RFC 7234 - Hypertext Transfer Protocol (HTTP/1.1): Caching

• Status: Proposed Standard
• Published: June 2014
• Stream: IETF
• Obsoletes: RFC 2616
• Obsoleted by: RFC 9111
• Errata: RFC 7234 Errata

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Document Information

• RFC Number: 7234
• Title: Hypertext Transfer Protocol (HTTP/1.1): Caching
• Authors: R. Fielding, Ed., M. Nottingham, Ed., J. Reschke, Ed.
• Date: June 2014
• Category: Standards Track
• Obsoletes: RFC 2616
• Obsoleted by: RFC 9111
• ISSN: 2070-1721

Abstract

The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7234.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.

Table of Contents

• 1. Introduction
  • 1.1. Conformance and Error Handling
  • 1.2. Syntax Notation
    • 1.2.1. Delta Seconds
• 2. Overview of Cache Operation
• 3. Storing Responses in Caches
  • 3.1. Storing Incomplete Responses
  • 3.2. Storing Responses to Authenticated Requests
  • 3.3. Combining Partial Content
• 4. Constructing Responses from Caches
  • 4.1. Calculating Secondary Keys with Vary
  • 4.2. Freshness
    • 4.2.1. Calculating Freshness Lifetime
    • 4.2.2. Calculating Heuristic Freshness
    • 4.2.3. Calculating Age
    • 4.2.4. Serving Stale Responses
  • 4.3. Validation
    • 4.3.1. Sending a Validation Request
    • 4.3.2. Handling a Received Validation Request
    • 4.3.3. Handling a Validation Response
    • 4.3.4. Freshening Stored Responses upon Validation
    • 4.3.5. Freshening Responses via HEAD
  • 4.4. Invalidation
• 5. Header Field Definitions
  • 5.1. Age
  • 5.2. Cache-Control
    • 5.2.1. Request Cache-Control Directives
      • 5.2.1.1. max-age
      • 5.2.1.2. max-stale
      • 5.2.1.3. min-fresh
      • 5.2.1.4. no-cache
      • 5.2.1.5. no-store
      • 5.2.1.6. no-transform
      • 5.2.1.7. only-if-cached
    • 5.2.2. Response Cache-Control Directives
      • 5.2.2.1. must-revalidate
      • 5.2.2.2. no-cache
      • 5.2.2.3. no-store
      • 5.2.2.4. no-transform
      • 5.2.2.5. public
      • 5.2.2.6. private
      • 5.2.2.7. proxy-revalidate
      • 5.2.2.8. max-age
      • 5.2.2.9. s-maxage
    • 5.2.3. Cache Control Extensions
  • 5.3. Expires
  • 5.4. Pragma
  • 5.5. Warning
    • 5.5.1. Warning: 110 - "Response is Stale"
    • 5.5.2. Warning: 111 - "Revalidation Failed"
    • 5.5.3. Warning: 112 - "Disconnected Operation"
    • 5.5.4. Warning: 113 - "Heuristic Expiration"
    • 5.5.5. Warning: 199 - "Miscellaneous Warning"
    • 5.5.6. Warning: 214 - "Transformation Applied"
    • 5.5.7. Warning: 299 - "Miscellaneous Persistent Warning"
• 6. History Lists
• 7. IANA Considerations
  • 7.1. Cache Directive Registry
    • 7.1.1. Procedure
    • 7.1.2. Considerations for New Cache Control Directives
    • 7.1.3. Registrations
  • 7.2. Warn Code Registry
    • 7.2.1. Procedure
    • 7.2.2. Registrations
  • 7.3. Header Field Registration
• 8. Security Considerations
• 9. Acknowledgments
• 10. References
  • 10.1. Normative References
  • 10.2. Informative References
• Authors' Addresses

Appendices

• Appendix A. Changes from RFC 2616
• Appendix B. Imported ABNF
• Appendix C. Collected ABNF
• Index

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Related Resources

• Official RFC: RFC 7234
• DataTracker: RFC 7234 Info
• Errata: RFC Editor Errata
• Obsoleted by: RFC 9111