Forward logs to Discord

[Zabuzard]

Overview

This is a convenience replacement for the (broken/deactivated) Logviewer project.

It forwards all logs to a Discord channel, via webhooks.

Info/Error channel

The day to day routine will be that we want to be notified when an error/warning happened, but not for info logs. Therefore, we set up 2 channels with separate webhooks. One for errors, one for infos:

Now, users can mute one channel and keep notifications on for the other.

Security

Note that logs can contain sensitive information (for example when banning an user). Therefore, a new log marker LogMarkers.SENSITIVE has been added. Logs with that marker are not forwarded to Discord. All existing logs have been checked and adjusted. Looks something like this:

logger.warn(LogMarkers.SENSITIVE, "Banned user {} for reason: {}", user, reason);

Details

Queue

The implementation is relatively straightforward, but has some non trivial complexity. In a nutshell, it buffers all incoming logs in a PriorityQueue (ordered on the timestamp to ensure correct log order). The queue has a max size of 10_000 logs and ideally is never hit in practice (this is to protect RAM, in case).

The queue is then processed each 5 seconds with a ScheduledExecutorService. The service then polls and sends a maximum of 10 logs in a batch request to Discord.

Failures

If the request fails, the logs are put back into the queue. If a batch fails 3 times, it is discarded to not entirely block the whole mechanism forever.

Rate limitting

When we send too much, Discord hits us with rate limits (429 http status). When this happens, we extract the end of the limitation from the retry-after header and skip the ScheduledExecutorService calls until Instant.now() is after that time.

Logging the logger

The whole system also has logging/error reporting itself. Its logs all have a LogMarkers.NO_DISCORD though, to prevent that it forwards its own logs - which could lead to a potential infinite loop of spawning logs in an erroneous scenario.

Config

The config has been changed, add:

"logInfoChannelWebhook": "<put_your_webhook_here>", "logErrorChannelWebhook": "<put_your_webhook_here>"

Checklist

• Appender
• Add to config
• Configurable webhook
• Proper embeds
• Error handling
• Rate limitting / queue / buffer
• Split info/error channel
• Javadoc

[Zabuzard]

a week old, a semi approval. merging this

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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