refactored file format magic numbers code

2 files changed, 81 insertions, 48 deletions

diff --git a/Pristine/Tar.pm b/Pristine/Tar.pm
index abe0255..a6a8446 100644
--- a/Pristine/Tar.pm
+++ b/Pristine/Tar.pm
@@ -93,52 +93,4 @@ sub dispatch {
 	$i->[0]->(@ARGV);
 }
 
-
-# magic identification
-use constant GZIP_ID1            => 0x1F;
-use constant GZIP_ID2            => 0x8B;
-use constant BZIP2_ID1           => 0x42;
-use constant BZIP2_ID2           => 0x5a;
-
-# compression methods
-# 0x00-0x07 are reserved
-use constant GZIP_METHOD_DEFLATE => 0x08;
-# 'h' for Bzip2 ('H'uffman coding)
-use constant BZIP2_METHOD_HUFFMAN => 0x68;
-
-# flags
-use constant {
-	GZIP_FLAG_FTEXT		 => 0,
-	GZIP_FLAG_FHCRC		 => 1,
-	GZIP_FLAG_FEXTRA	 => 2,
-	GZIP_FLAG_FNAME		 => 3,
-	GZIP_FLAG_FCOMMENT	 => 4,
-	# the rest are reserved
-};
-# compression level
-use constant {
-	GZIP_COMPRESSION_NORMAL	 => 0,
-	GZIP_COMPRESSION_BEST	 => 2,
-	GZIP_COMPRESSION_FAST	 => 4,
-};
-# operating systems
-use constant {
-	GZIP_OS_MSDOS		 => 0,
-	GZIP_OS_AMIGA		 => 1,
-	GZIP_OS_VMS		 => 2,
-	GZIP_OS_UNIX		 => 3,
-	GZIP_OS_VMCMS		 => 4,
-	GZIP_OS_ATARI		 => 5,
-	GZIP_OS_HPFS		 => 6,
-	GZIP_OS_MACINTOSH	 => 7,
-	GZIP_OS_ZSYSTEM		 => 8,
-	GZIP_OS_CPM		 => 9,
-	GZIP_OS_TOPS		 => 10,
-	GZIP_OS_NTFS		 => 11,
-	GZIP_OS_QDOS		 => 12,
-	GZIP_OS_RISCOS		 => 13,
-	GZIP_OS_VFAT             => 14,
-	GZIP_OS_UNKNOWN		 => 255,
-};
-
 1
diff --git a/Pristine/Tar/Formats.pm b/Pristine/Tar/Formats.pm
new file mode 100644
index 0000000..a141a3d
--- /dev/null
+++ b/Pristine/Tar/Formats.pm
@@ -0,0 +1,81 @@
+#!/usr/bin/perl
+# pristine-tar file format parsing
+
+package Pristine::Tar::Formats;
+
+use warnings;
+use strict;
+use Exporter q{import};
+our @EXPORT=qw{is_gz is_bz2 %fconstants};
+
+our %fconstants=(
+	# magic identification
+	GZIP_ID1 => 0x1F,
+	GZIP_ID2 => 0x8B,
+	BZIP2_ID1 => 0x42,
+	BZIP2_ID2 => 0x5a,
+
+	# compression methods
+	# 0x00-0x07 are reserved
+	GZIP_METHOD_DEFLATE => 0x08,
+	# 'h' for Bzip2 ('H'uffman coding)
+	BZIP2_METHOD_HUFFMAN => 0x68,
+
+	# flags
+	GZIP_FLAG_FTEXT => 0,
+	GZIP_FLAG_FHCRC => 1,
+	GZIP_FLAG_FEXTRA => 2,
+	GZIP_FLAG_FNAME => 3,
+	GZIP_FLAG_FCOMMENT => 4,
+	# the rest are reserved
+
+	# compression level
+	GZIP_COMPRESSION_NORMAL => 0,
+	GZIP_COMPRESSION_BEST => 2,
+	GZIP_COMPRESSION_FAST => 4,
+
+	# operating systems
+	GZIP_OS_MSDOS => 0,
+	GZIP_OS_AMIGA => 1,
+	GZIP_OS_VMS => 2,
+	GZIP_OS_UNIX => 3,
+	GZIP_OS_VMCMS => 4,
+	GZIP_OS_ATARI => 5,
+	GZIP_OS_HPFS => 6,
+	GZIP_OS_MACINTOSH => 7,
+	GZIP_OS_ZSYSTEM => 8,
+	GZIP_OS_CPM => 9,
+	GZIP_OS_TOPS => 10,
+	GZIP_OS_NTFS => 11,
+	GZIP_OS_QDOS => 12,
+	GZIP_OS_RISCOS => 13,
+	GZIP_OS_VFAT => 14,
+	GZIP_OS_UNKNOWN => 255,
+);
+
+sub magic {
+	my $file=shift;
+
+	open (my $in, "<", $file) || die "$file: $!";
+	my $count=$#_+1;
+	my ($chars, @bits);
+	my $ret = (
+		read($in, $chars, $count) == $count &&
+		(@bits = unpack(("C" x $count), $chars)) &&
+		(! grep { $bits[$_] != $_[$_] } (0..$count-1))
+    	);
+	close $in;
+	return $ret;
+}
+
+sub is_gz {
+	magic(shift, $fconstants{GZIP_ID1}, $fconstants{GZIP_ID2},
+		$fconstants{GZIP_METHOD_DEFLATE});
+}
+
+sub is_bz2 {
+	magic(shift, $fconstants{BZIP2_ID1}, $fconstants{BZIP2_ID2},
+		$fconstants{BZIP2_METHOD_HUFFMAN});
+}
+
+1