The reason that uploading file larger than 2GB will be truncated.

[kmiku7]

When I upload multipart-encoded file larger than 2GB in python2 environment, the body will be truncated. Server side can not read data completely. But the content-length value in header is expected. At client side, it do not send all data.

After tracing of function calls, it is caused by python2 socket library bug. Requests will use socket.sendall() to send body, but it use int type to keep bytes need be sent and has sent: python2-socket-lib. I also create a issue to report this bug to python team.

Rather than waiting python team fix it, I thought Requests can fix quickly. After search it has also been reported many times.
Requests lib can split encoded string body into many segments each one smaller than 2GB, and send segments one by one. Or wrapping string body as as file-like object is also works, like this:

from cStringIO import StringIO
body=StringIO(request.body)