http.client: CannotSendRequest after TimeoutError

[7cff]

Bug report

Bug description:

When using the low-level http.client API, connection timeouts cause the Connection object to enter an improper state which seemingly cannot be reset short of creating a new Connection object.

To reproduce, you'll need an address that produces a timeout. This can be done locally using Python's http.server and whichever firewall solution your OS has (since I'm on Linux, this means nftables):

table ip filter {
	chain input {
		type filter hook input priority filter;
		tcp dport 8000 drop
	}
}

python -m http.server

Finally, in a Python interpreter, do the following:

from http.client import HTTPConnection
conn = HTTPConnection('127.0.0.1', 8000)
# this request throws TimeoutError
conn.request('HEAD', '/')
# this request throws CannotSendRequest
conn.request('HEAD', '/')

The following do not fix the state of the Connection:

• getresponse(): Returns AttributeError
• connect(): Even if the later connection to the address works, the Connection remains in an invalid state

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-141938/fix-http-client-state-reset #141941