fix(caldav): store markdown descriptions as HTML, skip spurious updates

Incoming CalDAV descriptions are markdown; convert them back to canonical HTML
(rebuilding mentions) before persisting. Skip the conversion when the markdown
is unchanged from the stored HTML so a passthrough sync doesn't churn the value
or bump the ETag.

pkg/routes/caldav/description_test.go

@@ -0,0 +1,88 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package caldav
+
+import (
+	"testing"
+
+	"code.vikunja.io/api/pkg/db"
+	"code.vikunja.io/api/pkg/models"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestApplyDescriptionFromMarkdown(t *testing.T) {
+	t.Run("unchanged round trip keeps stored html verbatim", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		const stored = `<p>Hello <strong>world</strong></p>`
+		vTask := &models.Task{Description: "Hello **world**"}
+
+		require.NoError(t, applyDescriptionFromMarkdown(s, vTask, stored))
+		assert.Equal(t, stored, vTask.Description)
+	})
+
+	t.Run("edited markdown is converted to html", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		const stored = `<p>Hello <strong>world</strong></p>`
+		vTask := &models.Task{Description: "Hello **mars**"}
+
+		require.NoError(t, applyDescriptionFromMarkdown(s, vTask, stored))
+		assert.Equal(t, "<p>Hello <strong>mars</strong></p>", vTask.Description)
+	})
+
+	t.Run("mention is rebuilt from markdown", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		vTask := &models.Task{Description: "ping @user1"}
+
+		require.NoError(t, applyDescriptionFromMarkdown(s, vTask, ""))
+		assert.Contains(t, vTask.Description, `<mention-user data-id="user1"`)
+	})
+
+	t.Run("new task markdown description becomes html", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		vTask := &models.Task{Description: "- [x] done"}
+
+		require.NoError(t, applyDescriptionFromMarkdown(s, vTask, ""))
+		assert.Contains(t, vTask.Description, `data-type="taskList"`)
+		assert.Contains(t, vTask.Description, `data-checked="true"`)
+		assert.Contains(t, vTask.Description, "<p>done</p>")
+	})
+
+	t.Run("emptying a description is honoured", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		vTask := &models.Task{Description: ""}
+
+		require.NoError(t, applyDescriptionFromMarkdown(s, vTask, "<p>was here</p>"))
+		assert.Empty(t, vTask.Description)
+	})
+}

pkg/routes/caldav/listStorageProvider.go

@@ -28,6 +28,7 @@ import (
 	"code.vikunja.io/api/pkg/events"
 	"code.vikunja.io/api/pkg/log"
 	"code.vikunja.io/api/pkg/models"
+	"code.vikunja.io/api/pkg/richtext"
 	user2 "code.vikunja.io/api/pkg/user"
 	"code.vikunja.io/api/pkg/web"
 	"github.com/samedi/caldav-go/data"
@@ -364,6 +365,14 @@ func (vcls *VikunjaCaldavProjectStorage) CreateResource(rpath, content string) (
 		return nil, errs.ForbiddenError
 	}
 
+	// Inbound CalDAV descriptions are markdown; store them as canonical HTML.
+	if err := applyDescriptionFromMarkdown(s, vTask, ""); err != nil {
+		log.Errorf("[CALDAV] Failed to convert description in CreateResource: %v", err)
+		_ = s.Rollback()
+		events.CleanupPending(s)
+		return nil, err
+	}
+
 	// Create the task
 	err = vTask.Create(s, vcls.user)
 	if err != nil {
@@ -408,6 +417,23 @@ func (vcls *VikunjaCaldavProjectStorage) CreateResource(rpath, content string) (
 	return &r, nil
 }
 
+// applyDescriptionFromMarkdown converts a task's inbound CalDAV description
+// (markdown) to canonical HTML, rebuilding @mentions. Unchanged markdown keeps the
+// stored HTML verbatim, so a no-op read-modify-write doesn't churn it or move Updated.
+func applyDescriptionFromMarkdown(s *xorm.Session, vTask *models.Task, storedHTML string) error {
+	if !richtext.Changed(storedHTML, vTask.Description) {
+		vTask.Description = storedHTML
+		return nil
+	}
+
+	htmlDesc, err := richtext.MarkdownToHTMLWithMentions(s, vTask.Description)
+	if err != nil {
+		return err
+	}
+	vTask.Description = htmlDesc
+	return nil
+}
+
 // UpdateResource updates a resource
 func (vcls *VikunjaCaldavProjectStorage) UpdateResource(rpath, content string) (*data.Resource, error) {
 
@@ -443,6 +469,14 @@ func (vcls *VikunjaCaldavProjectStorage) UpdateResource(rpath, content string) (
 		return nil, errs.ForbiddenError
 	}
 
+	// Inbound markdown → canonical HTML, kept verbatim when unchanged.
+	if err := applyDescriptionFromMarkdown(s, vTask, vcls.task.Description); err != nil {
+		log.Errorf("[CALDAV] Failed to convert description in UpdateResource: %v", err)
+		_ = s.Rollback()
+		events.CleanupPending(s)
+		return nil, err
+	}
+
 	// Update the task
 	err = vTask.Update(s, vcls.user)
 	if err != nil {