#!/usr/local/bin/perl -w
use strict;

my %Mime_table;			# See RFC-2045.
@Mime_table{'A'..'Z', 'a'..'z', 0..9, '+', '/'} = 
    map{scalar(reverse(unpack('b6', chr($_))));} (0..63);
$Mime_table{'='} = '000000';	# padding

my $Mime_version;
my $Input_line;
# do {
#     $Input_line = <>;
#     if (eof) {
# 	die "No MIME header found.\n";
#     }
# } until ($Input_line =~ /^mime-version:/i);

my $Boundary;
do {
    $Input_line = <>;
    $Mime_version = 1 if ($Input_line =~ /^mime-version:/i);
    if (eof) {
	die "EOF reached before MIME boundary definition found.\n";
    }
} until ($Input_line =~ /boundary="([^"]+)"/i);
$Boundary = $1;

do {
    $Input_line = <>;
    $Mime_version = 1 if ($Input_line =~ /^mime-version:/i);
    if (eof) {
	die "EOF reached before any MIME boundaries found.\n";
    }
} until ($Input_line =~ /$Boundary/);

die "No MIME version header found before first apparent boundary.\n"
	unless $Mime_version;

my $Output_file = '';
my $b64 = 0;
SKIPFILE: while (!eof) {
  HEADER: while (defined($Input_line = <>)) {
      if ($Input_line =~ /^--$Boundary/) {
	  $Output_file = '';
          $b64 = 0;
          redo SKIPFILE;
      }
      if ($Input_line =~ m/name="([^"]+)"/i) {
	  $Output_file = $1;
	  next HEADER;
      }
      if ($Input_line =~ m/^Content\-.*base64/i) {
	  $b64 = 1;
	  next HEADER;
      }
      if ($Input_line =~ /^\s*$/) {
	  last HEADER;
      }
  }

    if ($Output_file eq '' or $b64 == 0) {
        next SKIPFILE;
    }

    open(OUT, ">$Output_file") or
        die "Could not open $Output_file for write, $!";

  BODY: while (defined($Input_line = <>)) {
      if ($Input_line =~ /^--$Boundary/) {
	  close(OUT) or die "Error on file close, $!";
	  $Output_file = '';
	  $b64 = 0;
	  redo SKIPFILE;
      }
      chomp $Input_line;
      my $Offset = 0;
      my $Length = length($Input_line);
      my $Excess = '';
    DECODE: while ($Offset < $Length) {
	my $Block = substr($Input_line, $Offset, 4);
	if (length($Block) < 4) {
	    $Excess = $Block;
	    last DECODE;
	}
	my $Output = pack("B24", join('', map {
	    $Mime_table{$_}} split('',$Block,4)));
	if ($Block =~ /(=){1,2}$/) {
	    substr($Output, -1, length($1)) = '';
	}
	print OUT $Output;
	$Offset += 4;
    }

      if ($Excess ne '') {
	  $Input_line = $Excess . <>;
	  redo BODY;
      }
  }
} continue {
    while (defined($Input_line = <>)) {
	last SKIPFILE if eof;
	last SKIPFILE if ($Input_line =~ /^--${Boundary}--/);
        last if ($Input_line =~ /^--$Boundary/);
    }
    $Output_file = '';
    $b64 = 0;
}