small pixel drawing of a pufferfish clist

mail/main.go

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package parsemail

import (
	"bytes"
	"encoding/base64"
	"fmt"
	"io"
	"io/ioutil"
	"mime"
	"mime/multipart"
	"net/mail"
	"strings"
	"time"
)

const contentTypeMultipartMixed = "multipart/mixed"
const contentTypeMultipartAlternative = "multipart/alternative"
const contentTypeMultipartRelated = "multipart/related"
const contentTypeTextHtml = "text/html"
const contentTypeTextPlain = "text/plain"

// Parse an email message read from io.Reader into parsemail.Email struct
func Parse(r io.Reader) (email Email, err error) {
	msg, err := mail.ReadMessage(r)
	if err != nil {
		return
	}

	email, err = createEmailFromHeader(msg.Header)
	if err != nil {
		return
	}

	contentType, params, err := parseContentType(msg.Header.Get("Content-Type"))
	if err != nil {
		return
	}

	switch contentType {
	case contentTypeMultipartMixed:
		email.TextBody, email.HTMLBody, email.Attachments, email.EmbeddedFiles, err = parseMultipartMixed(msg.Body, params["boundary"])
	case contentTypeMultipartAlternative:
		email.TextBody, email.HTMLBody, email.EmbeddedFiles, err = parseMultipartAlternative(msg.Body, params["boundary"])
	case contentTypeTextPlain:
		message, _ := ioutil.ReadAll(msg.Body)
		email.TextBody = strings.TrimSuffix(string(message[:]), "\n")
	case contentTypeTextHtml:
		message, _ := ioutil.ReadAll(msg.Body)
		email.HTMLBody = strings.TrimSuffix(string(message[:]), "\n")
	default:
		err = fmt.Errorf("Unknown top level mime type: %s", contentType)
	}

	return
}

func createEmailFromHeader(header mail.Header) (email Email, err error) {
	hp := headerParser{header: &header}

	email.Subject = decodeMimeSentence(header.Get("Subject"))
	email.From = hp.parseAddressList(header.Get("From"))
	email.Sender = hp.parseAddress(header.Get("Sender"))
	email.ReplyTo = hp.parseAddressList(header.Get("Reply-To"))
	email.To = hp.parseAddressList(header.Get("To"))
	email.Cc = hp.parseAddressList(header.Get("Cc"))
	email.Bcc = hp.parseAddressList(header.Get("Bcc"))
	email.Date = hp.parseTime(header.Get("Date"))
	email.ResentFrom = hp.parseAddressList(header.Get("Resent-From"))
	email.ResentSender = hp.parseAddress(header.Get("Resent-Sender"))
	email.ResentTo = hp.parseAddressList(header.Get("Resent-To"))
	email.ResentCc = hp.parseAddressList(header.Get("Resent-Cc"))
	email.ResentBcc = hp.parseAddressList(header.Get("Resent-Bcc"))
	email.ResentMessageID = hp.parseMessageId(header.Get("Resent-Message-ID"))
	email.MessageID = hp.parseMessageId(header.Get("Message-ID"))
	email.InReplyTo = hp.parseMessageIdList(header.Get("In-Reply-To"))
	email.References = hp.parseMessageIdList(header.Get("References"))
	email.ResentDate = hp.parseTime(header.Get("Resent-Date"))

	if hp.err != nil {
		err = hp.err
		return
	}

	//decode whole header for easier access to extra fields
	//todo: should we decode? aren't only standard fields mime encoded?
	email.Header, err = decodeHeaderMime(header)
	if err != nil {
		return
	}

	return
}

func parseContentType(contentTypeHeader string) (contentType string, params map[string]string, err error) {
	if contentTypeHeader == "" {
		contentType = contentTypeTextPlain
		return
	}

	return mime.ParseMediaType(contentTypeHeader)
}

func parseMultipartRelated(msg io.Reader, boundary string) (textBody, htmlBody string, embeddedFiles []EmbeddedFile, err error) {
	pmr := multipart.NewReader(msg, boundary)
	for {
		part, err := pmr.NextPart()

		if err == io.EOF {
			break
		} else if err != nil {
			return textBody, htmlBody, embeddedFiles, err
		}

