gzip/zlib media types: The 'application/zlib' and 'application/gzip' Media Types

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/rfc6713.

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1.  Introduction

   zlib [RFC1950] and gzip [RFC1952] 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 [RFC1951].

   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 [RFC1950] 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: [RFC1950]

   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.

      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 [RFC1952] 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: [RFC1952]

   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/
   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 [RFC1950], Section 6 of [RFC1951], and
   Section 4 of [RFC1952].

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

   [RFC1950]  Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format
              Specification version 3.3", RFC 1950, May 1996.

   [RFC1951]  Deutsch, P., "DEFLATE Compressed Data Format Specification
              version 1.3", RFC 1951, May 1996.

   [RFC1952]  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