Motivation:
HttpClientUpgradeHandler currently throws an IllegalStateException when
the server sends a '101 Switching Protocols' response that has no
'Upgrade' header.
Some servers do not send the 'Upgrade' header on a successful protocol
upgrade and we could safely assume that the server accepted the
requested protocol upgrade in such a case, looking from the response
status code (101)
Modifications:
- Do not throw an IllegalStateException when the server responded 101
without a 'Upgrade' header
- Note that we still check the equality of the 'Upgrade' header when it
is present.
Result:
- Fixes#4523
- Better interoperability
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