在App Engine上存储二进制数据的最有效方法？

Question

I am using AppEngine, Cloud Endpoints and Objectify. I want to store a binary (approximately 2 kB) which may contain either of a binary (image file), string and XML. There is no need to list or index the content on App Engine. It should just be stored alongside the entity.

I know I could, but I don't want to store that information on GCS.

I used a byte array server-side, which Objectify persists fine, but I realized that Cloud Endpoints converts it to String for the client, which I think is not very efficient as I would need to convert a client-generated binary (image file) first to String so that the Cloud Endpoints converts it back to byte[].

I tried to use a byte array client-side, which Cloud Endpoints cannot process because it "contains invalid characters", such as spaces. When I URLEncode it, Endpoints complains about % as illegal character. So this seems not to be the way that Google planned to use.

Any suggestions or experiences if there is a datatype which can be transported over Endpoints and persisted by Objectify, in order to avoid inefficient conversions on both sides, and which can host binaries as well as text Strings?

Answer 1

How about using encoding your binary data into a Base64 String when sending it through Cloud Endpoints ? No need to change anything on the storage side, it will remain a byte[] .

Just put your byte[] in a dedicated class and declare an @ApiTransformer for it :

@ApiTransformer(BinaryDataOrStringOrXMLTransformer.class)
public class BinaryDataOrStringOrXML {
  private final byte[] data;
  //add constructor, getters and setters
}

The transformer code :

public class BinaryDataOrStringOrXMLTransformerimplements Transformer<BinaryDataOrStringOrXML, String> {
  public String transformTo(BinaryDataOrStringOrXML in) {
    return Base64.getEncoder().encodeToString(in.getData());
  }

  public BinaryDataOrStringOrXML transformFrom(String in) {
    return new BinaryDataOrStringOrXML(Base64.getDecoder().decode(in));
  }
}

You might have to test getUrlDecoder() and getDecoder() , I am not sure which one will work with Cloud Endpoints.

On the client side, you will also need to decode the Base64. If you're in Android that will be very easy. In javascript it might be a bit more complicated, but there are some helpful libraries out there.