title: How to forward event downstream from a Punctuator instance in a ValueTransformer?
body: <p>In KafkaStream, when implementing a <strong>ValueTransformer</strong> or <strong>ValueTransformerWithKey</strong>, on <strong>transform()</strong> call, I schedule a new Punctuator. When method <strong>punctuate()</strong> of the <strong>Punctuator</strong> is executed I want it to forward an event downstream using the context instance. However, the context instance seems not defined when part of a DSL topology.</p>
  
  <p>Any clue on how to do this with a Transformer ? </p>
  
  <p>Using the same logic in a Processor, implementing the low-level processor topology it works.</p>
  
  <p>In ValueTransformerWithKey:</p>
  
  <pre><code>@Override 
      public Event transform(final String key, final Event event) { 
          this.context.schedule(timeout.toMillis(), PunctuationType.WALL_CLOCK_TIME, new MyPunctuator(context, key, event));
          return null;
  }
  </code></pre>
  
  <p>In MyPunctuator:</p>
  
  <pre><code>private class MytPunctuator implements Punctuator {
      private String key;
      private ProcessorContext context;
      private Event event;
  
      MyPunctuator(ProcessorContext context, String key, Event event)
      {
          this.context = context;
          this.key = key;
          this.event = event;
      }
  
      @Override
      public void punctuate(final long timestamp) {
          context.forward(key, AlertEvent.builder().withSource(event).build());
          context.commit();
      }
  }
  </code></pre>
  
  <p>When executing</p>
  
  <pre><code>myStream
      .groupByKey(Serialized.with(Serdes.String(), Event.serde()))
      .reduce((k, v) -&gt; v)
      .transformValues(() -&gt; valueTransformerWithKey)
      .toStream().to(ALARM_TOPIC, Produced.with(Serdes.String(), AlarmEvent.serde()));
  </code></pre>
  
  <p>I expect the Alarm event produced by the punctuator to be forwared to the ALARM topic once expired.</p>
  
  <p>Instead I got the following exception: ProcessorContext.forward() not supported.</p>