Question

I’m using the high performance image serving feature in App Engine to serve up images from the blobstore. However, I’d like users to be able to modify those images (e.g. rotate, crop etc.) and then write those change back to the blobstore, overwriting the original blob. I know I can write to new blobs in the blobstore, as documented here: http://code.google.com/appengine/docs/python/blobstore/overview.html#Writing_Files_to_the_Blobstore

but I don’t see a way to overwrite existing blobs. Is this possible in App Engine?

My use case is as follows:

1. User uploads image, and app engine generates a link via
   get_serving_url
2. The user may then use that link outside of my app, e.g. link to it
   on their blog to display the image
3. If that image is changed later on in my app (rotation, etc.) , I’d
   like their image link to reflect those changes

Answer 1

Files stored in blobstore are immutable, once they have been written than can not be changed (only served or deleted).