How to use $key for internal Kafka partitioning logic on producer

[mrdvt92]

I'm not a pro at C but it appears that we can pass a -1 as the partition and then the $key will go through the crc32 logic for automatic partitioning. Is that correct?

If so, can that be documented. Also supporting undef() would make for a better perl-ish API.

$err = $topic->produce($partition, $msgflags, $payload, $key);
$err = $topic->produce(-1, $msgflags, $payload, $key); #auto partition based on $key
$err = $topic->produce(undef(), $msgflags, $payload, $key); #future auto partition based on $key

[plicease]

$partition set to -1 is RD_KAFKA_PARTITION_UA: (unassigned) for automatic partitioning using the topic's partitioner function.
https://docs.confluent.io/2.0.0/clients/librdkafka/rdkafka_8h.html#a95e4f88cc907347eee16ff36ab58d10e

I think rather than documenting -1 or making undef map to -1, it would be better to add RD_KAFKA_PARTITION_UA as an exportable constant.