Streams fetched by data-providers are never closed

[heruan]

Description of the bug

Let’s say I have a backend data-provider for a stream of strings read from a BufferedReader, e.g.

public Stream<String> fetchFromBackend(Query<String> query) {
    var reader = createBufferedReader();
    return reader.lines().skip(query.getOffset()).limit(query.getLimit()).onClose(reader::close);
}

In this case I want to be sure to close the reader when the stream reaches a terminal operation, so I do onClose(reader::close). Problem is, when the DataCommunicator gets that stream:

flow/flow-data/src/main/java/com/vaadin/flow/data/provider/DataCommunicator.java

Line 1055 in b8a992a

Stream<T> stream = getDataProvider().fetch(query);

then it is never closed. This also applies to the DataView API, e.g.

flow/flow-data/src/main/java/com/vaadin/flow/data/provider/AbstractDataView.java

Lines 153 to 155 in b8a992a

	public Stream<T> getItems() {
	return dataProviderSupplier.get().fetch(new Query<>());
	}

Expected behavior

Upon calling terminal operations, the stream is then closed.

Minimal reproducible example

See code snippet in the description above.

Versions

• Vaadin / Flow version: 24.4
• Java version: 21
• OS version: macOS 14.2.1

[vaadin-bot]

This ticket/PR has been released with Vaadin 24.3.4.