https://tools.ietf.org/html/rfc6455 https://tools.ietf.org/html/rfc6455
7.4.1. Defined Status Codes
Endpoints MAY use the following pre-defined status codes when sending
a Close frame.
1000
1000 indicates a normal closure, meaning that the purpose for
which the connection was established has been fulfilled.
1001
1001 indicates that an endpoint is "going away", such as a server
going down or a browser having navigated away from a page.
1002
1002 indicates that an endpoint is terminating the connection due
to a protocol error.
1003
1003 indicates that an endpoint is terminating the connection
because it has received a type of data it cannot accept (e.g., an
endpoint that understands only text data MAY send this if it
receives a binary message).
Fette & Melnikov Standards Track [Page 45]
RFC 6455 The WebSocket Protocol December 2011 1004 Reserved. The specific meaning might be defined in the future. 1005 1005 is a reserved value and MUST NOT be set as a status code in a Close control frame by an endpoint. It is designated for use in applications expecting a status code to indicate that no status code was actually present. 1006 1006 is a reserved value and MUST NOT be set as a status code in a Close control frame by an endpoint. It is designated for use in applications expecting a status code to indicate that the connection was closed abnormally, e.g., without sending or receiving a Close control frame. 1007 1007 indicates that an endpoint is terminating the connection because it has received data within a message that was not consistent with the type of the message (e.g., non-UTF-8 [RFC3629] data within a text message). 1008 1008 indicates that an endpoint is terminating the connection because it has received a message that violates its policy. This is a generic status code that can be returned when there is no other more suitable status code (e.g., 1003 or 1009) or if there is a need to hide specific details about the policy. 1009 1009 indicates that an endpoint is terminating the connection because it has received a message that is too big for it to process. 1010 1010 indicates that an endpoint (client) is terminating the connection because it has expected the server to negotiate one or more extension, but the server didn't return them in the response message of the WebSocket handshake. The list of extensions that Fette & Melnikov Standards Track [Page 46]
RFC 6455 The WebSocket Protocol December 2011 are needed SHOULD appear in the /reason/ part of the Close frame. Note that this status code is not used by the server, because it can fail the WebSocket handshake instead. 1011 1011 indicates that a server is terminating the connection because it encountered an unexpected condition that prevented it from fulfilling the request. 1015 1015 is a reserved value and MUST NOT be set as a status code in a Close control frame by an endpoint. It is designated for use in applications expecting a status code to indicate that the connection was closed due to a failure to perform a TLS handshake (e.g., the server certificate can't be verified).
7.4.2. Reserved Status Code Ranges
0-999
Status codes in the range 0-999 are not used.
1000-2999
Status codes in the range 1000-2999 are reserved for definition by
this protocol, its future revisions, and extensions specified in a
permanent and readily available public specification.
3000-3999
Status codes in the range 3000-3999 are reserved for use by
libraries, frameworks, and applications. These status codes are
registered directly with IANA. The interpretation of these codes
is undefined by this protocol.
4000-4999
Status codes in the range 4000-4999 are reserved for private use
and thus can't be registered. Such codes can be used by prior
agreements between WebSocket applications. The interpretation of
these codes is undefined by this protocol.