:branch: master

=== Google Cloud Functions (Alpha)

The Google Cloud Functions adapter enables Spring Cloud Function apps to run on the https://cloud.google.com/functions[Google Cloud Functions] serverless platform.
You can either run the function locally using the open source https://github.com/GoogleCloudPlatform/functions-framework-java[Google Functions Framework for Java] or on GCP.

==== Project Dependencies

Start by adding the `spring-cloud-function-adapter-gcp` dependency to your project.

[source, xml]
----
<dependencies>
	<dependency>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-function-adapter-gcp</artifactId>
	</dependency>

	...
</dependencies>
----

In addition, add the `spring-boot-maven-plugin` which will build the JAR of the function to deploy.

NOTE: Notice that we also reference `spring-cloud-function-adapter-gcp` as a dependency of the `spring-boot-maven-plugin`. This is necessary because it modifies the plugin to package your function in the correct JAR format for deployment on Google Cloud Functions.

[source, xml]
----
<plugin>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-maven-plugin</artifactId>
	<configuration>
		<outputDirectory>target/deploy</outputDirectory>
	</configuration>
	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-function-adapter-gcp</artifactId>
		</dependency>
	</dependencies>
</plugin>
----

Finally, add the Maven plugin provided as part of the Google Functions Framework for Java.
This allows you to test your functions locally via `mvn function:run`.

NOTE: The function target should always be set to `org.springframework.cloud.function.adapter.gcp.GcfJarLauncher`; this is an adapter class which acts as the entry point to your Spring Cloud Function from the Google Cloud Functions platform.

[source,xml]
----
<plugin>
	<groupId>com.google.cloud.functions</groupId>
	<artifactId>function-maven-plugin</artifactId>
	<version>0.9.1</version>
	<configuration>
		<functionTarget>org.springframework.cloud.function.adapter.gcp.GcfJarLauncher</functionTarget>
		<port>8080</port>
	</configuration>
</plugin>
----

A full example of a working `pom.xml` can be found in the https://github.com/spring-cloud/spring-cloud-function/blob/master/spring-cloud-function-samples/function-sample-gcp-http/pom.xml[Spring Cloud Functions GCP sample].

==== HTTP Functions

Google Cloud Functions supports deploying https://cloud.google.com/functions/docs/writing/http[HTTP Functions], which are functions that are invoked by HTTP request. The sections below describe instructions for deploying a Spring Cloud Function as an HTTP Function.

===== Getting Started

Let’s start with a simple Spring Cloud Function example:

[source, java]
----
@SpringBootApplication
public class CloudFunctionMain {

	public static void main(String[] args) {
		SpringApplication.run(CloudFunctionMain.class, args);
	}

	@Bean
	public Function<String, String> uppercase() {
		return value -> value.toUpperCase();
	}
}
----

Specify your configuration main class in `resources/META-INF/MANIFEST.MF`.

[source]
----
Main-Class: com.example.CloudFunctionMain
----

Then run the function locally.
This is provided by the Google Cloud Functions `function-maven-plugin` described in the project dependencies section.

----
mvn function:run
----

Invoke the HTTP function:

----
curl http://localhost:8080/ -d "hello"
----

===== Deploy to GCP

As of March 2020, Google Cloud Functions for Java is in Alpha.
You can get on the https://docs.google.com/forms/d/e/1FAIpQLScC98jGi7CfG0n3UYlj7Xad8XScvZC8-BBOg7Pk3uSZx_2cdQ/viewform[whitelist] to try it out.

Start by packaging your application.

----
mvn package
----

If you added the custom `spring-boot-maven-plugin` plugin defined above, you should see the resulting JAR in `target/deploy` directory.
This JAR is correctly formatted for deployment to Google Cloud Functions.

Next, make sure that you have the https://cloud.google.com/sdk/install[Cloud SDK CLI] installed.

From the project base directory run the following command to deploy.

