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Convert::BinHex(3)    User Contributed Perl Documentation   Convert::BinHex(3)

NAME
       Convert::BinHex - extract data from Macintosh BinHex files

       ALPHA WARNING: this code is currently in its Alpha release.  Things may
       change drastically until the interface is hammered out: if you have
       suggestions or objections, please speak up now!

SYNOPSIS
       Simple functions:

	   use Convert::BinHex qw(binhex_crc macbinary_crc);

	   # Compute HQX7-style CRC for data, pumping in old CRC if desired:
	   $crc = binhex_crc($data, $crc);

	   # Compute the MacBinary-II-style CRC for the data:
	   $crc = macbinary_crc($data, $crc);

       Hex to bin, low-level interface.	 Conversion is actually done via an
       object ("Convert::BinHex::Hex2Bin") which keeps internal conversion
       state:

	   # Create and use a "translator" object:
	   my $H2B = Convert::BinHex->hex2bin;	  # get a converter object
	   while (<STDIN>) {
	       print $STDOUT $H2B->next($_);	    # convert some more input
	   }
	   print $STDOUT $H2B->done;		  # no more input: finish up

       Hex to bin, OO interface.  The following operations must be done in the
       order shown!

	   # Read data in piecemeal:
	   $HQX = Convert::BinHex->open(FH=>\*STDIN) || die "open: $!";
	   $HQX->read_header;		       # read header info
	   @data = $HQX->read_data;	       # read in all the data
	   @rsrc = $HQX->read_resource;	       # read in all the resource

       Bin to hex, low-level interface.	 Conversion is actually done via an
       object ("Convert::BinHex::Bin2Hex") which keeps internal conversion
       state:

	   # Create and use a "translator" object:
	   my $B2H = Convert::BinHex->bin2hex;	  # get a converter object
	   while (<STDIN>) {
	       print $STDOUT $B2H->next($_);	    # convert some more input
	   }
	   print $STDOUT $B2H->done;		  # no more input: finish up

       Bin to hex, file interface.  Yes, you can convert to BinHex as well as
       from it!

	   # Create new, empty object:
	   my $HQX = Convert::BinHex->new;

	   # Set header attributes:
	   $HQX->filename("logo.gif");
	   $HQX->type("GIFA");
	   $HQX->creator("CNVS");

	   # Give it the data and resource forks (either can be absent):
	   $HQX->data(Path => "/path/to/data");	      # here, data is on disk
	   $HQX->resource(Data => $resourcefork);     # here, resource is in core

	   # Output as a BinHex stream, complete with leading comment:
	   $HQX->encode(\*STDOUT);

       PLANNED!!!! Bin to hex, "CAP" interface.	 Thanks to Ken Lunde for
       suggesting this.

	   # Create new, empty object from CAP tree:
	   my $HQX = Convert::BinHex->from_cap("/path/to/root/file");
	   $HQX->encode(\*STDOUT);

DESCRIPTION
       BinHex is a format used by Macintosh for transporting Mac files safely
       through electronic mail, as short-lined, 7-bit, semi-compressed data
       streams.	 Ths module provides a means of converting those data streams
       back into into binary data.

FORMAT
       (Some text taken from RFC-1741.)	 Files on the Macintosh consist 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 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.	The BinHex format
       squashes that data into transmittable ASCII as follows:

       1.  The file is output as a byte stream consisting of some basic header
	   information (filename, type, creator), then the data fork, then the
	   resource fork.

       2.  The byte stream is compressed by looking for series of duplicated
	   bytes and representing them using a special binary escape sequence
	   (of course, any occurences of the escape character must also be
	   escaped).

       3.  The compressed stream is encoded via the "6/8 hemiola" common to
	   base64 and uuencode: each group of three 8-bit bytes (24 bits) is
	   chopped into four 6-bit numbers, which are used as indexes into an
	   ASCII "alphabet".  (I assume that leftover bytes are zero-padded;
	   documentation is thin).

FUNCTIONS
   CRC computation
       macbinary_crc DATA, SEED
	   Compute the MacBinary-II-style CRC for the given DATA, with the CRC
	   seeded to SEED.  Normally, you start with a SEED of 0, and you pump
	   in the previous CRC as the SEED if you're handling a lot of data
	   one chunk at a time.	 That is:

	       $crc = 0;
	       while (<STDIN>) {
		   $crc = macbinary_crc($_, $crc);
	       }

	   Note: Extracted from the mcvert utility (Doug Moore, April '87),
	   using a "magic array" algorithm by Jim Van Verth for efficiency.
	   Converted to Perl5 by Eryq.	Untested.

       binhex_crc DATA, SEED
	   Compute the HQX-style CRC for the given DATA, with the CRC seeded
	   to SEED.  Normally, you start with a SEED of 0, and you pump in the
	   previous CRC as the SEED if you're handling a lot of data one chunk
	   at a time.  That is:

	       $crc = 0;
	       while (<STDIN>) {
		   $crc = binhex_crc($_, $crc);
	       }

	   Note: Extracted from the mcvert utility (Doug Moore, April '87),
	   using a "magic array" algorithm by Jim Van Verth for efficiency.
	   Converted to Perl5 by Eryq.

