Support Response(content=<bytes iterator>)

[tomchristie]

Refs #1253

Support Response(content=<bytes iterator>) and Response(content=<bytes aiterator>).

Related follow ups will be...

• Adding support for Response(content=<byte stream>)
• Adding support for Request(content=<bytes|bytes iterator|bytes aiterator|byte stream)
• Deprecating Response(stream=...) and Request(stream=...)

A good motivation when considering this pull request in isolation, is to look over the test cases that were previously importing from the private API - from httpx._content_streams import AsyncIteratorStream and from httpx._content_streams import IteratorStream

For instance we've got cases that currently look like this...

# Bit grungy, since `IteratorStream` is a private implementation detail inside `httpx`
stream = IteratorStream(iterator=streaming_body())
response = httpx.Response(200, stream=stream)

After this pull request they get slimmed down to a more natural looking API...

response = httpx.Response(200, content=streaming_body())

[tomchristie]

I'm going to merge this one in, since I don't think it's all that controversial, and it's blocking some other work from progressing at the moment. (Update: see #1281)

I think it makes sense to use the merge-without-a-review admin privileges occasionally, so long as it's treated carefully like this (eg. controversial PRs, that have had a few days breathing room), since practically I've got a lot more time available to this right now than the rest of the maintenance team, so we're getting a bit bottle necked.

(But happy to talk about any of that if needed.)

[JayH5]

Maybe you were already aware, but a thing I just learned from reviewing encode/starlette#1041: collections.abc.AsyncIterator/collections.abc.Iterator (which the typing equivalents derive from) have a subclasshook which I think means you could just do:

    elif isinstance(content, typing.AsyncIterator):
          return AsyncIteratorStream(aiterator=content)

Also technically you may be casting Iterables to Iterators here by just checking for the presence of __aiter__, though it seems unlikely to cause problems.

[JayH5]

@tomchristie