Fix chunked_data requests in urequests.py

[bwhitman]

Chunked detection does not work on current Micropython as it never has an __iter__ attribute to a generator. It does add __next__ to them, so this test in urequests for chunked detection did not work. I've changed it to __next__. I can post a failing example in the PR.

[bwhitman]

Example:

def read_in_chunks(file_object, chunk_size=4096):
    while True:
        data = file_object.read(chunk_size)
        if not data:
            break
        yield data

file = open(filename, "rb")
r = urequests.post(url, data=read_in_chunks(file))

On current urequests, this will fail as chunked_data is not detected properly as read_in_chunks() does not have an __iter__ attr. Changing the test to __next__ works and the example works.

[andrewleech]

Good pickup! I'm not sure whether the original library author tested this chunked data handling in a different way, or perhaps just copied cpython code without testing... either way it's true that __iter__ isn't exposed on common micropython generators like yielding functions or "tuple comprehension":

$ micropython
MicroPython v1.19.1-1014-gbde222ce8 on 2023-04-14; linux [GCC 9.4.0] version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>> def gen():
...     yield 'hi'
...     yield 'there'
...
>>> g = gen()
>>> dir(g)
['__class__', '__next__', 'close', 'send', 'throw', 'pend_throw']
>>>
>>> dir((a for a in [1, 2]))
['__class__', '__next__', 'close', 'send', 'throw', 'pend_throw']
>>>

vs python

$ python
Python 3.8.10 (default, Mar 15 2022, 12:22:08)
>>> def gen():
...     yield 'hi'
...     yield 'there'
...
>>> g = gen()
>>> dir(g)
['__class__', '__del__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__lt__', '__name__', '__ne__', '__new__', '__next__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'close', 'gi_code', 'gi_frame', 'gi_running', 'gi_yieldfrom', 'send', 'throw']
>>>
>>> dir((a for a in [1, 2]))
['__class__', '__del__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__lt__', '__name__', '__ne__', '__new__', '__next__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'close', 'gi_code', 'gi_frame', 'gi_running', 'gi_yieldfrom', 'send', 'throw']

It's very common for micropython to not expose "little-used" attributes on objects as every attribute exposed comes with a notable code size cost.

Your fix looks fairly appropriate to me; no extra code size added and meets the needs of your example, which also matches the official requests example of this functionality: https://requests.readthedocs.io/en/latest/user/advanced/#chunk-encoded-requests

I'd also support adding your example above to a new example_chunked_post.py file, this sort of iterative / chunked handling is very valuable in micropython to limit buffer size and therefore ram use!

[andrewleech]

LGTM

[dpgeorge]

Thanks for the contribution!