OO INTERFACE
   Conversion
       bin2hex
	   Class method, constructor.  Return a converter object.  Just
	   creates a new instance of "Convert::BinHex::Bin2Hex"; see that
	   class for details.

       hex2bin
	   Class method, constructor.  Return a converter object.  Just
	   creates a new instance of "Convert::BinHex::Hex2Bin"; see that
	   class for details.

   Construction
       new PARAMHASH
	   Class method, constructor.  Return a handle on a BinHex'able
	   entity.  In general, the data and resource forks for such an entity
	   are stored in native format (binary) format.

	   Parameters in the PARAMHASH are the same as header-oriented method
	   names, and may be used to set attributes:

	       $HQX = new Convert::BinHex filename => "icon.gif",
					  type	  => "GIFB",
					  creator => "CNVS";

       open PARAMHASH
	   Class method, constructor.  Return a handle on a new BinHex'ed
	   stream, for parsing.	 Params are:

	   Data
	       Input a HEX stream from the given data.	This can be a scalar,
	       or a reference to an array of scalars.

	   Expr
	       Input a HEX stream from any open()able expression.  It will be
	       opened and binmode'd, and the filehandle will be closed either
	       on a "close()" or when the object is destructed.

	   FH  Input a HEX stream from the given filehandle.

	   NoComment
	       If true, the parser should not attempt to skip a leading "(This
	       file...)"  comment.  That means that the first nonwhite
	       characters encountered must be the binhex'ed data.

   Get/set header information
       creator [VALUE]
	   Instance method.  Get/set the creator of the file.  This is a four-
	   character string (though I don't know if it's guaranteed to be
	   printable ASCII!)  that serves as part of the Macintosh's version
	   of a MIME "content-type".

	   For example, a document created by "Canvas" might have creator
	   "CNVS".

       data [PARAMHASH]
	   Instance method.  Get/set the data fork.  Any arguments are passed
	   into the new() method of "Convert::BinHex::Fork".

       filename [VALUE]
	   Instance method.  Get/set the name of the file.

       flags [VALUE]
	   Instance method.  Return the flags, as an integer.  Use bitmasking
	   to get as the values you need.

       header_as_string
	   Return a stringified version of the header that you might use for
	   logging/debugging purposes.	It looks like this:

	       X-HQX-Software: BinHex 4.0 (Convert::BinHex 1.102)
	       X-HQX-Filename: Something_new.eps
	       X-HQX-Version: 0
	       X-HQX-Type: EPSF
	       X-HQX-Creator: ART5
	       X-HQX-Data-Length: 49731
	       X-HQX-Rsrc-Length: 23096

	   As some of you might have guessed, this is RFC-822-style, and may
	   be easily plunked down into the middle of a mail header, or split
	   into lines, etc.

       requires [VALUE]
	   Instance method.  Get/set the software version required to convert
	   this file, as extracted from the comment that preceded the actual
	   binhex'ed data; e.g.:

	       (This file must be converted with BinHex 4.0)

	   In this case, after parsing in the comment, the code:

	       $HQX->requires;

	   would get back "4.0".

       resource [PARAMHASH]
	   Instance method.  Get/set the resource fork.	 Any arguments are
	   passed into the new() method of "Convert::BinHex::Fork".

       type [VALUE]
	   Instance method.  Get/set the type of the file.  This is a four-
	   character string (though I don't know if it's guaranteed to be
	   printable ASCII!)  that serves as part of the Macintosh's version
	   of a MIME "content-type".

	   For example, a GIF89a file might have type "GF89".

       version [VALUE]
	   Instance method.  Get/set the version, as an integer.

   Decode, high-level
       read_comment
	   Instance method.  Skip past the opening comment in the file, which
	   is of the form:

	      (This file must be converted with BinHex 4.0)

	   As per RFC-1741, this comment must immediately precede the BinHex
	   data, and any text before it will be ignored.

