fix(GODT-1804): Only promote content headers if non-empty

When attaching public key, we take the root mime part, create a new root,
and put the old root alongside an additional public key mime part.
But when moving the root, we would copy all content headers, even empty ones.
So we’d be left with Content-Disposition: "" which would fail to parse.

internal/bridge/send_test.go

@@ -18,10 +18,12 @@
 package bridge_test
 
 import (
+	"bytes"
 	"context"
 	"crypto/tls"
 	"fmt"
 	"net"
+	"os"
 	"strings"
 	"testing"
 	"time"
@@ -217,3 +219,114 @@ func TestBridge_SendDraftFlags(t *testing.T) {
 		})
 	})
 }
+
+func TestBridge_SendInvite(t *testing.T) {
+	withEnv(t, func(ctx context.Context, s *server.Server, netCtl *proton.NetCtl, locator bridge.Locator, storeKey []byte) {
+		// Create a recipient user.
+		_, _, err := s.CreateUser("recipient", password)
+		require.NoError(t, err)
+
+		// Set "attach public keys" to true for the user.
+		withClient(ctx, t, s, username, password, func(ctx context.Context, client *proton.Client) {
+			settings, err := client.SetAttachPublicKey(ctx, proton.SetAttachPublicKeyReq{AttachPublicKey: true})
+			require.NoError(t, err)
+			require.Equal(t, proton.Bool(true), settings.AttachPublicKey)
+		})
+
+		// The sender should be fully synced.
+		withBridge(ctx, t, s.GetHostURL(), netCtl, locator, storeKey, func(bridge *bridge.Bridge, _ *bridge.Mocks) {
+			syncCh, done := chToType[events.Event, events.SyncFinished](bridge.GetEvents(events.SyncFinished{}))
+			defer done()
+
+			userID, err := bridge.LoginFull(ctx, username, password, nil, nil)
+			require.NoError(t, err)
+
+			require.Equal(t, userID, (<-syncCh).UserID)
+		})
+
+		// Start the bridge.
+		withBridge(ctx, t, s.GetHostURL(), netCtl, locator, storeKey, func(bridge *bridge.Bridge, _ *bridge.Mocks) {
+			// Get the sender user info.
+			userInfo, err := bridge.QueryUserInfo(username)
+			require.NoError(t, err)
+
+			// Connect the sender IMAP client.
+			imapClient, err := client.Dial(net.JoinHostPort(constants.Host, fmt.Sprint(bridge.GetIMAPPort())))
+			require.NoError(t, err)
+			require.NoError(t, imapClient.Login(userInfo.Addresses[0], string(userInfo.BridgePass)))
+			defer imapClient.Logout() //nolint:errcheck
+
+			// The message to send.
+			b, err := os.ReadFile("testdata/invite.eml")
+			require.NoError(t, err)
+
+			// Save a draft.
+			require.NoError(t, imapClient.Append("Drafts", []string{imap.DraftFlag}, time.Now(), bytes.NewReader(b)))
+
+			// Assert that the draft exists and is marked as a draft.
+			{
+				messages, err := clientFetch(imapClient, "Drafts")
+				require.NoError(t, err)
+				require.Len(t, messages, 1)
+				require.Contains(t, messages[0].Flags, imap.DraftFlag)
+			}
+
+			// Connect the SMTP client.
+			smtpClient, err := smtp.Dial(net.JoinHostPort(constants.Host, fmt.Sprint(bridge.GetSMTPPort())))
+			require.NoError(t, err)
+			defer smtpClient.Close() //nolint:errcheck
+
+			// Upgrade to TLS.
+			require.NoError(t, smtpClient.StartTLS(&tls.Config{InsecureSkipVerify: true}))
+
+			// Authorize with SASL PLAIN.
+			require.NoError(t, smtpClient.Auth(sasl.NewPlainClient(
+				userInfo.Addresses[0],
+				userInfo.Addresses[0],
+				string(userInfo.BridgePass)),
+			))
+
+			// Send the message.
+			require.NoError(t, smtpClient.SendMail(
+				userInfo.Addresses[0],
+				[]string{"recipient@" + s.GetDomain()},
+				bytes.NewReader(b),
+			))
+
+			// Delete the draft: add the \Deleted flag and expunge.
+			{
+				status, err := imapClient.Select("Drafts", false)
+				require.NoError(t, err)
+				require.Equal(t, uint32(1), status.Messages)
+
+				// Add the \Deleted flag.
+				require.NoError(t, clientStore(imapClient, 1, 1, true, imap.FormatFlagsOp(imap.AddFlags, true), imap.DeletedFlag))
+
+				// Expunge.
+				require.NoError(t, imapClient.Expunge(nil))
+			}
+
+			// Assert that the draft is eventually gone.
+			require.Eventually(t, func() bool {
+				status, err := imapClient.Select("Drafts", false)
+				require.NoError(t, err)
+				return status.Messages == 0
+			}, 10*time.Second, 100*time.Millisecond)
+
+			// Assert that the message is eventually in the sent folder.
+			require.Eventually(t, func() bool {
+				messages, err := clientFetch(imapClient, "Sent")
+				require.NoError(t, err)
+				return len(messages) == 1
+			}, 10*time.Second, 100*time.Millisecond)
+
+			// Assert that the message is not marked as a draft.
+			{
+				messages, err := clientFetch(imapClient, "Sent")
+				require.NoError(t, err)
+				require.Len(t, messages, 1)
+				require.NotContains(t, messages[0].Flags, imap.DraftFlag)
+			}
+		})
+	})
+}