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Web Socket Protocol Handshake vs. Switching Protocols

There is no difference whatsoever. What is important is the 101 response code to indicate the handshake is progressing. This is defined in RFC 6455:

The leading line from the client follows the Request-Line format. The leading line from the server follows the Status-Line format. The Request-Line and Status-Line productions are defined in [RFC2616].

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The handshake from the server is much simpler than the client handshake. The first line is an HTTP Status-Line, with the status code 101:

HTTP/1.1 101 Switching Protocols

Any status code other than 101 indicates that the WebSocket handshake has not completed and that the semantics of HTTP still apply.

The text of the Status-Line is arbitrary, the server can use whatever text it wants, per RFC 2616:

Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF

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The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes are fully defined in section 10. The Reason-Phrase is intended to give a short textual description of the Status-Code. The Status-Code is intended for use by automata and the Reason-Phrase is intended for the human user. The client is not required to examine or display the Reason-Phrase.

Switching Protocols just happens to be what the examples in RFC 6455 use, but that is not a requirement.





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