Don't modify the response if the body is frozen (#212)

Fixes an incompatibility with webmock since 3.19, where it started to
freeze the response body for performance reasons

Signed-off-by: Earlopain <14981592+Earlopain@users.noreply.github.com>

CHANGELOG.md

@@ -7,6 +7,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Deprecated
 ### Removed
 ### Fixed
+- Fixed the response body being force-encoded when it was already in UTF-8 ([#212](https://github.com/opensearch-project/opensearch-ruby/issues/212))
 ### Security
 
 ## [3.0.1]

lib/opensearch/transport/transport/response.rb

@@ -39,7 +39,7 @@ def initialize(status, body, headers = {})
           @status = status
           @body = body
           @headers = headers
-          @body = body.force_encoding('UTF-8') if body.respond_to?(:force_encoding)
+          @body = body.force_encoding('UTF-8') if body.respond_to?(:force_encoding) && body.encoding != Encoding::UTF_8
         end
       end
     end

test/transport/unit/response_test.rb

@@ -28,14 +28,19 @@
 
 class OpenSearch::Transport::Transport::ResponseTest < Minitest::Test
   context "Response" do
-
-    should "force-encode the body into UTF" do
+    should "force-encode the body into UTF-8" do
       body = "Hello Encoding!".encode(Encoding::ISO_8859_1)
       assert_equal 'ISO-8859-1', body.encoding.name
 
       response = OpenSearch::Transport::Transport::Response.new 200, body
       assert_equal 'UTF-8', response.body.encoding.name
     end
 
+    should "not force-encode the body if it is already encoded as UTF-8" do
+      body = "Hello Frozen!".freeze
+      response = OpenSearch::Transport::Transport::Response.new 200, body
+
+      assert_equal body, response.body
+    end
   end
 end