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Unraveling Status Code 226 IM Used: Definition and Usage

1. Explanation of Response code 226 "IM Used"

1.1. What is Status Code 226

Response code 226 "IM Used" is a non-standard HTTP response code.


It's used in the following cases:

  • HTTP/2: The server informs the client that delta encoding was applied to the response to the GET request.
  • WebDAV: The server informs the client that a resource property was changed using IM (instance manipulation).

Additionally, the presence of the 226 IM Used status code indicates that the A-IM header from the client was successfully received, and the server returns content considering the specified parameters.

  • HTTP/2 Usage:

In the context of HTTP/2, the 226 status code "IM Used" signifies that the server has employed delta encoding to respond to a GET request from the client. Delta encoding, also known as delta compression or delta encoding with context, is a technique used to reduce the amount of data transmitted over the network by sending only the differences between the requested resource and a previously cached version. This approach is particularly beneficial in scenarios where the requested resource is similar to a previously cached version, allowing for more efficient data transfer and improved performance.

  • WebDAV Implementation:

Within the WebDAV (Web Distributed Authoring and Versioning) protocol, code 226 indicates that the server has modified a resource property using instance manipulation (IM). Instance manipulation refers to the manipulation of resource instances, which are individual representations of a resource at a specific point in time. By using IM, the server can change resource properties while preserving the integrity and consistency of the resource itself. This allows for seamless management and manipulation of resources within the WebDAV framework, facilitating collaborative authoring and versioning of web content.

  • A-IM Header Acceptance:

Additionally, when the server returns a 226 IM Used status code, it signifies that the A-IM header provided by the client was successfully accepted. The client uses the A-IM (Accept-Instance-Manipulation) header to indicate its willingness to accept instance manipulation instructions from the server. By acknowledging the A-IM header and returning the 226 status code, the server confirms that it has processed the client's preferences regarding instance manipulation, ensuring that the content returned adheres to the specified parameters.

In summary, the 226 "IM Used" status code is a specialized HTTP response code utilized in HTTP/2 and WebDAV contexts to indicate the application of delta encoding for efficient data transmission, the modification of resource properties using instance manipulation, and the acceptance of client-specified instance manipulation parameters through the A-IM header.

1.2. Support:

Not all browsers support code 226.

  • List of browsers that support code 226:

o Chrome (from version 80)
o Firefox (from version 78)
o Edge (from version 80)
o Safari (from version 14)

  • Not supported:

o Internet Explorer
o Opera Mini
o UC Browser

It is important to note that using the 226 code is not mandatory. However, understanding how code 226 works can be helpful for developers who are troubleshooting HTTP connections.

1.3. Usage:

  • The server may send code 226 when:
o The client requests a resource already used in an instant messaging (IM) session.
o The server wants the client to replace the requested resource with another resource.

  • Contents of the response:
o The content of response 226 is undefined.
o In some cases, the server may include additional information in the response.

2. Difference from Other Codes

  • 200 OK: Used when the request has been successfully processed, and the server has sent the requested resource.
  • 204 No Content: Used when the request was successfully processed, but the server has nothing to send.
  • 304 Not Modified: Used when the requested resource has not been modified.

3. Recommendations for Clients

  • Read response header: The response header may contain additional information about why the server sent the 226 code.
  • Check cache: If the client caches responses, it can check the cache to see if the requested resource has already been received.
  • Replace the requested resource if the client cannot find it.

4. Recommendations for Servers

  • Use code 226 only as a last resort: Code 226 is not a standard response code, and its use may result in incompatibility.

5. Examples of Use

Instant Messaging: The server can send code 226.

HTTP/2:

  • Gzip compression: The server can use code 226 to respond to a GET request with gzip-compressed content.
  • Broadcasting: The server may use code 226 to respond to the request

WebDAV:

  • Property changes: The server can use code 226 to respond to requests.

HTTP extensions:

  • Non-standard implementations: Some HTTP extensions.

Proxy servers:

  • Caching: The proxy server may use code 226 to respond to API:
  • Restricted access: API can use code 226
The 226 status code falls within the 2xx Success category of server response codes. It indicates that the server has successfully processed the request, even though the response may include multiple status codes related to different parts of the response body. For a comprehensive understanding of 2xx status codes, please refer to our general HTTP 2xx status codes article.

Ensuring that all website or web application pages are operational and returning a status code of 200 for successful requests is essential. Monitoring this aspect can be streamlined using the Atomseo Broken Links Checker tool, which identifies server errors, including reason code 226, and allows free daily checks of up to 1500 links.
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6. Learn About Other 2xx Status Codes