Wt

When a user selects an item from a WSuggestionPopup, the server permanently retains a stale (pre-selection) value for the associated edit widget in formDataCache_. Any subsequent HTTP request that does not re-send the field reads the stale value from the cache.

Minimal reproducible example¶

        auto* edit = root()->addNew<Wt::WLineEdit>();
        Wt::WSuggestionPopup::Options opts{ "<b>", "</b>", ',', " \n", "-., \"@\n;", "", "" };
        auto* popup = root()->addNew<Wt::WSuggestionPopup>(opts);
        popup->addSuggestion("apple");
        popup->forEdit(edit);
        auto* btn  = root()->addNew<Wt::WPushButton>("Submit");
        auto* result = root()->addNew<Wt::WText>();
        btn->clicked().connect([edit, result] {
            result->setText("Server received: " + edit->text().toUTF8());
        });

1. Type a
2. Click apple in the popup
3. Click Submit

Expected: Server received: apple
Actual: Server received: a
Workaround: set <cache-form-data>false</cache-form-data> in wt_config.xml

Probable root cause¶

As I can see from the network console, when selecting the suggestion, WSuggestionPopup emits multiple events in a single request, of which the third one, prefixed with e2, contains the new value apple. On the server this is cached with the e2 prefix in formDataCache_ in WebSession. Possibly the value for the unprefixed key in formDataCache_ is not updated, causing subsequent requests to fall back to the old cached value.