Fix `io_buffer_get_string` default length computation. (#8427)

* Fix `io_buffer_get_string` default length computation.

When an offset bigger than the size is given, the resulting length will be
computed incorrectly. Raise an argument error in this case.

* Validate all arguments.

1 files changed, 6 insertions, 2 deletions

diff --git a/test/ruby/test_io_buffer.rb b/test/ruby/test_io_buffer.rb
index d6931119f2..0c62216642 100644
--- a/test/ruby/test_io_buffer.rb
+++ b/test/ruby/test_io_buffer.rb
@@ -238,13 +238,17 @@ class TestIOBuffer < Test::Unit::TestCase
     chunk = buffer.get_string(0, message.bytesize, Encoding::BINARY)
     assert_equal Encoding::BINARY, chunk.encoding
 
-    assert_raise_with_message(ArgumentError, /exceeds buffer size/) do
+    assert_raise_with_message(ArgumentError, /bigger than the buffer size/) do
       buffer.get_string(0, 129)
     end
 
-    assert_raise_with_message(ArgumentError, /exceeds buffer size/) do
+    assert_raise_with_message(ArgumentError, /bigger than the buffer size/) do
       buffer.get_string(129)
     end
+
+    assert_raise_with_message(ArgumentError, /Offset can't be negative/) do
+      buffer.get_string(-1)
+    end
   end
 
   # We check that values are correctly round tripped.