Failing websocket handshake with case-sensitive header value

[robilkot]

While performing websocket handshake with server, client sends header 'Connection' with value 'upgrade' instead of 'Upgrade'. Since values are case-sensitive, protocol switching may not be performed depending on server-side request processing (faced this issue while working with https://github.com/gilmaimon/ArduinoWebsockets). In comparison, Postman sends value 'Upgrade' and everything works just fine

[FredyH]

You are right that header values can be case sensitive. It is not our library that handles the upgrading of the HTTP connection, so we do not have access to change the case that is used. However, it seems like sending upgrade rather than Upgrade should work according to the standard, see the first example here.

In fact, the specification of the Connection header only specifies example values in lower case.

[robilkot]

Thanks for the answer. Interestingly, mdn also provides examples with upper-case 'Upgrade' here and down the link you sent