Extract detection of compression types

Separate out detecting compression types from uncompressing and staging.

1 files changed, 25 insertions, 0 deletions

diff --git a/Library/Homebrew/extend/pathname.rb b/Library/Homebrew/extend/pathname.rb
index 3dda828d5..515356861 100644
--- a/Library/Homebrew/extend/pathname.rb
+++ b/Library/Homebrew/extend/pathname.rb
@@ -240,6 +240,31 @@ class Pathname
     nil
   end
 
+  def compression_type
+    # Don't treat jars as compressed
+    return nil if self.extname == '.jar'
+
+    # OS X installer package
+    return :pkg if self.extname == '.pkg'
+
+    # get the first six bytes
+    magic_bytes = nil
+    File.open(self) { |f| magic_bytes = f.read(6) }
+
+    # magic numbers stolen from /usr/share/file/magic/
+    case magic_bytes
+    when /^PK\003\004/   then :zip
+    when /^\037\213/     then :gzip
+    when /^BZh/          then :bzip2
+    when /^\037\235/     then :compress
+    when /^\xFD7zXZ\x00/ then :xz
+    when /^Rar!/         then :rar
+    else
+      # Assume it is not an archive
+      nil
+    end
+  end
+
   def incremental_hash(hasher)
     incr_hash = hasher.new
     self.open('r') do |f|