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= Contributor Code of Conduct
As contributors and maintainers of this project, and in the interest of fostering an open
and welcoming community, we pledge to respect all people who contribute through reporting
issues, posting feature requests, updating documentation, submitting pull requests or
patches, and other activities.
We are committed to making participation in this project a harassment-free experience for
everyone, regardless of level of experience, gender, gender identity and expression,
sexual orientation, disability, personal appearance, body size, race, ethnicity, age,
religion, or nationality.
Examples of unacceptable behavior by participants include:
* The use of sexualized language or imagery
* Personal attacks
* Trolling or insulting/derogatory comments
* Public or private harassment
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without explicit permission
* Other unethical or unprofessional conduct
Project maintainers have the right and responsibility to remove, edit, or reject comments,
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Code of Conduct, or to ban temporarily or permanently any contributor for other behaviors
that they deem inappropriate, threatening, offensive, or harmful.
By adopting this Code of Conduct, project maintainers commit themselves to fairly and
consistently applying these principles to every aspect of managing this project. Project
maintainers who do not follow or enforce the Code of Conduct may be permanently removed
from the project team.
This Code of Conduct applies both within project spaces and in public spaces when an
individual is representing the project or its community.
Instances of abusive, harassing, or otherwise unacceptable behavior may be reported by
contacting a project maintainer at spring-code-of-conduct@pivotal.io . All complaints will
be reviewed and investigated and will result in a response that is deemed necessary and
appropriate to the circumstances. Maintainers are obligated to maintain confidentiality
with regard to the reporter of an incident.
This Code of Conduct is adapted from the
https://contributor-covenant.org[Contributor Covenant], version 1.3.0, available at
https://contributor-covenant.org/version/1/3/0/[contributor-covenant.org/version/1/3/0/]

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= Contributing to Spring Pulsar
Spring Pulsar is released under the Apache 2.0 license. If you would like to contribute something, or want to hack on the code this document should help you get started.
== Code of Conduct
This project adheres to the Contributor Covenant link:CODE_OF_CONDUCT.adoc[code of conduct].
By participating, you are expected to uphold this code. Please report unacceptable behavior to spring-code-of-conduct@pivotal.io.
== Using GitHub Issues
We use GitHub issues to track bugs and enhancements.
// NYI
// If you have a general usage question please ask on https://stackoverflow.com[Stack Overflow].
// The Spring Pulsar team and the broader community monitor the https://stackoverflow.com/tags/spring-pulsar[`spring-pulsar`] tag.
If you are reporting a bug, please help to speed up problem diagnosis by providing as much information as possible.
Ideally, that would include a small sample project that reproduces the problem.
== Reporting Security Vulnerabilities
If you think you have found a security vulnerability in Spring Pulsar please *DO NOT* disclose it publicly until we've had a chance to fix it.
Please don't report security vulnerabilities using GitHub issues, instead head over to https://spring.io/security-policy and learn how to disclose them responsibly.
== Sign the Contributor License Agreement
Before we accept a non-trivial patch or pull request we will need you to https://cla.pivotal.io/sign/spring[sign the Contributor License Agreement].
Signing the contributor's agreement does not grant anyone commit rights to the main repository, but it does mean that we can accept your contributions, and you will get an author credit if we do.
Active contributors might be asked to join the core team, and given the ability to merge pull requests.
== Code Conventions and Housekeeping
None of these is essential for a pull request, but they will all help. They can also be
added after the original pull request but before a merge.
* We use the https://github.com/spring-io/spring-javaformat/[Spring JavaFormat] project to apply code formatting conventions.
If you use Eclipse and you follow the '`Importing into eclipse`' instructions below you should get project specific formatting automatically.
You can also install the https://github.com/spring-io/spring-javaformat/#intellij-idea[Spring JavaFormat IntelliJ Plugin] or format the code from the Gradle build by running `./gradlew format`.
// NYI: Note that if you have format violations in `buildSrc`, you can fix them by running `./gradlew -p buildSrc format` from the project root directory.
* The build includes Checkstyle rules for many of our code conventions. Run `./gradlew checkstyleMain checkstyleTest` if you want to check your changes are compliant.
* Make sure all new `.java` files have a Javadoc class comment with at least an `@author` tag identifying you, and preferably at least a paragraph on what the class is for.
