This patch adds a framework to automatically generate the request/response classes for Kafka's protocol. The code will be updated to use the generated classes in follow-up patches. Below is a brief summary of the included components:
**buildSrc/src**
The message generator code is here. This code is automatically re-run by gradle when one of the schema files changes. The entire directory is processed at once to minimize the number of times we have to start a new JVM. We use Jackson to translate the JSON files into Java objects.
**clients/src/main/java/org/apache/kafka/common/protocol/Message.java**
This is the interface implemented by all automatically generated messages.
**clients/src/main/java/org/apache/kafka/common/protocol/MessageUtil.java**
Some utility functions used by the generated message code.
**clients/src/main/java/org/apache/kafka/common/protocol/Readable.java, Writable.java, ByteBufferAccessor.java**
The generated message code uses these classes for writing to a buffer.
**clients/src/main/message/README.md**
This README file explains how the JSON schemas work.
**clients/src/main/message/\*.json**
The JSON files in this directory implement every supported version of every Kafka API. The unit tests automatically validate that the generated schemas match the hand-written schemas in our code. Additionally, there are some things like request and response headers that have schemas here.
**clients/src/main/java/org/apache/kafka/common/utils/ImplicitLinkedHashSet.java**
I added an optimization here for empty sets. This is useful here because I want all messages to start with empty sets by default prior to being loaded with data. This is similar to the "empty list" optimizations in the `java.util.ArrayList` class.
Reviewers: Stanislav Kozlovski <stanislav_kozlovski@outlook.com>, Ismael Juma <ismael@juma.me.uk>, Bob Barrett <bob.barrett@outlook.com>, Jason Gustafson <jason@confluent.io>
See https://github.com/spotbugs/spotbugs/issues/756 for details on
the false positives affecting try with resources. An example is:
> RCN | Nullcheck of fc at line 629 of value previously dereferenced in
> org.apache.kafka.common.utils.Utils.readFileAsString(String, Charset)
Reviewers: Manikumar Reddy <manikumar.reddy@gmail.com>
findBugs is abandoned, it doesn't work with Java 9 and the Gradle plugin will be deprecated in
Gradle 5.0: https://github.com/gradle/gradle/pull/6664
spotBugs is actively maintained and it supports Java 8, 9 and 10. Java 11 is not supported yet,
but it's likely to happen soon.
Also fixed a file leak in Connect identified by spotbugs.
Manually tested spotBugsMain, jarAll and importing kafka in IntelliJ and running
a build in the IDE.
Author: Ismael Juma <ismael@juma.me.uk>
Reviewers: Colin Patrick McCabe <colin@cmccabe.xyz>, Dong Lin <lindong28@gmail.com>
Closes#5625 from ijuma/kafka-5887-spotbugs
Colin Patrick McCabe
Ismael Juma
Joan Goyeau