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IETF RFC 6713



Last modified on Tuesday, August 21st, 2012

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Internet Engineering Task Force (IETF)                         J. Levine
Request for Comments: 6713                          Taughannock Networks
Category: Informational                                    August 2012
ISSN: 2070-1721


       The 'application/zlib' and 'application/gzip' Media Types

 Abstract

   This document defines the 'application/gzip' and 'application/zlib'
   media types for compressed data using the gzip and zlib compression
   formats.

 Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/RFC 6713.

 Copyright Notice

   Copyright (c) 2012 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.







Levine                        Informational                  PAGE 1 top


RFC 6713 Media Types 'zlib' and 'gzip' August 2012 1. Introduction zlib [RFC 1950] and gzip [RFC 1952] are widely used compression formats. zlib is a stream format, while gzip adds header and trailer fields more appropriate for a file format. Both implement the DEFLATE compression scheme described in [RFC 1951]. They are used to compress a wide variety of material, from unstructured text to structured data to executable code. Some applications have informally used media types such as application/gzip-compressed, application/gzipped, application/ x-gunzip, application/x-gzip, application/x-gzip-compressed, and gzip/document to describe data compressed with gzip. The media types defined in this document should replace those media types in future applications. 2. The 'application/zlib' Media Type The 'application/zlib' media type describes a block of data that is compressed using zlib [RFC 1950] compression. The data is a stream of bytes as described in RFC 1950. 2.1. Registration Details Type name: application Subtype name: zlib Required parameters: N/A Optional parameters: N/A Encoding considerations: Binary Security considerations: See Section 4 below. Interoperability considerations: N/A Published specification: [RFC 1950] Applications that use this media type: anywhere data size is an issue Additional information: Magic number(s): first byte is usually 0x78 but can also be 0x08, 0x18, 0x28, 0x38, 0x48, 0x58, or 0x68. The first two bytes, when interpreted as an unsigned 16-bit number in big-endian byte order, contain a value that is a multiple of 31. Levine Informational PAGE 2 top

RFC 6713 Media Types 'zlib' and 'gzip' August 2012 File extension(s): N/A Macintosh file type code(s): N/A Person and email address to contact for further information: see http://www.zlib.net/ Intended usage: COMMON Restrictions on usage: N/A Author: John Levine Change controller: IETF 3. The 'application/gzip' Media Type The 'application/gzip' media type describes a block of data that is compressed using gzip [RFC 1952] compression. The data is a stream of bytes as described in RFC 1952. 3.1. Registration Details Type name: application Subtype name: gzip Required parameters: N/A Optional parameters: N/A Encoding considerations: Binary Security considerations: See Section 4 below. Interoperability considerations: N/A Published specification: [RFC 1952] Applications that use this media type: anywhere data size is an issue Additional information: Magic number(s): first two bytes are 0x1f, 0x8b. File extension(s): gz Macintosh file type code(s): N/A Person and email address to contact for further information: see http://www.gzip.org/ Levine Informational PAGE 3 top

RFC 6713 Media Types 'zlib' and 'gzip' August 2012 Intended usage: COMMON Restrictions on usage: N/A Author: John Levine Change controller: IETF 4. Security Considerations zlib and gzip compression can be used to compress arbitrary binary data such as hostile executable code. Also, data that purports to be in zlib or gzip format may not be, and fields that are supposed to be flags, lengths, or pointers could contain anything. Applications should treat any data with due skepticism. Also see the security considerations in the underlying format documents: Section 5 of [RFC 1950], Section 6 of [RFC 1951], and Section 4 of [RFC 1952]. 5. IANA Considerations IANA has updated the "Application Media Types" registry to include 'application/zlib' as described in Section 2 and 'application/gzip' as described in Section 3. 6. Normative References [RFC 1950] Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format Specification version 3.3", RFC 1950, May 1996. [RFC 1951] Deutsch, P., "DEFLATE Compressed Data Format Specification version 1.3", RFC 1951, May 1996. [RFC 1952] Deutsch, P., "GZIP file format specification version 4.3", RFC 1952, May 1996. Author's Address John Levine Taughannock Networks PO Box 727 Trumansburg, NY 14886 Phone: +1 831 480 2300 EMail: standards@taugh.com Levine Informational PAGE 4 top

RFC TOTAL SIZE: 6525 bytes PUBLICATION DATE: Tuesday, August 21st, 2012 LEGAL RIGHTS: The IETF Trust (see BCP 78)


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