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From "Richard Xia (JIRA)" <>
Subject [jira] [Created] (LIBCLOUD-903) AWS S3 upload_object_via_stream fails on non-file iterable due to missing Content-Length header
Date Thu, 09 Mar 2017 07:33:37 GMT
Richard Xia created LIBCLOUD-903:

             Summary: AWS S3 upload_object_via_stream fails on non-file iterable due to missing
Content-Length header
                 Key: LIBCLOUD-903
             Project: Libcloud
          Issue Type: Bug
            Reporter: Richard Xia

The issue I am seeing appears to be due to the incorrect integration of 4 separate libraries,
but I believe the real problem is here in libcloud, in the {{upload_object_via_stream()}}
method on the S3 storage driver.
I am using Python 3.5.1 and the the four libraries I am using are:               
* Django 1.10.6                                                                  
* django-storages 1.5.2                                                          
* libcloud v2.0.0rc1-tentative                                                   
* requests 2.13.0                                                                
Specifically, when I try to use a Django [ContentFile|],
Django's own file-like wrapper for strings, to save a new file to S3 via the Libcloud backend
of django-storages, I get the following error:
<?xml version="1.0" encoding="UTF-8"?>\n<Error><Code>NotImplemented</Code><Message>A
header you provided implies functionality that is not implemented</Message><Header>Transfer-Encoding</Header><RequestId>A2FC4D5109083076</RequestId><HostId>K9WGhd18iqQHyIyv+GxWcxHexvapVSidTtHzSqujtT9nT5LhmIEygMKOfR/7F0v7ujnlE/CoYiM=</HostId></Error>
The reason this happens is because Libcloud is generating an HTTP request to AWS S3 that is
missing the {{Content-Length}} header. AWS S3 requires the {{Content-Length}} header for file
uploads *unless* if it is a multi-part upload. This is why this used to work on the 1.5.0
release of {{libcloud}}, because even single-part uploads were done as a one-part multi-part
I've traced my bug down through all four libraries and have determined exactly why the {{Content-Length}}
header is missing in my particular use case. The {{upload_object_via_stream()}} has an {{iterator}}
argument that should yield the content body data, and it eventually passes that argument directly
to the {{requests}} library. The {{requests}} library will actually [try very hard to add
the {{Content-Length}} header|],
even for certain types of iterator streams. In particular it can determine the length of file-like
objects which support stat operations and it can handle StringIO/BytesIO objects. However,
the Django {{ContentFile}} is neither, and {{requests}} cannot extract the length of the stream
without consuming the iterator, so it does not try.
Here's some (Python 3) code to demonstrate the bug:                              
from io import BytesIO                                                           
class MyWrapper(object):                                                         
    """A contrived wrapper that acts similar to BytesIO."""                      
    def __init__(self, content):                                                 
        self.content = BytesIO(content)                                          
    def __iter__(self):                                                                                                              
# Assume driver is already set to some S3 provider w/ credentials                
container = driver.get_container(container_name='my-container')                  
driver.upload_object_via_stream(iterator=iter(MyWrapper(b'hello world')),        
I think the proper solution to this will require all calls to the S3 {{upload_object_via_stream()}}
to use the multi-part uploader in order to eschew the need for the {{Content-Length}} header.
If desired, you could make the same optimizations that the request library makes by checking
for certain common cases where you do know the file size and only using the multi-part uploader
when necessary.

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