fix(GODT-2887): Inline images with Apple Mail

Fix sending of inline images with Apple Mail when not using rich text.

internal/bridge/send_test.go

@@ -336,6 +336,9 @@ func TestBridge_SendInvite(t *testing.T) {
 }
 
 func TestBridge_SendAddTextBodyPartIfNotExists(t *testing.T) {
+	// NOTE: Prior to GODT-2887, these tests had inline images, however after the implementation to support
+	// inline images new parts are injected to reference inline images without content-id set. The images
+	// in this test have been changed to regular attachments to keep the original checks in place.
 	const messageMultipartWithoutText = `Content-Type: multipart/mixed;
   boundary="Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84"
 Subject: A new message
@@ -343,7 +346,7 @@ Date: Mon, 13 Mar 2023 16:06:16 +0100
 
 
 --Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84
-Content-Disposition: inline;
+Content-Disposition: attachment;
   filename=Cat_August_2010-4.jpeg
 Content-Type: image/jpeg;
   name="Cat_August_2010-4.jpeg"
@@ -360,7 +363,7 @@ Subject: A new message Part2
 Date: Mon, 13 Mar 2023 16:06:16 +0100
 
 --Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84
-Content-Disposition: inline;
+Content-Disposition: attachment;
   filename=Cat_August_2010-4.jpeg
 Content-Type: image/jpeg;
   name="Cat_August_2010-4.jpeg"
@@ -520,3 +523,181 @@ SGVsbG8gd29ybGQK
 		})
 	})
 }
+
+func TestBridge_SendInlineImage(t *testing.T) {
+	const messageInlineImageOnly = `Content-Type: multipart/mixed;
+  boundary="Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84"
+Subject: A new message
+Date: Mon, 13 Mar 2023 16:06:16 +0100
+
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84
+Content-Disposition: inline;
+  filename=Cat_August_2010-4.jpeg
+Content-Type: image/jpeg;
+  name="Cat_August_2010-4.jpeg"
+Content-Transfer-Encoding: base64
+
+SGVsbG8gd29ybGQ=
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84--
+	`
+
+	const messageInlineImageWithHTML = `Content-Type: multipart/mixed;
+  boundary="Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84"
+Subject: A new message Part2 
+Date: Mon, 13 Mar 2023 16:06:16 +0100
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84
+Content-Type: text/html;charset=utf8
+Content-Transfer-Encoding: quoted-printable
+
+Hello world
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84
+Content-Disposition: inline;
+  filename=Cat_August_2010-4.jpeg
+Content-Type: image/jpeg;
+  name="Cat_August_2010-4.jpeg"
+Content-Transfer-Encoding: base64
+
+SGVsbG8gd29ybGQ=
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84--
+`
+
+	const messageInlineImageWithText = `Content-Type: multipart/mixed;
+  boundary="Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84"
+Subject: A new message Part3
+Date: Mon, 13 Mar 2023 16:06:16 +0100
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84
+Content-Type: text/plain;charset=utf8
+Content-Transfer-Encoding: quoted-printable
+
+Hello world
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84
+Content-Disposition: inline;
+  filename=Cat_August_2010-4.jpeg
+Content-Type: image/jpeg;
+  name="Cat_August_2010-4.jpeg"
+Content-Transfer-Encoding: base64
+
+SGVsbG8gd29ybGQ=
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84--
+`
+
+	const messageInlineImageFollowedByText = `Content-Type: multipart/mixed;
+  boundary="Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84"
+Subject: A new message Part4
+Date: Mon, 13 Mar 2023 16:06:16 +0100
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84
+Content-Disposition: inline;
+  filename=Cat_August_2010-4.jpeg
+Content-Type: image/jpeg;
+  name="Cat_August_2010-4.jpeg"
+Content-Transfer-Encoding: base64
+
+SGVsbG8gd29ybGQ=
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84
+Content-Type: text/plain;charset=utf8
+Content-Transfer-Encoding: quoted-printable
+
+Hello world
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84--
+`
