refactored file format magic numbers code

5 files changed, 113 insertions, 90 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
diff --git a/pristine-bz2 b/pristine-bz2
index 1c69c91..f43a0f0 100755
--- a/pristine-bz2
+++ b/pristine-bz2
@@ -84,6 +84,7 @@ use warnings;
 use strict;
 use Pristine::Tar;
 use Pristine::Tar::Delta;
+use Pristine::Tar::Formats;
 use File::Basename qw/basename/;
 use IO::Handle;
 
@@ -109,11 +110,15 @@ sub usage {
 
 sub readbzip2 {
 	my $filename = shift;
-	my $chars;
+
+	if (! is_bz2($filename)) {
+		error "This is not a valid BZip2 archive.";
+	}
 
 	open(BZIP2, "< $filename")
 		or die("Could not open '$filename' for reading: $!\n");
 
+	my $chars;
 	if (read(BZIP2, $chars, 4) != 4) {
 		die("Unable to read from input\n");
 	}
@@ -123,11 +128,8 @@ sub readbzip2 {
 	# we actually want the value, not the ascii position
 	$level-=48;
 
-	if ($id1 != Pristine::Tar::BZIP2_ID1 ||
-	    $id2 != Pristine::Tar::BZIP2_ID2 ||
-	    $method != Pristine::Tar::BZIP2_METHOD_HUFFMAN ||
-	    $level !~ /^[1-9]$/) {
-		die("This is not a valid BZip2 archive.\n");
+	if ($level !~ /^[1-9]$/) {
+		error "Unknown compression level $level\n";
 	}
 
 	close(BZIP2);
diff --git a/pristine-gz b/pristine-gz
index 9687c49..8caf59d 100755
--- a/pristine-gz
+++ b/pristine-gz
@@ -91,6 +91,7 @@ use warnings;
 use strict;
 use Pristine::Tar;
 use Pristine::Tar::Delta;
+use Pristine::Tar::Formats;
 use File::Basename qw/basename/;
 
 dispatch(
@@ -108,26 +109,25 @@ sub usage {
 
 sub readgzip {
 	my $filename = shift;
-	my $chars;
+	
+	if (! is_gz($filename)) {
+		error "This is not a valid GZip archive.";
+	}
 
 	open(GZIP, "< $filename")
 		or die("Could not open '$filename' for reading: $!\n");
 
+	my $chars;
 	if (read(GZIP, $chars, 10) != 10) {
-		die("Unable to read from input\n");
+		die("Unable to read 10 bytes from input\n");
 	}
 
 	my ($id1, $id2, $method, $flags, $timestamp, $level, $os, $name)
 		= (unpack("CCCb8VCC", $chars), '');
 
-	if ($id1 != Pristine::Tar::GZIP_ID1 ||
-	    $id2 != Pristine::Tar::GZIP_ID2 ||
-	    $method != Pristine::Tar::GZIP_METHOD_DEFLATE) {
-		die("This is not a valid GZip archive.\n");
-	}
 	my @flags = split(//, $flags);
 	
-	if ($flags[Pristine::Tar::GZIP_FLAG_FNAME]) {
+	if ($flags[$fconstants{GZIP_FLAG_FNAME}]) {
 		# read a null-terminated string
 		$name .= $chars
 			while (read(GZIP, $chars, 1) == 1 && ord($chars) != 0);
@@ -142,15 +142,15 @@ sub predictgzipargs {
 	my @flags = @$flags;
 
 	my @args;
-	unless ($flags[Pristine::Tar::GZIP_FLAG_FNAME]) {
+	unless ($flags[$fconstants{GZIP_FLAG_FNAME}]) {
 		push @args, '-n';
 		push @args, '-M' if $timestamp;
 	}
 
-	if ($level == Pristine::Tar::GZIP_COMPRESSION_BEST) {
+	if ($level == $fconstants{GZIP_COMPRESSION_BEST}) {
 		push @args, '-9'
 	}
-	elsif ($level == Pristine::Tar::GZIP_COMPRESSION_FAST) {
+	elsif ($level == $fconstants{GZIP_COMPRESSION_FAST}) {
 		push @args, '-1'
 	}
 
