merge revision(s) 35e1248: [Backport #20755]

	[Bug #20755] Frozen string should not be writable via IO::Buffer

Author: k0kubun

io_buffer.c

@@ -843,7 +843,8 @@ rb_io_buffer_get_bytes(VALUE self, void **base, size_t *size)
 static inline void
 io_buffer_get_bytes_for_writing(struct rb_io_buffer *buffer, void **base, size_t *size)
 {
-    if (buffer->flags & RB_IO_BUFFER_READONLY) {
+    if (buffer->flags & RB_IO_BUFFER_READONLY ||
+        (!NIL_P(buffer->source) && OBJ_FROZEN(buffer->source))) {
         rb_raise(rb_eIOBufferAccessError, "Buffer is not writable!");
     }
 

test/ruby/test_io_buffer.rb

@@ -248,6 +248,31 @@ def test_slice_readonly
     assert_equal "Hello World", hello
   end
 
+  def test_transfer
+    hello = %w"Hello World".join(" ")
+    buffer = IO::Buffer.for(hello)
+    transferred = buffer.transfer
+    assert_equal "Hello World", transferred.get_string
+    assert_predicate buffer, :null?
+    assert_raise IO::Buffer::AccessError do
+      transferred.set_string("Goodbye")
+    end
+    assert_equal "Hello World", hello
+  end
+
+  def test_transfer_in_block
+    hello = %w"Hello World".join(" ")
+    buffer = IO::Buffer.for(hello, &:transfer)
+    assert_equal "Hello World", buffer.get_string
+    buffer.set_string("Ciao!")
+    assert_equal "Ciao! World", hello
+    hello.freeze
+    assert_raise IO::Buffer::AccessError do
+      buffer.set_string("Hola")
+    end
+    assert_equal "Ciao! World", hello
+  end
+
   def test_locked
     buffer = IO::Buffer.new(128, IO::Buffer::INTERNAL|IO::Buffer::LOCKED)
 

version.h

@@ -11,7 +11,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 5
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 105
+#define RUBY_PATCHLEVEL 106
 
 #include "ruby/version.h"
 #include "ruby/internal/abi.h"