+	withEnv(t, func(ctx context.Context, s *server.Server, netCtl *proton.NetCtl, locator bridge.Locator, storeKey []byte) {
+		_, _, err := s.CreateUser("recipient", password)
+		require.NoError(t, err)
+
+		withBridge(ctx, t, s.GetHostURL(), netCtl, locator, storeKey, func(bridge *bridge.Bridge, _ *bridge.Mocks) {
+			smtpWaiter := waitForSMTPServerReady(bridge)
+			defer smtpWaiter.Done()
+
+			senderUserID, err := bridge.LoginFull(ctx, username, password, nil, nil)
+			require.NoError(t, err)
+
+			recipientUserID, err := bridge.LoginFull(ctx, "recipient", password, nil, nil)
+			require.NoError(t, err)
+
+			senderInfo, err := bridge.GetUserInfo(senderUserID)
+			require.NoError(t, err)
+
+			recipientInfo, err := bridge.GetUserInfo(recipientUserID)
+			require.NoError(t, err)
+
+			messages := []string{
+				messageInlineImageOnly,
+				messageInlineImageWithHTML,
+				messageInlineImageWithText,
+				messageInlineImageFollowedByText,
+			}
+
+			smtpWaiter.Wait()
+
+			for _, m := range messages {
+				// Dial the server.
+				client, err := smtp.Dial(net.JoinHostPort(constants.Host, fmt.Sprint(bridge.GetSMTPPort())))
+				require.NoError(t, err)
+				defer client.Close() //nolint:errcheck
+
+				// Upgrade to TLS.
+				require.NoError(t, client.StartTLS(&tls.Config{InsecureSkipVerify: true}))
+
+				// Authorize with SASL LOGIN.
+				require.NoError(t, client.Auth(sasl.NewLoginClient(
+					senderInfo.Addresses[0],
+					string(senderInfo.BridgePass)),
+				))
+
+				// Send the message.
+				require.NoError(t, client.SendMail(
+					senderInfo.Addresses[0],
+					[]string{recipientInfo.Addresses[0]},
+					strings.NewReader(m),
+				))
+			}
+
+			// Connect the sender IMAP client.
+			senderIMAPClient, err := eventuallyDial(net.JoinHostPort(constants.Host, fmt.Sprint(bridge.GetIMAPPort())))
+			require.NoError(t, err)
+			require.NoError(t, senderIMAPClient.Login(senderInfo.Addresses[0], string(senderInfo.BridgePass)))
+			defer senderIMAPClient.Logout() //nolint:errcheck
+
+			// Connect the recipient IMAP client.
+			recipientIMAPClient, err := eventuallyDial(net.JoinHostPort(constants.Host, fmt.Sprint(bridge.GetIMAPPort())))
+			require.NoError(t, err)
+			require.NoError(t, recipientIMAPClient.Login(recipientInfo.Addresses[0], string(recipientInfo.BridgePass)))
+			defer recipientIMAPClient.Logout() //nolint:errcheck
+
+			require.Eventually(t, func() bool {
+				messages, err := clientFetch(senderIMAPClient, `Sent`, imap.FetchBodyStructure)
+				require.NoError(t, err)
+				if len(messages) != 4 {
+					return false
+				}
+
+				// messages may not be in order
+				for _, message := range messages {
+					require.Equal(t, 1, len(message.BodyStructure.Parts))
+					require.Equal(t, "multipart", message.BodyStructure.MIMEType)
+					require.Equal(t, "mixed", message.BodyStructure.MIMESubType)
+					require.Equal(t, "multipart", message.BodyStructure.Parts[0].MIMEType)
+					require.Equal(t, "related", message.BodyStructure.Parts[0].MIMESubType)
+					require.Len(t, message.BodyStructure.Parts[0].Parts, 2)
+					require.Equal(t, "text", message.BodyStructure.Parts[0].Parts[0].MIMEType)
+					require.Equal(t, "html", message.BodyStructure.Parts[0].Parts[0].MIMESubType)
+					require.Equal(t, "image", message.BodyStructure.Parts[0].Parts[1].MIMEType)
+					require.Equal(t, "jpeg", message.BodyStructure.Parts[0].Parts[1].MIMESubType)
+				}
+
+				return true
+			}, 10*time.Second, 100*time.Millisecond)
+		})
+	})
+}

pkg/message/parser.go

@@ -32,6 +32,7 @@ import (
 	"github.com/ProtonMail/proton-bridge/v3/pkg/message/parser"
 	pmmime "github.com/ProtonMail/proton-bridge/v3/pkg/mime"
 	"github.com/emersion/go-message"
+	"github.com/google/uuid"
 	"github.com/jaytaylor/html2text"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
@@ -116,6 +117,10 @@ func parse(p *parser.Parser, allowInvalidAddressLists bool) (Message, error) {
 		return Message{}, errors.Wrap(err, "failed to convert foreign encodings")
 	}
 
