HTTP 101 (Switch Protocols): meaning and handling

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: HTTP 101 confirms that the server accepted a requested protocol upgrade on this connection.

Could be also:
Constant	Type	OS
ERROR_EXCL_SEM_ALREADY_OWNED	Win32 error	Windows
ENETUNREACH	errno	Linux
ETIME	errno	Mac
EADDRNOTAVAIL	errno	Windows
MEMORY1_INITIALIZATION_FAILED	BugCheck Code	Windows

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HTTP_STATUS_CONTINUE	HTTP_STATUS_PROCESSING

HTTP_STATUS_SWITCH_PROTOCOLS

HTTP 101 is sent after a successful protocol upgrade, such as a WebSocket upgrade. The protocol change applies only to the current connection, starting after the response header section.

When diagnosing a failed upgrade, compare the client Upgrade and Connection headers with the server response and the server-side protocol configuration. A 101 response itself is success, not an error.

The response is only an intermediate transition: after the 101 header section, communication continues using the negotiated protocol on the same connection. The Upgrade and Connection headers must agree with the requested change. Clients should not continue parsing subsequent bytes as ordinary HTTP messages once the protocol switch takes effect.

RFC 9110: HTTP Semantics

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