	   You don't need to invoke this method yourself; "read_header()" will
	   do it for you.  After the call, the version number in the comment
	   is accessible via the "requires()" method.

       read_header
	   Instance method.  Read in the BinHex file header.  You must do this
	   first!

       read_data [NBYTES]
	   Instance method.  Read information from the data fork.  Use it in
	   an array context to slurp all the data into an array of scalars:

	       @data = $HQX->read_data;

	   Or use it in a scalar context to get the data piecemeal:

	       while (defined($data = $HQX->read_data)) {
		  # do stuff with $data
	       }

	   The NBYTES to read defaults to 2048.

       read_resource [NBYTES]
	   Instance method.  Read in all/some of the resource fork.  See
	   "read_data()" for usage.

   Encode, high-level
       encode OUT
	   Encode the object as a BinHex stream to the given output handle
	   OUT.	 OUT can be a filehandle, or any blessed object that responds
	   to a "print()" message.

	   The leading comment is output, using the "requires()" attribute.

SUBMODULES
   Convert::BinHex::Bin2Hex
       A BINary-to-HEX converter.  This kind of conversion requires a certain
       amount of state information; it cannot be done by just calling a simple
       function repeatedly.  Use it like this:

	   # Create and use a "translator" object:
	   my $B2H = Convert::BinHex->bin2hex;	  # get a converter object
	   while (<STDIN>) {
	       print STDOUT $B2H->next($_);	     # convert some more input
	   }
	   print STDOUT $B2H->done;		  # no more input: finish up

	   # Re-use the object:
	   $B2H->rewind;		 # ready for more action!
	   while (<MOREIN>) { ...

       On each iteration, "next()" (and "done()") may return either a decent-
       sized non-empty string (indicating that more converted data is ready
       for you) or an empty string (indicating that the converter is waiting
       to amass more input in its private buffers before handing you more
       stuff to output.

       Note that "done()" always converts and hands you whatever is left.

       This may have been a good approach.  It may not.	 Someday, the
       converter may also allow you give it an object that responds to read(),
       or a FileHandle, and it will do all the nasty buffer-filling on its
       own, serving you stuff line by line:

	   # Someday, maybe...
	   my $B2H = Convert::BinHex->bin2hex(\*STDIN);
	   while (defined($_ = $B2H->getline)) {
	       print STDOUT $_;
	   }

       Someday, maybe.	Feel free to voice your opinions.

   Convert::BinHex::Hex2Bin
       A HEX-to-BINary converter. This kind of conversion requires a certain
       amount of state information; it cannot be done by just calling a simple
       function repeatedly.  Use it like this:

	   # Create and use a "translator" object:
	   my $H2B = Convert::BinHex->hex2bin;	  # get a converter object
	   while (<STDIN>) {
	       print STDOUT $H2B->next($_);	     # convert some more input
	   }
	   print STDOUT $H2B->done;		  # no more input: finish up

	   # Re-use the object:
	   $H2B->rewind;		 # ready for more action!
	   while (<MOREIN>) { ...

       On each iteration, "next()" (and "done()") may return either a decent-
       sized non-empty string (indicating that more converted data is ready
       for you) or an empty string (indicating that the converter is waiting
       to amass more input in its private buffers before handing you more
       stuff to output.

       Note that "done()" always converts and hands you whatever is left.

       Note that this converter does not find the initial "BinHex version"
       comment.	 You have to skip that yourself.  It only handles data between
       the opening and closing ":".

   Convert::BinHex::Fork
       A fork in a Macintosh file.

	   # How to get them...
	   $data_fork = $HQX->data;	 # get the data fork
	   $rsrc_fork = $HQX->resource;	 # get the resource fork

	   # Make a new fork:
	   $FORK = Convert::BinHex::Fork->new(Path => "/tmp/file.data");
	   $FORK = Convert::BinHex::Fork->new(Data => $scalar);
	   $FORK = Convert::BinHex::Fork->new(Data => \@array_of_scalars);

	   # Get/set the length of the data fork:
	   $len = $FORK->length;
	   $FORK->length(170);	      # this overrides the REAL value: be careful!

	   # Get/set the path to the underlying data (if in a disk file):
	   $path = $FORK->path;
	   $FORK->path("/tmp/file.data");

	   # Get/set the in-core data itself, which may be a scalar or an arrayref:
	   $data = $FORK->data;
	   $FORK->data($scalar);
	   $FORK->data(\@array_of_scalars);

	   # Get/set the CRC:
	   $crc = $FORK->crc;
	   $FORK->crc($crc);

UNDER THE HOOD
   Design issues
       BinHex needs a stateful parser
	   Unlike its cousins base64 and uuencode, BinHex format is not
	   amenable to being parsed line-by-line.  There appears to be no
	   guarantee that lines contain 4n encoded characters... and even if
	   there is one, the BinHex compression algorithm interferes: even
	   when you can decode one line at a time, you can't necessarily
	   decompress a line at a time.

