Add support for returning all possible mime types by magic.

lib/mimemagic.rb

@@ -76,19 +76,16 @@ class MimeMagic
   # Lookup mime type by magic content analysis.
   # This is a slow operation.
   def self.by_magic(io)
-    mime =
-      unless io.respond_to?(:seek) && io.respond_to?(:read)
-        str = io.respond_to?(:read) ? io.read : io.to_s
-        str = str.force_encoding(Encoding::BINARY) if str.respond_to? :force_encoding
-        MAGIC.find {|type, matches| magic_match_str(str, matches) }
-      else
-        io.binmode
-        io.set_encoding(Encoding::BINARY) if io.respond_to?(:set_encoding)
-        MAGIC.find {|type, matches| magic_match_io(io, matches) }
-      end
+    mime = magic_match(io, :find)
     mime && new(mime[0])
   end
 
+  # Lookup all mime types by magic content analysis.
+  # This is a slower operation.
+  def self.all_by_magic(io)
+    magic_match(io, :select).map { |mime| new(mime[0]) }
+  end
+
   # Return type as string
   def to_s
     type
@@ -109,6 +106,19 @@ class MimeMagic
     child == parent || TYPES.key?(child) && TYPES[child][1].any? {|p| child?(p, parent) }
   end
 
+  def self.magic_match(io, method)
+    mime_or_mimes = if io.respond_to?(:seek) && io.respond_to?(:read)
+                      io.binmode
+                      io.set_encoding(Encoding::BINARY) if io.respond_to?(:set_encoding)
+                      MAGIC.send(method) { |type, matches| magic_match_io(io, matches) }
+                    else
+                      str = io.respond_to?(:read) ? io.read : io.to_s
+                      str = str.force_encoding(Encoding::BINARY) if str.respond_to?(:force_encoding)
+                      MAGIC.send(method) { |type, matches| magic_match_str(str, matches) }
+                    end
+    method == :find ? [mime_or_mimes] : mime_or_mimes
+  end
+
   def self.magic_match_io(io, matches)
     matches.any? do |offset, value, children|
       match =
@@ -137,5 +147,5 @@ class MimeMagic
     end
   end
 
-  private_class_method :magic_match_io, :magic_match_str
+  private_class_method :magic_match, :magic_match_io, :magic_match_str
 end

test/mimemagic_test.rb

@@ -65,6 +65,13 @@ describe 'MimeMagic' do
     end
   end
 
+  it 'should recognize all by magic' do
+    require 'mimemagic/overlay'
+    file = 'test/files/application.vnd.openxmlformats-officedocument.spreadsheetml.sheet'
+    mimes = %w[application/vnd.openxmlformats-officedocument.spreadsheetml.sheet application/zip]
+    MimeMagic.all_by_magic(File.read(file)).map(&:type).should.equal mimes
+  end
+
   it 'should have add' do
     MimeMagic.add('application/mimemagic-test',
                   extensions: %w(ext1 ext2),