* Add the ASF license header comment to all new `.java` files (copy from existing files in the project).
* Add yourself as an `@author` to the `.java` files that you modify substantially (more than cosmetic changes).
* Add some Javadocs.
* A few unit tests would help a lot as well -- someone has to do it.
* Verification tasks, including tests and Checkstyle, can be executed by running `./gradlew check` from the project root.
Note that `SPRING_PROFILES_ACTIVE` environment variable might affect the result of tests, so in that case, you can prevent it by running `unset SPRING_PROFILES_ACTIVE` before running the task.
* If no-one else is using your branch, please rebase it against the current main branch (or other target branch in the project).
* When writing a commit message please follow https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html[these conventions].
== Working with the Code
**#TODO#**
For information on editing, building, and testing the code, see the https://github.com/spring-projects/spring-pulsar/wiki/Working-with-the-Code[Working with the Code] page on the project wiki.

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# Spring for Apache Pulsar
= Spring for Apache Pulsar
:docs: https://docs.spring.io/spring-pulsar/docs/current-SNAPSHOT/reference
:github: https://github.com/spring-projects-experimental/spring-pulsar
This project provides a basic Spring friendly API for developing https://pulsar.apache.org/[Apache Pulsar] applications.
Spring Pulsar provides a basic Spring-friendly API for developing https://pulsar.apache.org/[Apache Pulsar] applications.
Most of the ideas in this project are borrowed from the Spring for Apache Kafka project, thus a familiarity with the Spring support available in Spring for Apache Kafka would help a lot.
**#WARNING#**: This is a WIP project. Many of the support available at the moment are prototypes and experimental.
** #IMPORTANT#: This is a WIP project. Many of the support available at the moment are prototypes and experimental.
**#TIP#**: Most of the ideas in this project are borrowed from the Spring for Apache Kafka project, thus a familiarity with it would help.
### Building the project
== Getting Started
The {docs}/html/[reference documentation] includes a {docs}/html/#quick-tourhtml[quick tour] section.
#### Minimum Supported Versions
== Getting Help
Are you having trouble with Spring Pulsar? We want to help!
**JDK** - JDK 17
* Check the {docs}/html/[reference documentation]
* Learn the Spring basics -- Spring Pulsar builds on many other Spring projects; check the https://spring.io[spring.io] website for a wealth of reference documentation.
If you are new to Spring, try one of the https://spring.io/guides[guides].
// TODO (NYI): * If you are upgrading, read the {github}/wiki[release notes] for upgrade instructions and "new and noteworthy" features.
// TODO (NYI): * Ask a question -- we monitor https://stackoverflow.com[stackoverflow.com] for questions tagged with https://stackoverflow.com/tags/spring-pulsar[`spring-pulsar`].
* Report bugs with Spring Pulsar at {github}/issues[github.com/spring-projects-experimental/spring-pulsar/issues].
**Apache Pulsar** - 2.10.0
**Spring Boot** - 3.0.0
**Spring Framework** - 6.0.0
== Reporting Issues
Spring Pulsar uses GitHub's integrated issue tracking system to record bugs and feature requests.
If you want to raise an issue, please follow the recommendations below:
```
./gradlew clean build
```
* Before you log a bug, please search the {github}/issues[issue tracker] to see if someone has already reported the problem.
* If the issue doesn't already exist, {github}/issues/new[create a new issue].
* Please provide as much information as possible with the issue report.
We like to know the Spring Pulsar version, operating system, and JVM version you're using.
* If you need to paste code or include a stack trace, use Markdown +++```+++ escapes before and after your text.
* If possible, try to create a test case or project that replicates the problem and attach it to the issue.
The build will produce two artifacts -- `spring-pulsar` and `spring-pulsar-spring-boot-autoconfigure`
### Spring Boot Auto Configuration
We recommend using the library `spring-pulsar` in association with Spring Boot and therefore should also use `spring-pulsar-spring-boot-autoconfigure`.
If you simply use the module `spring-pulsar-spring-boot-autoconfigure`, then that will transitively include `spring-pulsar`.
== Building from Source
You don't need to build from source to use Spring Pulsar (binaries in https://repo.spring.io[repo.spring.io]), but if you want to try out the latest and greatest, Spring Pulsar can be built and published to your local Maven cache using the https://docs.gradle.org/current/userguide/gradle_wrapper.html[Gradle wrapper].
