Maintenance release

Default changes

• socket.max.fails changed to 1 to provide same functionality (fail request immediately on error) now when retries are working properly again.
• fetch.max.bytes (new config property) is automatically adjusted to be >= message.max.bytes, and receive.message.max.bytes is automatically adjusted to be > fetch.max.bytes. (#1616)

New features

• Message Headers support (with help from @johnistan)
• Java-compatible Murmur2 partitioners (#1468, @barrotsteindev)
• Add PKCS#12 Keystore support - ssl.keystore.location (#1494, @AMHIT)

Noteworthy fixes

• Formalise and fix Producer retries and retry-ordering (#623, #1092, #1432, #1476, #1421)
  • Ordering is now retained despite retries if max.in.flight=1.
  • Behaviour is now documented
• Fix timeouts for retried requests and properly handle retries for all request types (#1497)
• Add and use fetch.max.bytes to limit total Fetch response size (KIP-74, #1616). Fixes "Invalid response size" issues.

Enhancements

• Added sasl.mechanism and compression.type configuration property aliases for conformance with Java client.
• Improved Producer performance
• C++: add c_ptr() to Handle,Topic,Message classes to expose underlying librdkafka object
• Honour per-message partition in produce_batch() if MSG_F_PARTITION set (@barrotsteindev, closes #1604)
• Added on_request_sent() interceptor
• Added experimental flexible producer queuing.strategy=fifo|lifo
• Broker address DNS record round-robin: try to maintain round-robin position across resolve calls.
• Set system thread name for internal librdkafka threads (@tbsaunde)
• Added more concise and user-friendly 'consumer' debug context
• Add partitioner (string) topic configuration property to set the builtin partitioners
• Generate rdkafka-static.pc (pkg-config) for static linking

Fixes

• Fix producer memory leak on <0.11 brokers when compressed messageset is below copy threshold (closes #1534)
• CRC32C - fix unaligned access on ARM (@Soundman32)
• Fix read after free in buf_write_seek
• Fix broker wake up (#1667, @gduranceau)
• Fix consumer hang when rebalancing during commit (closes #1605, @ChenyuanHu)
• CMake fixes for Windows (@raulbocanegra)
• LeaveGroup was not sent on close when doing final offset commits
• Fix for consumer slowdown/stall on compacted topics where actual last offset < MsgSet.LastOffset (KAFKA-5443)
• Fix global->topic conf fallthru in C++ API
• Fix infinite loop on LeaveGroup failure
• Fix possible crash on OffsetFetch retry
• Incorporate compressed message count when deciding on fetch backoff (#1623)
• Fix debug-only crash on Solaris (%s NULL) (closes #1423)
• Drain broker ops queue on termination to avoid hang (closes #1596)
• cmake: Allow build static library (#1602, @proller)
• Don't store invalid offset as next one when pausing (#1453, @mfontanini)
• use #if instead of #ifdef / defined() for atomics (#1592, @vavrusa)
• fixed .lib paths in nuget packaging (#1587)
• Fixes strerror_r crash on alpine (#1580, @skarlsson)
• Allow arbitrary lengthed (>255) SASL PLAIN user/pass (#1691, #1692)
• Trigger ApiVersionRequest on reconnect if broker.version.fallback supports it (closes #1694)
• Read Fetch MsgAttributes as int8 (discovered by @tvoinarovskyi, closes #1689)
• Portability: stop using typeof in rdkafka_transport.c (#1708, @tbsaunde)
• Portability: replace use of #pragma once with header guards (#1688, @tbsaunde)
• mklove: add LIBS in reverse order to maintain dependency order
• Fix build when python is not available #1358