		contentType, params, err := mime.ParseMediaType(part.Header.Get("Content-Type"))
		if err != nil {
			return textBody, htmlBody, embeddedFiles, err
		}

		switch contentType {
		case contentTypeTextPlain:
			ppContent, err := ioutil.ReadAll(part)
			if err != nil {
				return textBody, htmlBody, embeddedFiles, err
			}

			textBody += strings.TrimSuffix(string(ppContent[:]), "\n")
		case contentTypeTextHtml:
			ppContent, err := ioutil.ReadAll(part)
			if err != nil {
				return textBody, htmlBody, embeddedFiles, err
			}

			htmlBody += strings.TrimSuffix(string(ppContent[:]), "\n")
		case contentTypeMultipartAlternative:
			tb, hb, ef, err := parseMultipartAlternative(part, params["boundary"])
			if err != nil {
				return textBody, htmlBody, embeddedFiles, err
			}

			htmlBody += hb
			textBody += tb
			embeddedFiles = append(embeddedFiles, ef...)
		default:
			if isEmbeddedFile(part) {
				ef, err := decodeEmbeddedFile(part)
				if err != nil {
					return textBody, htmlBody, embeddedFiles, err
				}

				embeddedFiles = append(embeddedFiles, ef)
			} else {
				return textBody, htmlBody, embeddedFiles, fmt.Errorf("Can't process multipart/related inner mime type: %s", contentType)
			}
		}
	}

	return textBody, htmlBody, embeddedFiles, err
}

func parseMultipartAlternative(msg io.Reader, boundary string) (textBody, htmlBody string, embeddedFiles []EmbeddedFile, err error) {
	pmr := multipart.NewReader(msg, boundary)
	for {
		part, err := pmr.NextPart()

		if err == io.EOF {
			break
		} else if err != nil {
			return textBody, htmlBody, embeddedFiles, err
		}

		contentType, params, err := mime.ParseMediaType(part.Header.Get("Content-Type"))
		if err != nil {
			return textBody, htmlBody, embeddedFiles, err
		}

		switch contentType {
		case contentTypeTextPlain:
			ppContent, err := ioutil.ReadAll(part)
			if err != nil {
				return textBody, htmlBody, embeddedFiles, err
			}

			textBody += strings.TrimSuffix(string(ppContent[:]), "\n")
		case contentTypeTextHtml:
			ppContent, err := ioutil.ReadAll(part)
			if err != nil {
				return textBody, htmlBody, embeddedFiles, err
			}

			htmlBody += strings.TrimSuffix(string(ppContent[:]), "\n")
		case contentTypeMultipartRelated:
			tb, hb, ef, err := parseMultipartRelated(part, params["boundary"])
			if err != nil {
				return textBody, htmlBody, embeddedFiles, err
			}

			htmlBody += hb
			textBody += tb
			embeddedFiles = append(embeddedFiles, ef...)
		default:
			if isEmbeddedFile(part) {
				ef, err := decodeEmbeddedFile(part)
				if err != nil {
					return textBody, htmlBody, embeddedFiles, err
				}

				embeddedFiles = append(embeddedFiles, ef)
			} else {
				return textBody, htmlBody, embeddedFiles, fmt.Errorf("Can't process multipart/alternative inner mime type: %s", contentType)
			}
		}
	}

	return textBody, htmlBody, embeddedFiles, err
}

func parseMultipartMixed(msg io.Reader, boundary string) (textBody, htmlBody string, attachments []Attachment, embeddedFiles []EmbeddedFile, err error) {
	mr := multipart.NewReader(msg, boundary)
	for {
		part, err := mr.NextPart()
		if err == io.EOF {
			break
		} else if err != nil {
			return textBody, htmlBody, attachments, embeddedFiles, err
		}

		contentType, params, err := mime.ParseMediaType(part.Header.Get("Content-Type"))
		if err != nil {
			return textBody, htmlBody, attachments, embeddedFiles, err
		}

