? HTTP Status Code 226 – IM Used

? Quick Overview

226 IM Used is an HTTP success status code indicating that the server has fulfilled a request using instance manipulations. It is mainly associated with Delta Encoding, where the response represents a modification of a previously retrieved resource.

? Key Concepts

• Part of the 2xx Success status code family
• Used with Delta Encoding (RFC 3229)
• Response contains a delta, not the full resource
• Optimizes bandwidth for large resources

? Syntax / Theory

When a client supports delta encoding, it may request only the changes since a previous version of a resource. If the server responds with status code 226, it means:

• The response body is a set of changes
• The client must apply these changes to its cached version
• The final reconstructed resource is equivalent to a full 200 OK response

? Code Example(s)

// Node.js example sending HTTP 226 IM Used response
const http = require("http");

http.createServer((req, res) => {
  res.writeHead(226, {
    "Content-Type": "text/plain",
    "IM": "vcdiff"
  });
  res.end("Delta changes applied to cached resource");
}).listen(3000);

? Live Output / Explanation

? Interactive Example

Simulate how a "Delta" response updates a cached file.

? Use Cases

• Large document synchronization
• Version-controlled APIs
• Efficient patch-based updates
• Low-bandwidth network environments