[PR #7644/6639f7df backport][3.9] Fixed 7616: EmptyStreamReader.iter_chunks() never ends

[patchback]

This is a backport of PR #7644 as merged into master (6639f7d).

What do these changes do?

Fixes an issue reported in 7616 - An iteration of the chunks of an EmptyStreamReader with iter_chunks() never ends.

Are there changes in behavior for the user?

• EmptyStreamReader iter_chunks() does not get stuck
• First call of EmptyStreamReader readchunk() now returns (b"", False). All the subsequent calls return (b"", True). Before this PR it was always (b"", True).

Related issue number

7616

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[rgeronimi]

A subtle bug comes from
https://github.com/aio-libs/aiohttp/blob/2a73d4699c0b7de1460d831eea48895edff6f9af/aiohttp/streams.py#L565C1-L565C14

which shares a single instance of the empty reader for all cases where an HTTP response has no body.

This instance being shared, it will not return properly (b"", False) on the first iteration call of each API client calling it. It will return it properly only for the very first API client

2 alternative solutions:

• Make it not shared, creating a new object every time an empty HTTP response is parsed
• Simplify the API contract to remove the obligation to return (b"", False) as the first iteration result. I don't know the reason why this contract was added in the first place (it was added through another issue)

[Dreamsorcerer]

• Make it not shared, creating a new object every time an empty HTTP response is parsed

Yes, maybe we can do that. Then also deprecate the EMPTY_PAYLOAD global as well, I guess. Not sure how better to solve it.

• Simplify the API contract to remove the obligation to return (b"", False) as the first iteration result. I don't know the reason why this contract was added in the first place (it was added through another issue)

From what I could see, that is the message sent when an EOF byte is received. So, I'm not sure this logic can be changed without breaking things.