caldav: return SupportedComponentSet in PROPFIND

I started using this project to export tasks over CalDav, more
specifically to Reminders on iOS/macOS. I quickly realized that
even if you specify that `SupportedComponentSet` contains `VTODO`, that
isn't reflected properly when doing the `PROPFIND`.

This patch should fix that, while keeping the behaviour of defaulting to
`VEVENT` for propfind. Also added some tests to make sure that I didn't
break anything (Which I hope I didn't 😅).

caldav/server.go

@@ -525,10 +525,16 @@ func (b *backend) propFindCalendar(ctx context.Context, propfind *internal.PropF
 			}, nil
 		},
 		supportedCalendarComponentSetName: func(*internal.RawXMLValue) (interface{}, error) {
+			components := []comp{}
+			if cal.SupportedComponentSet != nil {
+				for _, name := range cal.SupportedComponentSet {
+					components = append(components, comp{Name: name})
+				}
+			} else {
+				components = append(components, comp{Name: ical.CompEvent})
+			}
 			return &supportedCalendarComponentSet{
-				Comp: []comp{
-					{Name: ical.CompEvent},
-				},
+				Comp: components,
 			}, nil
 		},
 	}

caldav/server_test.go

@@ -0,0 +1,87 @@
+package caldav
+
+import (
+	"context"
+	"io"
+	"io/ioutil"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/emersion/go-ical"
+)
+
+var propFindSupportedCalendarComponentRequest = `
+<d:propfind xmlns:d="DAV:" xmlns:c="urn:ietf:params:xml:ns:caldav">
+  <d:prop>
+     <c:supported-calendar-component-set />
+  </d:prop>
+</d:propfind>
+`
+
+var testPropFindSupportedCalendarComponentCases = map[*Calendar][]string{
+	&Calendar{Path: "/user/calendars/cal"}:                                                     []string{"VEVENT"},
+	&Calendar{Path: "/user/calendars/cal", SupportedComponentSet: []string{"VTODO"}}:           []string{"VTODO"},
+	&Calendar{Path: "/user/calendars/cal", SupportedComponentSet: []string{"VEVENT", "VTODO"}}: []string{"VEVENT", "VTODO"},
+}
+
+func TestPropFindSupportedCalendarComponent(t *testing.T) {
+	for calendar, expected := range testPropFindSupportedCalendarComponentCases {
+		req := httptest.NewRequest("PROPFIND", calendar.Path, nil)
+		req.Body = io.NopCloser(strings.NewReader(propFindSupportedCalendarComponentRequest))
+		req.Header.Set("Content-Type", "application/xml")
+		w := httptest.NewRecorder()
+		handler := Handler{Backend: testBackend{calendar: calendar}}
+		handler.ServeHTTP(w, req)
+
+		res := w.Result()
+		defer res.Body.Close()
+		data, err := ioutil.ReadAll(res.Body)
+		if err != nil {
+			t.Error(err)
+		}
+		resp := string(data)
+		for _, comp := range expected {
+			// Would be nicer to do a proper XML-decoding here, but this is probably good enough for now.
+			if !strings.Contains(resp, comp) {
+				t.Errorf("Expected component: %v not found in response:\n%v", comp, resp)
+			}
+		}
+	}
+}
+
+type testBackend struct {
+	calendar *Calendar
+}
+
+func (t testBackend) Calendar(ctx context.Context) (*Calendar, error) {
+	return t.calendar, nil
+}
+
+func (t testBackend) CalendarHomeSetPath(ctx context.Context) (string, error) {
+	return "", nil
+}
+
+func (t testBackend) CurrentUserPrincipal(ctx context.Context) (string, error) {
+	return "", nil
+}
+
+func (t testBackend) DeleteCalendarObject(ctx context.Context, path string) error {
+	return nil
+}
+
+func (t testBackend) GetCalendarObject(ctx context.Context, path string, req *CalendarCompRequest) (*CalendarObject, error) {
+	return nil, nil
+}
+
+func (t testBackend) PutCalendarObject(ctx context.Context, path string, calendar *ical.Calendar, opts *PutCalendarObjectOptions) (string, error) {
+	return "", nil
+}
+
+func (t testBackend) ListCalendarObjects(ctx context.Context, req *CalendarCompRequest) ([]CalendarObject, error) {
+	return nil, nil
+}
+
+func (t testBackend) QueryCalendarObjects(ctx context.Context, query *CalendarQuery) ([]CalendarObject, error) {
+	return nil, nil
+}