You also need JDK 17.
#### Pulsar Client
[indent=0]
----
$ ./gradlew publishToMavenLocal
----
When using `spring-pulsar-spring-boot-autoconfigure`, you get the `PulsarClient` auto-configured.
This is done through a factory bean called `PulsarClientFactoryBean`, which takes a configuration object `PulsarClientConfiguration`.
By default, the application tries to connect a local Pulsar instance available at `pulsar://localhost:6650`.
This will build all of the jars and documentation and publish them to your local Maven cache.
It won't run any of the tests.
If you want to build everything, use the `build` task:
The properties listed below are available to be set on the Pulsar client.
[indent=0]
----
$ ./gradlew build
----
The same defaults expected by the Pulsar client are honored when no configuration provided for these properties.
```
spring.pulsar.client.serviceUrl
spring.pulsar.client.authPluginClassName
spring.pulsar.client.authParams
spring.pulsar.client.operationTimeoutMs
spring.pulsar.client.statsIntervalSeconds
spring.pulsar.client.numIoThreads
spring.pulsar.client.useTcpNoDelayuseTls
spring.pulsar.client.tlsAllowInsecureConnection
spring.pulsar.client.tlsHostnameVerificationEnable
spring.pulsar.client.concurrentLookupRequest
spring.pulsar.client.maxLookupRequest
spring.pulsar.client.maxNumberOfRejectedRequestPerConnection
spring.pulsar.client.keepAliveIntervalSeconds
spring.pulsar.client.connectionTimeoutMs
spring.pulsar.client.requestTimeoutMs
spring.pulsar.client.initialBackoffIntervalNanos
spring.pulsar.client.maxBackoffIntervalNanos;
```
#### Pulsar Producer
== Modules
There are several modules in Spring Pulsar. Here is a quick overview:
On the Pulsar producer side, Sprig Boot auto-configuration will provide a `PulsarTemplate` which is backed by a `PulsarProducerFactory`.
We will see more details of these components later in this document, but in this section, let us look at the configuration properties available on the producer.
=== spring-pulsar
The main library that provides the API to access Apache Pulsar.
These properties must be prefixed with `spring.pulsar.producer`.
=== spring-pulsar-dependencies
Provides a Gradle https://docs.gradle.org/current/userguide/java_platform_plugin.html[java-platform] that recommends dependency versions.
The same defaults expected by the Pulsar producer are honored when no configuration provided for these properties.
=== spring-pulsar-docs
Provides reference docs and handles aggregating javadocs.
```
spring.pulsar.producer.topicName
spring.pulsar.producer.producerName
spring.pulsar.producer.sendTimeoutMs
spring.pulsar.producer.blockIfQueueFull
spring.pulsar.producer.maxPendingMessages
spring.pulsar.producer.maxPendingMessagesAcrossPartitions
spring.pulsar.producer.messageRoutingMode
spring.pulsar.producer.hashingScheme
spring.pulsar.producer.cryptoFailureAction
spring.pulsar.producer.batchingMaxPublishDelayMicros
spring.pulsar.producer.batchingMaxMessages
spring.pulsar.producer.batchingEnabled
spring.pulsar.producer.chunkingEnabled
spring.pulsar.producer.compressionType
spring.pulsar.producer.initialSubscriptionName
spring.pulsar.producer.accessMode
```
=== spring-pulsar-spring-boot-autoconfigure
Provides Spring Boot auto-configuration for Spring Pulsar.
#### Pulsar Consumer
=== spring-pulsar-sample-apps
Provides sample applications to illustrate Spring Pulsar functionality as well as provide ability for quick manual verification during development.
When it comes to Pulsar consumer, we recommend the end user applications to make use of the `PulsarListener` annotation.
In order to use `PulsarListener`, you need to use the `EnablePulsar` annotation.
When using the Spring Boot support, it automatically enables this annotation and configures all the components necessary for `PulsarListener` such as the message listener infrastructure which is responsible for creating the Pulsar consumer.
`PulsarMessageListenerContainer` uses a `PulsarConsumerFactory` in order to create and manage the Pulsar consumer.
This consumer factory is auto-configured through Spring Boot.
Following are the consumer properties that you can configure through the Boot support.
