fix(master): redirect a cancelled Check now instead of an empty response (#35)

internal/master/poller/poller_test.go

@@ -1070,6 +1070,15 @@ func TestPollServiceOnlyThisService(t *testing.T) {
 	require.Len(t, st.available, 1)
 	assert.Equal(t, int64(1), st.available[0].id)
 	assert.Equal(t, []string{ref}, reg.sortedCalls())
+	for _, c := range st.pollErrors {
+		assert.NotContains(t, c.ids, int64(2))
+	}
+	for _, c := range st.newer {
+		assert.Equal(t, int64(1), c.id)
+	}
+	for _, c := range st.lastTag {
+		assert.Equal(t, int64(1), c.id)
+	}
 }
 
 func TestPollServiceCancelled(t *testing.T) {

internal/master/web/server.go

@@ -633,13 +633,15 @@ func (s *Server) pollService(w http.ResponseWriter, r *http.Request) {
 		s.renderServiceError(w, r, id, http.StatusConflict, "Cannot check: "+np.Reason+".")
 		return
 	case r.Context().Err() != nil:
-		return // the client is gone
+		// The client is gone or the master is shutting down. Redirect anyway:
+		// a browser still waiting gets the page, not an empty 200.
 	case err != nil:
 		s.failLookup(w, err)
 		return
-	}
+	default:
 		sess, _ := webauth.SessionFrom(r.Context())
 		s.log.Info("poll_requested", "service_id", id, "subject", sess.Subject)
+	}
 	http.Redirect(w, r, "/services/"+strconv.FormatInt(id, 10), http.StatusSeeOther)
 }