in_tail encoding enhancement

lib/fluent/plugin/in_tail.rb

@@ -171,6 +171,9 @@ def configure_encoding
 
       @encoding = parse_encoding_param(@encoding) if @encoding
       @from_encoding = parse_encoding_param(@from_encoding) if @from_encoding
+      if @encoding == @from_encoding
+        log.warn "'encoding' and 'from_encoding' are same encoding. No effect"
+      end
     end
 
     def parse_encoding_param(encoding_name)
@@ -657,6 +660,7 @@ class FIFO
         def initialize(from_encoding, encoding)
           @from_encoding = from_encoding
           @encoding = encoding
+          @need_enc = from_encoding != encoding
           @buffer = ''.force_encoding(from_encoding)
           @eol = "\n".encode(from_encoding).freeze
         end
@@ -682,11 +686,13 @@ def <<(chunk)
         end
 
         def convert(s)
-          if @from_encoding == @encoding
-            s
+          if @need_enc
+            s.encode!(@encoding, @from_encoding)
           else
-            s.encode(@encoding, @from_encoding)
+            s
           end
+        rescue
+          s.encode!(@encoding, @from_encoding, :invalid => :replace, :undef => :replace)
         end
 
         def next_line

test/plugin/test_in_tail.rb

@@ -649,6 +649,26 @@ def test_from_encoding_utf16
     assert_equal(Encoding::UTF_8, events[0][2]['message'].encoding)
   end
 
+  def test_encoding_with_bad_character
+    conf = config_element(
+      "", "", {
+        "format" => "/(?<message>.*)/",
+        "read_from_head" => "true",
+        "from_encoding" => "ASCII-8BIT",
+        "encoding" => "utf-8"
+      })
+    d = create_driver(conf)
+
+    d.run(expect_emits: 1) do
+      File.open("#{TMP_DIR}/tail.txt", "w") { |f|
+        f.write "te\x86st\n"
+      }
+    end
+
+    events = d.events
+    assert_equal("te\uFFFDst", events[0][2]['message'])
+    assert_equal(Encoding::UTF_8, events[0][2]['message'].encoding)
+  end
 
   sub_test_case "multiline" do
     data(flat: MULTILINE_CONFIG,