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Integration for Google Cloud Platform APIs with Spring

License: Apache License 2.0

Java 98.46% HTML 1.03% Kotlin 0.39% Shell 0.05% CSS 0.05% FreeMarker 0.01%

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markfisher viniciusccarvalho mbogoevici saturnism joaoandremartins garyrussell artembilan jabubake parkjam4 muthhus garyfub enhsuld sobychacko andy2003 maros7 zgzwelldone snicoll javaage dsyer mbrukman bygui86 kiwigrid mistic92 direkshan-digital 40a shankarnpal alpermulayim wendelicious azmym balopat ajeetj gustavo-gm-globant easongglin lfarmer hashimati weizai118 ekoca umangs9 mandelag ksushik tysewyn alewebmaste kv89 liuhe36 udoheld abr7823079250 sayi65 mukutbhattacharjee dhoard qitsweauca develasquez oksana-shevchenko matthew-dong romankharkiv ranjithswamy villcadiego olavloite vistajin ianouk12 killdeatha anwarchk pks-os paolocarta davinkevin sunkarasreenu gurupadamg guruisaguru elefeint santhh iamgituser27 spencergibb ilayaperumalg dzou shiraji henrypan hart199 mayur-patil rohanliston ksjamthe meltsufin adityasabadra evionce amairose-papajohns lokeshh sumitkanoje artemzi jingchen01 blacksoulgem95 anoophp777 zebugman hoangtuananh97 jarochp pietyta monasharma1991 eversonbadaro epalominola zmyer sricharankuna bigbri64 marcialr

spring-cloud-gcp's Issues

Integration inbound/outbound handlers for Storage

Create inbound/outbound gateways for Storage. Inbound should be based on AbstractRemoteFileStreamingMessageSource

Track usage of other APIs by Spring

We're currently working with the Pub/Sub team to fix the metrics backend to allow us to track Pub/Sub API usage by Spring integrations.

There are other APIs where we should also track usage. Right now, we're using:

Storage API
Cloud SQL Admin API

The Cloud SQL Admin API's SQLAdmin.Builder provides an applicationName parameter that we could populate. It's not clear that the Storage API provides any such method for usage tracking.

Use Pubsub instead of PubSub in identifiers

Example: PubsubTemplate rather than PubSubTemplate.

There are a few packages that aren't used currently and could cause user confusion.
org.springframework.cloud.gcp.pubsub.converters.* (except SimpleMessageConverter)
org.springframework.cloud.gcp.pubsub.converters.support
org.springframework.cloud.gcp.pubsub.*

We should remove them before launching anything to the public.

They cover areas that we already have issues for: (a)sync mode (#51) and topic/message conversion (#54). We should wait until those issues are worked on in order to provide those features. Until then, it's better to remove the classes so they don't confuse users.

@artembilan wdyt?

Support autoconfiguration of GCP Project ID

Project ID may be obtained from the environment on GCP using GOOGLE_CLOUD_PROJECT or the metadata server.

This may require introduction of GcpProjectIdProvider.

Add (a)sync mode to PubSubMessageHandler

There is an example on KafkaMessageProducerHandler.

Generate base documentation for website

Get the basics for our plugin to generate the website

Allow users to specify PubSub's subscriber callback

Right now we set the callback for the user, PubSubInboundChannelAdapter.receiveMessage().

We should add in a functional interface in the constructor to allow users to specify a callback.

There were also talks of specifying a MessageListenerContainer (?), but I haven't looked into this.

Support injection of Google Storage objects as Resource

The spring-cloud-gcp-starter-storage already supports loading gs://... resources using DefaultResourceLoader, but direct injection using @Value does not work.

@Value("gs://<bucket>/<object>")
private Resource gcsResource;

Currently, for some reason it tries to resolve the resource via ServletContext.

java.io.FileNotFoundException: Could not open ServletContext resource [/gs://<bucket>/<object>]
	at org.springframework.web.context.support.ServletContextResource.getInputStream(ServletContextResource.java:141) ~[spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at com.example.HelloController.readGcs(BootDemoApplication.java:164) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_73]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_73]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_73]
	at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_73]

Upgrade GoogleStorageResource to WritableResource

Implement ApiFuture -> ListenableFuture adapter for PubSubTemplate's send()

Currently, PubSubTemplate.send() returns a String with PubsubMessage's ID. We block the call to publish() and, ideally, we'd return a future instead.

