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draft-faltstrom-macmime2-00.txt
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Network Working Group Patrik Faltstrom
Internet Draft: draft-faltstrom-macmime2-00 Dave Crocker
Expiration 4/94 Erik E. Fair
October 15, 1993
MIME Content Type for BinHex encoded files
1. Status of this Memo
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute
working documents at any timne. It is not appropriate to use
Internet Drafts as reference material or to cite them other than as
a "working draft" or "work in progress". Please check the
1idabstracts.txt listing contained in the internet-drafts Shadow
Directories on nic.ddn.mil, nnsc.nsf.net, nic.nordu.net,
ftp.nisc.sri.com, or munnari.oz.au to learn the current status of
any Internet Draft.
This specification is intended as an Informational document for
transmission of files with the use of Macintosh specific encoding
using BinHex4.0. For maximal interoperability, it is recommended
that MIME-based application/applefile be used instead.
2. Abstract
This memo describes the format to use when sending BinHex4.0 files
via MIME [BORE93]. The format is compatible with existing
mechanisms for distributing Macintosh files. Only when available
software and/or user practice dictates, should this method be
employed. It is recommended to use application/applefile for
maximum interoperability.
3. Introduction
Files on the Macintosh consists of two parts, called forks:
DATA FORK: The actual data included in the file. The Data
fork is typically the only meaningful part of a
Macintosh file on a non-Macintosh computer system.
For example, if a Macintosh user wants to send a
file of data to a user on an IBM-PC, she would only
send the Data fork.
RESOURCE FORK: Contains a collection of arbitrary attribute/value
pairs, including program segments, icon bitmaps,
and parametric values.
Faltstrom, Crocker, Fair [Page 1]
Internet Draft Content Type for BinHex files October 15, 1993
Additional information regarding Macintosh files is stored by the
Finder has in a hidden file, called the "Desktop Database".
Because of the complications in storing different parts of a
Macintosh file in a non-Macintosh filesystem that only handles
consecutive data in one part, it is common to convert the Macintosh
file into some other format before transferring it over the network.
AppleDouble file format [APPL90], encoded in MIME as
multipart/appledouble and application/applefile is the preferred
format for a Macintosh file that is to be included in an Internet
mail message, because it provides recipients with Macintosh
computers the entire document, including Icons and other Macintosh
specific information, while other users easily can extract the Data
fork (the actual data).
However, this specification provides for use of the currently
popular BinHex4.0 encoding schemes, as a convinience to the
installed base of users.
4. MIME format for BinHex4.0
MIME-base Apple information is specified by:
MIME type-name: APPLICATION
MIME subtype name: MAC-BINHEX40
Required parameters: none
Optional parameters: NAME, which must only consist of
seven-bit US-ASCII characters excluding
SPACE, CTLS, and "tspecials" as defined
in RFC-1521 [BORE93].
Encoding considerations: none
Security considerations: See separate section in the document
Published specification: Appendix A
Rationale: Permits MIME-based transmission of data
with Apple Macintosh file system specific
information using a currently popular,
though platform specific, format.
4a. Detail specific to MIME-based usage
Macintosh documents do not always need to be sent in a special
format. Those documents with well-known MIME types and
non-existent or trivial resource forks can be sent as regular
MIME body parts, without use of AppleSingle, AppleDouble or
BinHex4.0.
Documents which lack a data fork should always be sent as
application/applefile.
Faltstrom, Crocker, Fair [Page 2]
Internet Draft Content Type for BinHex files October 15, 1993
All other documents should normally sent as
multipart/appledouble. This includes documents with non-trivial
resource forks, and documents without corresponding well-known
MIME types.
It may be valuable in some cases to allow the user to choose one
format over another, either because he disagrees with the
implementor's definition of "trivial" resource forks, or for
reasons of his own.
Only when available software and/or user practice dictates,
should application/mac-binhex40 be employed.
5. BinHex
BinHex 4.0 is a propular means of encoding Macintosh files for
archiving on non-Macintosh file systems and for transmission via
Internet mail. (See Appendix A for a brief description of the
BinHex 4.0 format.)
