Wrap any resource that can be opened, queried for next element and closed in an asynchronous way with three distinct functions into a source. This operator is the equivalent of @ref[unfoldResource](unfoldResource.md) but for resources with asynchronous APIs.
`Source.unfoldResourceAsync` allows us to safely extract stream elements from a resource with an async API by providing it with
three functions that all return a @scala[`Future`]@java[`CompletionStage`]:
1.`create`: Open or create the resource
1.`read`: Fetch the next element or signal that we reached the end of the stream by completing the @scala[`Future`]@java[`CompletionStage`] with a @java[`Optional.empty`]@scala[`None`]
1.`close`: Close the resource, invoked on end of stream or if the stream fails
All exceptions thrown by `create` and `close` as well as the @scala[`Future`]@java[`CompletionStage`]s completing with failure will
fail the stream. The supervision strategy is used to handle exceptions from `read`, `create` and from the @scala[`Future`]@java[`CompletionStage`]s.
Note that there are pre-built `unfoldResourceAsync`-like operators to wrap `java.io.InputStream`s in
@ref:[Additional Sink and Source converters](../index.md#additional-sink-and-source-converters),
`Iterator` in @ref:[fromIterator](fromIterator.md) and File IO in @ref:[File IO Sinks and Sources](../index.md#file-io-sinks-and-sources).
Additional prebuilt technology specific connectors can also be found in the [Alpakka project](https://doc.akka.io/docs/alpakka/current/).
## Examples
Imagine we have an async database API which we initially perform an async query and then can
check if there are more results in an asynchronous way.
