parser_json: fix wrong LoadError warning

lib/fluent/plugin/parser_json.rb

@@ -50,23 +50,15 @@ def configure(conf)
       def configure_json_parser(name)
         case name
         when :oj
-          raise LoadError unless Fluent::OjOptions.available?
-          [Oj.method(:load), Oj::ParseError]
+          return [Oj.method(:load), Oj::ParseError] if Fluent::OjOptions.available?
+
+          log&.info "Oj is not installed, and failing back to Yajl for json parser"
+          configure_json_parser(:yajl)
         when :json then [JSON.method(:load), JSON::ParserError]
         when :yajl then [Yajl.method(:load), Yajl::ParseError]
         else
           raise "BUG: unknown json parser specified: #{name}"
         end
-      rescue LoadError => ex
-        name = :yajl
-        if log
-          if /\boj\z/.match?(ex.message)
-            log.info "Oj is not installed, and failing back to Yajl for json parser"
-          else
-            log.warn ex.message
-          end
-        end
-        retry
       end
 
       def parse(text)

test/plugin/test_parser_json.rb

@@ -8,6 +8,37 @@ def setup
     @parser = Fluent::Test::Driver::Parser.new(Fluent::Plugin::JSONParser)
   end
 
+  sub_test_case "configure_json_parser" do
+    data("oj", [:oj, [Oj.method(:load), Oj::ParseError]])
+    data("json", [:json, [JSON.method(:load), JSON::ParserError]])
+    data("yajl", [:yajl, [Yajl.method(:load), Yajl::ParseError]])
+    def test_return_each_loader((input, expected_return))
+      result = @parser.instance.configure_json_parser(input)
+      assert_equal expected_return, result
+    end
+
+    def test_raise_exception_for_unknown_input
+      assert_raise RuntimeError do
+        @parser.instance.configure_json_parser(:unknown)
+      end
+    end
+
+    def test_fall_back_oj_to_yajl_if_oj_not_available
+      stub(Fluent::OjOptions).available? { false }
+
+      result = @parser.instance.configure_json_parser(:oj)
+
+      assert_equal [Yajl.method(:load), Yajl::ParseError], result
+      logs = @parser.logs.collect do |log|
+        log.gsub(/\A\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2} [-+]\d{4} /, "")
+      end
+      assert_equal(
+        ["[info]: Oj is not installed, and failing back to Yajl for json parser\n"],
+        logs
+      )
+    end
+  end
+
   data('oj' => 'oj', 'yajl' => 'yajl')
   def test_parse(data)
     @parser.configure('json_parser' => data)