DataObject::SaveToFilename() and ::SaveToString() fetch object a second time

[ErikMinekus]

Currently, DataObject's constructor fetches the object and stores its data in $this->data. However, SaveToFilename() and SaveToString() fetch the object again, which causes a lot of overhead (right now fetching a 6MB file takes about 6 seconds for us).

Unless there's a good reason for this, fixing SaveToString() should be as easy as return $this->data. Otherwise, please add a GetData() method that does just that. That way we have a choice.

[gecampbell]

Actually, I think the bug is that the constructor actually fetches the data. It should not do this, because the data size could vastly exceed the amount of memory available to PHP. Plus, it adds a ton of overhead; let's say that you wanted to list metadata about a thousand video files, each of which is 6GB; we certainly don't need to download all that data just to get at a few bytes of metadata.

What should happen, I think, is that the constructor should perform a HEAD request, getting the available metadata for the object, and then the SaveToFilename() or SaveToString() methods should use the GET to retrieve the actual data to either disk or memory. The intent of SaveToFilename() is to bypass memory and write directly to disk.

I'll put this in my queue to look at soon.