The same defaults expected by the Pulsar consumer are honored when no configuration provided for these properties.
```
spring.pulsar.consumer.topicNames
spring.pulsar.consumer.topicsPattern
spring.pulsar.consumer.subscriptionName
spring.pulsar.consumer.subscriptionType
spring.pulsar.consumer.receiverQueueSize
spring.pulsar.consumer.acknowledgementsGroupTimeMicros
spring.pulsar.consumer.negativeAckRedeliveryDelayMicros
spring.pulsar.consumer.maxTotalReceiverQueueSizeAcrossPartitions
spring.pulsar.consumer.consumerName
spring.pulsar.consumer.ackTimeoutMillis
spring.pulsar.consumer.tickDurationMillis
spring.pulsar.consumer.priorityLevel
spring.pulsar.consumer.cryptoFailureAction
spring.pulsar.consumer.properties
spring.pulsar.consumer.readCompacted
spring.pulsar.consumer.subscriptionInitialPosition
spring.pulsar.consumer.patternAutoDiscoveryPeriod
spring.pulsar.consumer.regexSubscriptionMode
spring.pulsar.consumer.autoUpdatePartitions
spring.pulsar.consumer.replicateSubscriptionState
spring.pulsar.consumer.autoAckOldestChunkedMessageOnQueueFull
spring.pulsar.consumer.maxPendingChunkedMessageexpireTimeOfIncompleteChunkedMessageMillis
```
### Sample Applications
In this section, we will show a number of various applications to demonstrate how you can use the Spring for Apache Pulsar library using Spring Boot.
Here are the maven coordinates of the artifacts needed for using this library.
```
<dependency>
<groupId>org.springframework.pulsar</groupId>
<artifactId>spring-pulsar</artifactId>
<version>0.1.0-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>org.springframework.pulsar</groupId>
<artifactId>spring-pulsar-boot-autoconfiguration</artifactId>
<version>0.1.0-SNAPSHOT</version>
</dependency>
```
If you simply include the `spring-pulsar-boot-autoconfiguration` module, then that will transitively include the `spring-pulsar` module.
#### Quick Primer on Publishing to and Consuming from an Apache Pulsar Topic
In order to publish to a Pulsar topic, the easiest way is to use the `PulsarTemplate` API.
Similarly, the easiest way to consume from a Pulsar topic is to use the `PulsarListener` annotation.
The following is a complete Spring Boot application that publishes to a Pulsar topic called `hello-pulsar` and then consumes from it.
```
@SpringBootApplication
public class PulsarBootHelloWorld {
public static void main(String[] args) {
SpringApplication.run(PulsarBootHelloWorld.class, args);
}
@Bean
public ApplicationRunner runner(PulsarTemplate<String> pulsarTemplate) {
pulsarTemplate.setDefaultTopicName("hello-pulsar");
return args -> {
for (int i = 0; i < 10; i ++) {
pulsarTemplate.send("This is message " + (i + 1));
}
};
}
@PulsarListener(subscriptionName = "hello-pulsar-subscription", topics = "hello-pulsar")
public void listen(String message) {
System.out.println("Message Received: " + message);
}
}
```
Although this is a very trivial application, it conveys several important concepts nonetheless. Let's take a look at them.
`PulsarTemplate` is autoconfigured by Spring Boot, and we are injecting that in the application.
There is a producer factory behind the scenes and properties can be provided to it using `spring.pulsar.producer...` (See above for more details).
When injecting, note that, we can provide a specific type - `String` in this case.
If we have a need for a different `PulsarTemplate` with a different type in the same application, then we can add another injection with that type.
`PulsarTemplate` currently requires the application to set a default topic.
Once the topic is set, then we can call the various `send` methods on it.
In this example, we are calling the very basic synchronous `send` method that is internally forwarded to the Pulsar producer that returns the `MessageId`.
We are ignoring the return value in this quick sample application.
`PulsarTemplate` also provides APIs for sending asynchronously among other send methods.
We will look at the details of it, later on in the reference documentation.
We use the `PulsarListener` annotation to consume from the topic.
We are providing the subscription and topic names as annotation arguments.
These are optional and the application may prefer to set them using the `spring.pulsar.consumer..` properties provided above.
There are four consumer level properties that you can set on the `PulsarListener` annotation - they are `topics`, `topicPattern`, `subscriptionName` and `subscriptionType`.
