botMessage handler in Assistant middleware does not work when other event listeners do not exist

[rbioteau]

When implementing the following example provided in the documentation an NPE prevent the proper execution of the use case.

App app = new App(AppConfig.builder()
  .singleTeamBotToken(System.getenv("SLACK_BOT_TOKEN"))
  .ignoringSelfAssistantMessageEventsEnabled(false)
  .build());

Assistant assistant = new Assistant(app.executorService());

assistant.threadStarted((req, ctx) -> {
  try {
    ctx.say(r -> r
      .text("Hi, how can I help you today?")
      .blocks(Arrays.asList(
        section(s -> s.text(plainText("Hi, how I can I help you today?"))),
        actions(a -> a.elements(Collections.singletonList(
          button(b -> b.actionId("assistant-generate-numbers").text(plainText("Generate numbers")))
        )))
      ))
    );
  } catch (Exception e) {
    ctx.logger.error("Failed to handle assistant thread started event: {e}", e);
  }
});

app.blockAction("assistant-generate-numbers", (req, ctx) -> {
  app.executorService().submit(() -> {
    Map<String, Object> eventPayload = new HashMap<>();
    eventPayload.put("num", 20);
    try {
      ctx.client().chatPostMessage(r -> r
        .channel(req.getPayload().getChannel().getId())
        .threadTs(req.getPayload().getMessage().getThreadTs())
        .text("OK, I will generate numbers for you!")
        .metadata(new Message.Metadata("assistant-generate-numbers", eventPayload))
      );
    } catch (Exception e) {
      ctx.logger.error("Failed to post a bot message: {e}", e);
    }
  });
  return ctx.ack();
});

assistant.botMessage((req, ctx) -> {
  if (req.getEvent().getMetadata() != null
    && req.getEvent().getMetadata().getEventType().equals("assistant-generate-numbers")) {
  try {
    ctx.setStatus("is typing...");
    Double num = (Double) req.getEvent().getMetadata().getEventPayload().get("num");
    Set<String> numbers = new HashSet<>();
    SecureRandom random = new SecureRandom();
    while (numbers.size() < num) {
      numbers.add(String.valueOf(random.nextInt(100)));
    }
    Thread.sleep(1000L);
    ctx.say(r -> r.text("Her you are: " + String.join(", ", numbers)));
  } catch (Exception e) {
    ctx.logger.error("Failed to handle assistant bot message event: {e}", e);
  }
  }
});

assistant.userMessage((req, ctx) -> {
  try {
    ctx.setStatus("is typing...");
    ctx.say(r -> r.text("Sorry, I couldn't understand your comment."));
  } catch (Exception e) {
    ctx.logger.error("Failed to handle assistant user message event: {e}", e);
    try {
      ctx.say(r -> r.text(":warning: Sorry, something went wrong during processing your request!"));
    } catch (Exception ee) {
      ctx.logger.error("Failed to inform the error to the end-user: {ee}", ee);
    }
  }
});

app.assistant(assistant);

In the above example we register a botMessage and a userMessage on the Assistant. However, when executing this simple app, these messages are never returned to my chat.

The problem occurs in the com.slack.api.bolt.util.EventsApiPayloadParser#buildEventPayload method where my eventClass is null. It seems to rely on a cache to retrieve a given Event class for an event name. The is cache is empty in my case and I need to explicitly call EventsApiPayloadParser.getEventTypeAndSubtype(MessageEvent.class) in my code to initialize the map.

Reproducible in:

