The maximum number of packets to capture.")
 	flags.StringVar(&conf.Expr, "e", "", `BPF filter expression. Example: "ip proto tcp"`)
-	flags.StringVar(&conf.Path, "f", "", "File path to write captured packet data to. Example: ./captured.txt")
-	flags.BoolFunc("pcap", "Whether to create PCAP file.", func(flagValue string) error {
+	flags.StringVar(&conf.File, "f", "", "File path to write captured packet data to. Defaults to stdout.")
+	flags.BoolFunc("pcap", "Create a PCAP file in the current working directory.", func(flagValue string) error {
 		conf.Pcap = true
 		return nil
 	})
-	flags.StringVar(&conf.PcapPath, "path", "", "Path to a PCAP file. Example: ./captured.pcap")
 	flags.BoolFunc("D", "Display list of interfaces and exit.", func(flagValue string) error {
 		if err := displayInterfaces(); err != nil {
 			fmt.Fprintf(os.Stderr, "mshark: %v\n", err)

mshark.go

@@ -33,9 +33,8 @@ type Config struct {
 	Timeout     time.Duration // The maximum duration of the packet capture process.
 	PacketCount int           // The maximum number of packets to capture.
 	Expr        string        // BPF filter expression.
-	Path        string        // File path to write captured packet data to.
-	Pcap        bool          // Whether to create PCAP file.
-	PcapPath    string        // Path to a PCAP file. Defaults to "mshark_timestamp.pcap" in the current working directory.
+	File        string        // File path to write captured packet data to. Defaults to /dev/stdout
+	Pcap        bool          // Create a PCAP file in the current working directory.
 }
 
 func OpenLive(conf *Config) error {
@@ -110,14 +109,14 @@ func OpenLive(conf *Config) error {
 
 	// file to write packets
 	var f *os.File
-	if conf.Path == "" {
-		f = os.Stdout
-	} else {
-		f, err = os.OpenFile(filepath.FromSlash(conf.Path), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	if conf.File != "" {
+		f, err = os.OpenFile(filepath.FromSlash(conf.File), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
 		if err != nil {
 			return fmt.Errorf("failed to open file: %v", err)
 		}
 		defer f.Close()
+	} else {
+		f = os.Stdout
 	}
 
 	// number of packets
@@ -162,10 +161,8 @@ func OpenLive(conf *Config) error {
 	// pcap file to write packets
 	var pcap *mpcap.PcapWriter
 	if conf.Pcap {
-		if conf.PcapPath == "" {
-			conf.PcapPath = fmt.Sprintf("./mshark_%s.pcap", time.Now().UTC().Format("20060102_150405"))
-		}
-		fpcap, err := os.OpenFile(filepath.FromSlash(conf.PcapPath), os.O_CREATE|os.O_WRONLY, 0644)
+		path := fmt.Sprintf("./mshark_%s.pcap", time.Now().UTC().Format("20060102_150405"))
+		fpcap, err := os.OpenFile(filepath.FromSlash(path), os.O_CREATE|os.O_WRONLY, 0644)
 		if err != nil {
 			return fmt.Errorf("failed to open file: %v", err)
 		}

mshark_test.go

@@ -12,7 +12,7 @@ func BenchmarkOpenLive(b *testing.B) {
 		Snaplen:     1600,
 		Promisc:     true,
 		PacketCount: b.N,
-		Path:        os.DevNull,
+		File:        os.DevNull,
 	}
 	if err := OpenLive(&conf); err != nil {
 		b.Fatal(err)