@@ -185,7 +185,7 @@ sub reproducegz {
 
 	my @try;
 
-	if ($os == Pristine::Tar::GZIP_OS_UNIX) {
+	if ($os == $fconstants{GZIP_OS_UNIX}) {
 		# for 98% of the cases the simple heuristic above works
 		# and it was produced by gnu gzip.
 		push @try, ['--gnu', @args];
@@ -200,7 +200,7 @@ sub reproducegz {
 
 	# set the Operating System flag to the one found in the original
 	# archive
-	push @args, ("--osflag", $os) if $os != Pristine::Tar::GZIP_OS_UNIX;
+	push @args, ("--osflag", $os) if $os != $fconstants{GZIP_OS_UNIX};
 
 	# many of the .gz out there are created using the BSD version of
 	# gzip which is using the zlib library; try with our version of
@@ -216,7 +216,7 @@ sub reproducegz {
 
 	# Windows' NTFS gzip implementation; quirk is really really evil
 	# it should be the last test: it can result in a corrupted archive!
-	if ($os == Pristine::Tar::GZIP_OS_NTFS) {
+	if ($os == $fconstants{GZIP_OS_NTFS}) {
 		pop @args; pop @args; # ntfs quirk implies NTFS osflag
 		push @try, [@args, '--quirk', 'ntfs'];
 	}
diff --git a/pristine-tar b/pristine-tar
index a741b92..e1621ab 100755
--- a/pristine-tar
+++ b/pristine-tar
@@ -167,6 +167,7 @@ use warnings;
 use strict;
 use Pristine::Tar;
 use Pristine::Tar::Delta;
+use Pristine::Tar::Formats;
 use File::Path;
 use File::Basename;
 use Cwd qw{getcwd abs_path};
@@ -386,15 +387,9 @@ sub gendelta {
 	my $tempdir=tempdir();
 	my %delta;
 
-	# Check to see if it's compressed.
+	# Check to see if it's compressed, and get uncompressed tarball.
 	my $compression=undef;
-	open (IN, "<", $tarball) || error "Cannot read $tarball: $!\n";
-	my ($chars, $id1, $id2, $method);
-	if (read(IN, $chars, 10) == 10 &&
-	    (($id1, $id2, $method) = unpack("CCC", $chars)) &&
-    	    $id1 == Pristine::Tar::GZIP_ID1 &&
-	    $id2 == Pristine::Tar::GZIP_ID2 &&
-	    $method == Pristine::Tar::GZIP_METHOD_DEFLATE) {
+	if (is_gz($tarball)) {
 	    	$compression='gz';
 		open(IN, "-|", "zcat", $tarball) || die "zcat: $!";
 		open(OUT, ">", "$tempdir/origtarball") || die "$tempdir/origtarball: $!";
@@ -402,20 +397,13 @@ sub gendelta {
 		close IN || die "zcat: $!";
 		close OUT || die "$tempdir/origtarball: $!";
 	}
-	else {
-		seek(IN, 0, 0) || die "seek: $!";
-		if (read(IN, $chars, 3) == 3 &&
-	            (($id1, $id2, $method) = unpack("CCC", $chars)) &&
-	            $id1 == Pristine::Tar::BZIP2_ID1 &&
-		    $id2 == Pristine::Tar::BZIP2_ID2 &&
-	            $method == Pristine::Tar::BZIP2_METHOD_HUFFMAN) {
-		    	$compression='bz2';
-			open(IN, "-|", "bzcat", $tarball) || die "bzcat: $!";
-			open(OUT, ">", "$tempdir/origtarball") || die "$tempdir/origtarball: $!";
-			print OUT $_ while <IN>;
-			close IN || die "bzcat: $!";
-			close OUT || die "$tempdir/origtarball: $!";
-		}
+	elsif (is_bz2($tarball)) {
+		$compression='bz2';
+		open(IN, "-|", "bzcat", $tarball) || die "bzcat: $!";
+		open(OUT, ">", "$tempdir/origtarball") || die "$tempdir/origtarball: $!";
+		print OUT $_ while <IN>;
+		close IN || die "bzcat: $!";
+		close OUT || die "$tempdir/origtarball: $!";
 	}
 	close IN;