parse MBOX file format for attachments

mbox.go

package main

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

func check(e error) {
	if e != nil {
		panic(e)
	}
}

func blocks(f io.Reader, match string) [][]byte {
	r := bufio.NewReader(f)
	var b bytes.Buffer
	lx := [][]byte{}
	for n := 0; ; n++ {
		l, err := r.ReadBytes('\n')
		if err != nil {
			break
		}
		if strings.Contains(string(l), match) {
			if n > 0 {
				lx = append(lx, b.Bytes())
			}
			b = bytes.Buffer{}
		}
		b.Write(l)
	}
	lx = append(lx, b.Bytes())
	return lx
}

func parseFiles(b []byte) {
	m, err := mail.ReadMessage(bytes.NewReader(b))
	defer func() {
		if r := recover(); r != nil {
			fmt.Println("Recovered in f", r, m.Header.Get("From"))
		}
	}()
	check(err)

	from := m.Header.Get("From")
	d, err := m.Header.Date()
	check(err)
	dir := d.Format("20060102") + from
	os.Mkdir(dir, 0777)

	mediaType, params, err := mime.ParseMediaType(m.Header.Get("Content-Type"))
	check(err)

	if strings.HasPrefix(mediaType, "multipart/") {
		mr := multipart.NewReader(m.Body, params["boundary"])
		for i := 0; ; i++ {
			p, err := mr.NextPart()
			if err == io.EOF {
				return
			}
			if err != nil {
				// log.Fatal(err)
				panic(err)
			}
			slurp, err := ioutil.ReadAll(p)
			if err != nil {
				// log.Fatal(err)
				panic(err)
			}

			name := p.FileName()
			data := slurp
			if name == "" {
				name = fmt.Sprintf("no-name-%d.html", i)
			} else {
				data, err = base64.StdEncoding.DecodeString(string(slurp))
				if err != nil {
					// fmt.Println("error:", err)
					panic(err)
					return
				}
			}
			x, err := os.Create(path.Join(dir, name))
			if err != nil {
				// fmt.Println("error:", err)
				panic(err)
				return
			}
			x.Write(data)
			x.Close()
		}
	}
}

func main() {
	f, err := os.Open(os.Args[1])
	check(err)
	defer f.Close()

	for _, l := range blocks(f, "From ") {
		parseFiles(l)
		// fmt.Println(i)
	}
}