We should implement a PubSub ApiFuture adapter to Spring's ListenableFuture, so the user doesn't have to use anything PubSub.

Refactor Pubsub* to PubSub* (revert #56)

Based on discussions with the Cloud Pub/Sub team, I submitted an issue on googleapis to have the PubSub proto refactored to PubSub instead of Pubsub. That probably isn't going to happen anytime soon due to all the dependencies, given this code was out there for 2 years now. However we can stop the pattern propagating and follow the style guide for the correct camel case.
note: this would be essentially the reversion of #56

Investigate metadata to correlate utilization

The idea is to provide a default header in our PubSubMessageTemplate that could be use to track utilization. Something on the same aspects as the Agent header of HTTP.

Let's take this as a Spike to verify first the feasibility of this approach

google-auth-library-credentials version collision in dependency tree

The spring-cloud-gcp-starter-pubsub 1.0.0.BUILD-SNAPSHOT artifact resolves differently in Maven and Gradle (works well in Gradle and breaks in Maven).

The correct version currently seems to be 0.7.0 of google-library-credentials:

        <dependency>
            <groupId>com.google.auth</groupId>
            <artifactId>google-auth-library-credentials</artifactId>
            <version>0.7.0</version>
        </dependency>

The maven and gradle dependency resolvers resolve the tree in different order and when the maven one finds the 0.4.0 version of google-authlibrary-credentials (pulled in by io.grpc:grpc-auth:jar:1.4.0:compile). 0.4.0 causes java.lang.ClassNotFoundException: com.google.auth.ServiceAccountSigner as mentioned here

See the partial dependency tree dumps below (left is maven right is gradle):

