How to extract Google PubSub publish time in Apach

Question

My goal is to be able to access PubSub message Publish Time as recorded and set by Google PubSub in Apache Beam (Dataflow).

    PCollection<PubsubMessage> pubsubMsg
            = pipeline.apply("Read Messages From PubSub",
            PubsubIO.readMessagesWithAttributes()
                .fromSubscription(pocOptions.getInputSubscription()));

Does not seem to contain one as an attribute. I have tried

 .withTimestampAttribute("publish_time")

No luck either. What am I missing? Is it possible to extract Google PubSub publish time in dataflow?

Answer 1

PubsubIO will read the message from Pub/Sub and assign the message publish time to the element as the record timestamp. Therefore, you can access it using ProcessContext.timestamp(). As an example:

p
    .apply("Read Messages", PubsubIO.readStrings().fromSubscription(subscription))
    .apply("Log Publish Time", ParDo.of(new DoFn<String, Void>() {
        @ProcessElement
        public void processElement(ProcessContext c) throws Exception {
            LOG.info("Message: " + c.element());
            LOG.info("Publish time: " + c.timestamp().toString());
            Date date= new Date();
            Long time = date.getTime();
            LOG.info("Processing time: " + new Instant(time).toString());
        }
    }));

I published a message a little bit ahead (to have a significant difference between event and processing time) and output with DirectRunner was:

Mar 27, 2019 11:03:08 AM com.dataflow.samples.LogPublishTime$1 processElement
INFO: Message: I published this message a little bit before
Mar 27, 2019 11:03:08 AM com.dataflow.samples.LogPublishTime$1 processElement
INFO: Publish time: 2019-03-27T09:57:07.005Z
Mar 27, 2019 11:03:08 AM com.dataflow.samples.LogPublishTime$1 processElement
INFO: Processing time: 2019-03-27T10:03:08.229Z

Minimal code here