Ensure compatibility with --enable-frozen-string-literal

Ref: https://bugs.ruby-lang.org/issues/20205

In Ruby 3.4 string literals will be "chilled" by default. Meaning
they are still mutable, but will pretend to be frozen.

In most case it has no impact, just emit a few warnings there and
there, but there is one thing it impacts is the `StringIO.new('')`
pattern. `StringIO` checks if the given string is frozen, and if
it is will act as a read only IO.

This breaks rubyzip 2.x.

This commit make the 2.x branch compatible with frozen string literals.

.github/workflows/tests.yml

@@ -8,7 +8,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu]
-        ruby: ['2.4', '2.5', '2.6', '2.7', '3.0', '3.1', jruby, truffleruby]
+        ruby: ['2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', jruby, truffleruby]
         include:
           - os: macos
             ruby: '2.4'
@@ -31,12 +31,36 @@ jobs:
         FULL_ZIP64_TEST: 1
       run: bundle exec rake
 
+  test-frozen-string-literal:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu]
+        ruby: ['3.3']
+    runs-on: ${{ matrix.os }}-latest
+    continue-on-error: true
+    steps:
+    - name: Checkout rubyzip code
+      uses: actions/checkout@v2
+
+    - name: Install and set up ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+
+    - name: Run the tests
+      env:
+        RUBYOPT: --enable-frozen-string-literal
+        FULL_ZIP64_TEST: 1
+      run: bundle exec rake
+
   test-yjit:
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu, macos]
-        ruby: ['3.1', head]
+        ruby: ['3.1', '3.2', '3.3', head]
     runs-on: ${{ matrix.os }}-latest
     continue-on-error: true
     steps:

