1 files changed, 32 insertions, 0 deletions
diff --git a/lib/rubygems/package/file_source.rb b/lib/rubygems/package/file_source.rb
new file mode 100644
index 0000000000..d9717e0f2a
--- /dev/null
+++ b/lib/rubygems/package/file_source.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+##
+# The primary source of gems is a file on disk, including all usages
+# internal to rubygems.
+#
+# This is a private class, do not depend on it directly. Instead, pass a path
+# object to `Gem::Package.new`.
+
+class Gem::Package::FileSource < Gem::Package::Source # :nodoc: all
+  attr_reader :path
+
+  def initialize(path)
+    @path = path
+  end
+
+  def start
+    @start ||= File.read path, 20
+  end
+
+  def present?
+    File.exist? path
+  end
+
+  def with_write_io(&block)
+    File.open path, "wb", &block
+  end
+
+  def with_read_io(&block)
+    File.open path, "rb", &block
+  end
+end