[INFO] +- org.springframework.cloud:spring-cloud-gcp-starter-pubsub:jar:1.0.0.BUILD-SNAPSHOT:compile                                    +--- org.springframework.cloud:spring-cloud-gcp-starter-pubsub:1.0.0.BUILD-SNAPSHOT
[INFO] |  +- org.springframework.cloud:spring-cloud-gcp-starter-core:jar:1.0.0.BUILD-SNAPSHOT:compile                                   |    +--- org.springframework.cloud:spring-cloud-gcp-starter-core:1.0.0.BUILD-SNAPSHOT
[INFO] |  |  \- org.springframework.cloud:spring-cloud-gcp-core:jar:1.0.0.BUILD-SNAPSHOT:compile                                        |    |    +--- org.springframework.cloud:spring-cloud-gcp-core:1.0.0.BUILD-SNAPSHOT
[INFO] |  +- org.springframework.cloud:spring-cloud-gcp-pubsub:jar:1.0.0.BUILD-SNAPSHOT:compile                                         |    |    |    +--- com.google.cloud:google-cloud-core:1.2.3
[INFO] |  |  \- org.springframework:spring-messaging:jar:4.3.8.RELEASE:compile                                                          |    |    |    |    +--- com.google.guava:guava:20.0
[INFO] |  +- com.google.cloud:google-cloud-pubsub:jar:0.20.1-beta:compile                                                               |    |    |    |    +--- joda-time:joda-time:2.9.2 -> 2.9.9
[INFO] |  |  +- io.netty:netty-tcnative-boringssl-static:jar:2.0.3.Final:compile                                                        |    |    |    |    +--- org.json:json:20160810 -> 20140107
[INFO] |  |  +- com.google.cloud:google-cloud-core:jar:1.2.1:compile                                                                    |    |    |    |    +--- com.google.api:api-common:1.1.0
[INFO] |  |  |  +- com.google.guava:guava:jar:20.0:compile                                                                              |    |    |    |    |    +--- com.google.code.findbugs:jsr305:3.0.0
[INFO] |  |  |  +- joda-time:joda-time:jar:2.9.9:compile                                                                                |    |    |    |    |    \--- com.google.guava:guava:19.0 -> 20.0
[INFO] |  |  |  +- org.json:json:jar:20140107:compile                                                                                   |    |    |    |    +--- com.google.api:gax:1.4.2
[INFO] |  |  |  +- com.google.api:api-common:jar:1.1.0:compile                                                                          |    |    |    |    |    +--- com.google.auto.value:auto-value:1.2
[INFO] |  |  |  |  \- com.google.code.findbugs:jsr305:jar:3.0.0:compile                                                                 |    |    |    |    |    +--- com.google.guava:guava:20.0
[INFO] |  |  |  +- com.google.api:gax:jar:1.4.1:compile                                                                                 |    |    |    |    |    +--- com.google.auth:google-auth-library-oauth2-http:0.7.0
[INFO] |  |  |  |  +- com.google.auto.value:auto-value:jar:1.2:compile                                                                  |    |    |    |    |    |    +--- com.google.auth:google-auth-library-credentials:0.7.0
[INFO] |  |  |  |  \- org.threeten:threetenbp:jar:1.3.3:compile                                                                         |    |    |    |    |    |    +--- com.google.http-client:google-http-client:1.19.0 -> 1.21.0
[INFO] |  |  |  +- com.google.protobuf:protobuf-java-util:jar:3.3.0:compile                                                             |    |    |    |    |    |    |    +--- com.google.code.findbugs:jsr305:1.3.9 -> 3.0.0
[INFO] |  |  |  |  \- com.google.code.gson:gson:jar:2.8.0:compile                                                                       |    |    |    |    |    |    |    \--- org.apache.httpcomponents:httpclient:4.0.1 -> 4.5.3
[INFO] |  |  |  +- com.google.api.grpc:proto-google-common-protos:jar:0.1.12:compile                                                    |    |    |    |    |    |    |         +--- org.apache.httpcomponents:httpcore:4.4.6
[INFO] |  |  |  \- com.google.api.grpc:proto-google-iam-v1:jar:0.1.12:compile                                                           |    |    |    |    |    |    |         +--- commons-logging:commons-logging:1.2
[INFO] |  |  +- com.google.cloud:google-cloud-core-grpc:jar:1.2.1:compile                                                               |    |    |    |    |    |    |         \--- commons-codec:commons-codec:1.9 -> 1.10
[INFO] |  |  |  +- com.google.protobuf:protobuf-java:jar:3.3.0:compile                                                                  |    |    |    |    |    |    +--- com.google.http-client:google-http-client-jackson2:1.19.0 -> 1.21.0
[INFO] |  |  |  +- io.grpc:grpc-protobuf:jar:1.4.0:compile                                                                              |    |    |    |    |    |    |    +--- com.google.http-client:google-http-client:1.21.0 (*)
[INFO] |  |  |  |  \- io.grpc:grpc-protobuf-lite:jar:1.4.0:compile                                                                      |    |    |    |    |    |    |    \--- com.fasterxml.jackson.core:jackson-core:2.1.3 -> 2.8.8
[INFO] |  |  |  +- io.grpc:grpc-context:jar:1.4.0:compile                                                                               |    |    |    |    |    |    \--- com.google.guava:guava:19.0 -> 20.0
[INFO] |  |  |  \- com.google.api:gax-grpc:jar:0.21.1:compile                                                                           |    |    |    |    |    +--- com.google.api:api-common:1.1.0 (*)
[INFO] |  |  +- com.google.api.grpc:proto-google-cloud-pubsub-v1:jar:0.1.12:compile                                                     |    |    |    |    |    +--- org.threeten:threetenbp:1.3.3
