Use duck typing to detect IO-like objects.

lib/zip/entry.rb

@@ -176,7 +176,7 @@ module Zip
       end
 
       def read_c_dir_entry(io) #:nodoc:all
-        path = if io.is_a?(::IO)
+        path = if io.respond_to?(:path)
                  io.path
                else
                  io
@@ -548,7 +548,7 @@ module Zip
     end
 
     def get_raw_input_stream(&block)
-      if @zipfile.is_a?(::IO) || @zipfile.is_a?(::StringIO)
+      if @zipfile.respond_to?(:seek) && @zipfile.respond_to?(:read)
         yield @zipfile
       else
         ::File.open(@zipfile, 'rb', &block)

lib/zip/file.rb

@@ -49,6 +49,7 @@ module Zip
     MAX_SEGMENT_SIZE     = 3_221_225_472
     MIN_SEGMENT_SIZE     = 65_536
     DATA_BUFFER_SIZE     = 8192
+    IO_METHODS           = [:tell, :seek, :read, :close]
 
     attr_reader :name
 
@@ -117,13 +118,13 @@ module Zip
       # (This can be used to extract data from a
       # downloaded zip archive without first saving it to disk.)
       def open_buffer(io, options = {})
-        unless io.is_a?(IO) || io.is_a?(String) || io.is_a?(Tempfile) || io.is_a?(StringIO)
+        unless IO_METHODS.map { |method| io.respond_to?(method) }.all? || io.is_a?(String)
-          raise "Zip::File.open_buffer expects an argument of class String, IO, StringIO, or Tempfile. Found: #{io.class}"
+          raise "Zip::File.open_buffer expects a String or IO-like argument (responds to #{IO_METHODS.join(', ')}). Found: #{io.class}"
         end
         if io.is_a?(::String)
           require 'stringio'
           io = ::StringIO.new(io)
-        elsif io.is_a?(IO)
+        elsif io.respond_to?(:binmode)
           # https://github.com/rubyzip/rubyzip/issues/119
           io.binmode
         end

lib/zip/input_stream.rb

@@ -111,8 +111,7 @@ module Zip
     protected
 
     def get_io(io_or_file, offset = 0)
-      case io_or_file
+      if io_or_file.respond_to?(:seek)
-      when IO, StringIO
         io = io_or_file.dup
         io.seek(offset, ::IO::SEEK_SET)
         io

test/input_stream_test.rb

@@ -3,6 +3,16 @@ require 'test_helper'
 class ZipInputStreamTest < MiniTest::Test
   include AssertEntry
 
+  class IOLike
+    extend Forwardable
+
+    def initialize(path, mode)
+      @file = File.new(path, mode)
+    end
+
+    delegate ::Zip::File::IO_METHODS => :@file
+  end
+
   def test_new
     zis = ::Zip::InputStream.new(TestZipFile::TEST_ZIP2.zip_name)
     assert_stream_contents(zis, TestZipFile::TEST_ZIP2)
@@ -48,6 +58,13 @@ class ZipInputStreamTest < MiniTest::Test
     assert_stream_contents(zis, TestZipFile::TEST_ZIP2)
   end
 
+  def test_open_io_like_with_block
+    ::Zip::InputStream.open(IOLike.new(TestZipFile::TEST_ZIP2.zip_name, 'rb')) do |zis|
+      assert_stream_contents(zis, TestZipFile::TEST_ZIP2)
+      assert_equal(true, zis.eof?)
+    end
+  end
+
   def test_incomplete_reads
     ::Zip::InputStream.open(TestZipFile::TEST_ZIP2.zip_name) do |zis|
       entry = zis.get_next_entry # longAscii.txt