Network Working Group                                       P. Faltstrom
Request for Comments: 1741                 Royal Institute of Technology
Category: Informational                                       D. Crocker
                                                 Brandenburg Consulting
                                                                E. Fair
                                                    Apple Computer Inc.
                                                          December 1994


              MIME Content Type for BinHex Encoded Files

Status of this Memo

  This memo provides information for the Internet community.  This memo
  does not specify an Internet standard of any kind.  Distribution of
  this memo is unlimited.

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 [FALT94] for maximum
  interoperability.

1.  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.

  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.



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RFC 1741             Content Type for BinHex Files         December 1994


  AppleDouble file format [APPL90], encoded in MIME as
  multipart/appledouble [FALT94] and application/applefile [FALT94] 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.

2.  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 be a "value" 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.

  2a.  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 must be sent as AppleSingle
     according to RFC 1740 [FALT94].

     Unless there are strong reasons not to, all other documents should
     be sent as AppleDouble according to RFC 1740 [FALT94].  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.



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RFC 1741             Content Type for BinHex Files         December 1994


     Only when available software and/or user practice dictates, should
     BinHex 4.0 be employed.

3.  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 be a "value" as defined by RFC-
  1521 [BORE93].  Note that this restricts the value to seven-bit US-
  ASCII characters.

  3a.  BinHex example

       Content-Type: application/mac-binhex40; name="car.hqx"

           [The BinHex4.0 file goes here]

4.  References

  APPL90   AppleSingle/AppleDouble Formats for Foreign Files
           Developer's Note, Apple Computer, Inc., 1990.

  FALT94   Faltstrom P., Crocker, D., and E. Fair, "MIME
           Encapsulation of Macintosh Files - MacMIME", RFC 1740,
           KTH, Brandenburg Consulting, Apple Computer Inc.,
           December 1994.

  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.








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RFC 1741             Content Type for BinHex Files         December 1994


5.  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.

6.  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,
     and Peter Svanberg.

7.  Authors' Addresses

     Patrik Faltstrom
     Department of Numerical Analysis and Computing Science
     Royal Institute of Technology
     S-100 44 Stockholm
     Sweden

     EMail: [email protected]


     Dave Crocker
     Brandenburg Consulting
     675 Spruce Dr.
     Sunnyvale, CA  94086

     EMail: [email protected]


     Erik E. Fair
     Engineering Computer Operations
     Apple Computer Inc.

     EMail: [email protected]









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RFC 1741             Content Type for BinHex Files         December 1994


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:

  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):





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RFC 1741             Content Type for BinHex Files         December 1994


   (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












































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