Not Extended
Production Risk
Low. Its usage is so rare that it is unlikely to be encountered. If it is, it points to a specific, non-standard server requirement.
Further extensions to the request are required for the server to fulfill it. The server should specify what extensions are needed.
- 1The request does not contain an extension that the server requires to process it.
- 2This is part of an experimental RFC and is not widely used.
- 3The server policy requires a certain HTTP extension that the client did not use.
A client makes a request to a server that requires a mandatory (but non-standard) HTTP extension for all incoming requests, and the client did not provide it.
GET / HTTP/1.1 Host: example.com
expected output
HTTP/1.1 510 Not Extended
Fix
Include the required HTTP extension in the request
WHEN The server documentation specifies which extension is required
GET / HTTP/1.1 Host: example.com C-Ext: mandatory-extension-name
Why this works
510 is exceedingly rare in practice. Read the server's documentation or error response body to identify the required extension, then add it as a request header.
✕ Assume a 510 is a misconfigured 500
510 specifically signals a missing HTTP extension, which is a client-side protocol requirement gap, not a generic server fault.
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