When provided on the annotation, they get preference regardless of what is set through consumer properties.
By default, `PulsarListener` uses an exclusive subscription type and this can be changed by using the `subscriptionType` property on the annotation or through the consumer property.
`PulsarListener` internally creates a message listener container.
The message listener container is responsible for creating the Pulsar Consumer using a consumer factory.
When the consumer receives data, the container calls a message listener.
This message listener is an adapter around the user provided method - the `listen` method in this case.
The message listener container delegates to the adapter with the received data and the adapter then invokes the user method.
In order to complete the discussion about this sample application, we also need to chime in on how data conversion is done.
In the user method, we receive the data as `String`, but we don't specify any schema types.
Internally, the framework by default relies on Pulsar's schema mechanism to convert the data to the required type.
The framework detects that you are expecting the `String` type and then infer the schema type based on that information.
Then it provides that schema to the consumer.
For all the primitive types in Java, the framework does this inference.
For any complex types, such as JSON, AVRO etc. the framework cannot do this inference and the user needs to provide the schema type on the annotation using the `schemaType` property.
In the example above, and in the ones that follows below, we provide both producer and consumer as part of the same application.
However, in real apps, you might find it as convenient to separate them especially if you are following a microservice style architecture.
#### Partitioned topics - Publishing and Consuming.
In the sample below, we are publishing to a topic called `hello-pulsar-partitioned`.
It is a topic that is partitioned and for this sample we assume that the topic is already created with three partitions.
```
@SpringBootApplication
public class PulsarBootPartitioned {
public static void main(String[] args) {
SpringApplication.run(PulsarBootPartitioned.class, "--spring.pulsar.producer.messageRoutingMode=CustomPartition");
}
@Bean
public ApplicationRunner runner(PulsarTemplate<String> pulsarTemplate) {
pulsarTemplate.setDefaultTopicName("hello-pulsar-partitioned");
return args -> {
for (int i = 0; i < 10; i++) {
pulsarTemplate.sendAsync("hello john doe 0 ", new FooRouter());
pulsarTemplate.sendAsync("hello alice doe 1", new BarRouter());
pulsarTemplate.sendAsync("hello buzz doe 2", new BuzzRouter());
}
};
}
@PulsarListener(subscriptionName = "hello-pulsar-partitioned-subscription", topics = "hello-pulsar-partitioned")
public void listen(String message) {
System.out.println("Message Received: " + message);
}
static class FooRouter implements MessageRouter {
@Override
public int choosePartition(Message<?> msg, TopicMetadata metadata) {
return 0;
}
}
static class BarRouter implements MessageRouter {
@Override
public int choosePartition(Message<?> msg, TopicMetadata metadata) {
return 1;
}
}
static class BuzzRouter implements MessageRouter {
@Override
public int choosePartition(Message<?> msg, TopicMetadata metadata) {
return 2;
}
}
}
```
A few things require explanation in the application above.
We are publishing to a partitioned topic and we would like to publish some data segment to a specific partition.
If you leave it to Pulsar's default, it follows a round-robin mode of partition assignments, and we would like to override that.
In order to do that, we are providing a message router object with the send method.
Look at the three message routers implemented.
`FooRouter` always sends data to partition `0`, `BarRouter` to partition `1` and `BuzzRouter` to partition `2`.
Also note that, we are now using the `sendAsync` method of `PulsarTemplate` that returns a `CompletableFuture`.
When running the application, we also need to set the `messageRoutingMode` on the producer to `CustomPartition` (`spring.pulsar.producer.messageRoutingMode`).
On the consumer side, we are using a `PulsarListener` with the exclusive subscription type.
This means that data from all the partitions will end up in the same consumer and there is no ordering guarantee.
What can we do if we want each partition to be consumed by a single distinct consumer?
We can switch to the `failover` subscription mode and add three separate consumers.
Here is an example.
