WebSocket 1010 Mandatory Extension vs 1011 Internal Error
Both WebSocket 1010 (Mandatory Extension) and 1011 (Internal Error) belong to the WebSocket Close Codes category. 1010 indicates that the client is terminating the connection because the server did not negotiate one or more expected extensions in the handshake response. Meanwhile, 1011 means that the server is terminating the connection because it encountered an unexpected condition that prevented it from fulfilling the request.
Description
The client is terminating the connection because the server did not negotiate one or more expected extensions in the handshake response.
When You See It
The client requested a required WebSocket extension (e.g., permessage-deflate compression) during the handshake, but the server did not include it in its response.
How to Fix
Enable the required extension on the server, or update the client to make the extension optional. Check the Sec-WebSocket-Extensions header in the handshake response.
Description
The server is terminating the connection because it encountered an unexpected condition that prevented it from fulfilling the request.
When You See It
The server hit an unhandled exception or crashed while processing a WebSocket message. This is the WebSocket equivalent of HTTP 500 Internal Server Error.
How to Fix
Check the server-side application logs for stack traces and exceptions. Fix the underlying bug that caused the crash and add proper error handling around message processing.
Key Differences
WebSocket 1010: The client is terminating the connection because the server did not negotiate one or more expected extensions in the handshake response.
WebSocket 1011: The server is terminating the connection because it encountered an unexpected condition that prevented it from fulfilling the request.
You encounter 1010 when the client requested a required WebSocket extension (e.g., permessage-deflate compression) during the handshake, but the server did not include it in its response.
You encounter 1011 when the server hit an unhandled exception or crashed while processing a WebSocket message. This is the WebSocket equivalent of HTTP 500 Internal Server Error.
When to Use Which
For 1010 (Mandatory Extension): Enable the required extension on the server, or update the client to make the extension optional. Check the Sec-WebSocket-Extensions header in the handshake response. For 1011 (Internal Error): Check the server-side application logs for stack traces and exceptions. Fix the underlying bug that caused the crash and add proper error handling around message processing.