README.md

@@ -188,7 +188,7 @@ If `::Zip::InputStream` finds such entry in the zip archive it will raise an exc
 Rubyzip supports reading/writing zip files with traditional zip encryption (a.k.a. "ZipCrypto"). AES encryption is not yet supported. It can be used with buffer streams, e.g.:
 
 ```ruby
-Zip::OutputStream.write_buffer(::StringIO.new(''), Zip::TraditionalEncrypter.new('password')) do |out|
+Zip::OutputStream.write_buffer(::StringIO.new, Zip::TraditionalEncrypter.new('password')) do |out|
   out.put_next_entry("my_file.txt")
   out.write my_data
 end.string

lib/zip/extra_field/zip64.rb

@@ -59,7 +59,7 @@ def pack_for_local
 
     def pack_for_c_dir
       # central directory entries contain only fields that didn't fit in the main entry part
-      packed = ''.force_encoding('BINARY')
+      packed = ''.b
       packed << [@original_size].pack('Q<') if @original_size
       packed << [@compressed_size].pack('Q<') if @compressed_size
       packed << [@relative_header_offset].pack('Q<') if @relative_header_offset

lib/zip/file.rb

@@ -140,7 +140,7 @@ def open(file_name, dep_create = false, create: false, **options)
       def add_buffer
         Zip.warn_about_v3_api('Zip::File.add_buffer')
 
-        io = ::StringIO.new('')
+        io = ::StringIO.new
         zf = ::Zip::File.new(io, true, true)
         yield zf
         zf.write_buffer(io)
@@ -411,7 +411,7 @@ def commit
     end
 
     # Write buffer write changes to buffer and return
-    def write_buffer(io = ::StringIO.new(''))
+    def write_buffer(io = ::StringIO.new)
       return unless commit_required?
 
       ::Zip::OutputStream.write_buffer(io) do |zos|

lib/zip/filesystem.rb

@@ -239,7 +239,7 @@ def directory?(filename)
       end
 
       def open(filename, mode = 'r', permissions = 0o644, &block)
-        mode.delete!('b') # ignore b option
+        mode = mode.delete('b') # ignore b option
         case mode
         when 'r'
           @mapped_zip.get_input_stream(filename, &block)
@@ -619,7 +619,7 @@ def each
       end
 
       def expand_path(path)
-        expanded = path.start_with?('/') ? path : ::File.join(@pwd, path)
+        expanded = path.start_with?('/') ? path.dup : ::File.join(@pwd, path)
         expanded.gsub!(/\/\.(\/|$)/, '')
         expanded.gsub!(/[^\/]+\/\.\.(\/|$)/, '')
         expanded.empty? ? '/' : expanded

lib/zip/inflater.rb

@@ -3,11 +3,11 @@ class Inflater < Decompressor #:nodoc:all
     def initialize(*args)
       super
 
-      @buffer = +''
+      @buffer = ''.b
       @zlib_inflater = ::Zlib::Inflate.new(-Zlib::MAX_WBITS)
     end
 
-    def read(length = nil, outbuf = '')
+    def read(length = nil, outbuf = ''.b)
       return (length.nil? || length.zero? ? '' : nil) if eof
 
       while length.nil? || (@buffer.bytesize < length)

lib/zip/ioextras.rb

@@ -6,14 +6,14 @@ module IOExtras #:nodoc:
 
     class << self
       def copy_stream(ostream, istream)
-        ostream.write(istream.read(CHUNK_SIZE, '')) until istream.eof?
+        ostream.write(istream.read(CHUNK_SIZE, ''.b)) until istream.eof?
       end
 
       def copy_stream_n(ostream, istream, nbytes)
         toread = nbytes
         while toread > 0 && !istream.eof?
           tr = toread > CHUNK_SIZE ? CHUNK_SIZE : toread
-          ostream.write(istream.read(tr, ''))
+          ostream.write(istream.read(tr, ''.b))
           toread -= tr
         end
       end

lib/zip/ioextras/abstract_input_stream.rb

@@ -11,13 +11,13 @@ def initialize
         super
         @lineno        = 0
         @pos           = 0
-        @output_buffer = ''
+        @output_buffer = ''.b
       end
 
       attr_accessor :lineno
       attr_reader :pos
 
-      def read(number_of_bytes = nil, buf = '')
+      def read(number_of_bytes = nil, buf = ''.b)
         tbuf = if @output_buffer.bytesize > 0
                  if number_of_bytes <= @output_buffer.bytesize
                    @output_buffer.slice!(0, number_of_bytes)
@@ -26,7 +26,7 @@ def read(number_of_bytes = nil, buf = '')
                    rbuf = sysread(number_of_bytes, buf)
                    out  = @output_buffer
                    out << rbuf if rbuf
-                   @output_buffer = ''
+                   @output_buffer = ''.b
                    out
                  end
                else
@@ -93,7 +93,7 @@ def ungetc(byte)
 
       def flush
         ret_val        = @output_buffer
-        @output_buffer = ''
+        @output_buffer = ''.b
         ret_val
       end
 

lib/zip/output_stream.rb

@@ -62,7 +62,7 @@ def open(file_name, dep_encrypter = nil, encrypter: nil)
       end
 
       # Same as #open but writes to a filestream instead
-      def write_buffer(io = ::StringIO.new(''), dep_encrypter = nil, encrypter: nil)
+      def write_buffer(io = ::StringIO.new, dep_encrypter = nil, encrypter: nil)
         Zip.warn_about_v3_api('Zip::OutputStream.write_buffer') unless dep_encrypter.nil?
 
         io.binmode if io.respond_to?(:binmode)

lib/zip/pass_thru_decompressor.rb

@@ -5,7 +5,7 @@ def initialize(*args)
       @read_so_far = 0
     end
 
