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510 Not Extended

Description

The 510 Not Extended status code indicates that the server requires an extension to fulfill the request, but the client did not include the required extension in the request. This status code is defined in RFC 2774, which specifies a framework for HTTP protocol extensions.

This error occurs when:

  • The server requires a specific HTTP extension to process the request
  • The client did not include the required extension in the request
  • The server cannot or will not process the request without the extension

The 510 status code is relatively rare in practice, as most modern HTTP implementations handle protocol extensions in different ways. However, it remains part of the HTTP standard for cases where a server strictly requires certain protocol extensions.

Syntax

HTTP/1.1 510 Not Extended
Content-Type: application/json
Content-Length: 198

{
  "error": {
    "code": 510,
    "message": "Not Extended",
    "details": "The server requires an extension to fulfill this request, but the extension was not included in the request."
  }
}

Examples

Example 1: Missing Required Extension

A server requires a specific HTTP extension for processing a particular type of request, but the client did not include it.

Request: 

POST /api/secure-transaction HTTP/1.1
Host: example.com
Content-Type: application/json
Content-Length: 156

{
  "account": "123456789",
  "amount": 1000.00,
  "currency": "USD",
  "recipient": "987654321"
}

Response: 

HTTP/1.1 510 Not Extended
Content-Type: application/json
Content-Length: 247

{
  "error": {
    "code": 510,
    "message": "Not Extended",
    "details": "This request requires the 'Transaction-Integrity' extension. Please include the 'Transaction-Integrity' header with your request."
  }
}

Example 2: Custom Protocol Extension Required

An API requires a custom protocol extension for certain operations, but the client did not signal support for the extension.

Request: 

GET /api/real-time-data HTTP/1.1
Host: example.com
Accept: application/json
Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...

Response: 

HTTP/1.1 510 Not Extended
Content-Type: application/json
Content-Length: 265

{
  "error": {
    "code": 510,
    "message": "Not Extended",
    "details": "Real-time data requests require the 'Streaming-Mode' extension. Please include 'Opt: \"urn:example:streaming-mode\"' in your request headers."
  }
}

Example 3: Security Extension Requirement

A server requires a security-related HTTP extension for sensitive operations, but the client did not include it.

Request: 

PUT /api/user/profile HTTP/1.1
Host: example.com
Content-Type: application/json
Content-Length: 245
Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...

{
  "name": "John Doe",
  "email": "[email protected]",
  "phone": "+1234567890",
  "address": {
    "street": "123 Main St",
    "city": "Anytown",
    "country": "US"
  }
}

Response: 

HTTP/1.1 510 Not Extended
Content-Type: application/json
Content-Length: 271

{
  "error": {
    "code": 510,
    "message": "Not Extended",
    "details": "Profile updates require the 'Enhanced-Security' extension. Please include 'Opt: \"urn:example:enhanced-security\"; ns=1' and '1-Signature' headers in your request."
  }
}

Summary

The 510 Not Extended status code indicates that the server requires an extension to fulfill the request, but the client did not include the required extension. It's part of the HTTP protocol extension framework defined in RFC 2774.

Key points about 510 Not Extended:

  1. It indicates that a required HTTP extension was not included in the client's request
  2. It's defined in RFC 2774 (An HTTP Extension Framework)
  3. It's relatively rare in modern HTTP implementations
  4. The response should specify which extension is required and how to include it
  5. It differs from 501 Not Implemented, which indicates the server doesn't support a requested functionality
  6. It's a client error in the sense that the client needs to modify the request to include the required extension
  7. Clients receiving this status should retry the request with the specified extension if they support it
  8. The HTTP extension framework uses the Opt header to signal extension usage