Provide the ability to run user-defined cron tasks

Mount individual shell scripts (with the `*.sh` extension) inside `/cron-scripts/` in the
container. The cron daemon will automatically run these scripts inside the Nextcloud
container for you. Write the scripts as if they will run in the Nextcloud container
itself.

Dockerfile

@@ -7,6 +7,7 @@ ENV NEXTCLOUD_PROJECT_NAME=
 ENV NEXTCLOUD_CRON_MINUTE_INTERVAL=15
 
 COPY scripts/*.sh /
+COPY scripts/cron-scripts /cron-scripts
 
 ENTRYPOINT ["/entrypoint.sh"]
 

README.md

@@ -67,13 +67,57 @@ is checked every interval of the health check. If any of these checks fail, it i
 container's health status will become *unhealthy*. In this case, you should restart the container.
 
 1. The `crond` process must be running.
-2. The Nextcloud container must be available and running. One important note here: When this
+1. The Nextcloud container must be available and running. One important note here: When this
    container starts up, it immediately searches for the container by name and remembers it by the
    container's ID. If for whatever reason the Nextcloud container changes in such a way that the ID
    is no longer valid, the health check would fail.
 
+# Customizing Cron Tasks
+
+This container provides the ability for you to run additional tasks inside the Nextcloud container
+in addition to the default `cron.php` task. To add your custom tasks, follow these steps:
+
+1. Write a shell script that runs the commands that will be part of your task. This shell script
+   must have the `.sh` extension. An example of the contents of such a script is below. As an
+   optional security measure, do not make this shell script executable. The contents of the file are
+   piped into `bash`, so the executable bit is not used.
+
+   ```sh
+   #!/usr/bin/env bash
+   php -f /var/www/html/cron.php
+   ```
+1. Mount this shell script inside the `/cron-scripts` directory. Here's an example if you're using
+   `docker-compose.yml`:
+
+   ```yml
+   services:
+     cron:
+       image: voidpointer/nextcloud-cronjob
+       volumes:
+       - ./my-scripts/do-something.sh:/cron-scripts/do-something.sh:ro
+   ```
+1. Recreate the container. Your script will now execute in the Nextcloud container at a regular
+   interval.
+
+## Notes
+
+* All cron task shell scripts run at the same interval defined by `NEXTCLOUD_CRON_MINUTE_INTERVAL`.
+* Modification of your own shell scripts on the host do not require that you restart/recreate the
+  container.
+
 # Debugging
 
 All logs from `crond` are configured to print to stdout, so you can monitor container logs (via
 `docker-compose logs -f`). This should allow you to make sure your cron job is working. You can also
-use the "Overview" page in Nextcloud Settings to see if the cron job is being run regularly.
+use the "Overview" page in Nextcloud Settings to see if the cron job is being run regularly. Here is
+an example of the logs you will see:
+
+```
+Started crond
+-------------------------------------------------------------
+ Executing Cron Tasks: Thu Dec  6 17:28:00 CST 2018
+-------------------------------------------------------------
+> Running Script: occ-preview-pre-generate.sh
+> Running Script: run_cron_php.sh
+> Done
+```

scripts/cron-scripts/run-cron-php.sh

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+php -f /var/www/html/cron.php

scripts/cron-tasks.sh

@@ -1,5 +1,17 @@
 #!/usr/bin/env bash
-set -ex
+set -e
 
-containerName="$1"
-docker exec "$containerName" php -f /var/www/html/cron.php
+echo "-------------------------------------------------------------"
+echo " Executing Cron Tasks: $(date)"
+echo "-------------------------------------------------------------"
+
+# Loop through all shell scripts and execute the contents of those scripts in the Nextcloud
+# container. It's done this way so that the user may mount more scripts to be executed in addition
+# to the default ones.
+cd /cron-scripts
+for script in *.sh; do
+    echo "> Running Script: $script"
+    docker exec -i "$1" bash < $script
+done
+
+echo "> Done"

scripts/entrypoint.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-set -ex
+set -e
 
 if [[ -z "$NEXTCLOUD_CONTAINER_NAME" ]]; then
     echo "NEXTCLOUD_CONTAINER_NAME is a required variable"