+	if err := patchInlineImages(p); err != nil {
+		return Message{}, err
+	}
+
 	m, err := parseMessageHeader(p.Root().Header, allowInvalidAddressLists)
 	if err != nil {
 		return Message{}, errors.Wrap(err, "failed to parse message header")
@@ -636,3 +641,168 @@ func forEachDecodedHeaderField(h message.Header, fn func(string, string) error)
 
 	return nil
 }
+
+func patchInlineImages(p *parser.Parser) error {
+	// This code will only attempt to patch the root level children. I tested with different email clients and as soon
+	// as you reply/forward a message the entire content gets converted into HTML (Apple Mail/Thunderbird/Evolution).
+	// If you are forcing text formatting (Evolution), the inline images of the original email are stripped.
+	// The only reason we need to apply this modification is that Apple Mail can send out text + inline image parts
+	// if the text does not exceed the 76 char column limit.
+	// Based on this, it's unlikely we will see any other variations.
+	root := p.Root()
+
+	children := root.Children()
+
+	if len(children) < 2 {
+		return nil
+	}
+
+	result := make([]inlinePatchJob, len(children))
+
+	var (
+		transformationNeeded bool
+		prevPart             *parser.Part
+		prevContentType      string
+		prevContentTypeMap   map[string]string
+	)
+
+	for i := 0; i < len(children); i++ {
+		curPart := children[i]
+
+		contentType, contentTypeMap, err := curPart.ContentType()
+		if err != nil {
+			return fmt.Errorf("failed to get content type for for child %v:%w", i, err)
+		}
+
+		if rfc822.MIMEType(contentType) == rfc822.TextPlain {
+			result[i] = &inlinePatchBodyOnly{part: curPart, contentTypeMap: contentTypeMap}
+		} else if strings.HasPrefix(contentType, "image/") {
+			disposition, _, err := curPart.ContentDisposition()
+			if err != nil {
+				return fmt.Errorf("failted to get content disposition for child %v:%w", i, err)
+			}
+
+			if disposition == "inline" && !curPart.HasContentID() {
+				if rfc822.MIMEType(prevContentType) == rfc822.TextPlain {
+					result[i-1] = &inlinePatchBodyWithInlineImage{
+						textPart:           prevPart,
+						imagePart:          curPart,
+						textContentTypeMap: prevContentTypeMap,
+					}
+				} else {
+					result[i] = &inlinePatchInlineImageOnly{part: curPart, partIndex: i, root: root}
+				}
+				transformationNeeded = true
+			}
+		}
+		prevPart = curPart
+		prevContentType = contentType
+		prevContentTypeMap = contentTypeMap
+	}
+
+	if !transformationNeeded {
+		return nil
+	}
+
+	for _, t := range result {
+		if t != nil {
+			t.Patch()
+		}
+	}
+
+	return nil
+}
+
+type inlinePatchJob interface {
+	Patch()
+}
+
+// inlinePatchBodyOnly is meant to be used for standalone text parts that need to be converted to html once we applty
+// one of the changes.
+type inlinePatchBodyOnly struct {
+	part           *parser.Part
+	contentTypeMap map[string]string
+}
+
+func (i *inlinePatchBodyOnly) Patch() {
+	newBody := []byte(`<html><body><p>`)
+	newBody = append(newBody, patchNewLineWithHTMLBreaks(i.part.Body)...)
+	newBody = append(newBody, []byte(`</p></body></html>`)...)
+
+	i.part.Body = newBody
+	i.part.Header.SetContentType("text/html", i.contentTypeMap)
+}
+
+// inlinePatchBodyWithInlineImage patches a previous text part so that it refers to that inline image.
+type inlinePatchBodyWithInlineImage struct {
+	textPart           *parser.Part
+	textContentTypeMap map[string]string
+	imagePart          *parser.Part
+}
+
+// inlinePatchInlineImageOnly handle the case where the inline image is not proceeded by a text part. To avoid
+// having to parse any possible previous part, we just inject a new part that references this image.
+type inlinePatchInlineImageOnly struct {
+	part      *parser.Part
+	partIndex int
+	root      *parser.Part
+}
+
+func (i inlinePatchInlineImageOnly) Patch() {
+	contentID := uuid.NewString()
+	// Convert previous part to text/html && inject image.
+	newBody := []byte(fmt.Sprintf(`<html><body><img src="cid:%v"/></body></html>`, contentID))
+
+	i.part.Header.Set("content-id", contentID)
+
+	// create new text part
+	textPart := &parser.Part{
+		Header: message.Header{},
+		Body:   newBody,
+	}
+
+	textPart.Header.SetContentType("text/html", map[string]string{"charset": "UTF-8"})
+
+	i.root.InsertChild(i.partIndex, textPart)
+}
+
+func (i *inlinePatchBodyWithInlineImage) Patch() {
+	contentID := uuid.NewString()
+	// Convert previous part to text/html && inject image.
+	newBody := []byte(`<html><body><p>`)
+	newBody = append(newBody, patchNewLineWithHTMLBreaks(i.textPart.Body)...)
+	newBody = append(newBody, []byte(`</p>`)...)
+	newBody = append(newBody, []byte(fmt.Sprintf(`<img src="cid:%v"/>`, contentID))...)
+	newBody = append(newBody, []byte(`</body></html>`)...)
+
+	i.textPart.Body = newBody
+	i.textPart.Header.SetContentType("text/html", i.textContentTypeMap)
+
+	// Add content id to curPart
+	i.imagePart.Header.Set("content-id", contentID)
+}
+
+func patchNewLineWithHTMLBreaks(input []byte) []byte {
+	dst := make([]byte, 0, len(input))
+	index := 0
+	for {
+		slice := input[index:]
+		newLineIndex := bytes.IndexByte(slice, '\n')
+
+		if newLineIndex == -1 {
+			dst = append(dst, input[index:]...)
+			return dst
+		}
+
+		injectIndex := newLineIndex
+		if newLineIndex > 0 && slice[newLineIndex-1] == '\r' {
+			injectIndex--
+		}
+
+		dst = append(dst, slice[0:injectIndex]...)
+		dst = append(dst, '<', 'b', 'r', '/', '>')
+		dst = append(dst, slice[injectIndex:newLineIndex+1]...)
+
+		index += newLineIndex + 1
+	}
+}