```
@PulsarListener(subscriptionName = "hello-pulsar-partitioned-subscription", topics = "hello-pulsar-partitioned", subscriptionType = "failover")
public void listen1(String foo) {
System.out.println("Message Received 1: " + foo);
}
@PulsarListener(subscriptionName = "hello-pulsar-partitioned-subscription", topics = "hello-pulsar-partitioned", subscriptionType = "failover")
public void listen2(String foo) {
System.out.println("Message Received 2: " + foo);
}
@PulsarListener(subscriptionName = "hello-pulsar-partitioned-subscription", topics = "hello-pulsar-partitioned", subscriptionType = "failover")
public void liste3n(String foo) {
System.out.println("Message Received 3: " + foo);
}
```
When following this approach, you can see that a single partition always gets consumed by a dedicated consumer.
In the similar vein, if you want to use Pulsar's shared consumer type, you can use the subscription type `shared`.
Keep in mind though, that when using the `shared` mode, you lose any ordering guarantees as a single consumer may receive messages from all the partitions before another consumer gets a chance.
Here is an example.
```
@PulsarListener(subscriptionName = "hello-pulsar-shared-subscription", topics = "hello-pulsar-partitioned", subscriptionType = "shared")
public void listen1(String foo) {
System.out.println("Message Received 1: " + foo);
}
@PulsarListener(subscriptionName = "hello-pulsar-shared-subscription", topics = "hello-pulsar-partitioned", subscriptionType = "shared")
public void listen2(String foo) {
System.out.println("Message Received 2: " + foo);
}
```
#### Consuming Messages in Batch Mode
In the examples above, we used `PulsarListener` in record mode, i.e. we receive a single message on each method invocation.
Sometimes, for various reasons, we may want to receive Pulsar messages in batch mode. Here is a `PulsarListener` that is enabled with batch consumption.
```
@PulsarListener(subscriptionName = "batch-subscription", topics = "hello-pulsar", batch = "true")
public void listen(List<String> records) {
System.out.println("Message Received from batch: " + records);
}
```
In order to enable batch consumption, you need to set the `batch` property to `true` on `PulsarListener`.
Then you can receive the records as a `List` type.
Based on the actual type that the `List` holds, the framework tries to infer the schema to use.
If the `List` contains a complex type, then the `schemaType` still needs to be provided on `PulsarListener`.
#### Accessing the Pulsar Message Object
In your `PulsarListener` method, you can receive the record directly as a Pulsar Message instead of the actual payload type.
Here is an example.
```
@PulsarListener(subscriptionName = "hello-pulsar-subscription", topics = "hello-pulsar")
public void listen(org.apache.pulsar.client.api.Message<String> message) {
System.out.println("Data Received: " + message.getValue());
}
```
#### Accessing the Pulsar Messages Object
When consuming messages in batch mode using `PulsarListener`, instead of receiving them as a `List`, you can receive them as Pulsar Messages type.
Here is an example.
```
@PulsarListener(subscriptionName = "batch-subscription", topics = "hello-pulsar", batch = "true")
public void listen(org.apache.pulsar.client.api.Messages<String> messages) {
// Iterate on the messages
// Each iteration gives access to a org.apache.pulsar.client.api.Message object
}
```
#### Accessing the Pulsar Consumer Object
Sometimes, it is necessary to gain direct access to the Pulsar Consumer object.
Here is how you may do so.
```
@PulsarListener(subscriptionName = "hello-pulsar-subscription", topics = "hello-pulsar")
public void listen(String message, org.apache.pulsar.client.api.Consumer<String> consumer) {
System.out.println("Message Received: " + message);
ConsumerStats stats = consumer.getStats();
...
}
```
When accessing the `Consumer` object this way, make sure NOT to invoke any operations that would change the Consumer's cursor position by invoking any receive methods.
All such operations must be done by the container.
#### Specify schema information
As indicated above, for normal Java types (the primitive ones), Spring Pulsar framework can infer the proper Schema to use on the `PulsarListener`.
However, for more complex types such as JSON or AVRO, you need to specify the schema type on the annotation.
Here is how you provide that.
```
@PulsarListener(subscriptionName = "json-subscription", topics = "hello-pulsar-json", schemaType = SchemaType.JSON)
public void listen(Foo foo) {
System.out.println("Message received: " + foo);
}
```
On the producer side also, for the Java primitive types, the framework can infer the Schema, but for any other types, you need set that on the `PulsarTemmplate`.
#### PulsarTemplate API details
### More support to come -- stay tuned...
== License
Spring Pulsar is Open Source software released under the https://www.apache.org/licenses/LICENSE-2.0.html[Apache 2.0 license].