Wait until event handler is started to initialize intermediate buffer…

… used by StreamingEncoder

Deciding if an intermediate buffer is required or not in the constructor was not a good idea: the encoder is not yet known at this point (still null).

src/main/java/net/logstash/logback/appender/AbstractLogstashTcpSocketAppender.java

@@ -354,9 +354,9 @@ private class TcpSendingEventHandler implements EventHandler<LogEvent<Event>>, L
 
         /**
          * Intermediate ByteBuffer used to store content generated by {@link StreamingEncoder}.
-         * Stays uninitialized if encoder is a "raw" {@link Encoder}.
+         * Set when {@link #onStart()} but stays uninitialized if encoder is a "raw" {@link Encoder}.
          */
-        private final ReusableByteBuffer buffer;
+        private ReusableByteBuffer buffer;
 
         /**
          * When run, if the {@link AbstractLogstashTcpSocketAppender#keepAliveDuration}
@@ -511,17 +511,6 @@ public void run() {
                 }
             }
         }
-
-
-        TcpSendingEventHandler() {
-            if (encoder instanceof CompositeJsonEncoder) {
-                this.buffer = new ReusableByteBuffer(((CompositeJsonEncoder<Event>) encoder).getMinBufferSize());
-            } else if (encoder instanceof StreamingEncoder) {
-                this.buffer = new ReusableByteBuffer();
-            } else {
-                this.buffer = null;
-            }
-        }
 
 
         @Override
@@ -664,6 +653,13 @@ private boolean hasKeepAliveDurationElapsed(long lastSentNanoTime, long currentN
         @Override
         public void onStart() {
             this.destinationAttemptStartTimes = new long[destinations.size()];
+
+            if (encoder instanceof CompositeJsonEncoder) {
+                this.buffer = new ReusableByteBuffer(((CompositeJsonEncoder<Event>) encoder).getMinBufferSize());
+            } else if (encoder instanceof StreamingEncoder) {
+                this.buffer = new ReusableByteBuffer();
+            }
+
             openSocket();
             scheduleKeepAlive(System.nanoTime());
             scheduleWriteTimeout();
@@ -825,6 +821,7 @@ private synchronized void closeSocket() {
 
         private void closeEncoder() {
             encoder.stop();
+            buffer = null;
         }
 
         private synchronized void scheduleKeepAlive(long basedOnNanoTime) {