-    def read(length = nil, outbuf = '')
+    def read(length = nil, outbuf = ''.b)
       return (length.nil? || length.zero? ? '' : nil) if eof
 
       if length.nil? || (@read_so_far + length) > decompressed_size

test/encryption_test.rb

@@ -19,7 +19,7 @@ def test_encrypt
     @rand = [250, 143, 107, 13, 143, 22, 155, 75, 228, 150, 12]
     @output = ::Zip::DOSTime.stub(:now, ::Zip::DOSTime.new(2014, 12, 17, 15, 56, 24)) do
       Random.stub(:rand, ->(_range) { @rand.shift }) do
-        Zip::OutputStream.write_buffer(::StringIO.new(''), Zip::TraditionalEncrypter.new('password')) do |zos|
+        Zip::OutputStream.write_buffer(::StringIO.new, Zip::TraditionalEncrypter.new('password')) do |zos|
           zos.put_next_entry('file1.txt')
           zos.write ::File.open(INPUT_FILE1).read
         end.string

test/file_test.rb

@@ -503,7 +503,7 @@ def test_write_buffer
     zf = ::Zip::File.new(TEST_ZIP.zip_name)
     old_name = zf.entries.first
     zf.rename(old_name, new_name)
-    io = ::StringIO.new('')
+    io = ::StringIO.new
     buffer = zf.write_buffer(io)
     File.open(TEST_ZIP.zip_name, 'wb') { |f| f.write buffer.string }
     zf_read = ::Zip::File.new(TEST_ZIP.zip_name)

test/input_stream_test.rb

@@ -136,7 +136,7 @@ def test_rewind
       assert_equal(TestZipFile::TEST_ZIP2.entry_names[0], e.name)
 
       # Do a little reading
-      buf = ''
+      buf = ''.b
       buf << zis.read(100)
       assert_equal(100, zis.pos)
       buf << (zis.gets || '')
@@ -145,7 +145,7 @@ def test_rewind
 
       zis.rewind
 
-      buf2 = ''
+      buf2 = ''.b
       buf2 << zis.read(100)
       buf2 << (zis.gets || '')
       buf2 << (zis.gets || '')

test/ioextras/abstract_output_stream_test.rb

@@ -8,7 +8,7 @@ class TestOutputStream
     attr_accessor :buffer
 
     def initialize
-      @buffer = ''
+      @buffer = ''.b
     end
 
     def <<(data)
@@ -58,12 +58,12 @@ def test_print
     assert_equal("hello world. You ok out there?\nI sure hope so!\n", @output_stream.buffer)
 
     $, = 'X'
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.print('monkey', 'duck', 'zebra')
     assert_equal("monkeyXduckXzebra\n", @output_stream.buffer)
 
     $\ = nil
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.print(20)
     assert_equal('20', @output_stream.buffer)
   end
@@ -87,19 +87,19 @@ def test_puts
     @output_stream.puts('hello', 'world')
     assert_equal("\nhello\nworld\n", @output_stream.buffer)
 
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.puts("hello\n", "world\n")
     assert_equal("hello\nworld\n", @output_stream.buffer)
 
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.puts(%W[hello\n world\n])
     assert_equal("hello\nworld\n", @output_stream.buffer)
 
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.puts(%W[hello\n world\n], 'bingo')
     assert_equal("hello\nworld\nbingo\n", @output_stream.buffer)
 
-    @output_stream.buffer = ''
+    @output_stream.buffer = ''.b
     @output_stream.puts(16, 20, 50, 'hello')
     assert_equal("16\n20\n50\nhello\n", @output_stream.buffer)
   end

test/output_stream_test.rb

@@ -23,7 +23,7 @@ def test_open
   end
 
   def test_write_buffer
-    io = ::StringIO.new('')
+    io = ::StringIO.new
     buffer = ::Zip::OutputStream.write_buffer(io) do |zos|
       zos.comment = TEST_ZIP.comment
       write_test_zip(zos)
@@ -33,7 +33,7 @@ def test_write_buffer
   end
 
   def test_write_buffer_binmode
-    io = ::StringIO.new('')
+    io = ::StringIO.new
     buffer = ::Zip::OutputStream.write_buffer(io) do |zos|
       zos.comment = TEST_ZIP.comment
       write_test_zip(zos)

test/test_helper.rb

@@ -145,7 +145,7 @@ class TestOutputStream
     attr_accessor :buffer
 
     def initialize
-      @buffer = ''
+      @buffer = ''.b
     end
 
     def <<(data)

test/version_3_api_test.rb

@@ -177,7 +177,7 @@ def test_open
 
     def test_open_buffer
       assert_v3_api_warning do
-        ::Zip::InputStream.open_buffer(StringIO.new(''))
+        ::Zip::InputStream.open_buffer(StringIO.new)
       end
     end
   end
@@ -194,11 +194,11 @@ def test_new
       end
 
       refute_v3_api_warning do
-        ::Zip::OutputStream.new(StringIO.new(''), stream: true)
+        ::Zip::OutputStream.new(StringIO.new, stream: true)
       end
 
       assert_v3_api_warning do
-        ::Zip::OutputStream.new(StringIO.new(''), true)
+        ::Zip::OutputStream.new(StringIO.new, true)
       end
 
       refute_v3_api_warning do
@@ -226,15 +226,15 @@ def test_open
 
     def test_write_buffer
       refute_v3_api_warning do
-        ::Zip::OutputStream.write_buffer(StringIO.new('')) {}
+        ::Zip::OutputStream.write_buffer(StringIO.new) {}
       end
 
       refute_v3_api_warning do
-        ::Zip::OutputStream.write_buffer(StringIO.new(''), encrypter: true) {}
+        ::Zip::OutputStream.write_buffer(StringIO.new, encrypter: true) {}
       end
 
       assert_v3_api_warning do
-        ::Zip::OutputStream.write_buffer(StringIO.new(''), true) {}
+        ::Zip::OutputStream.write_buffer(StringIO.new, true) {}
       end
     end
   end