multipart-specialchar.go

package main

import (
	"io"
	"log"
	"mime"
	"mime/multipart"
	"net/mail"
	"strings"
	"net/textproto"
	"bufio"
	"io/ioutil"
	"fmt"
)

const mailHeader = "Return-Path: <bounce+05185b.8e06-JohnDoe=redacted.fr@slack.com>\r\n" +
	"Delivered-To: JohnDoe@redacted.fr\r\n" +
	"To: JohnDoe@redacted.fr\r\n" +
	"Subject: =?utf-8?Q?=5bSlack=5d_Notifications_from_the_redacted_Team_team_for_Mar_=32nd=2c_=32=30=31=37_at__=37=3a=35=39_PM?=\r\n" +
	"From: \"Slack\" <no-reply@slack.com>\r\n" +
	"Reply-To: no-reply@slack.com\r\n" +
	"MIME-Version: 1.0\r\n" +
	"Content-Type: multipart/alternative; boundary=\"__slack_1715508436__\"\r\n" +
	"Date: Thu,  2 Mar 2017 10:59:08 -0800 (PST)\r\n" +
	"\r\n" +
	"\r\n"

const mailBody = "--__slack_1715508436__\r\n" +
	"Content-Type: text/plain; charset=\"utf-8\"\r\n" +
	"Content-Transfer-Encoding: quoted-printable\r\n" +
	"Content-Disposition: inline\r\n" +
	"\r\n" +
	"Cat Fact 20: Cats are often lactose intolerant, so stop givin’ them\r\n" +
	"milk!\r\n" +
	"\r\n" +
	":cat: :cat: :cat:\r\n" +
	"\r\n" +
	"--__slack_1715508436__\r\n" +
	"Content-Type: text/html; charset=\"utf-8\"\r\n" +
	"Content-Disposition: inline\r\n" +
	"\r\n" +
	"Cat Fact 20: Cats are often lactose intolerant, so stop givin’ them milk!<br><br><img src=\"https://a.slack-edge.com/d4bf/img/emoji_2015_2/apple/1f431.png\"  title=\":cat:\" width=\"20\" height=\"20\" style=\"-ms-interpolation-mode: bicubic; outline: none; text-decoration: none; vertical-align: bottom;\"><img src=\"https://a.slack-edge.com/d4bf/img/emoji_2015_2/apple/1f431.png\"  title=\":cat:\" width=\"20\" height=\"20\" style=\"-ms-interpolation-mode: bicubic; outline: none; text-decoration: none; vertical-align: bottom;\"><img src=\"https://a.slack-edge.com/d4bf/img/emoji_2015_2/apple/1f431.png\"  title=\":cat:\" width=\"20\" height=\"20\" style=\"-ms-interpolation-mode: bicubic; outline: none; text-decoration: none; vertical-align: bottom;\"></div>\r\n\r\n" +
	"--__slack_1715508436__--\r\n"

func main() {
	tp := textproto.NewReader(bufio.NewReader(strings.NewReader(mailHeader + mailBody)))

	mimeHeader, err := tp.ReadMIMEHeader()
	if err != nil {
		panic(err)
	}

	msg := &mail.Message{
		Header: map[string][]string(mimeHeader),
		Body:   strings.NewReader(mailHeader + mailBody),
	}
	mediaType, params, err := mime.ParseMediaType(msg.Header.Get("Content-Type"))
	if err != nil {
		log.Fatalf("Failed to parse mediaType: %s", err)
	}
	if strings.HasPrefix(mediaType, "multipart/") {
		mr := multipart.NewReader(msg.Body, params["boundary"])
		for {
			p, err := mr.NextPart()
			if err == io.EOF {
				return
			}
			if err != nil {
				log.Fatalf("Error parsing NextPart: %s", err)
			}

			slurp, err := ioutil.ReadAll(p)
			if err != nil {
				log.Fatalf("Failed to read all part: %s", err)
			}
			fmt.Printf("Part %q: %q\n", p.Header.Get("Foo"), slurp)
		}
	}

}