[INFO] |  |  +- com.google.api.grpc:grpc-google-cloud-pubsub-v1:jar:0.1.12:compile                                                      |    |    |    |    |    \--- com.google.code.findbugs:jsr305:3.0.0
[INFO] |  |  +- io.grpc:grpc-netty:jar:1.4.0:compile                                                                                    |    |    |    |    +--- com.google.protobuf:protobuf-java-util:3.3.0 -> 3.3.1
[INFO] |  |  |  +- io.grpc:grpc-core:jar:1.4.0:compile (version selected from constraint [1.4.0,1.4.0])                                 |    |    |    |    |    +--- com.google.protobuf:protobuf-java:3.3.1
[INFO] |  |  |  |  +- com.google.errorprone:error_prone_annotations:jar:2.0.19:compile                                                  |    |    |    |    |    +--- com.google.guava:guava:19.0 -> 20.0
[INFO] |  |  |  |  \- com.google.instrumentation:instrumentation-api:jar:0.4.2:compile                                                  |    |    |    |    |    \--- com.google.code.gson:gson:2.7 -> 2.8.0
[INFO] |  |  |  +- io.netty:netty-codec-http2:jar:4.1.11.Final:compile (version selected from constraint [4.1.11.Final,4.1.11.Final])   |    |    |    |    +--- com.google.api.grpc:proto-google-common-protos:0.1.13
[INFO] |  |  |  |  +- io.netty:netty-codec-http:jar:4.1.11.Final:compile                                                                |    |    |    |    |    +--- com.google.protobuf:protobuf-java:3.3.0 -> 3.3.1
[INFO] |  |  |  |  |  \- io.netty:netty-codec:jar:4.1.11.Final:compile                                                                  |    |    |    |    |    \--- com.google.api:api-common:1.1.0 (*)
[INFO] |  |  |  |  \- io.netty:netty-handler:jar:4.1.11.Final:compile                                                                   |    |    |    |    \--- com.google.api.grpc:proto-google-iam-v1:0.1.13
[INFO] |  |  |  |     \- io.netty:netty-buffer:jar:4.1.11.Final:compile                                                                 |    |    |    |         +--- com.google.protobuf:protobuf-java:3.3.0 -> 3.3.1
[INFO] |  |  |  |        \- io.netty:netty-common:jar:4.1.11.Final:compile                                                              |    |    |    |         +--- com.google.api:api-common:1.1.0 (*)
[INFO] |  |  |  \- io.netty:netty-handler-proxy:jar:4.1.11.Final:compile                                                                |    |    |    |         \--- com.google.api.grpc:proto-google-common-protos:0.1.13 (*)
[INFO] |  |  |     +- io.netty:netty-transport:jar:4.1.11.Final:compile                                                                 |    |    |    \--- org.slf4j:slf4j-api:1.7.25
[INFO] |  |  |     |  \- io.netty:netty-resolver:jar:4.1.11.Final:compile                                                               |    |    +--- com.google.cloud:google-cloud-pubsub:0.20.1-beta
[INFO] |  |  |     \- io.netty:netty-codec-socks:jar:4.1.11.Final:compile                                                               |    |    |    +--- io.netty:netty-tcnative-boringssl-static:2.0.3.Final
[INFO] |  |  +- io.grpc:grpc-stub:jar:1.4.0:compile                                                                                     |    |    |    +--- com.google.cloud:google-cloud-core:1.2.1 -> 1.2.3 (*)
[INFO] |  |  \- io.grpc:grpc-auth:jar:1.4.0:compile                                                                                     |    |    |    +--- com.google.cloud:google-cloud-core-grpc:1.2.1
[INFO] |  |     \- com.google.auth:google-auth-library-credentials:jar:0.4.0:compile                                                    |    |    |    |    +--- com.google.cloud:google-cloud-core:1.2.1 -> 1.2.3 (*)
[INFO] |  +- com.google.cloud:google-cloud-storage:jar:1.2.1:compile                                                                    |    |    |    |    +--- com.google.guava:guava:20.0
[INFO] |  |  +- com.google.cloud:google-cloud-core-http:jar:1.2.1:compile                                                               |    |    |    |    +--- com.google.protobuf:protobuf-java:3.3.0 -> 3.3.1
[INFO] |  |  |  +- com.google.auth:google-auth-library-oauth2-http:jar:0.7.0:compile                                                    |    |    |    |    +--- com.google.protobuf:protobuf-java-util:3.3.0 -> 3.3.1 (*)
[INFO] |  |  |  |  \- com.google.http-client:google-http-client-jackson2:jar:1.19.0:compile                                             |    |    |    |    +--- io.grpc:grpc-protobuf:1.4.0
[INFO] |  |  |  +- com.google.http-client:google-http-client:jar:1.21.0:compile                                                         |    |    |    |    |    +--- io.grpc:grpc-core:1.4.0
[INFO] |  |  |  |  \- org.apache.httpcomponents:httpclient:jar:4.5.3:compile                                                            |    |    |    |    |    |    +--- com.google.guava:guava:19.0 -> 20.0
[INFO] |  |  |  |     +- org.apache.httpcomponents:httpcore:jar:4.4.6:compile                                                           |    |    |    |    |    |    +--- com.google.errorprone:error_prone_annotations:2.0.19
[INFO] |  |  |  |     \- commons-codec:commons-codec:jar:1.10:compile                                                                   |    |    |    |    |    |    +--- com.google.code.findbugs:jsr305:3.0.0
[INFO] |  |  |  +- com.google.oauth-client:google-oauth-client:jar:1.21.0:compile                                                       |    |    |    |    |    |    +--- io.grpc:grpc-context:1.4.0
[INFO] |  |  |  +- com.google.api-client:google-api-client:jar:1.21.0:compile                                                           |    |    |    |    |    |    \--- com.google.instrumentation:instrumentation-api:0.4.2

