proton-bridge/pkg/message/build_rfc822.go

// Copyright (c) 2021 Proton Technologies AG
//
// This file is part of ProtonMail Bridge.
//
// ProtonMail Bridge is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// ProtonMail Bridge is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with ProtonMail Bridge.  If not, see <https://www.gnu.org/licenses/>.

package message

import (
	"bytes"
	"encoding/base64"
	"io/ioutil"
	"mime"
	"net/mail"
	"strings"
	"time"
	"unicode/utf8"

	"github.com/ProtonMail/go-rfc5322"
	"github.com/ProtonMail/gopenpgp/v2/crypto"
	"github.com/ProtonMail/proton-bridge/pkg/pmapi"
	"github.com/emersion/go-message"
	"github.com/pkg/errors"
)

func buildRFC822(kr *crypto.KeyRing, msg *pmapi.Message, attData [][]byte, opts JobOptions) ([]byte, error) {
	switch {
	case len(msg.Attachments) > 0:
		return buildMultipartRFC822(kr, msg, attData, opts)

	case msg.MIMEType == "multipart/mixed":
		return buildEncryptedRFC822(kr, msg, opts)

	default:
		return buildSimpleRFC822(kr, msg, opts)
	}
}

func buildSimpleRFC822(kr *crypto.KeyRing, msg *pmapi.Message, opts JobOptions) ([]byte, error) {
	dec, err := msg.Decrypt(kr)
	if err != nil {
		if !opts.IgnoreDecryptionErrors {
			return nil, errors.Wrap(ErrDecryptionFailed, err.Error())
		}

		return buildMultipartRFC822(kr, msg, nil, opts)
	}

	hdr := getTextPartHeader(getMessageHeader(msg, opts), dec, msg.MIMEType)

	buf := new(bytes.Buffer)

	w, err := message.CreateWriter(buf, hdr)
	if err != nil {
		return nil, err
	}

	if _, err := w.Write(dec); err != nil {
		return nil, err
	}

	if err := w.Close(); err != nil {
		return nil, err
	}

	return buf.Bytes(), nil
}

func buildMultipartRFC822(
	kr *crypto.KeyRing,
	msg *pmapi.Message,
	attData [][]byte,
	opts JobOptions,
) ([]byte, error) {
	boundary := newBoundary(msg.ID)

	hdr := getMessageHeader(msg, opts)

	hdr.SetContentType("multipart/mixed", map[string]string{"boundary": boundary.gen()})

	buf := new(bytes.Buffer)

	w, err := message.CreateWriter(buf, hdr)
	if err != nil {
		return nil, err
	}

	var (
		inlineAtts []*pmapi.Attachment
		inlineData [][]byte
		attachAtts []*pmapi.Attachment
		attachData [][]byte
	)

	for i, att := range msg.Attachments {
		if att.Disposition == pmapi.DispositionInline {
			inlineAtts = append(inlineAtts, att)
			inlineData = append(inlineData, attData[i])
		} else {
			attachAtts = append(attachAtts, att)
			attachData = append(attachData, attData[i])
		}
	}

	if len(inlineAtts) > 0 {
		if err := writeRelatedParts(w, kr, boundary, msg, inlineAtts, inlineData, opts); err != nil {
			return nil, err
		}
	} else if err := writeTextPart(w, kr, msg, opts); err != nil {
		return nil, err
	}

	for i, att := range attachAtts {
		if err := writeAttachmentPart(w, kr, att, attachData[i], opts); err != nil {
			return nil, err
		}
	}

	if err := w.Close(); err != nil {
		return nil, err
	}

	return buf.Bytes(), nil
}

func writeTextPart(
	w *message.Writer,
	kr *crypto.KeyRing,
	msg *pmapi.Message,
	opts JobOptions,
) error {
	dec, err := msg.Decrypt(kr)
	if err != nil {
		if !opts.IgnoreDecryptionErrors {
			return errors.Wrap(ErrDecryptionFailed, err.Error())
		}