[INFO] com.bonitasoft:my-slackbot:jar:0.0.1-SNAPSHOT
[INFO] +- org.springframework.boot:spring-boot-starter-web:jar:3.4.1:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter:jar:3.4.1:compile
[INFO] |  |  +- org.springframework.boot:spring-boot:jar:3.4.1:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-autoconfigure:jar:3.4.1:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-starter-logging:jar:3.4.1:compile
[INFO] |  |  |  +- ch.qos.logback:logback-classic:jar:1.5.12:compile
[INFO] |  |  |  |  \- ch.qos.logback:logback-core:jar:1.5.12:compile
[INFO] |  |  |  +- org.apache.logging.log4j:log4j-to-slf4j:jar:2.24.3:compile
[INFO] |  |  |  |  \- org.apache.logging.log4j:log4j-api:jar:2.24.3:compile
[INFO] |  |  |  \- org.slf4j:jul-to-slf4j:jar:2.0.16:compile
[INFO] |  |  +- jakarta.annotation:jakarta.annotation-api:jar:2.1.1:compile
[INFO] |  |  \- org.yaml:snakeyaml:jar:2.3:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter-json:jar:3.4.1:compile
[INFO] |  |  +- com.fasterxml.jackson.core:jackson-databind:jar:2.18.2:compile
[INFO] |  |  |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.18.2:compile
[INFO] |  |  |  \- com.fasterxml.jackson.core:jackson-core:jar:2.18.2:compile
[INFO] |  |  +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.18.2:compile
[INFO] |  |  +- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.18.2:compile
[INFO] |  |  \- com.fasterxml.jackson.module:jackson-module-parameter-names:jar:2.18.2:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter-tomcat:jar:3.4.1:compile
[INFO] |  |  +- org.apache.tomcat.embed:tomcat-embed-core:jar:10.1.34:compile
[INFO] |  |  +- org.apache.tomcat.embed:tomcat-embed-el:jar:10.1.34:compile
[INFO] |  |  \- org.apache.tomcat.embed:tomcat-embed-websocket:jar:10.1.34:compile
[INFO] |  +- org.springframework:spring-web:jar:6.2.1:compile
[INFO] |  |  +- org.springframework:spring-beans:jar:6.2.1:compile
[INFO] |  |  \- io.micrometer:micrometer-observation:jar:1.14.2:compile
[INFO] |  |     \- io.micrometer:micrometer-commons:jar:1.14.2:compile
[INFO] |  \- org.springframework:spring-webmvc:jar:6.2.1:compile
[INFO] |     +- org.springframework:spring-aop:jar:6.2.1:compile
[INFO] |     +- org.springframework:spring-context:jar:6.2.1:compile
[INFO] |     \- org.springframework:spring-expression:jar:6.2.1:compile
[INFO] +- com.slack.api:bolt-jakarta-servlet:jar:1.45.0:compile
[INFO] |  +- com.slack.api:slack-api-model:jar:1.45.0:compile
[INFO] |  |  \- com.google.code.gson:gson:jar:2.11.0:compile
[INFO] |  |     \- com.google.errorprone:error_prone_annotations:jar:2.27.0:compile
[INFO] |  +- com.slack.api:slack-api-client:jar:1.45.0:compile
[INFO] |  |  +- com.squareup.okhttp3:okhttp:jar:4.12.0:compile
[INFO] |  |  |  +- com.squareup.okio:okio:jar:3.6.0:compile
[INFO] |  |  |  |  \- com.squareup.okio:okio-jvm:jar:3.6.0:compile
[INFO] |  |  |  |     \- org.jetbrains.kotlin:kotlin-stdlib-common:jar:1.9.25:compile
[INFO] |  |  |  \- org.jetbrains.kotlin:kotlin-stdlib-jdk8:jar:1.9.25:compile
[INFO] |  |  |     +- org.jetbrains.kotlin:kotlin-stdlib:jar:1.9.25:compile
[INFO] |  |  |     |  \- org.jetbrains:annotations:jar:13.0:compile
[INFO] |  |  |     \- org.jetbrains.kotlin:kotlin-stdlib-jdk7:jar:1.9.25:compile
[INFO] |  |  \- org.slf4j:slf4j-api:jar:2.0.16:compile
[INFO] |  +- com.slack.api:slack-app-backend:jar:1.45.0:compile
[INFO] |  \- com.slack.api:bolt:jar:1.45.0:compile
[INFO] |     \- org.apache.commons:commons-text:jar:1.13.0:compile
[INFO] |        \- org.apache.commons:commons-lang3:jar:3.17.0:compile
[INFO] \- org.springframework.boot:spring-boot-starter-test:jar:3.4.1:test
[INFO]    +- org.springframework.boot:spring-boot-test:jar:3.4.1:test
[INFO]    +- org.springframework.boot:spring-boot-test-autoconfigure:jar:3.4.1:test
[INFO]    +- com.jayway.jsonpath:json-path:jar:2.9.0:test
[INFO]    +- jakarta.xml.bind:jakarta.xml.bind-api:jar:4.0.2:test
[INFO]    |  \- jakarta.activation:jakarta.activation-api:jar:2.1.3:test
[INFO]    +- net.minidev:json-smart:jar:2.5.1:test
[INFO]    |  \- net.minidev:accessors-smart:jar:2.5.1:test
[INFO]    |     \- org.ow2.asm:asm:jar:9.6:test
[INFO]    +- org.assertj:assertj-core:jar:3.26.3:test
[INFO]    |  \- net.bytebuddy:byte-buddy:jar:1.15.11:test
[INFO]    +- org.awaitility:awaitility:jar:4.2.2:test
[INFO]    +- org.hamcrest:hamcrest:jar:2.2:test
[INFO]    +- org.junit.jupiter:junit-jupiter:jar:5.11.4:test
[INFO]    |  +- org.junit.jupiter:junit-jupiter-api:jar:5.11.4:test
[INFO]    |  |  +- org.opentest4j:opentest4j:jar:1.3.0:test
[INFO]    |  |  +- org.junit.platform:junit-platform-commons:jar:1.11.4:test
[INFO]    |  |  \- org.apiguardian:apiguardian-api:jar:1.1.2:test
[INFO]    |  +- org.junit.jupiter:junit-jupiter-params:jar:5.11.4:test
[INFO]    |  \- org.junit.jupiter:junit-jupiter-engine:jar:5.11.4:test
[INFO]    |     \- org.junit.platform:junit-platform-engine:jar:1.11.4:test
[INFO]    +- org.mockito:mockito-core:jar:5.14.2:test
[INFO]    |  +- net.bytebuddy:byte-buddy-agent:jar:1.15.11:test
[INFO]    |  \- org.objenesis:objenesis:jar:3.3:test
[INFO]    +- org.mockito:mockito-junit-jupiter:jar:5.14.2:test
[INFO]    +- org.skyscreamer:jsonassert:jar:1.5.3:test
[INFO]    |  \- com.vaadin.external.google:android-json:jar:0.0.20131108.vaadin1:test
[INFO]    +- org.springframework:spring-core:jar:6.2.1:compile
[INFO]    |  \- org.springframework:spring-jcl:jar:6.2.1:compile
[INFO]    +- org.springframework:spring-test:jar:6.2.1:test
[INFO]    \- org.xmlunit:xmlunit-core:jar:2.10.0:test

