[3.11] gh-121650: Encode newlines in headers, and verify headers are sound (GH-122233) #122608
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Per RFC 2047:
It seems that the "quoted-word" scheme is a valid way to include a newline character in a header value, just like we already allow undecodable bytes or control characters.
They do need to be properly quoted when serialized to text, though.
GH-GH- Verify that email headers are well-formed
This should fail for custom fold() implementations that aren't careful about newlines.
(cherry picked from commit 0976339)
📚 Documentation preview 📚: https://cpython-previews--122608.org.readthedocs.build/