Python App Engine - Blobstore for non-images

Question

In my Python Appengine 'app' I have been asked to 'attach any file' so I have the following code snippet to 'display' those files...

blobattach = ''
blobmime   = 'None'
if pattachment.blobkey <> None:
    blobattach = get_serving_url(pattachment.blobkey)  # <-- line 104
    blob_info  = blobstore.BlobInfo.get(pattachment.blobkey)
    blobmime   = blob_info.content_type[:5]
    blobname   = blob_info.filename

Using the following HTML

{% if blobmime == 'None' %}
{% else %}
    {% if blobmime == 'image' %}
        <img src="{{ blobattach }}" alt='Attachment'/>
    {% else %}
        <br/>
        <small><a class="fswideb" href="{{blobattach}}" Title="Download to view"><span>Download to view {{ blobname }}</span></a></small>
    {% endif %}
{% endif %}

If the attachment is an image, it is displayed (blobmime=='image'). If not, a link is displayed so the user can download the file and view it however they can.

However, while this works in development, on my laptop (Google App Engine Launcher), I get the following error when trying to 'serve' a .xls file. (No error with .jpg attachments)

File "/base/data/home/apps/s~fs-rentals/20140101.382312463312950329/fmntjobattachmaint.py", line 104, in display
blobattach = get_serving_url(pattachment.blobkey)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/api/images/__init__.py", line 1794, in get_serving_url
return rpc.get_result()
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/api/apiproxy_stub_map.py", line 613, in get_result
return self.__get_result_hook(self)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/api/images/__init__.py", line 1892, in get_serving_url_hook
raise _ToImagesError(e, readable_blob_key)

TransformationError

All of the examples use images and I have no problems with them, indeed no problems in development. Any thoughts on what I could have missed?

Many thanks David

As suggested I changed the above to use Google Cloud Storage. I still get exactly the same error. The get_serving_url function errors if the blob is not an image. Is there an equivalent for a file that is not an image?

The sample at https://cloud.google.com/appengine/docs/python/tools/webapp/blobstorehandlers#BlobstoreUploadHandler provides a really good example of what I am trying to do except that I may want to add the person's CV instead of their photo.

Thanks David

When you say "this works in development" I think you mean the opposite -- that it works when deployed to appspot but not in the development app server, e.g "on your laptop". I would recommend avoiding blobstore and using the newer, shiny cloud.google.com/appengine/docs/python/googlecloudstorageclient instead (in deployment the old blobstore API's implemented on top of that -- but going with the real GCS should work fine both in deployment and local development, in the latter case GCS being implemented on top of your own local times). — Alex Martelli
I'll have a look and let you know. Thanks for the quick response. — David Freeman
I still see you using the blobstore API in your Q -- where's your code switched to cloud.google.com/appengine/docs/python/googlecloudstorageclient ...? — Alex Martelli

David Freeman David Freeman · Accepted Answer · 2015-02-23T00:14:20

Fixed my problem. I was trying to do too much on one 'screen'

If the blob is an image - get_serving_url as above.
If the blob is not an image - display a link to a different page (target='_blank') that does the following (pretty much copied from another SO post):

    if rmntjobattach.mntjobattachid <> 0 \
    and rmntjobattach.blobkey:
        blob_info = blobstore.BlobInfo.get(rmntjobattach.blobkey)
        self.send_blob(blob_info)
    else:
        self.error(404)

The trick was to display an image blob on the same page and everything else on the new page when the user requested it (clicked the link)

David

Python App Engine - Blobstore for non-images

1 Answers