Slack Plugin Error Handling

[waab76]

As a Graylog engineer, I want to improve error handling in the Slack Notification plugin in order to better detect, report, and recover from errors.

Input Criteria

• [x] Slack notifications plugin works

Output Criteria

• [ ] SlackClient no longer uses EventNotificationExceptions
• [ ] SlackClient appropriately signals temporary/recoverable exceptions such as HTTP 5xx codes and network timeout errors
• [ ] SlackClient appropriately signals permanent/unrecoverable exceptions such as HTTP 4xx codes
• [ ] SlackEventNotification properly handles both temporary and permanent exceptions thrown by SlackClient by throwing temporary and permanent EventNotificationExceptions
• [ ] SlackEventNotification raises a UI notification when an permanent exception is encountered
• [ ] JUnit tests exist to validate behavior of SlackClient
• [ ] JUnit tests exist to validate behavior of SlackEventNotification

Tasks

• [ ] Update error handling in SlackClient
• [ ] Update JUnit tests for SlackClient
• [ ] Update error handling in SlackEventNotification
• [ ] Update JUnit tests for SlackEventNotification
• [ ] Manually verify behavior

[waab76]

Slack returns 429 for too many requests, need to consider how to handle that