fix(GODT-2479): Ensure messages always have a text body part

Proton Backend requires that all messages have at least one text/plain
or text/html body part, even if it is empty.

internal/bridge/send_test.go

@@ -330,3 +330,182 @@ func TestBridge_SendInvite(t *testing.T) {
 		})
 	})
 }
+
+func TestBridge_SendAddTextBodyPartIfNotExists(t *testing.T) {
+	const messageMultipartWithoutText = `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 messageMultipartWithText = `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-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/html;charset=utf8
+Content-Transfer-Encoding: quoted-printable
+
+Hello world
+
+--Apple-Mail=_E7AC06C7-4EB2-4453-8CBB-80F4412A7C84--
+`
+
+	const messageWithTextOnly = `Content-Type: text/plain;charset=utf8
+Content-Transfer-Encoding: quoted-printable
+Subject: A new message Part3
+Date: Mon, 13 Mar 2023 16:06:16 +0100
+
+Hello world
+
+`
+
+	const messageMultipartWithoutTextWithTextAttachment = `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-Type: text/plain; charset=UTF-8; name="text.txt"
+Content-Disposition: attachment; filename="text.txt"
+Content-Transfer-Encoding: base64
+
+SGVsbG8gd29ybGQK
+
+--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) {
+			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{
+				messageMultipartWithoutText,
+				messageMultipartWithText,
+				messageWithTextOnly,
+				messageMultipartWithoutTextWithTextAttachment,
+			}
+
+			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 := client.Dial(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 := client.Dial(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)
+				require.Equal(t, 4, len(messages))
+
+				// messages may not be in order
+				for _, message := range messages {
+					switch {
+					case message.Envelope.Subject == "A new message":
+						// The message that was sent should now include an empty text/plain body part since there was none
+						// in the original message.
+						require.Equal(t, 2, len(message.BodyStructure.Parts))
+
+						require.Equal(t, "text", message.BodyStructure.Parts[0].MIMEType)
+						require.Equal(t, "plain", message.BodyStructure.Parts[0].MIMESubType)
+						require.Equal(t, uint32(0), message.BodyStructure.Parts[0].Size)
+						require.Equal(t, "image", message.BodyStructure.Parts[1].MIMEType)
+						require.Equal(t, "jpeg", message.BodyStructure.Parts[1].MIMESubType)
+
+					case message.Envelope.Subject == "A new message Part2":
+						// This message already has a text body, should be unchanged
+						require.Equal(t, 2, len(message.BodyStructure.Parts))
+
+						require.Equal(t, "image", message.BodyStructure.Parts[1].MIMEType)
+						require.Equal(t, "jpeg", message.BodyStructure.Parts[1].MIMESubType)
+						require.Equal(t, "text", message.BodyStructure.Parts[0].MIMEType)
+						require.Equal(t, "html", message.BodyStructure.Parts[0].MIMESubType)
+
+					case message.Envelope.Subject == "A new message Part3":
+						// This message already has a text body, should be unchanged
+						require.Equal(t, 0, len(message.BodyStructure.Parts))
+
+						require.Equal(t, "text", message.BodyStructure.MIMEType)
+						require.Equal(t, "plain", message.BodyStructure.MIMESubType)
+
+					case message.Envelope.Subject == "A new message Part4":
+						// The message that was sent should now include an empty text/plain body part since even though
+						// there was only a text/plain attachment in the original message.
+						require.Equal(t, 2, len(message.BodyStructure.Parts))
+
+						require.Equal(t, "text", message.BodyStructure.Parts[0].MIMEType)
+						require.Equal(t, "plain", message.BodyStructure.Parts[0].MIMESubType)
+						require.Equal(t, uint32(0), message.BodyStructure.Parts[0].Size)
+						require.Equal(t, "text", message.BodyStructure.Parts[1].MIMEType)
+						require.Equal(t, "plain", message.BodyStructure.Parts[1].MIMESubType)
+						require.Equal(t, "attachment", message.BodyStructure.Parts[1].Disposition)
+					}
+				}
+
+				return true
+			}, 10*time.Second, 100*time.Millisecond)
+		})
+	})
+}

internal/bridge/sync_test.go

@@ -351,7 +351,7 @@ func withClient(ctx context.Context, t *testing.T, s *server.Server, username st
 	fn(ctx, c)
 }
 
-func clientFetch(client *client.Client, mailbox string) ([]*imap.Message, error) {
+func clientFetch(client *client.Client, mailbox string, extraItems ...imap.FetchItem) ([]*imap.Message, error) {
 	status, err := client.Select(mailbox, false)
 	if err != nil {
 		return nil, err
@@ -363,10 +363,13 @@ func clientFetch(client *client.Client, mailbox string) ([]*imap.Message, error)
 
 	resCh := make(chan *imap.Message)
 
+	fetchItems := []imap.FetchItem{imap.FetchFlags, imap.FetchEnvelope, imap.FetchUid, imap.FetchBodyStructure, "BODY.PEEK[]"}
+	fetchItems = append(fetchItems, extraItems...)
+
 	go func() {
 		if err := client.Fetch(
 			&imap.SeqSet{Set: []imap.Seq{{Start: 1, Stop: status.Messages}}},
-			[]imap.FetchItem{imap.FetchFlags, imap.FetchEnvelope, imap.FetchUid, "BODY.PEEK[]"},
+			fetchItems,
 			resCh,
 		); err != nil {
 			panic(err)

internal/user/smtp.go

@@ -117,6 +117,10 @@ func (user *User) sendMail(authID string, from string, to []string, r io.Reader)
 				return fmt.Errorf("failed to get first key: %w", err)
 			}
 
+			// Ensure that there is always a text/html or text/plain body part. This is required by the API. If none
+			// exists and empty text part will be added.
+			parser.AttachEmptyTextPartIfNoneExists()
+
 			// If we have to attach the public key, do it now.
 			if settings.AttachPublicKey {
 				key, err := addrKR.GetKey(0)

pkg/message/parser/parser.go

@@ -20,6 +20,7 @@ package parser
 import (
 	"fmt"
 	"io"
+	"strings"
 
 	"github.com/emersion/go-message"
 	"github.com/sirupsen/logrus"
@@ -81,6 +82,39 @@ func (p *Parser) AttachPublicKey(key, keyName string) {
 	})
 }
 
+func (p *Parser) AttachEmptyTextPartIfNoneExists() {
+	root := p.Root()
+	if root.isMultipartMixed() {
+		for _, v := range root.children {
+			// Must be an attachment of sorts, skip.
+			if v.Header.Has("Content-Disposition") {
+				continue
+			}
+			contentType, _, err := v.Header.ContentType()
+			if err == nil && strings.HasPrefix(contentType, "text/") {
+				// Message already has text part
+				return
+			}
+		}
+	} else {
+		contentType, _, err := root.Header.ContentType()
+		if err == nil && strings.HasPrefix(contentType, "text/") {
+			// Message already has text part
+			return
+		}
+	}
+
+	h := message.Header{}
+
+	h.Set("Content-Type", "text/plain;charset=utf8")
+	h.Set("Content-Transfer-Encoding", "quoted-printable")
+
+	p.Root().AddChild(&Part{
+		Header: h,
+		Body:   nil,
+	})
+}
+
 // Section returns the message part referred to by the given section. A section
 // is zero or more integers. For example, section 1.2.3 will return the third
 // part of the second part of the first part of the message.