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.

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.

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.

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