Optimize GoogleStorageResource

The blob property must be volatile.
The resolve() method should not be synchronized from the first row.
We can use " Double-Checked Locking" pattern do not block all the threads if blob is already initialized:

  class Foo {
        private volatile Helper helper = null;
        public Helper getHelper() {
            if (helper == null) {
                synchronized(this) {
                    if (helper == null)
                        helper = new Helper();
                }
            }
            return helper;
        }
    }

https://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html

Replace ChannelProvider.Builder.setCredentialsProvider by new method

setCredentialsProvider is deprecated on google-cloud-java 0.20.1-alpha and there is a new way to provide credentials.

Create module for interaction with Google Storage

Provide a module to interact with Google Storage
The minimum requirement is to provide a Resource resolver to spring, so users could inject resources using something like : gs://<bucket_name>/<object_name>

Use CompositeMessageConverter in PubSubTemplate

There have been suggestions to chain MessageConverters in PubSubTemplate, e.g., through the use of a CompositeMessageConverter.

Need to look more deeply into this, including how it's done in other parts of Spring.

Allow ExecutorProvider to be passed in to PubSubTemplate

In #50, some suggested polishing changes surfaced a bigger issue. We might want to either use the default ExecutorProvider (with 4 threads by default) or, instead, allow the user to specify their own ExecutorProvider implementation.

We should look into injecting the ExecutorProvider into the PubSubTemplate which, right now, isn't possible in SI, since PubSubMessageHandler uses new PubSubTemplate() instead of injecting it.

Another issue is that re-using the same ExecutorProvider does not guarantee that only one Executor is generated, thereby reducing the number of created threads, which was the motivation behind the reuse.

Create a PubSubAdmin utility

Much like we have today with RabbitMQ, it would be nice to extract all the admin stuff from pubsub into a separate class.

One of the main reasons, besides good separation of concerns, is that we could use it to create topics from the storage module when users decide to enable notification from a bucket.

Add Continuous Integration to GitHub repo

We've been using self hosted Jenkins in other neighbour projects and I think it's been good so far.

Refactor project modules

We should refactor the project to allow addition of the spring-integration-gcp module as well as the starters.

We will probably end with:

[Library modules]

spring-cloud-gcp-core
spring-cloud-gcp-pubsub
spring-cloud-gcp-storage
spring-cloud-gcp-spanner

[Integration module]

spring-integration-gcp (optional dependencies to all modules above)

[Starters modules]

spring-cloud-gcp-starters
- spring-cloud-gcp-starter-pubsub
- spring-cloud-gcp-starter-storage
- spring-cloud-gcp-starter-sql
- spring-cloud-gcp-starter-spanner

Provide ACK control

Spring Messaging in general has the notion of a MessageListenerContainer, which allows configuration of different settings such as ACK mode, concurrent listeners.

We need to add same behavior here not only to be consistent with the Spring ecosystem, but to allow our users to control those parameters.

As usual, let's use the spring-kafka project (https://github.com/spring-projects/spring-kafka/tree/master/spring-kafka/src/main/java/org/springframework/kafka/listener) as source of inspiration, since it's a new take on a well stablished concept

Investigate and add missing unit tests

Now that we have the project base and some code already in, we should look into missing unit tests and add them as soon as possible.

Create basic project structure with readme and poms

Add sample application for PubSub Channel Adapter

Maybe Storage Resource Abstraction as well.

Change GCPProperties.jsonKeyFile type to Resource

It should probably also be renamed to something else, since JSON isn't the only format supported by Google's OAuth2 credentials.

org.springframework.integration.gcp.outbound.PubsubMessageHandler swallows errors on published messages

The following line in org.springframework.integration.gcp.outbound.PubsubMessageHandler should be a blocking call to be able to determine whether the returned listenableFuture failed or succeeded:

    protected void handleMessageInternal(Message<?> message) throws Exception {
        this.pubsubTemplate.send(this.topic, message); // this fails silently if e.g. a topic is not defined
    }

This could be just a simple .get() call, or we can even have a debug log which would print out the result in case of success.

Optionally we could even take into account timeout configuration?

Sanitize PubsubMessage headers

Currently, the SI-generated headers, like ID and timestamp, are being preserved on message conversion (Spring to PubsubMessage).

We should remove those messages on conversion, as well as any GcpHeaders, while at the same time, providing some means of preserving those headers if the users wants.

More details here.