	   For example: a decoded line ending with the byte "\x90" (the escape
	   or "mark" character) is ambiguous: depending on the next decoded
	   byte, it could mean a literal "\x90" (if the next byte is a
	   "\x00"), or it could mean n-1 more repetitions of the previous
	   character (if the next byte is some nonzero "n").

	   For this reason, a BinHex parser has to be somewhat stateful: you
	   cannot have code like this:

	       #### NO! #### NO! #### NO! #### NO! #### NO! ####
	       while (<STDIN>) {	    # read HEX
		   print hexbin($_);	      # convert and write BIN
	       }

	   unless something is happening "behind the scenes" to keep track of
	   what was last done.	The dangerous thing, however, is that this
	   approach will seem to work, if you only test it on BinHex files
	   which do not use compression and which have 4n HEX characters on
	   each line.

	   Since we have to be stateful anyway, we use the parser object to
	   keep our state.

       We need to be handle large input files
	   Solutions that demand reading everything into core don't cut it in
	   my book.  The first MPEG file that comes along can louse up your
	   whole day.  So, there are no size limitations in this module: the
	   data is read on-demand, and filehandles are always an option.

       Boy, is this slow!
	   A lot of the byte-level manipulation that has to go on,
	   particularly the CRC computing (which involves intensive bit-
	   shifting and masking) slows this module down significantly.	What
	   is needed perhaps is an optional extension library where the slow
	   pieces can be done more quickly... a Convert::BinHex::CRC, if you
	   will.  Volunteers, anyone?

	   Even considering that, however, it's slower than I'd like.  I'm
	   sure many improvements can be made in the HEX-to-BIN end of things.
	   No doubt I'll attempt some as time goes on...

   How it works
       Since BinHex is a layered format, consisting of...

	     A Macintosh file [the "BIN"]...
		Encoded as a structured 8-bit bytestream, then...
		   Compressed to reduce duplicate bytes, then...
		      Encoded as 7-bit ASCII [the "HEX"]

       ...there is a layered parsing algorithm to reverse the process.
       Basically, it works in a similar fashion to stdio's fread():

	      0. There is an internal buffer of decompressed (BIN) data,
		 initially empty.
	      1. Application asks to read() n bytes of data from object
	      2. If the buffer is not full enough to accomodate the request:
		   2a. The read() method grabs the next available chunk of input
		       data (the HEX).
		   2b. HEX data is converted and decompressed into as many BIN
		       bytes as possible.
		   2c. BIN bytes are added to the read() buffer.
		   2d. Go back to step 2a. until the buffer is full enough
		       or we hit end-of-input.

       The conversion-and-decompression algorithms need their own internal
       buffers and state (since the next input chunk may not contain all the
       data needed for a complete conversion/decompression operation).	These
       are maintained in the object, so parsing two different input streams
       simultaneously is possible.

WARNINGS
       Only handles "Hqx7" files, as per RFC-1741.

       Remember that Macintosh text files use "\r" as end-of-line: this means
       that if you want a textual file to look normal on a non-Mac system, you
       probably want to do this to the data:

	   # Get the data, and output it according to normal conventions:
	   foreach ($HQX->read_data) { s/\r/\n/g; print }

CHANGE LOG
       Current version: $Id: BinHex.pm,v 1.119 1997/06/28 05:12:42 eryq Exp $

       Version 1.118
	   Ready to go public (with Paul's version, patched for native Mac
	   support)!  Warnings have been suppressed in a few places where
	   undefined values appear.

       Version 1.115
	   Fixed another bug in comp2bin, related to the MARK falling on a
	   boundary between inputs.  Added testing code.

       Version 1.114
	   Added BIN-to-HEX conversion.	 Eh.  It's a start.  Also, a lot of
	   documentation additions and cleanups.  Some methods were also
	   renamed.

       Version 1.103
	   Fixed bug in decompression (wasn't saving last character).  Fixed
	   "NoComment" bug.

       Version 1.102
	   Initial release.

AUTHOR AND CREDITS
       Written by Eryq, http://www.enteract.com/~eryq / eryq@enteract.com

       Support for native-Mac conversion, plus invaluable contributions in
       Alpha Testing, plus a few patches, plus the baseline binhex/debinhex
       programs, were provided by Paul J. Schinder (NASA/GSFC).

       Ken Lunde (Adobe) suggested incorporating the CAP file representation.

TERMS AND CONDITIONS
       Copyright (c) 1997 by Eryq.  All rights reserved.  This program is free
       software; you can redistribute it and/or modify it under the same terms
       as Perl itself.

       This software comes with NO WARRANTY of any kind.  See the COPYING file
       in the distribution for details.

perl v5.16.2			  1997-06-27		    Convert::BinHex(3)
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