		return writeCustomTextPart(w, msg, err)
	}

	part, err := w.CreatePart(getTextPartHeader(message.Header{}, dec, msg.MIMEType))
	if err != nil {
		return err
	}

	if _, err := part.Write(dec); err != nil {
		return err
	}

	return part.Close()
}

func writeAttachmentPart(
	w *message.Writer,
	kr *crypto.KeyRing,
	att *pmapi.Attachment,
	attData []byte,
	opts JobOptions,
) error {
	kps, err := base64.StdEncoding.DecodeString(att.KeyPackets)
	if err != nil {
		return err
	}

	msg := crypto.NewPGPSplitMessage(kps, attData).GetPGPMessage()

	dec, err := kr.Decrypt(msg, nil, crypto.GetUnixTime())
	if err != nil {
		if !opts.IgnoreDecryptionErrors {
			return errors.Wrap(ErrDecryptionFailed, err.Error())
		}

		return writeCustomAttachmentPart(w, att, msg, err)
	}

	part, err := w.CreatePart(getAttachmentPartHeader(att))
	if err != nil {
		return err
	}

	if _, err := part.Write(dec.GetBinary()); err != nil {
		return err
	}

	return part.Close()
}

func writeRelatedParts(
	w *message.Writer,
	kr *crypto.KeyRing,
	boundary *boundary,
	msg *pmapi.Message,
	atts []*pmapi.Attachment,
	attData [][]byte,
	opts JobOptions,
) error {
	hdr := message.Header{}

	hdr.SetContentType("multipart/related", map[string]string{"boundary": boundary.gen()})

	rel, err := w.CreatePart(hdr)
	if err != nil {
		return err
	}

	if err := writeTextPart(rel, kr, msg, opts); err != nil {
		return err
	}

	for i, att := range atts {
		if err := writeAttachmentPart(rel, kr, att, attData[i], opts); err != nil {
			return err
		}
	}

	return rel.Close()
}

func buildEncryptedRFC822(kr *crypto.KeyRing, msg *pmapi.Message, opts JobOptions) ([]byte, error) {
	hdr := getMessageHeader(msg, opts)

	hdr.SetContentType("multipart/mixed", map[string]string{"boundary": newBoundary(msg.ID).gen()})

	buf := new(bytes.Buffer)

	w, err := message.CreateWriter(buf, hdr)
	if err != nil {
		return nil, err
	}

	dec, err := msg.Decrypt(kr)
	if err != nil {
		return nil, errors.Wrap(ErrDecryptionFailed, err.Error())
	}

	ent, err := message.Read(bytes.NewReader(dec))
	if err != nil {
		return nil, err
	}

	part, err := w.CreatePart(ent.Header)
	if err != nil {
		return nil, err
	}

	body, err := ioutil.ReadAll(ent.Body)
	if err != nil {
		return nil, err
	}

	if _, err := part.Write(body); err != nil {
		return nil, err
	}

	if err := part.Close(); err != nil {
		return nil, err
	}

	if err := w.Close(); err != nil {
		return nil, err
	}

	return buf.Bytes(), nil
}

func getMessageHeader(msg *pmapi.Message, opts JobOptions) message.Header { // nolint[funlen]
	hdr := toMessageHeader(msg.Header)

	// SetText will RFC2047-encode.
	if msg.Subject != "" {
		hdr.SetText("Subject", msg.Subject)
	}

	// mail.Address.String() will RFC2047-encode if necessary.
	if msg.Sender != nil {
		hdr.Set("From", msg.Sender.String())
	}

	if len(msg.ReplyTos) > 0 {
		hdr.Set("Reply-To", toAddressList(msg.ReplyTos))
	}

	if len(msg.ToList) > 0 {
		hdr.Set("To", toAddressList(msg.ToList))
	}

	if len(msg.CCList) > 0 {
		hdr.Set("Cc", toAddressList(msg.CCList))
	}

	if len(msg.BCCList) > 0 {
		hdr.Set("Bcc", toAddressList(msg.BCCList))
	}

	// Set Message-Id from ExternalID or ID if it's not already set.
	if hdr.Get("Message-Id") == "" {
		if msg.ExternalID != "" {
			hdr.Set("Message-Id", "<"+msg.ExternalID+">")
		} else {
			hdr.Set("Message-Id", "<"+msg.ID+"@"+pmapi.InternalIDDomain+">")
		}
	}

