in_tcp: skip emitting an empty event stream

lib/fluent/plugin/in_tcp.rb

@@ -202,7 +202,7 @@ def start
               es.add(time, record)
             end
           end
-          router.emit_stream(@tag, es)
+          router.emit_stream(@tag, es) unless es.empty?
           buf.slice!(0, pos) if pos > 0
           # If the buffer size exceeds the limit here, it means that the next message will definitely exceed the limit.
           # So we should clear the buffer here. Otherwise, it will keep storing useless data until the next delimiter comes.

test/plugin/test_in_tcp.rb

@@ -281,6 +281,25 @@ def create_tcp_socket(host, port, &block)
 
       assert_equal(["hello", "world"], d.events.collect { |event| event[2]["message"] })
     end
+
+    test "do not emit an empty event stream for a read without a complete message" do |data|
+      d = create_driver(base_config + %!
+        <parse>
+          @type none
+        </parse>
+        #{data[:extract]}
+      !)
+      d.run(expect_records: 1, timeout: 10) do
+        create_tcp_socket('127.0.0.1', @port) do |sock|
+          sock.send("hel", 0)
+          sleep 1
+          sock.send("lo\n", 0)
+        end
+      end
+
+      assert_equal(["hello"], d.events.collect { |event| event[2]["message"] })
+      assert_equal(1, d.emit_count)
+    end
   end
 
   sub_test_case "message_length_limit" do