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

The Zlib and gzip formats 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 . 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 including 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.

The application/zlib media type describes a block of data that is compressed using Zlib compression. The data is a stream of bytes as described in RFC 1950.

Type name: application Subtype name: zlib Required parameters: N/A Optional parameters: N/A Encoding considerations: Binary. Security considerations: See section below Interoperability considerations: N/A Published specification: 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

The application/gzip media type describes a block of data that is compressed using gzip compression. The data is a stream of bytes as described in RFC 1952.

Type name: application Subtype name: gzip Required parameters: N/A Optional parameters: N/A Encoding considerations: Binary. Security considerations: See section below Interoperability considerations: N/A Published specification: 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

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 , Section 6 of , and Section 4 of .

IANA is requested to update the MIME Media Types registry to include application/zlib as described in Section and application/gzip as described in Section .

&RFC1950; &RFC1951; &RFC1952;

Note to editor: Please remove this section before publication.

Add IANA considerations Simplify encoding: binary and fix typos

Fix gzip.org Note other former names

Note former x-gzip Refer to security sections in underlying format docs