pkg/message/parser/part.go

@@ -27,6 +27,7 @@ import (
 	"github.com/PuerkitoBio/goquery"
 	"github.com/emersion/go-message"
 	"github.com/sirupsen/logrus"
+	"golang.org/x/exp/slices"
 	"golang.org/x/net/html"
 	"golang.org/x/net/html/charset"
 	"golang.org/x/text/encoding"
@@ -52,6 +53,14 @@ func (p *Part) ContentType() (string, map[string]string, error) {
 	return t, params, err
 }
 
+func (p *Part) ContentDisposition() (string, map[string]string, error) {
+	return p.Header.ContentDisposition()
+}
+
+func (p *Part) HasContentID() bool {
+	return len(p.Header.Get("content-id")) != 0
+}
+
 func (p *Part) Child(n int) (part *Part, err error) {
 	if len(p.children) < n {
 		return nil, errors.New("no such part")
@@ -81,6 +90,14 @@ func (p *Part) AddChild(child *Part) {
 	}
 }
 
+func (p *Part) InsertChild(index int, child *Part) {
+	if p.isMultipartMixedOrRelated() {
+		p.children = slices.Insert(p.children, index, child)
+	} else {
+		p.AddChild(child)
+	}
+}
+
 func (p *Part) ConvertToUTF8() error {
 	logrus.Trace("Converting part to utf-8")
 
@@ -183,6 +200,15 @@ func (p *Part) isMultipartMixed() bool {
 	return t == "multipart/mixed"
 }
 
