HTTP 226 IM Used — Delta Encoding Applied

Overview

HTTP 226 IM Used indicates the server applied instance manipulations (delta encoding) to the response as requested by the client.

Key Details

• Defined in RFC 3229 for delta encoding in HTTP
• The response is a delta (difference) from a previous version
• Reduces bandwidth by sending only changes instead of the full resource
• The A-IM header specifies the instance manipulation type (vcdiff, diffe, etc)
• Rarely implemented in practice despite being standardized

Common Causes

• Client sent A-IM header requesting delta encoding
• Server supports instance manipulations and applied them
• Feed aggregator using delta encoding for efficient updates

Steps

1. 1No fix needed — 226 indicates successful delta response
2. 2If developing a client, apply the delta to your cached version to reconstruct the full resource
3. 3The response includes IM: header specifying which manipulation was applied
4. 4If you want the full resource, omit the A-IM header in your request
5. 5Test your delta decoding logic against the full resource for correctness

Tags

More in 2xx Success

Frequently Asked Questions