	// Sanitize the date; it needs to have a valid unix timestamp.
	if opts.SanitizeDate {
		if date, err := rfc5322.ParseDateTime(hdr.Get("Date")); err != nil || date.Before(time.Unix(0, 0)) {
			if msgTime := time.Unix(msg.Time, 0); msgTime.After(time.Unix(0, 0)) {
				hdr.Set("Date", msgTime.In(time.UTC).Format(time.RFC1123Z))
			} else {
				// No message should realistically be older than RFC822 itself.
				hdr.Set("Date", time.Date(1982, 8, 13, 0, 0, 0, 0, time.UTC).Format(time.RFC1123Z))
			}

			// We clobbered the date so we save it under X-Original-Date.
			hdr.Set("X-Original-Date", date.In(time.UTC).Format(time.RFC1123Z))
		}
	}

	// Set our internal ID if requested.
	// This is important for us to detect whether APPENDed things are actually "move like outlook".
	if opts.AddInternalID {
		hdr.Set("X-Pm-Internal-Id", msg.ID)
	}

	// Set our external ID if requested.
	// This was useful during debugging of applemail recovered messages; doesn't help with any behaviour.
	if opts.AddExternalID {
		hdr.Set("X-Pm-External-Id", "<"+msg.ExternalID+">")
	}

	// Set our server date if requested.
	// Can be useful to see how long it took for a message to arrive.
	if opts.AddMessageDate {
		hdr.Set("X-Pm-Date", time.Unix(msg.Time, 0).In(time.UTC).Format(time.RFC1123Z))
	}

	// Include the message ID in the references (supposedly this somehow improves outlook support...).
	if opts.AddMessageIDReference {
		if references := hdr.Get("References"); !strings.Contains(references, msg.ID) {
			hdr.Set("References", references+" <"+msg.ID+"@"+pmapi.InternalIDDomain+">")
		}
	}

	return hdr
}

func getTextPartHeader(hdr message.Header, body []byte, mimeType string) message.Header {
	params := make(map[string]string)

	if utf8.Valid(body) {
		params["charset"] = "utf-8"
	}

	hdr.SetContentType(mimeType, params)

	// Use quoted-printable for all text/... parts
	hdr.Set("Content-Transfer-Encoding", "quoted-printable")

	return hdr
}

func getAttachmentPartHeader(att *pmapi.Attachment) message.Header {
	hdr := toMessageHeader(mail.Header(att.Header))

	// All attachments have a content type.
	hdr.SetContentType(att.MIMEType, map[string]string{"name": mime.QEncoding.Encode("utf-8", att.Name)})

	// All attachments have a content disposition.
	hdr.SetContentDisposition(att.Disposition, map[string]string{"filename": mime.QEncoding.Encode("utf-8", att.Name)})

	// Use base64 for all attachments except embedded RFC822 messages.
	if att.MIMEType != "message/rfc822" {
		hdr.Set("Content-Transfer-Encoding", "base64")
	} else {
		hdr.Del("Content-Transfer-Encoding")
	}

	return hdr
}

func toMessageHeader(hdr mail.Header) message.Header {
	var res message.Header

	for key, val := range hdr {
		for _, val := range val {
			res.Add(key, val)
		}
	}

	return res
}

func toAddressList(addrs []*mail.Address) string {
	res := make([]string, len(addrs))

	for i, addr := range addrs {
		res[i] = addr.String()
	}

	return strings.Join(res, ", ")
}