		if contentType == contentTypeMultipartAlternative {
			textBody, htmlBody, embeddedFiles, err = parseMultipartAlternative(part, params["boundary"])
			if err != nil {
				return textBody, htmlBody, attachments, embeddedFiles, err
			}
		} else if contentType == contentTypeMultipartRelated {
			textBody, htmlBody, embeddedFiles, err = parseMultipartRelated(part, params["boundary"])
			if err != nil {
				return textBody, htmlBody, attachments, embeddedFiles, err
			}
		} else if isAttachment(part) {
			at, err := decodeAttachment(part)
			if err != nil {
				return textBody, htmlBody, attachments, embeddedFiles, err
			}

			attachments = append(attachments, at)
		} else {
			return textBody, htmlBody, attachments, embeddedFiles, fmt.Errorf("Unknown multipart/mixed nested mime type: %s", contentType)
		}
	}

	return textBody, htmlBody, attachments, embeddedFiles, err
}

func decodeMimeSentence(s string) string {
	result := []string{}
	ss := strings.Split(s, " ")

	for _, word := range ss {
		dec := new(mime.WordDecoder)
		w, err := dec.Decode(word)
		if err != nil {
			if len(result) == 0 {
				w = word
			} else {
				w = " " + word
			}
		}

		result = append(result, w)
	}

	return strings.Join(result, "")
}

func decodeHeaderMime(header mail.Header) (mail.Header, error) {
	parsedHeader := map[string][]string{}

	for headerName, headerData := range header {

		parsedHeaderData := []string{}
		for _, headerValue := range headerData {
			parsedHeaderData = append(parsedHeaderData, decodeMimeSentence(headerValue))
		}

		parsedHeader[headerName] = parsedHeaderData
	}

	return mail.Header(parsedHeader), nil
}

func decodePartData(part *multipart.Part) (io.Reader, error) {
	encoding := part.Header.Get("Content-Transfer-Encoding")

	if strings.EqualFold(encoding, "base64") {
		dr := base64.NewDecoder(base64.StdEncoding, part)
		dd, err := ioutil.ReadAll(dr)
		if err != nil {
			return nil, err
		}

		return bytes.NewReader(dd), nil
	}

	return nil, fmt.Errorf("Unknown encoding: %s", encoding)
}

func isEmbeddedFile(part *multipart.Part) bool {
	return part.Header.Get("Content-Transfer-Encoding") != ""
}

func decodeEmbeddedFile(part *multipart.Part) (ef EmbeddedFile, err error) {
	cid := decodeMimeSentence(part.Header.Get("Content-Id"))
	decoded, err := decodePartData(part)
	if err != nil {
		return
	}

	ef.CID = strings.Trim(cid, "<>")
	ef.Data = decoded
	ef.ContentType = part.Header.Get("Content-Type")

	return
}

func isAttachment(part *multipart.Part) bool {
	return part.FileName() != ""
}

func decodeAttachment(part *multipart.Part) (at Attachment, err error) {
	filename := decodeMimeSentence(part.FileName())
	decoded, err := decodePartData(part)
	if err != nil {
		return
	}

	at.Filename = filename
	at.Data = decoded
	at.ContentType = strings.Split(part.Header.Get("Content-Type"), ";")[0]

	return
}

type headerParser struct {
	header *mail.Header
	err    error
}

func (hp headerParser) parseAddress(s string) (ma *mail.Address) {
	if hp.err != nil {
		return nil
	}

	if strings.Trim(s, " \n") != "" {
		ma, hp.err = mail.ParseAddress(s)

		return ma
	}

	return nil
}

func (hp headerParser) parseAddressList(s string) (ma []*mail.Address) {
	if hp.err != nil {
		return
	}

	if strings.Trim(s, " \n") != "" {
		ma, hp.err = mail.ParseAddressList(s)
		return
	}

	return
}

func (hp headerParser) parseTime(s string) (t time.Time) {
	if hp.err != nil || s == "" {
		return
	}

	t, hp.err = time.Parse(time.RFC1123Z, s)
	if hp.err == nil {
		return t
	}

	t, hp.err = time.Parse("Mon, 2 Jan 2006 15:04:05 -0700", s)

	return
}

func (hp headerParser) parseMessageId(s string) string {
	if hp.err != nil {
		return ""
	}

	return strings.Trim(s, "<> ")
}

func (hp headerParser) parseMessageIdList(s string) (result []string) {
	if hp.err != nil {
		return
	}

	for _, p := range strings.Split(s, " ") {
		if strings.Trim(p, " \n") != "" {
			result = append(result, hp.parseMessageId(p))
		}
	}

	return
}

// Attachment with filename, content type and data (as a io.Reader)
type Attachment struct {
	Filename    string
	ContentType string
	Data        io.Reader
}