+func (p *Part) isMultipartMixedOrRelated() bool {
+	t, _, err := p.ContentType()
+	if err != nil {
+		return false
+	}
+
+	return t == "multipart/mixed" || t == "multipart/related"
+}
+
 func getContentHeaders(header message.Header) message.Header {
 	var res message.Header
 

pkg/message/parser_test.go

@@ -19,6 +19,7 @@ package message
 
 import (
 	"bytes"
+	"fmt"
 	"image/png"
 	"io"
 	"os"
@@ -312,11 +313,13 @@ func TestParseTextPlainWithImageInline(t *testing.T) {
 	m, err := Parse(f)
 	require.NoError(t, err)
 
+	require.NotEmpty(t, m.Attachments[0].ContentID)
+
 	assert.Equal(t, `"Sender" <sender@pm.me>`, m.Sender.String())
 	assert.Equal(t, `"Receiver" <receiver@pm.me>`, m.ToList[0].String())
 
-	assert.Equal(t, "body", string(m.RichBody))
 	assert.Equal(t, "body", string(m.PlainBody))
+	assert.Equal(t, fmt.Sprintf(`<html><body><p>body</p><img src="cid:%v"/></body></html>`, m.Attachments[0].ContentID), string(m.RichBody))
 
 	// The inline image is an 8x8 mic-dropping gopher.
 	require.Len(t, m.Attachments, 1)
@@ -326,6 +329,69 @@ func TestParseTextPlainWithImageInline(t *testing.T) {
 	assert.Equal(t, 8, img.Height)
 }
 
+func TestParseTextPlainWithImageInlineWithMoreTextParts(t *testing.T) {
+	// Inline image test with text - image - text, ensure all parts are convert to html
+	f := getFileReader("text_plain_image_inline2.eml")
+
+	m, err := Parse(f)
+	require.NoError(t, err)
+
+	require.NotEmpty(t, m.Attachments[0].ContentID)
+	assert.Equal(t, "bodybody2", string(m.PlainBody))
+	assert.Equal(t, fmt.Sprintf("<html><body><p>body</p><img src=\"cid:%v\"/></body></html><html><body><p>body2<br/>\n</p></body></html>", m.Attachments[0].ContentID), string(m.RichBody))
+
+	// The inline image is an 8x8 mic-dropping gopher.
+	require.Len(t, m.Attachments, 1)
+	img, err := png.DecodeConfig(bytes.NewReader(m.Attachments[0].Data))
+	require.NoError(t, err)
+	assert.Equal(t, 8, img.Width)
+	assert.Equal(t, 8, img.Height)
+}
+
+func TestParseTextPlainWithImageInlineAfterOtherAttachment(t *testing.T) {
+	// Inline image test with text - image - text, ensure all parts are convert to html
+	f := getFileReader("text_plain_image_inline2.eml")
+
+	m, err := Parse(f)
+	require.NoError(t, err)
+
+	require.NotEmpty(t, m.Attachments[0].ContentID)
+	assert.Equal(t, "bodybody2", string(m.PlainBody))
+	assert.Equal(t, fmt.Sprintf("<html><body><p>body</p><img src=\"cid:%v\"/></body></html><html><body><p>body2<br/>\n</p></body></html>", m.Attachments[0].ContentID), string(m.RichBody))
+
+	// The inline image is an 8x8 mic-dropping gopher.
+	require.Len(t, m.Attachments, 1)
+	img, err := png.DecodeConfig(bytes.NewReader(m.Attachments[0].Data))
+	require.NoError(t, err)
+	assert.Equal(t, 8, img.Width)
+	assert.Equal(t, 8, img.Height)
+}
+
+func TestParseTextPlainWithImageBetweenAttachments(t *testing.T) {
+	// Inline image test with text - pdf - image - text. A new part must be created to be injected.
+	f := getFileReader("text_plain_image_inline_between_attachment.eml")
+
+	m, err := Parse(f)
+	require.NoError(t, err)
+
+	require.Empty(t, m.Attachments[0].ContentID)
+	require.NotEmpty(t, m.Attachments[1].ContentID)
+	assert.Equal(t, "bodybody2", string(m.PlainBody))
+	assert.Equal(t, fmt.Sprintf("<html><body><p>body</p></body></html><html><body><img src=\"cid:%v\"/></body></html><html><body><p>body2<br/>\n</p></body></html>", m.Attachments[1].ContentID), string(m.RichBody))
+}
+
+func TestParseTextPlainWithImageFirst(t *testing.T) {
+	// Inline image test with text - pdf - image - text. A new part must be created to be injected.
+	f := getFileReader("text_plain_image_inline_attachment_first.eml")
+
+	m, err := Parse(f)
+	require.NoError(t, err)
+
+	require.NotEmpty(t, m.Attachments[0].ContentID)
+	assert.Equal(t, "body", string(m.PlainBody))
+	assert.Equal(t, fmt.Sprintf("<html><body><img src=\"cid:%v\"/></body></html><html><body><p>body</p></body></html>", m.Attachments[0].ContentID), string(m.RichBody))
+}
+
 func TestParseTextPlainWithDuplicateCharset(t *testing.T) {
 	f := getFileReader("text_plain_duplicate_charset.eml")
 
