Some Google App Engine BlobStore Problems

I have googled and read the docs on Google App Engine official site about BlobStore but there are some problems that I still dont understand. My Platform is webapp.

Docs I have read:

• webapp Blobstore Handlers

• Blobstore Python API Overview

• The Blobstore Python API

After reading all these docs, I still have some problems:

1. In Blobstore Python API Overview it says: maximum size of Blobstore data that can be read by the app with one API call is 1MB. What does this mean? Does this 1MB limit apply to sendblob()? Take the following code from webapp Blobstore Handlers as an example:

   class ViewPhotoHandler(blobstore_handlers.BlobstoreDownloadHandler):
       def get(self, photo_key):
           self.send_blob(photo_key)
   

   Does that mean the photo ( which is uploaded and stored in the blobstore )associated with the photo_key must be less than 1MB? From the context, I dont think so. I think the the photo can be as large as 2GB. But I am not sure.

2. How is the ContentType determine开发者_如何学God on send_blob()? Is it text/html or image/jpeg? Can I set somewhere it myself? The following explanation from webapp Blobstore Handlers is so confusing. Quite difficult for a non-english speaker. Can someone paraphrase it with code samples? Where is the docs for send_blob()? I cant find it.

   The send_blob() method accepts a save_as argument that determines whether the blob data is sent as raw response data or as a MIME attachment with a filename, which prompts web browsers to save the file with the given name instead of displaying it. If the value of the argument is a string, the blob is sent as an attachment, and the string value is used as the filename. If True and blob_key_or_info is a BlobInfo object, the filename from the object is used. By default, the blob data is sent as the body of the response and not as a MIME attachment.

3. There is a file http://www.example.com/example.avi which is 20MB or even 2GB. I want to fetch example.avi from the internet and store it in the BlobStore. I checked, the urlfetch request size limit is 1MB. I searched and hadnt found a solution.

Thanks a lot!

1. send_blob() doesn't involve your application reading the file from the API, so the 1MB limit doesn't apply. The frontend service that returns the response to the user will read the entire blob and return all of it in the response (it most likely does the reading in chunks, but this is an implementation detail that you don't have to worry about.

2. send_blob() sets the content type to either the Blob's internal stored type, or the type you specify with an optional content_type parameter to send_blob(). For the documentation, it seems to need to RTFS; there's a docstring (in the google.appengine.ext.webapp.blobstore_handlers package.)

3. There's really no great solution for fetching arbitrary files from the web and storing them in Blobstore. Most likely you'd need a service running elsewhere, like your own machine or an EC2 instance, to fetch the files and POST them to a blobstore handler in your application.