Reduce garbage on MQTT encoding
Motivation:
MQTT encoding and decoding is doing unnecessary object allocation in a number of places:
- MqttEncoder create many byte[] to encode Strings into UTF-8 bytes
- MqttProperties uses Integer keys instead of int
- Some enums valueOf create unnecessary arrays on the hot paths
- MqttDecoder was using unecessary Result<T>
Modification:
- ByteBufUtil::utf8Bytes and ByteBufUtil::reserveAndWriteUtf8 allows to perform the same operation GC-free
- MqttProperties uses a primitive key map
- Implemented GC free const table lookup/switch valueOf
- Use some bit-tricks to pack 2 ints into a single primitive long to store both result and numberOfBytesConsumed and use byte[].length to compute numberOfByteConsumed on fly. These changes allowed to save creating Result<T>.
Result:
Significantly less garbage produced in MQTT encoding/decoding
Motivation:
MQTT Specification version 5 was released over a year ago,
netty-codec-mqtt should be changed to support it.
Modifications:
Added more message and header types in `io.netty.handler.codec.mqtt`
package in `netty-coded-mqtt` subproject,
changed `MqttEncoder` and `MqttDecoder` to handle them properly,
added attribute `NETTY_CODEC_MQTT_VERSION` to track protocol version
Result:
`netty-codec-mqtt` supports both MQTT5 and MQTT3 now.
Motivation
ByteBuf has an isAccessible method which was introduced as part of ref
counting optimizations but there are some places still doing
accessibility checks by accessing the volatile refCnt() directly.
Modifications
- Have PooledNonRetained(Duplicate|Sliced)ByteBuf#isAccessible() use
their refcount delegate's isAccessible() method
- Add static isAccessible(buf) and ensureAccessible(buf) methods to
ByteBufUtil
(since ByteBuf#isAccessible() is package-private)
- Adjust DefaultByteBufHolder and similar classes to use these methods
rather than access refCnt() directly
Result
- More efficient accessibility checks in more places
Motivation:
Mqtt procotol defines packetId instead of messageId, replace deprecated method to match protocol definition
Modification:
Replace messageId() to packetId() in MqttEncoder
Result:
Match mqtt protocol definition and improve readability.
Motivation:
Currently, the only way to create fixed-header only messages PINGREQ,
PINGRESP and DISCONNECT is to explicitly instantiate a `MqttFixedHeader` like:
```
MqttFixedHeader disconnectFixedHeader = new MqttFixedHeader(MqttMessageType.DISCONNECT,
false, MqttQoS.AT_MOST_ONCE, false, 0);
MqttMessage disconnectMessage = new MqttMessage(disconnectFixedHeader);
```
According to the MQTT spec
(http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718077),
the fixed-header flags for these messages are reserved and must be set to zero, otherwise
the receiver must close the connection. It's easy to mess this up when
you're creating the header explicitly, for e.g by setting the QoS bit to
`AT_LEAST_ONCE`.
As such, provide static constants for PINGREQ, PINGRESP and
DISCONNECT messages that will set the flags correctly for the developer.
Modification:
Add static constants to MqttMessage class to construct PINGREQ, PINGRESP and
DISCONNECT messages that will set the fixed-header flags correctly to 0.
Result:
Easier usage.
Motivation:
The toString() method should use Arrays.toString() to produce a meaningful String representation for arrays.
Modification:
Use Arrays.toString()
Result:
More useful toString() implementation
Motivation:
The toString() methods of MqttSubscribePayload and MqttUnsubscribePayload are causing exceptions when no topics are set.
Modification:
The toString() methods will not throw Excpetions anymore.
Result:
Fixes#9197
Motivation:
Most of the maven modules do not explicitly declare their
dependencies and rely on transitivity, which is not always correct.
Modifications:
For all maven modules, add all of their dependencies to pom.xml
Result:
All of the (essentially non-transitive) depepdencies of the modules are explicitly declared in pom.xml