@@ -428,11 +494,12 @@ func TestParseTextHTMLWithImageInline(t *testing.T) {
 	assert.Equal(t, `"Sender" <sender@pm.me>`, m.Sender.String())
 	assert.Equal(t, `"Receiver" <receiver@pm.me>`, m.ToList[0].String())
 
-	assert.Equal(t, "<html><head></head><body>This is body of <b>HTML mail</b> with attachment</body></html>", string(m.RichBody))
+	require.Len(t, m.Attachments, 1)
+
+	assert.Equal(t, fmt.Sprintf(`<html><head></head><body>This is body of <b>HTML mail</b> with attachment</body></html><html><body><img src="cid:%v"/></body></html>`, m.Attachments[0].ContentID), string(m.RichBody))
 	assert.Equal(t, "This is body of *HTML mail* with attachment", string(m.PlainBody))
 
 	// The inline image is an 8x8 mic-dropping gopher.
-	require.Len(t, m.Attachments, 1)
 	img, err := png.DecodeConfig(bytes.NewReader(m.Attachments[0].Data))
 	require.NoError(t, err)
 	assert.Equal(t, 8, img.Width)
@@ -719,6 +786,23 @@ func TestParseTextPlainWithDocxAttachmentCyrillic(t *testing.T) {
 	assert.Equal(t, "АБВГДЃЕЖЗЅИЈКЛЉМНЊОПРСТЌУФХЧЏЗШ.docx", m.Attachments[0].Name)
 }
 
+func TestPatchNewLineWithHtmlBreaks(t *testing.T) {
+	{
+		input := []byte("\nfoo\nbar\n\n\nzz\nddd")
+		expected := []byte("<br/>\nfoo<br/>\nbar<br/>\n<br/>\n<br/>\nzz<br/>\nddd")
+
+		result := patchNewLineWithHTMLBreaks(input)
+		require.Equal(t, expected, result)
+	}
+	{
+		input := []byte("\r\nfoo\r\nbar\r\n\r\n\r\nzz\r\nddd")
+		expected := []byte("<br/>\r\nfoo<br/>\r\nbar<br/>\r\n<br/>\r\n<br/>\r\nzz<br/>\r\nddd")
+
+		result := patchNewLineWithHTMLBreaks(input)
+		require.Equal(t, expected, result)
+	}
+}
+
 func getFileReader(filename string) io.Reader {
 	f, err := os.Open(filepath.Join("testdata", filename))
 	if err != nil {