// EmbeddedFile with content id, content type and data (as a io.Reader)
type EmbeddedFile struct {
	CID         string
	ContentType string
	Data        io.Reader
}

func commaSep(mails []*mail.Address) string {
	var response []string
	var sm string
	for _, m := range mails {
		sm = m.String()
		response = append(response, sm)
	}
	return strings.Join(response, ",")
}

func (e *Email) ToBytes() []byte {
	var buf bytes.Buffer
	fmt.Fprintf(&buf, "Sender: %s\r\n", e.Sender)
	fmt.Fprintf(&buf, "From: %s\r\n", commaSep(e.From))
	if len(e.To) > 0 {
		fmt.Fprintf(&buf, "To: %s\r\n", commaSep(e.To))
	}
	if len(e.Cc) > 0 {
		fmt.Fprintf(&buf, "Cc: %s\r\n", commaSep(e.Cc))
	}
	if !e.Date.IsZero() {
		fmt.Fprintf(&buf, "Date: %s\r\n", e.Date)
	}
	if len(e.MessageID) > 0 {
		fmt.Fprintf(&buf, "Message-ID: %s\r\n", e.MessageID)
	}
	if len(e.InReplyTo) > 0 {
		fmt.Fprintf(&buf, "In-Reply-To: %s\r\n", strings.Join(e.InReplyTo, ","))
	}
	if len(e.Header.Get("List-Id")) > 0 {
		fmt.Fprintf(&buf, "List-Id: %s\r\n", e.Header.Get("List-Id"))
	}
	if len(e.Header.Get("List-Post")) > 0 {
		fmt.Fprintf(&buf, "List-Post: %s\r\n", e.Header.Get("List-Post"))
	}
	if len(e.Header.Get("List-Help")) > 0 {
		fmt.Fprintf(&buf, "List-Help: %s\r\n", e.Header.Get("List-Help"))
	}
	if len(e.Header.Get("List-Subscribe")) > 0 {
		fmt.Fprintf(&buf, "List-Subscribe: %s\r\n", e.Header.Get("List-Subscribe"))
	}
	if len(e.Header.Get("List-Unsubscribe")) > 0 {
		fmt.Fprintf(&buf, "List-Unsubscribe: %s\r\n", e.Header.Get("List-Unsubscribe"))
	}
	if len(e.Header.Get("List-Owner")) > 0 {
		fmt.Fprintf(&buf, "List-Owner: %s\r\n", e.Header.Get("List-Owner"))
	}
	if len(e.Header.Get("Precedence")) > 0 {
		fmt.Fprintf(&buf, "Precedence: %s\r\n", e.Header.Get("Precedence"))
	}
	if len(e.Header.Get("List-Archive")) > 0 {
		fmt.Fprintf(&buf, "List-Archive: %s\r\n", e.Header.Get("List-Archive"))
	}
	fmt.Fprintf(&buf, "Subject: %s\r\n", e.Subject)
	fmt.Fprintf(&buf, "\r\n%s", e.TextBody)

	return buf.Bytes()
}

// Email with fields for all the headers defined in RFC5322 with it's attachments and
type Email struct {
	Header mail.Header

	Subject    string
	Sender     *mail.Address
	From       []*mail.Address
	ReplyTo    []*mail.Address
	To         []*mail.Address
	Cc         []*mail.Address
	Bcc        []*mail.Address
	Date       time.Time
	MessageID  string
	InReplyTo  []string
	References []string

	ResentFrom      []*mail.Address
	ResentSender    *mail.Address
	ResentTo        []*mail.Address
	ResentDate      time.Time
	ResentCc        []*mail.Address
	ResentBcc       []*mail.Address
	ResentMessageID string

	HTMLBody string
	TextBody string

	Attachments   []Attachment
	EmbeddedFiles []EmbeddedFile
}