java-slack-sdk: Failing to parse request body when using along with Spring Boot 2.1

Reproducible in:

The Slack SDK version

Note: I’ve tried several versions of bolt/bolt-servlet between 1.0.0-1.2.0 inclusive and gotten the same behavior.

[INFO] +- com.slack.api:bolt:jar:1.1.5:compile
[INFO] |  +- com.slack.api:slack-api-model:jar:1.1.5:compile
[INFO] |  +- com.slack.api:slack-api-client:jar:1.1.5:compile
[INFO] |  \- com.slack.api:slack-app-backend:jar:1.1.5:compile
[INFO] +- com.slack.api:bolt-servlet:jar:1.1.5:compile

Java Runtime version

Java 8 SE 1.8.0_221

OS info

So far I have only tested this in local dev environments using ngrok to communicate with Slack. I don’t expect this is the cause of the problem, but just in case:

ProductName:	Mac OS X
ProductVersion:	10.14.6
BuildVersion:	18G95
Darwin Kernel Version 18.7.0: Tue Aug 20 16:57:14 PDT 2019; root:xnu-4903.271.2~2/RELEASE_X86_64

Steps to reproduce:

I am trying to do a slack command integration. The server receives the HTTP POST request from Slack that appears to contain all the correct information and in the correct format according to the API documentation, but my handler never actually gets executed.

Expected result:

My slash command handler defined below to get executed:

        app.command("/do-the-thing", (req, context) -> {
            
            SlashCommandPayload command = req.getPayload();
            
            slackMessageHandler.handleSlashCommand(command, context);
            
            return context.ack();
        });

Actual result:

The Slack Request parser receives an empty string as a body, and doesn’t know what to do with it. Bolt acknowledges the request with a 200 but doesn’t do anything because it doesn’t recognize the request as a slash command.

 WARN  c.s.api.bolt.util.SlackRequestParser - No request pattern detected for 

(blank, because the body given to the method is blank.)

I did some debugging and found that everything appears to be going fine until this line. The HttpServletRequest has the information in its reader, but this method fails to extract it. Ultimately, a blank String is sent as the body to SlackRequestParser.parse

Other notes

As an experiment, when I mock a mostly identical request to our URL where the only change is changing content-type Header to text/plain as opposed to x-www-form-urlencoded it works, or at least, the parser a) receives a body with actual content and b) recognizes the content as a slash command.

This issue is also unique to slash commands. I am able to successfully receive and process events pushed to our URL from the events API.

Our basic code structure:

//SlackBotApplication.java
@SpringBootApplication
@EnableConfigurationProperties
@ServletComponentScan
public class SlackBotApplication {
 
    public static void main(String[] args) {
        try {
            ConfigurableApplicationContext applicationContext = new SpringApplicationBuilder()
                    .sources(SlackBotApplication.class)
                    .run(args);
            Thread.currentThread().join();
        } catch (Exception e) {
            System.out.println("Something went wrong " + e.getMessage());
}
}        }
    }
 
//SlackBotController.java
@WebServlet("/slack/events")
public class SlackAppController extends SlackAppServlet {
    public SlackAppController(App app) {
        super(app);
    }
}
 
//SlackBotConfigs.java
@Configuration
public class SlackBotConfigs {
    
    ...
    
    @Bean
    public App initSlackApp(SlackMessageHandler slackMessageHandler) {
        
        AppConfig appConfig = new AppConfig();
        
        appConfig.setSigningSecret(retrieveConfigurations().getSigningSecret());
        appConfig.setSingleTeamBotToken(retrieveConfigurations().getSlackbotToken());
        
        App app = new App(appConfig);
        
        app.event(AppMentionEvent.class, (payload, ctx) ->  {
            // do some stuff
              return ctx.ack()
        });
 
      app.event(MessageBotEvent.class, (payload, ctx) ->  {
          // do some stuff
          return ctx.ack()
      });
  
      app.command("/do-the-thing", (req, context) -> {
            
          //Do some stuff. Note that this handler never gets executed as a result of the issues we are facing           
          return context.ack();
       });
   }
    ...
}