pkg/message/testdata/text_plain_image_inline2.eml

@@ -0,0 +1,39 @@
+From: Sender <sender@pm.me>
+To: Receiver <receiver@pm.me>
+Content-Type: multipart/related; boundary=longrandomstring
+
+--longrandomstring
+
+body
+--longrandomstring
+Content-Type: image/png
+Content-Disposition: inline
+Content-Transfer-Encoding: base64
+
+iVBORw0KGgoAAAANSUhEUgAAAAgAAAAICAYAAADED76LAAAABGdBTUEAALGPC/xhBQAAACBjSFJ
+NAAB6JgAAgIQAAPoAAACA6AAAdTAAAOpgAAA6mAAAF3CculE8AAAAhGVYSWZNTQAqAAAACAAFAR
+IAAwAAAAEAAQAAARoABQAAAAEAAABKARsABQAAAAEAAABSASgAAwAAAAEAAgAAh2kABAAAAAEAA
+ABaAAAAAAAAASwAAAABAAABLAAAAAEAA6ABAAMAAAABAAEAAKACAAQAAAABAAAACKADAAQAAAAB
+AAAACAAAAAAAXWZ6AAAACXBIWXMAAC4jAAAuIwF4pT92AAACZmlUWHRYTUw6Y29tLmFkb2JlLnh
+tcAAAAAAAPHg6eG1wbWV0YSB4bWxuczp4PSJhZG9iZTpuczptZXRhLyIgeDp4bXB0az0iWE1QIE
+NvcmUgNS40LjAiPgogICA8cmRmOlJERiB4bWxuczpyZGY9Imh0dHA6Ly93d3cudzMub3JnLzE5O
+TkvMDIvMjItcmRmLXN5bnRheC1ucyMiPgogICAgICA8cmRmOkRlc2NyaXB0aW9uIHJkZjphYm91
+dD0iIgogICAgICAgICAgICB4bWxuczp0aWZmPSJodHRwOi8vbnMuYWRvYmUuY29tL3RpZmYvMS4
+wLyIKICAgICAgICAgICAgeG1sbnM6ZXhpZj0iaHR0cDovL25zLmFkb2JlLmNvbS9leGlmLzEuMC
+8iPgogICAgICAgICA8dGlmZjpPcmllbnRhdGlvbj4xPC90aWZmOk9yaWVudGF0aW9uPgogICAgI
+CAgICA8dGlmZjpSZXNvbHV0aW9uVW5pdD4yPC90aWZmOlJlc29sdXRpb25Vbml0PgogICAgICAg
+ICA8ZXhpZjpDb2xvclNwYWNlPjE8L2V4aWY6Q29sb3JTcGFjZT4KICAgICAgICAgPGV4aWY6UGl
+4ZWxYRGltZW5zaW9uPjE2PC9leGlmOlBpeGVsWERpbWVuc2lvbj4KICAgICAgICAgPGV4aWY6UG
+l4ZWxZRGltZW5zaW9uPjE2PC9leGlmOlBpeGVsWURpbWVuc2lvbj4KICAgICAgPC9yZGY6RGVzY
+3JpcHRpb24+CiAgIDwvcmRmOlJERj4KPC94OnhtcG1ldGE+CgZBD4sAAAEISURBVBgZY2CAAO5F
+x07Zz96xZ0Pn4lXqIKGGhgYmsFTHvAWdW6/dvnb89Yf/B5+9/r/y9IXzbVPahCH6/jMysfAJygo
+JC2r++/T619Mb139J8HIb8Gs5hYMUzJ+/gJ1Jmo9H6c+L5wz3bt5iEeLmYOHn42fQ4vyacqGNQS
+0xMfEHc7Cvl6CYho4rh5jUPyYefqafLKyMbH9+/d28/dFfdWtfDaZvTy7Zvv72nYGZkeEvw98/f
+5j//2P4yCvxq/nU7zVs//8yM2gzMMitOnnu5cUff/8ff/v5/5Xf///vuHBhJcSRDAws9aEMr38c
+W7XjNgvzexZ2rn9vbjx/IXl/M9iLM2fOZAUAKCZv7dU+UgAAAAAASUVORK5CYII=
+
+--longrandomstring
+
+body2
+
+--longrandomstring--

pkg/message/testdata/text_plain_image_inline_attachment_first.eml

@@ -0,0 +1,35 @@
+From: Sender <sender@pm.me>
+To: Receiver <receiver@pm.me>
+Content-Type: multipart/related; boundary=longrandomstring
+
+--longrandomstring
+Content-Type: image/png
+Content-Disposition: inline
+Content-Transfer-Encoding: base64
+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=
+
+--longrandomstring
+
+body
+--longrandomstring--

