QtWebSockets checks HTTP headers without ignoring case.

On connect if the HTTP headers are not cased exactly as the string literals in the source, then a connection will not be made, and the error message around line 926 of src/websockets/qwebsocket_p.cpp is shown (it says "QWebSocketPrivate::processHandshake: Invalid statusline in response: %1."), but the status line will be a perfectly legal status line:

HTTP/1.1 101 Switching Protocols

This error message is given because of the if statement around line 917, which tests for much more than a bad status line: specifically it tests to see if some string values pulled from a QMap<QString,QString> have expected values. They have empty string values if the HTTP headers are not cased the same as the string literals in the source.

In other words, the code expects a response such as

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk=
Sec-WebSocket-Protocol: chat

when what is received is

HTTP/1.1 101 Switching Protocols
upgrade: websocket
connection: Upgrade
sec-websocket-accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk=
sec-websocket-protocol: chat

(Note the capitalization of the header keys).

A possible fix is to change the line around 190 from

headers.insertMulti(headerField[0], headerField[1]);

to

headers.insertMulti(headerField[0].toLower(), headerField[1]);

, and changing all string literals that act as keys to this QMap to be lower case (it's a local variable, and there are only 2 or 3 of such literals).