#24: make draft autosave replace the previous draft

The autosave I had just added appended a new message on every debounce, so a
few minutes of typing would have left the Drafts folder holding a dozen copies
of the same unfinished mail. Caught before deploying.

The composer now returns the stored UID and sends it back as replace_uid on
the next save; the use case expunges the superseded draft, but only after the
replacement has committed, so a failure leaves the older draft in place rather
than losing both. Expunge is a soft delete matching the expunged_at column the
schema already uses, and it locates the message by mailbox as well as UID so a
caller cannot delete someone else's mail by guessing a number.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

services/protocols/internal/application/port/webmail_repository.go

@@ -61,4 +61,6 @@ type WebmailRepository interface {
 	GetMessageBlob(ctx context.Context, mailboxID, folderName string, uid uint32) (uuid.UUID, error)
 	// MarkSeen records that the user opened the message.
 	MarkSeen(ctx context.Context, mailboxID, folderName string, uid uint32, seen bool) error
+	// Expunge soft-deletes one message, keeping the folder counters in step.
+	Expunge(ctx context.Context, mailboxID, folderName string, uid uint32) error
 }

services/protocols/internal/application/usecase/webmail_compose_test.go

@@ -1,8 +1,13 @@
 package usecase
 
 import (
+	"context"
 	"strings"
 	"testing"
+
+	"github.com/google/uuid"
+
+	"lambdamail/protocols/internal/application/port"
 )
 
 // Every one of these reproduces a way the composer's mail was being mangled or
@@ -112,3 +117,96 @@ func TestHtmlToPlainTextIsReadable(t *testing.T) {
 		t.Errorf("markup survived into the plain-text part:\n%s", got)
 	}
 }
+
+// --- draft storage -------------------------------------------------------
+
+type stubWebmailRepo struct {
+	mailboxID  string
+	expunged   []uint32
+	expungeErr error
+}
+
+func (s *stubWebmailRepo) FindMailboxIDByAddress(context.Context, string) (string, error) {
+	return s.mailboxID, nil
+}
+func (s *stubWebmailRepo) ListFolders(context.Context, string) ([]port.WebmailFolder, error) {
+	return nil, nil
+}
+func (s *stubWebmailRepo) ListMessages(context.Context, string, string, string, int, int) ([]port.WebmailMessage, error) {
+	return nil, nil
+}
+func (s *stubWebmailRepo) GetMessageBlob(context.Context, string, string, uint32) (uuid.UUID, error) {
+	return uuid.Nil, nil
+}
+func (s *stubWebmailRepo) MarkSeen(context.Context, string, string, uint32, bool) error { return nil }
+func (s *stubWebmailRepo) Expunge(_ context.Context, _, _ string, uid uint32) error {
+	s.expunged = append(s.expunged, uid)
+	return s.expungeErr
+}
+
+type stubAuthRepo struct{ account *port.MailboxAuth }
+
+func (s *stubAuthRepo) FindByAddress(context.Context, string) (*port.MailboxAuth, error) {
+	return s.account, nil
+}
+
+// Autosaving must replace the previous draft, not pile up another copy of the
+// same half-written message every time the typing pauses.
+func TestDraftAutosaveReplacesThePreviousOne(t *testing.T) {
+	mailboxID := uuid.New()
+	repo := &stubWebmailRepo{mailboxID: mailboxID.String()}
+	messages := &recordingMessageRepository{}
+	blobs := &stubBlobStorage{ref: port.BlobRef{ID: uuid.New(), SHA256: "d", SizeBytes: 5}}
+
+	uc := (&WebmailUseCase{
+		repo:      repo,
+		auth:      &stubAuthRepo{account: &port.MailboxAuth{ID: mailboxID, EmailAddress: "me@example.test"}},
+		localHost: "mail.example.test",
+	}).WithLocalFiling(blobs, messages)
+
+	first, err := uc.SaveDraft(context.Background(), ComposeInput{
+		From: "me@example.test", Subject: "Half", HTML: "<p>writ</p>",
+	}, 0)
+	if err != nil {
+		t.Fatalf("first save: %v", err)
+	}
+	if len(repo.expunged) != 0 {
+		t.Errorf("the first save has nothing to replace, expunged %v", repo.expunged)
+	}
+
+	if _, err := uc.SaveDraft(context.Background(), ComposeInput{
+		From: "me@example.test", Subject: "Half", HTML: "<p>written</p>",
+	}, first); err != nil {
+		t.Fatalf("second save: %v", err)
+	}
+
+	if len(repo.expunged) != 1 || repo.expunged[0] != first {
+		t.Errorf("the superseded draft was not removed: expunged %v, want [%d]", repo.expunged, first)
+	}
+	if len(messages.persisted) != 2 {
+		t.Fatalf("want 2 writes, got %d", len(messages.persisted))
+	}
+	if messages.persisted[0].TargetFolderName != "Drafts" {
+		t.Errorf("draft filed in %q, want Drafts", messages.persisted[0].TargetFolderName)
+	}
+}
+
+// A draft is a half-written message by definition; it must save with no
+// recipients, where Send would rightly refuse.
+func TestDraftSavesWithoutRecipients(t *testing.T) {
+	mailboxID := uuid.New()
+	uc := (&WebmailUseCase{
+		repo:      &stubWebmailRepo{mailboxID: mailboxID.String()},
+		auth:      &stubAuthRepo{account: &port.MailboxAuth{ID: mailboxID, EmailAddress: "me@example.test"}},
+		localHost: "mail.example.test",
+	}).WithLocalFiling(
+		&stubBlobStorage{ref: port.BlobRef{ID: uuid.New(), SHA256: "d", SizeBytes: 5}},
+		&recordingMessageRepository{},
+	)
+
+	if _, err := uc.SaveDraft(context.Background(), ComposeInput{
+		From: "me@example.test", Subject: "no recipients yet",
+	}, 0); err != nil {
+		t.Fatalf("a draft with no recipients must still save: %v", err)
+	}
+}

