Bug - handler.body returns a str resulting in TypeError: a bytes-like object is required, not 'str'

[nathanglover]

First this bug was introduced post 0.11.0 when the handlers were refactored.

Traceback

Exception in 'http' protocol.
--
Traceback (most recent call last):
File "/function/src/mangum/mangum/protocols/http.py", line 81, in run
await app(self.request.scope, self.receive, self.send)
File "/usr/local/lib/python3.8/dist-packages/django/core/handlers/asgi.py", line 149, in __call__
body_file = await self.read_body(receive)
File "/usr/local/lib/python3.8/dist-packages/django/core/handlers/asgi.py", line 181, in read_body
body_file.write(message['body'])
File "/usr/lib/python3.8/tempfile.py", line 896, in write
rv = file.write(s)
TypeError: a bytes-like object is required, not 'str'

---

I was able to trace the issue down to the def body() method in the handler classes. Adding assert type(handler.body) == bytes to the _basic tests will reveal the error.

        handler = AwsAlb(example_event, example_context)
>       assert type(handler.body) == bytes
E       AssertionError: assert <class 'str'> == <class 'bytes'>
E         +<class 'str'>
E         -<class 'bytes'>

In 0.11.0 the body was guaranteed to be bytes because of the following snippet:

is_binary = event.get("isBase64Encoded", False)
initial_body = event.get("body") or b""
if is_binary:
    initial_body = base64.b64decode(initial_body)
elif not isinstance(initial_body, bytes):  # forces strings to be bytes.
     initial_body = initial_body.encode()

For most handlers the refactored code looks like this:

@property
def body(self) -> bytes:
    body = self.trigger_event.get("body", b"")
    if self.trigger_event.get("isBase64Encoded", False):
        body = base64.b64decode(body)
    return body

If self.trigger_event has a body key than the body returned will be whatever the type of the value is, which might not be bytes.

The solution I believe is to add the code from 0.11.0 to the body function.:

if not isinstance(body, bytes):
    body = body.encode()

I'll work on updating the tests and putting a PR with the fix if the above seems correct.

[nathanglover]

FYI I found this while testing a potential solution for #178 on a lambda function being served by an ALB.