506 Variant Also Negotiates
The HTTP506 Variant Also Negotiatesserver error response status code is returned during content negotiation when there is recursive loop in the process of selecting a resource.
Agent-driven content negotiation enables a client and server to collaboratively decide the best variant of a given resource when the server has multiple variants.A server sends a506 status code due to server misconfiguration that results in circular references when creating responses.
Lack of standardization of how clients automatically choose from responses, and the additional round-trips that slow down client-server interaction mean this mechanism is rarely used.Server-driven content negotiation is far more common, where a server directly chooses the most appropriate resource for the client based on the request headers (Accept-Language,Accept, etc.).
Status
506 Variant Also NegotiatesExamples
Resource with variants
In the following example, a client requests a page in thefr locale using theAccept-Language header.This can be performed using curl:
curl -H "Negotiate: trans" -H "Accept-Language: fr;" http://example.com/indexThis produces the following request:
GET /index HTTP/1.1Host: example.comUser-Agent: curl/8.7.1Accept: */*Negotiate: transAccept-Language: frDue to server misconfiguration, the variant response forfr points to atype map which itself causes transparent negotiation to be performed.The server may detect this condition by the presence of aTCN header in a choice response before it is sent:
HTTP/1.1 506 Variant Also NegotiatesDate: Mon, 22 Jul 2024 10:00:00 GMTServer: Apache/2.4.41 (Unix)Content-Type: text/html; charset=UTF-8Content-Length: 233TCN: listVary: negotiate,accept-languageAlternates: {"index.html.en" 1 {type text/html} {language en} {length 48}}, {"another-map.html.fr.map" 1 {type text/html} {language fr} {length 45}}}}<html><head> <title>506 Variant Also Negotiates</title></head><body> <h1>Variant Also Negotiates</h1> <p>A variant for the requested resource is itself a negotiable resource. This indicates a configuration error.</p></body></html>Specifications
| Specification |
|---|
| RFC 2295 # section-8.1 |
See also
300 Multiple Choices- RFC 2295
- Content negotiation
- HTTP response status codes
- Content Negotiation in Apache HTTP Server documentation
- Apache httpd
mod_negotiation.csource showing conditions that triggerHTTP_VARIANT_ALSO_VARIESresponse.