services/protocols/internal/application/usecase/webmail_mail.go

@@ -223,7 +223,11 @@ func (uc *WebmailUseCase) fileLocalCopy(
 // from a setTimeout, with no request behind it, and closing the tab lost the
 // message. Drafts are whole RFC 5322 messages like any other, so they are
 // readable over IMAP too.
-func (uc *WebmailUseCase) SaveDraft(ctx context.Context, input ComposeInput) (uint32, error) {
+// replaceUID is the draft this one supersedes, or 0 for the first save of a
+// message. Without it every autosave would append another copy and a few
+// minutes of typing would leave the Drafts folder full of the same half-written
+// message.
+func (uc *WebmailUseCase) SaveDraft(ctx context.Context, input ComposeInput, replaceUID uint32) (uint32, error) {
 	account, err := uc.auth.FindByAddress(ctx, input.From)
 	if err != nil {
 		return 0, err
@@ -261,6 +265,18 @@ func (uc *WebmailUseCase) SaveDraft(ctx context.Context, input ComposeInput) (ui
 	if err != nil {
 		return 0, err
 	}
+
+	// Only after the replacement is committed, so a failure here leaves the
+	// older draft in place rather than losing both.
+	if replaceUID != 0 {
+		mailboxID, idErr := uc.mailboxID(ctx, account.EmailAddress)
+		if idErr == nil {
+			if err := uc.repo.Expunge(ctx, mailboxID, "Drafts", replaceUID); err != nil {
+				log.Printf("webmail: could not remove the superseded draft %d: %v", replaceUID, err)
+			}
+		}
+	}
+
 	if len(uids) == 0 {
 		return 0, nil
 	}