The Slack SDK version

[INFO] +- com.slack.api:bolt-jakarta-servlet:jar:1.45.0:compile
[INFO] | +- com.slack.api:slack-api-model:jar:1.45.0:compile
[INFO] | +- com.slack.api:slack-api-client:jar:1.45.0:compile
[INFO] | +- com.slack.api:slack-app-backend:jar:1.45.0:compile
[INFO] | - com.slack.api:bolt:jar:1.45.0:compile

Java Runtime version

openjdk version "21.0.4" 2024-07-16 LTS
OpenJDK Runtime Environment Temurin-21.0.4+7 (build 21.0.4+7-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.4+7 (build 21.0.4+7-LTS, mixed mode, sharing)

OS info

Distributor ID: Ubuntu
Description: Ubuntu 24.04.1 LTS
Release: 24.04
Codename: noble

Steps to reproduce:

Run the springboot example with the code sample for Agent & Assistant from the documentation, See snippet above.

Expected result:

The botMessage handler should be executed.

Actual result:

The botMessage handler is not executed due to a NPE when retrieving the botId in the Assistant#apply method.

Requirements

Please make sure if this topic is specific to this SDK. For general questions/issues about Slack API platform or its server-side, could you submit questions at https://my.slack.com/help/requests/new instead. 🙇

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you agree to those rules.

[seratch]

Hi @rbioteau, thanks for asking the question. I've checked the code snippet using Socket Mode and I couldn't reproduce the NPE you've faced.

One thing I am wonderfing is this error may be due to how you configure the Spring Boot app. As mentioned in this document page, bolt-java works properly only when using WebServiet + no additional request body parser in the Spring app: https://tools.slack.dev/java-slack-sdk/guides/supported-web-frameworks#spring-boot

If your Spring Boot app already follows the above guidance, could you share the whole project (as minimal working example) and the stacktrace you've got when the NPE occurs?

[rbioteau]

Thanks to take the time to have a look.

Here is a minimal reproducer.

I do not use Websocket, and the NPE is not logged (occurs in a FutureTask).

[seratch]

Thank you so much for reporting this issue. I just submitted a pull request #1415 resolving this issue. If the CI builds pass, I will release a patch version shortly.

[seratch]

@rbioteau Thanks again for taking the time to report this issue and we're sorry for the disruption. The latest version 1.45.1 should resolve the issue for you! https://github.com/slackapi/java-slack-sdk/releases/tag/v1.45.1