----
gcloud alpha functions deploy function-sample-gcp-http \
--entry-point org.springframework.cloud.function.adapter.gcp.GcfJarLauncher \
--runtime java11 \
--trigger-http \
--source target/deploy \
--memory 512MB
----

Invoke the HTTP function:

----
curl https://REGION-PROJECT_ID.cloudfunctions.net/function-sample-gcp-http -d "hello"
----

==== Background Functions

Google Cloud Functions also supports deploying https://cloud.google.com/functions/docs/writing/background[Background Functions] which are invoked indirectly in response to an event, such as a message on a https://cloud.google.com/pubsub[Cloud Pub/Sub] topic, a change in a https://cloud.google.com/storage[Cloud Storage] bucket, or a https://firebase.google.com/[Firebase] event.

The `spring-cloud-function-adapter-gcp` allows for functions to be deployed as background functions as well.

The sections below describe the process for writing a Cloud Pub/Sub topic background function.
However, there are a number of different event types that can trigger a background function to execute which are not discussed here; these are described in the https://cloud.google.com/functions/docs/calling[Background Function triggers documentation].

===== Getting Started

Let’s start with a simple Spring Cloud Function which will run as a GCF background function:

[source, java]
----
@SpringBootApplication
public class BackgroundFunctionMain {

	public static void main(String[] args) {
		SpringApplication.run(BackgroundFunctionMain.class, args);
	}

	@Bean
	public Consumer<PubSubMessage> pubSubFunction() {
		return message -> System.out.println("The Pub/Sub message data: " + message.getData());
	}
}
----

In addition, create `PubSubMessage` class in the project with the below definition.
This class represents the https://cloud.google.com/functions/docs/calling/pubsub#event_structure[Pub/Sub event structure] which gets passed to your function on a Pub/Sub topic event.

[source, java]
----
public class PubSubMessage {

	private String data;

	private Map<String, String> attributes;

	private String messageId;

	private String publishTime;

	public String getData() {
		return data;
	}

	public void setData(String data) {
		this.data = data;
	}

	public Map<String, String> getAttributes() {
		return attributes;
	}

	public void setAttributes(Map<String, String> attributes) {
		this.attributes = attributes;
	}

	public String getMessageId() {
		return messageId;
	}

	public void setMessageId(String messageId) {
		this.messageId = messageId;
	}

	public String getPublishTime() {
		return publishTime;
	}

	public void setPublishTime(String publishTime) {
		this.publishTime = publishTime;
	}

}
----

Specify your configuration main class in `resources/META-INF/MANIFEST.MF`.

[source]
----
Main-Class: com.example.BackgroundFunctionMain
----

Then run the function locally.
This is provided by the Google Cloud Functions `function-maven-plugin` described in the project dependencies section.

----
mvn function:run
----

Invoke the HTTP function:

----
curl localhost:8080 -H "Content-Type: application/json" -d '{"data":"hello"}'
----

Verify that the function was invoked by viewing the logs.

===== Deploy to GCP

In order to deploy your background function to GCP, first package your application.

----
mvn package
----

If you added the custom `spring-boot-maven-plugin` plugin defined above, you should see the resulting JAR in `target/deploy` directory.
This JAR is correctly formatted for deployment to Google Cloud Functions.

Next, make sure that you have the https://cloud.google.com/sdk/install[Cloud SDK CLI] installed.

From the project base directory run the following command to deploy.

----
gcloud alpha functions deploy function-sample-gcp-background \
--entry-point org.springframework.cloud.function.adapter.gcp.GcfJarLauncher \
--runtime java11 \
--trigger-topic my-functions-topic \
--source target/deploy \
--memory 512MB
----

Google Cloud Function will now invoke the function every time a message is published to the topic specified by `--trigger-topic`.

For a walkthrough on testing and verifying your background function, see the instructions for running the https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-samples/function-sample-gcp-background/[GCF Background Function sample].

==== Sample Functions

The project provides the following sample functions as reference:

* The https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-samples/function-sample-gcp-http/[function-sample-gcp-http] is an HTTP Function which you can test locally and try deploying.
* The https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-samples/function-sample-gcp-background/[function-sample-gcp-background] shows an example of a background function that is triggered by a message being published to a specified Pub/Sub topic.
