147 lines
4.0 KiB
Markdown
147 lines
4.0 KiB
Markdown
---
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title: Discord Webhooks via NixOS and Systemd Timers
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date: 2020-11-30
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series: howto
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tags:
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- nixos
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- discord
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- systemd
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---
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# Discord Webhooks via NixOS and Systemd Timers
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Recently I needed to set up a Discord message on a cronjob as a part of
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moderating a guild I've been in for years. I've done this before using
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[cronjobs](/blog/howto-automate-discord-webhook-cron-2018-03-29), however this
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time we will be using [NixOS](https://nixos.org/) and [systemd
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timers](https://wiki.archlinux.org/index.php/Systemd/Timers). Here's what you
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will need to follow along:
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- A machine running NixOS
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- A [Discord](https://discord.com/) account
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- A
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[webhook](https://support.discord.com/hc/en-us/articles/228383668-Intro-to-Webhooks)
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configured for a channel
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- A message you want to send to Discord
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[If you don't have moderation permissions in any guilds, make your own for
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testing! You will need the "Manage Webhooks" permission to create a
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webhook.](conversation://Mara/hacker)
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## Setting Up Timers
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systemd timers are like cronjobs, except they trigger systemd services instead
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of shell commands. For this example, let's create a daily webhook reminder to
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check on your Animal Crossing island at 9 am.
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Let's create the systemd service at the end of the machine's
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`configuration.nix`:
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```nix
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systemd.services.acnh-island-check-reminder = {
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serviceConfig.Type = "oneshot";
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script = ''
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MESSAGE="It's time to check on your island! Check those stonks!"
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WEBHOOK="${builtins.readFile /home/cadey/prefix/secrets/acnh-webhook-secret}"
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USERNAME="Domo"
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${pkgs.curl}/bin/curl \
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-X POST \
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-F "content=$MESSAGE" \
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-F "username=$USERNAME" \
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"$WEBHOOK"
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'';
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};
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```
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[This service is a <a href="https://stackoverflow.com/a/39050387">oneshot</a>
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unit, meaning systemd will launch this once and not expect it to always stay
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running.](conversation://Mara/hacker)
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Now let's create a timer for this service. We need to do the following:
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- Associate the timer with that service
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- Assign a schedule to the timer
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Add this to the end of your `configuration.nix`:
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```nix
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systemd.timers.acnh-island-check-reminder = {
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wantedBy = [ "timers.target" ];
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partOf = [ "acnh-island-check-reminder.service" ];
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timerConfig.OnCalendar = "TODO(Xe): this";
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};
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```
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Before we mentioned that we want to trigger this reminder every morning at 9 am.
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systemd timers specify their calendar config in the following format:
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```
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DayOfWeek Year-Month-Day Hour:Minute:Second
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```
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So for something that triggers every day at 9 AM, it would look like this:
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```
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*-*-* 8:00:00
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```
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[You can ignore the day of the week if it's not
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relevant!](conversation://Mara/hacker)
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So our final timer definition would look like this:
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```nix
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systemd.timers.acnh-island-check-reminder = {
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wantedBy = [ "timers.target" ];
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partOf = [ "acnh-island-check-reminder.service" ];
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timerConfig.OnCalendar = "*-*-* 8:00:00";
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};
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```
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## Deployment and Testing
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Now we can deploy this with `nixos-rebuild`:
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```console
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$ sudo nixos-rebuild switch
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```
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You should see a line that says something like this in the `nixos-rebuild`
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output:
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```
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starting the following units: acnh-island-check-reminder.timer
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```
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Let's test the service out using `systemctl`:
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```console
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$ sudo systemctl start acnh-island-check-reminder.service
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```
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And you should then see a message on Discord. If you don't see a message, check
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the logs using `journalctl`:
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```console
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$ journalctl -u acnh-island-check-reminder.service
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```
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If you see an error that looks like this:
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```
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curl: (26) Failed to open/read local data from file/application
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```
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This usually means that you tried to do a role or user mention at the beginning
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of the message and curl tried to interpret that as a file input. Add a word like
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"hey" at the beginning of the line to disable this behavior. See
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[here](https://stackoverflow.com/questions/6408904/send-request-to-curl-with-post-data-sourced-from-a-file)
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for more information.
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---
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Also happy December! My site has the [snow
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CSS](https://christine.website/blog/let-it-snow-2018-12-17) loaded for the
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month. Enjoy!
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