CredentialsAutoConfiguration: use Resource.getInputStream() directly

Right now we have a code:

return GoogleCredentials.fromStream(
					new FileInputStream(resourceLoader.getResource(
							this.environment.getProperty(AUTH_LOCATION_KEY)).getFile()));

Where it doesn't not make sense to try to get file and wrap it into FileInputStream when we can use Resource.getInputStream() directly.

OTOH not all Resource implementations provide getFile(). I can use something like ByteArrayResource to load credentials from my local DB, for example.

Create project ID and GcpProject configuration provider

On a Spring Boot scenario, it would be nice to have things like the GCP project ID injected as a String bean, as well as a potential GcpProject or even GcpConfiguration @ConfigurationProperties object.

This would be useful even in non Spring Boot scenarios, like SI or even plain Spring Framework.

Start google-cloud-gcp-pubsub

Starter project to deal with MessaConverters, ResourceManagement, MessagingTemplate, MessageContainers.
Making the bridge between spring-messaging and pubsub

Provide auto/manual acknowledgement mode

Right now, we're sending PubSub's AckReplyConsumer back to the user so they can ack/nack the message.
We should provide the option to ack messages automatically, and use a sensible default.

Fix dependency hell

Right now dependency management is very chaotic. Depending on the google-cloud-java is a problem for modules that really do not depend on all the libs.

Just to make the project build, right now all projects depend on google-cloud-java which is an abuse of dependencies.

Enhance the PubsubTemplate

This is more of a placeholder for whomever is going to work in this story. Just make sure we have a good implementation with reasonable defaults for users to springify their pubsub experience ;)

Add Cloud SQL Boot starter

Still thinking what this will entail.

Setup GitHub Pages for Project Page

Add starter module to inject GoogleCredentials into application context

The basis for any interaction with google libs is it's credentials object being available. There are a handful of ways to bootstrap it.
This module should provide a boot starter that will bootstrap a bean of type Credential and will use Conditinal logic to determine what type of Credential it will create

Change Spring Integration module group

The SI module is currently a child of the parent spring-cloud pom. We need to look in a way to make it more consistent with other SI modules and probably let it live on it's own pom.

Here's some things to keep in mind:

Doing this and leaving the module on this repo will cause issues on build process, as it would not be built with mvn commands
We will need a separate BOM to make sure that we are pulling and syncing the right libraries from spring-cloud-gcp

Add Maven wrapper to the project to avoid confused in different target developers evnironments

PubsubInboundChannelAdapter swallows error when connected to non-existent subscription

Currently if I connect a PubsubInboundChannelAdapter to a non-existent subscription, it silently fails.
We could change this behaviour by changing this line:

    protected void doStart() {
        super.doStart();
        this.subscriber = this.subscriberFactory.getSubscriber(this.subscriptionName, this::receiveMessage);
        this.subscriber.startAsync(); // <---- this fails silently. 
    }

We could add an .awaitRunning() to ensure that when the subscriber started that it is actually running.

Support PubSub topic resolution from message header

Header would have precedence over PubSubTemplate's topic field.

Some good examples are the Kafka and Kinesis adapters:
https://github.com/spring-projects/spring-integration-aws/blob/master/src/main/java/org/springframework/integration/aws/outbound/KinesisMessageHandler.java#L93
https://github.com/spring-projects/spring-integration-kafka/blob/master/src/main/java/org/springframework/integration/kafka/outbound/KafkaProducerMessageHandler.java#L147

More discussion here.

Spring Boot apps using Pubsub channel adapters hang on shutdown

I noticed this happens when terminating my toy app. I suspect the delays are taking place at resource cleanup, more specifically, terminating connections to Google Cloud Pub/Sub.

Just leaving it here for future reference. We would want to get to the bottom of it before any alpha release.

Add EventDriven Inbound Storage Source

The AbstractRemoteFileStreamingMessageSource follows a polling mechanism to fetch changed data on the remote storage.
Google Storage supports notifications via PubSub. We should provide a event driven approach that can listen for messages on the specified topic and then fetch the changed files

Reconsider to move subscriber instantiation outside of the PubSubInboundChannelAdapter.start()

Right now we get a new Subscriber in the PubSubInboundChannelAdapter.start() each time we stop()/start() the channel adapter.

I'm pretty fine to have it as a single instance during the whole PubSubInboundChannelAdapter lifecycle.
Therefore Subscriber.defaultBuilder() should be done from the onInit().

Of course, that should be done only if Subscriber can be stopped and started again at run time.

Create a PubSubException class that descends from NestedRuntimeException and make sure we are using it across the PubSubTemplate, and the Message channel Adapters