The content-type application/mac-binhex40 indicates that the body of
the mail is a BinHex4.0 file. Even though the BinHex encoding
consists of characters which are not the same as those used in
Base64 (those regarded as safe according to RFC-1521 [BORE93]) a
transportation encoding should not be done.
Even though a BinHex file includes the original Macintosh filename,
it is recommended that a name parameter be included on the
Content-Type header to give the recipient a hint as to what file is
attached. The value of the name parameter must consist of seven-bit
US-ASCII characters excluding SPACE, CTLS, and "tspecials" as
defined in RFC- 1521 [BORE93].
5a. BinHex example
Content-Type: application/mac-binhex40; name="car.hqx"
[The BinHex4.0 file goes here]
6. References
APPL90 AppleSingle/AppleDouble Formats for Foreign Files
Developer's Note, Apple Computer, Inc., 1990
BORE93 Borenstein N., and N. Freed, MIME (Multipurpose Internet
Mail Extensions): Mechanisms for Specifying and Describing
the Format of Internet Message Bodies, RFC 1521, Bellcore,
Innosoft, September 1993.
Faltstrom, Crocker, Fair [Page 3]
Internet Draft Content Type for BinHex files October 15, 1993
7. Security Considerations
To the extent that application/mac-binhex40 facilitates the
transmission of operating-system sensitive data, it may open a door
for easier relaxation of security rules than is intended either by
the sender of the administrator of the sender's system.
8. Acknowledgements
Thanks to all of the people on the ietf-822 list who have provided
much meaningful input for this document. Some of them must though
be remembered by name, because they have almost crushed my mailbox
the last weeks with a very nice and interesting debate:
Johan Berglund, Steve Dorner, David Gelhar, David Herron,
Raymond Lau, Jamey Maze, John B. Melby, Jan Michael Rynning,
Rens Troost, Peter Svanberg
9. Authors Addresses
Patrik Faltstrom
Department of Numerical Analysis and Computing Science
Royal Institute of Technology
S-100 44 Stockholm
Sweden
Email: paf@nada.kth.se
Dave Crocker
675 Spruce. Dr.
Sunnyvale, CA 94086
USA
Email: dcrocker@mordor.stanford.edu
Erik E. Fair
Engineering Computer Operations
Apple Computer Inc.
Email: fair@apple.com
Appendix A. The BinHex format
Here is a description of the Hqx7 (7 bit format as implemented in
BinHex 4.0) formats for Macintosh Application and File transfers.
The main features of the format are:
Faltstrom, Crocker, Fair [Page 4]
Internet Draft Content Type for BinHex files October 15, 1993
1) Error checking even using ASCII download
2) Compression of repetitive characters
3) 7 bit encoding for ASCII download
The format is processed at three different levels:
1) 8 bit encoding of the file:
Byte: Length of FileName (1->63)
Bytes: FileName ("Length" bytes)
Byte: Version
Long: Type
Long: Creator
Word: Flags (And $F800)
Long: Length of Data Fork
Long: Length of Resource Fork
Word: CRC
Bytes: Data Fork ("Data Length" bytes)
Word: CRC
Bytes: Resource Fork ("Rsrc Length" bytes)
Word: CRC
2) Compression of repetitive characters.
($90 is the marker, encoding is made for 3->255 characters)
00 11 22 33 44 55 66 77 -> 00 11 22 33 44 55 66 77
11 22 22 22 22 22 22 33 -> 11 22 90 06 33
11 22 90 33 44 -> 11 22 90 00 33 44
The whole file is considered as a stream of bits. This stream will
be divided in blocks of 6 bits and then converted to one of 64
characters contained in a table. The characters in this table have
been chosen for maximum noise protection. The format will start
with a ":" (first character on a line) and end with a ":".
There will be a maximum of 64 characters on a line. It must be
preceded, by this comment, starting in column 1 (it does not start
in column 1 in this document):
(This file must be converted with BinHex 4.0)
Any text before this comment is to be ignored.
The characters used is:
!"#$%&'()*+,- 012345689@ABCDEFGHIJKLMNPQRSTUVXYZ[`abcdefhijklmpqr
Faltstrom, Crocker, Fair [Page 5]