How to properly read streamed entities with Cloud SDK

[vmikhailenko]

We (CAP Java) team want to implement access to the entity's media properties via streams.

I noticed that response is always buffered. How we can get "true" stream from the CloudSDK?

[newtork]

When using the generator, in OData v4 it'll create class fields of type URI. You can run your requests to that address however you see fit.

In OData v2 you can use fetchMediaStream() on the entity API. It's true, the implementation has implicit buffering.

You can either (a) ask for a feature request to toggle buffering on fetchMediaStream() API, or (b) use the implementation as inspiration to run a Generic OData Client request instead:

  Destination destination = ...

  ODataResourcePath resource =
    ODataResourcePath
      .of(getEntityCollection(), ODataEntityKey.of(getKey(), ODataProtocol.V2))
      .addSegment("$value");

  ODataRequestReadByKey request =
    new ODataRequestReadByKey(getServicePathForFetch(), resource, null, ODataProtocol.V2);

  HttpClient httpClient = HttpClientAccessor.getHttpClient(destination);
  ODataRequestResultGeneric result = request.execute(httpClient);
+ result.disableBufferingHttpResponse();
  HttpEntity entity = result.getHttpResponse().getEntity();
  InputStream stream = entity.getContent();

[vmikhailenko]

I tried the option (b), but when I request the result I see a warning in the log that entity is already buffered when I call this method.

[newtork]

I think you're right!

For every low-level request we run a health check on the response payload.
https://github.com/SAP/cloud-sdk-java/blob/main/datamodel/odata-client/src/main/java/com/sap/cloud/sdk/datamodel/odata/client/request/ODataRequestGeneric.java#L233

Inside ODataHealthyResponseValidator.requireHealthyResponse(..) we invoke ODataRequestResult#getHttpResponse(). Primarily we are interested in the status code. The buffering is an unintentional side effect.
https://github.com/SAP/cloud-sdk-java/blob/main/datamodel/odata-client/src/main/java/com/sap/cloud/sdk/datamodel/odata/client/request/ODataHealthyResponseValidator.java#L41

This looks like a bug to me.
We should do further testing.

[rpanackal]

Dear @vmikhailenko ,

We have released the latest version SAP Cloud SDK Java 5.20.0, with the bug fix for response buffering included.