request.stream doesn't always return a stream.

[alexgmin]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

On a Custom authentication scheme, try to access the request.stream as a stream.

Expected behavior

A stream instance is always returned

Actual behavior

A request instance is returned if request._read_started is false and a Stream is returned when it's true.

Example:

def authenticate(self, request):
    foo = request.body
    bar = request.stream
    value = request.stream.getvalue()

This works because request.stream returns a StringIO instance.

def authenticate(self, request):
    # foo = request.body
    # bar = request.stream
    value = request.stream.getvalue()

This doesn't because request.stream returns a Request instance (WSGIRequest in my case)

Removing this conditional solves the problem in this case, but i don't know what other implications it has.

[carltongibson]

@alexgmin Fancy doing a little research into the history here?

I seem to have vague memories of something about not being able to access the stream if it had already been read, but I can't bring it to mind exactly instantly.

[alexgmin]

@carltongibson
Investigating a bit, it seems that this pull #4500 added the condition, related to this issue. #3951
So yeah, you can only access the stream once,

[carltongibson]

@alexgmin OK. That was it yes.

This may just be something you'll have to work around.

The discussion on #3951 suggests we fallback to using the request is if the steam is already exhausted. Looking now, I can't see exactly where that Request type return is employed. Given the discussion I suspect we are but, if we were not using that then maybe we could adjust the return here, to e.g. None or such.

I think I'm going to close this as is. I'm not sure there's anything obviously actionable for us.

If you want to dig into it more I'm very happy to review concrete suggestions.