Update Slack Plugin

[lingpri]

Description

The Slack Plugin need to be updated to work with the new notification/alerting system:

graylog-labs/graylog-plugin-slack#89

Why

We have paying customers (viasat) that make use of that and putting pressure on us to make this work again.

Broad Strokes

• build UI
• build back end
• local testing
• code refactoring ( eslint warning about stateless function, color picker, fix all or some of the todo's that bernd suggested )
• unit testing

Fine grained Tasks

• AddNotificationType causes guice error  #576
• Task - Unable to execute test notification #580
• write junit test for slackClient.java
• user doesn't need to configure the proxy server in the slack notification settings.
• setup tests to understand existing behavior before refactoring.
• transform EventNotificationModelData into Map<String, Object> and then manually add the additional attributes to the map.
• remove BacklogItemModelData and CustomMessageModelData
• change access modifier for getDummyContext to public  graylog2-server#9176

How to test this slack Plugin ?

slack notification is auto-triggered during an occurrence of an event definition (filter and aggregate on a search query)

Questions

1. what are some attributes , that a user needs to fill in to successfully test this functionality ?

color,webhookUrl,channel,customMessage,backlogItemMessage, userName,notifyChannel,linkNames,iconUrl,iconEmoji,graylogUrl,proxy

2. can this be tested without a web interface ?

3. what protocol do we use to test this plugin ? (SMTP,TCP, Http).

4. is the reminder an alert ?

5. can I assume the email notification works ? yes.

6. how do i test the email notification in graylog?
   https://community.graylog.org/t/how-to-send-email-alerts-using-gmail/4103

7. where do i find the information to test my gmail email ?
   https://www.gmass.co/blog/gmail-smtp/

8. which graylog ui component, should I use for each of the attribute in question 1?
   Refer : https://github.com/graylog-labs/graylog-plugin-slack

9. what is the difference between okhttpclient vs httpclient ?
   https://square.github.io/okhttp/recipes/
   https://openjdk.java.net/groups/net/httpclient/recipes.html#proxy

10. Test webhook url : https://hooks.slack.com/services/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

11. curl command : curl -X POST -H 'Content-type: application/json' --data '{"text":"Hello, World!"}' https://hooks.slack.com/services/xxx/xxx/xxxxx678

Ref :

http://docs.graylog.org/en/3.1/pages/streams/alerts.html
https://api.slack.com/messaging/webhooks

Reference

https://github.com/sportalliance/graylog-plugin-slack-notification
Graylog2/graylog2-server#8893

[lingpri]

Issue transferred from https://github.com/Graylog2/graylog-plugin-enterprise/issues/1217

[lingpri]

[bud1979]

Looking good. We need to add back in the field of "Backlog Messages Size", so we can limit how many logs we are attaching the alert going to slack. We would want this separate from the Alert definitions backlog setting, with the Slack Setting over-riding the alert setting. In case the Alert is set at 50 Messages, but you really only want to send 3 messages for brevity to slack.

Also need to make sure that is noted below the field for clarity that the Slack setting over-rides the alert setting.

Lennart said this field was not in the code, so we need to make sure it is in working order, with current test we could set this to 1 and enable the rule to fire.