Extract email attachments

extract_email_attachments.go

package main

import (
	"bufio"
	"encoding/base64"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"mime"
	"mime/multipart"
	"net/mail"
	"os"
	"strings"
)

func main() {
	flag.Parse()
	files := flag.Args()
	for _, file := range files {
		extractFiles(file)
	}
}

func panicIfErr(err error, msg string) {
	if err != nil {
		panic(msg + ":" + err.Error())
	}
}

func extractFiles(filename string) {
	f, err := os.Open(filename)
	panicIfErr(err, "Cannot open file "+filename)

	msg, err := mail.ReadMessage(f)
	panicIfErr(err, "Cannor read file "+filename)

	mediaType, params, err := mime.ParseMediaType(msg.Header.Get("Content-Type"))
	panicIfErr(err, "Cannot parse media type")

	if !strings.HasPrefix(mediaType, "multipart/") {
		fmt.Println("Not a multipart message " + filename)
		return
	}

	mr := multipart.NewReader(msg.Body, params["boundary"])
	for {
		p, err := mr.NextPart()
		if err == io.EOF {
			return
		}
		panicIfErr(err, "Cannot read next part")

		fmt.Println(p.FileName())

		if len(p.FileName()) > 0 {
			slurp, err := ioutil.ReadAll(p)
			panicIfErr(err, "Cannot read "+filename)

			reader := bufio.NewReader(os.Stdin)
			fmt.Printf("Write %d bytes to %s: [y/N]", len(slurp), p.FileName())
			text, _ := reader.ReadString('\n')
			text = strings.ToLower(strings.TrimSpace(text))

			if text == "y" {
				writeFile(p.FileName(), slurp)
			}
		}
	}
}

func writeFile(filename string, bytes []byte) {
	f, err := os.Create(filename)
	panicIfErr(err, "Cannot write to "+filename)

	data, err := base64.StdEncoding.DecodeString(string(bytes))
	panicIfErr(err, "Cannot base64 decode")
	fmt.Printf("%q\n", data)

	_, err = f.Write(data)
	panicIfErr(err, "Cannot write to "+filename)

	fmt.Printf("Written to %s\n", filename)
}