services/protocols/internal/infrastructure/postgres/webmail_repository.go

@@ -200,3 +200,63 @@ func (r *WebmailRepository) MarkSeen(
 
 	return tx.Commit(ctx)
 }
+
+// Expunge marks one message deleted and keeps the folder counters in step.
+//
+// Soft delete, matching the expunged_at column the rest of the schema uses: the
+// blob stays referenced until the retention sweep, so a mistaken delete is
+// recoverable and IMAP clients holding the UID still resolve it.
+//
+// The message is located by mailbox as well as UID, so a caller cannot expunge
+// somebody else's mail by guessing a number.
+func (r *WebmailRepository) Expunge(
+	ctx context.Context, mailboxID, folderName string, uid uint32,
+) error {
+	tx, err := r.pool.Begin(ctx)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback(ctx)
+
+	var messageID uuid.UUID
+	var folderID string
+	var wasUnread bool
+	err = tx.QueryRow(ctx, `
+		SELECT e.id, f.id::text,
+		       NOT EXISTS (SELECT 1 FROM message_flags mf
+		                    WHERE mf.message_id = e.id AND mf.flag = '\Seen')
+		  FROM email_messages e
+		  JOIN folders f ON f.id = e.folder_id
+		 WHERE e.mailbox_id = $1 AND `+folderCondition+`
+		   AND e.uid = $3 AND e.expunged_at IS NULL
+	`, mailboxID, folderName, int64(uid)).Scan(&messageID, &folderID, &wasUnread)
+	if errors.Is(err, pgx.ErrNoRows) {
+		return ErrMessageNotFound
+	}
+	if err != nil {
+		return err
+	}
+
+	if _, err := tx.Exec(ctx,
+		`UPDATE email_messages SET expunged_at = NOW() WHERE id = $1`, messageID); err != nil {
+		return err
+	}
+
+	// GREATEST guards the counters against ever going negative, which a
+	// double expunge of the same row would otherwise cause.
+	unreadDelta := 0
+	if wasUnread {
+		unreadDelta = -1
+	}
+	if _, err := tx.Exec(ctx, `
+		UPDATE folders
+		   SET total_count = GREATEST(0, total_count - 1),
+		       unread_count = GREATEST(0, unread_count + $2),
+		       highest_modseq = highest_modseq + 1
+		 WHERE id = $1
+	`, folderID, unreadDelta); err != nil {
+		return err
+	}
+
+	return tx.Commit(ctx)
+}

services/protocols/internal/presentation/http/mail_api.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"errors"
+	"io"
 	"mime"
 	"net/http"
 	"strconv"
@@ -264,12 +265,13 @@ func (m *mailAPI) handleSaveDraft(w http.ResponseWriter, r *http.Request) {
 	if !ok {
 		return
 	}
-	input, ok := m.decodeCompose(w, r, session.Email)
+	// The body is read once, so replace_uid has to come out of the same decode.
+	input, replaceUID, ok := m.decodeDraft(w, r, session.Email)
 	if !ok {
 		return
 	}
 
-	uid, err := m.useCase.SaveDraft(r.Context(), input)
+	uid, err := m.useCase.SaveDraft(r.Context(), input, replaceUID)
 	if err != nil {
 		m.fail(w, err)
 		return
@@ -339,3 +341,29 @@ func (m *mailAPI) fail(w http.ResponseWriter, err error) {
 		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Request could not be processed")
 	}
 }
+
+// decodeDraft reads a composed message plus the draft it supersedes.
+//
+// replace_uid carries the UID of the previous autosave so the new one takes
+// its place. Without it each keystroke pause would leave another copy behind
+// and the Drafts folder would fill with the same unfinished message.
+func (m *mailAPI) decodeDraft(
+	w http.ResponseWriter, r *http.Request, sender string,
+) (usecase.ComposeInput, uint32, bool) {
+	raw, err := io.ReadAll(http.MaxBytesReader(w, r.Body, maxComposeBytes))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "BAD_REQUEST", "Could not read the request")
+		return usecase.ComposeInput{}, 0, false
+	}
+
+	var meta struct {
+		ReplaceUID uint32 `json:"replace_uid"`
+	}
+	// A missing or malformed replace_uid is not fatal: the draft is still
+	// worth saving, it just will not supersede anything.
+	_ = json.Unmarshal(raw, &meta)
+
+	r.Body = io.NopCloser(bytes.NewReader(raw))
+	input, ok := m.decodeCompose(w, r, sender)
+	return input, meta.ReplaceUID, ok
+}

services/webmail/src/app/(user)/user/compose/page.tsx

@@ -54,6 +54,9 @@ export default function ComposePage({
   const [undoSeconds, setUndoSeconds] = useState<number | null>(null);
   const [draftStatus, setDraftStatus] = useState<string>("");
   const [sendError, setSendError] = useState<string | null>(null);
+  // The UID of the draft already stored for this message. Sent back on each
+  // autosave so the server replaces it instead of leaving another copy.
+  const draftUidRef = useRef<number>(0);
 
   const editorRef = useRef<HTMLDivElement>(null);
 
@@ -81,8 +84,13 @@ export default function ComposePage({
           bcc: splitAddresses(bcc),
           subject,
           html,
+          replace_uid: draftUidRef.current,
         }),
       });
+      if (res.ok) {
+        const data = await res.json().catch(() => ({}));
+        if (typeof data.uid === "number") draftUidRef.current = data.uid;
+      }
       setDraftStatus(res.ok ? t("mail.draftSaved") : t("mail.draftSaveFailed"));
     } catch {
       setDraftStatus(t("mail.draftSaveFailed"));