pkg/message/testdata/text_plain_image_inline_between_attachment.eml

@@ -0,0 +1,46 @@
+From: Sender <sender@pm.me>
+To: Receiver <receiver@pm.me>
+Content-Type: multipart/related; boundary=longrandomstring
+
+--longrandomstring
+
+body
+--longrandomstring
+Content-Type: application/pdf
+Content-Disposition: inline
+Content-Transfer-Encoding: base64
+
+aGVsbG8gd29ybGQgcGRm
+
+--longrandomstring
+Content-Type: image/png
+Content-Disposition: inline
+Content-Transfer-Encoding: base64
+
+iVBORw0KGgoAAAANSUhEUgAAAAgAAAAICAYAAADED76LAAAABGdBTUEAALGPC/xhBQAAACBjSFJ
+NAAB6JgAAgIQAAPoAAACA6AAAdTAAAOpgAAA6mAAAF3CculE8AAAAhGVYSWZNTQAqAAAACAAFAR
+IAAwAAAAEAAQAAARoABQAAAAEAAABKARsABQAAAAEAAABSASgAAwAAAAEAAgAAh2kABAAAAAEAA
+ABaAAAAAAAAASwAAAABAAABLAAAAAEAA6ABAAMAAAABAAEAAKACAAQAAAABAAAACKADAAQAAAAB
+AAAACAAAAAAAXWZ6AAAACXBIWXMAAC4jAAAuIwF4pT92AAACZmlUWHRYTUw6Y29tLmFkb2JlLnh
+tcAAAAAAAPHg6eG1wbWV0YSB4bWxuczp4PSJhZG9iZTpuczptZXRhLyIgeDp4bXB0az0iWE1QIE
+NvcmUgNS40LjAiPgogICA8cmRmOlJERiB4bWxuczpyZGY9Imh0dHA6Ly93d3cudzMub3JnLzE5O
+TkvMDIvMjItcmRmLXN5bnRheC1ucyMiPgogICAgICA8cmRmOkRlc2NyaXB0aW9uIHJkZjphYm91
+dD0iIgogICAgICAgICAgICB4bWxuczp0aWZmPSJodHRwOi8vbnMuYWRvYmUuY29tL3RpZmYvMS4
+wLyIKICAgICAgICAgICAgeG1sbnM6ZXhpZj0iaHR0cDovL25zLmFkb2JlLmNvbS9leGlmLzEuMC
+8iPgogICAgICAgICA8dGlmZjpPcmllbnRhdGlvbj4xPC90aWZmOk9yaWVudGF0aW9uPgogICAgI
+CAgICA8dGlmZjpSZXNvbHV0aW9uVW5pdD4yPC90aWZmOlJlc29sdXRpb25Vbml0PgogICAgICAg
+ICA8ZXhpZjpDb2xvclNwYWNlPjE8L2V4aWY6Q29sb3JTcGFjZT4KICAgICAgICAgPGV4aWY6UGl
+4ZWxYRGltZW5zaW9uPjE2PC9leGlmOlBpeGVsWERpbWVuc2lvbj4KICAgICAgICAgPGV4aWY6UG
+l4ZWxZRGltZW5zaW9uPjE2PC9leGlmOlBpeGVsWURpbWVuc2lvbj4KICAgICAgPC9yZGY6RGVzY
+3JpcHRpb24+CiAgIDwvcmRmOlJERj4KPC94OnhtcG1ldGE+CgZBD4sAAAEISURBVBgZY2CAAO5F
+x07Zz96xZ0Pn4lXqIKGGhgYmsFTHvAWdW6/dvnb89Yf/B5+9/r/y9IXzbVPahCH6/jMysfAJygo
+JC2r++/T619Mb139J8HIb8Gs5hYMUzJ+/gJ1Jmo9H6c+L5wz3bt5iEeLmYOHn42fQ4vyacqGNQS
+0xMfEHc7Cvl6CYho4rh5jUPyYefqafLKyMbH9+/d28/dFfdWtfDaZvTy7Zvv72nYGZkeEvw98/f
+5j//2P4yCvxq/nU7zVs//8yM2gzMMitOnnu5cUff/8ff/v5/5Xf///vuHBhJcSRDAws9aEMr38c
+W7XjNgvzexZ2rn9vbjx/IXl/M9iLM2fOZAUAKCZv7dU+UgAAAAAASUVORK5CYII=
+
+--longrandomstring
+
+body2
+
+--longrandomstring--