Mock Lambda event server gets stuck on responses with large response sizes when using Jackson

[c-classen]

Describe the bug

When using the Lambda event server and requesting data from an endpoint, the HTTP response gets stuck after sending about 10KB for large responses.

Expected behavior

10 KB should be not issue. AWS Lambda supports up to 10 MB of response size.

Actual behavior

The response to the request never gets completed

How to Reproduce?

Reproducer: lambda-gets-stuck.zip

or

1. Go to https://code.quarkus.io/ and add AWS Lambda HTTP and REST Jackson.
2. Replace the content of the hello() method in GreetingResource with

   List<String> greetings = new ArrayList<>();
   for (int i = 0; i < 580; i++) {
       greetings.add("Hello World " + i);
   }
   return greetings;

3. Start the dev server and run curl localhost:8080/hello

It should just get stuck and never finish, although a lot of the response is displayed.

Output of uname -a or ver

Linux clemens-WAPP-Laptop 6.8.0-45-generic #45~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Sep 11 15:25:05 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

Output of java -version

openjdk version "21.0.2" 2024-01-16 LTS OpenJDK Runtime Environment Corretto-21.0.2.14.1 (build 21.0.2+14-LTS) OpenJDK 64-Bit Server VM Corretto-21.0.2.14.1 (build 21.0.2+14-LTS, mixed mode, sharing)

Quarkus version or git rev

3.16.3

Build tool (ie. output of mvnw --version or gradlew --version)

wrapperVersion=3.3.2

Additional information

It seems to me that the following factors need to come together to provoke this behavior:

1. Running the dev server: When deploying to AWS, it seems to work
2. Large response size:. Interestingly, reducing 580 to 570 will get it stuck earlier, but with 200, it works for me. Since there might be timing issues at play, this could vary and you might need to increase 580 to a sufficiently high number.
3. JSON serialization: Adding @Produces(MediaType.TEXT_PLAIN) causes the bug to disappear, even when using much higher upper bounds in the for loop such as 10_000.
4. Lambda HTTP Dependency: Commenting out the quarkus-amazon-lambda-http dependency in the pom.xml will also make the bug disappear.

[quarkus-bot]

/cc @geoand (jackson), @gsmet (jackson), @mariofusco (jackson), @matejvasek (amazon-lambda), @patriot1burke (amazon-lambda)

[c-classen]

@patriot1burke It would already help a lot if there was a configuration option to disable the mock Lambda event server when running the application in dev mode without having to remove the dependency to AWS Lambda HTTP.

[andrezimmermann]

If the type of response is set to something like @Produces(MediaType.TEXT_PLAIN)

    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public List<String> hello() {
        List<String> greetings = new ArrayList<>();
        for (int i = 0; i < 580; i++) {
            greetings.add("Hello World " + i);
        }
        return greetings;
    }

It will run correctly

I believe if there is no explicit content type, Quarkus will see the List<> and default to a Server Side Event response.
https://quarkus.io/guides/rest#server-sent-event-sse-support

Not sure how the Quarkus AWS Lambda HTTP implements it, but you need set the AWS Lambda itself as a "Streaming" response.
https://aws.amazon.com/blogs/compute/introducing-aws-lambda-response-streaming/
I'd assume that this feature is out of the scope of the Quarkus AWS Lambda HTTP

In any case, as good practice always annotate the controller's response types with @Produces to avoid the wrong default being used.

[c-classen]

@andrezimmermann Thank you for your help. I tried setting @Produces(MediaType.TEXT_PLAIN) and it did indeed complete the response without getting stuck.

However, I still want my endpoint to return JSON (and also have the spec generate accordingly and the Content-Type header set), so I would need to use @Produces(MediaType.APPLICATION_JSON). And when I set this instead, I still run into the same issue, even though a default to @Produces(MediaType.SERVER_SENT_EVENTS) as mentioned in the first link would not make sense to me when explicitly specifying @Produces(MediaType.APPLICATION_JSON).

Regarding the streaming response setting, please consider that the code runs fine on the actual AWS Lambda. It is just the Quarkus dev mode run locally that has the issue.

[geoand]

Is there a chance you can check with Quarkus main and see if the problem persists?
Asking because we made a fix to another issue that might be related to this.

[geoand]

@c-classen any chance you can check the above comment?

[c-classen]

@geoand Sorry, I had a lot to do and kind of forgot about this. I used the snapshot described in the link you provided and within my reproducer application, the issue stopped appearing, so thank you for fixing it!

Also thanks for providing the nightly snapshots and the guide to try them out. That was a lot easier than building Quarkus myself. Maybe you could put in a little hint that the settings.xml should go in the .m2 directory in the home directory. I know it is not hard to google, but it would just make it more convenient for people like me who usually only use Gradle.

[geoand]

Thanks a lot for the info @c-classen!

Would you like to contribute the settings.xml clarification you mention?