librdkafka v1.6.1

librdkafka v1.6.1 is a maintenance release.

Upgrade considerations

• Fatal idempotent producer errors are now also fatal to the transactional
  producer. This is a necessary step to maintain data integrity prior to
  librdkafka supporting KIP-360. Applications should check any transactional
  API errors for the is_fatal flag and decommission the transactional producer
  if the flag is set.
• The consumer error raised by auto.offset.reset=error now has error-code
  set to ERR__AUTO_OFFSET_RESET to allow an application to differentiate
  between auto offset resets and other consumer errors.

Fixes

General fixes

• Admin API and transactional send_offsets_to_transaction() coordinator
  requests, such as TxnOffsetCommitRequest, could in rare cases be sent
  multiple times which could cause a crash.
• ssl.ca.location=probe is now enabled by default on Mac OSX since the
  librdkafka-bundled OpenSSL might not have the same default CA search paths
  as the system or brew installed OpenSSL. Probing scans all known locations.

Transactional Producer fixes

• Fatal idempotent producer errors are now also fatal to the transactional
  producer.
• The transactional producer could crash if the transaction failed while
  send_offsets_to_transaction() was called.
• Group coordinator requests for transactional
  send_offsets_to_transaction() calls would leak memory if the
  underlying request was attempted to be sent after the transaction had
  failed.
• When gradually producing to multiple partitions (resulting in multiple
  underlying AddPartitionsToTxnRequests) sub-sequent partitions could get
  stuck in pending state under certain conditions. These pending partitions
  would not send queued messages to the broker and eventually trigger
  message timeouts, failing the current transaction. This is now fixed.
• Committing an empty transaction (no messages were produced and no
  offsets were sent) would previously raise a fatal error due to invalid state
  on the transaction coordinator. We now allow empty/no-op transactions to
  be committed.

Consumer fixes

• The consumer will now retry indefinitely (or until the assignment is changed)
  to retrieve committed offsets. This fixes the issue where only two retries
  were attempted when outstanding transactions were blocking OffsetFetch
  requests with ERR_UNSTABLE_OFFSET_COMMIT. #3265