1 files changed, 30 insertions, 0 deletions
diff --git a/lib/gitlab/git/bundle_file.rb b/lib/gitlab/git/bundle_file.rb
new file mode 100644
index 00000000000..8384a436fcc
--- /dev/null
+++ b/lib/gitlab/git/bundle_file.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Git
+    class BundleFile
+      # All git bundle files start with this string
+      #
+      # https://github.com/git/git/blob/v2.20.1/bundle.c#L15
+      MAGIC = "# v2 git bundle\n"
+
+      InvalidBundleError = Class.new(StandardError)
+
+      attr_reader :filename
+
+      def self.check!(filename)
+        new(filename).check!
+      end
+
+      def initialize(filename)
+        @filename = filename
+      end
+
+      def check!
+        data = File.open(filename, 'r') { |f| f.read(MAGIC.size) }
+
+        raise InvalidBundleError, 'Invalid bundle file' unless data == MAGIC
+      end
+    end
+  end
+end