docs: added in-depth build explanation

docs/config.toml

@@ -37,7 +37,7 @@ enableGitInfo = true
   url = "https://rustybever.be/man/vieter/vieter.1.html"
   weight = 20
 [[menu.after]]
-  name = "Git"
+  name = "Vieter"
   url = "https://git.rustybever.be/vieter/vieter"
   weight = 30
 [[menu.after]]

docs/content/other/builds-in-depth.md

@@ -2,3 +2,80 @@
 
 For those interested, this page describes how the build system works
 internally.
+
+## Builder image
+
+Every cron daemon perodically creates a builder image that is then used as a
+base for all builds. This is done to prevent build containers having to pull
+down a bunch of updates when they update their system.
+
+The build container is created by running the following commands inside a
+container started from the image defined in `base_image`:
+
+```sh
+# Update repos & install required packages
+pacman -Syu --needed --noconfirm base-devel git
+# Add a non-root user to run makepkg
+groupadd -g 1000 builder
+useradd -mg builder builder
+# Make sure they can use sudo without a password
+echo 'builder ALL=(ALL) NOPASSWD: ALL' >> /etc/sudoers
+# Create the directory for the builds & make it writeable for the
+# build user
+mkdir /build
+chown -R builder:builder /build
+```
+
+This script updates the packages to their latest versions & creates a non-root
+user to use when running `makepkg`.
+
+This script is base64-encoded & passed to the container as an environment
+variable. The container's entrypoint is set to `/bin/sh -c` & its command
+argument to `echo $BUILD_SCRIPT | base64 -d | /bin/sh -e`, with the
+`BUILD_SCRIPT` environment variable containing the base64-encoded script.
+
+Once the container exits, a new Docker image is created from it. This image is
+then used as the base for any builds.
+
+## Running builds
+
+Each build has its own Docker container, using the builder image as its base.
+The same base64-based technique as above is used, just with a different script.
+To make the build logs more clear, each command is appended by an echo command
+printing the next command to stdout.
+
+Given the Git repository URL is `https://examplerepo.com` with branch `main`,
+the URL of the Vieter server is `https://example.com` and `vieter` is the
+repository we wish to publish to, we get the following script:
+
+```sh
+echo -e '+ echo -e '\''[vieter]\\nServer = https://example.com/$repo/$arch\\nSigLevel = Optional'\'' >> /etc/pacman.conf'
+echo -e '[vieter]\nServer = https://example.com/$repo/$arch\nSigLevel = Optional' >> /etc/pacman.conf
+echo -e '+ pacman -Syu --needed --noconfirm'
+pacman -Syu --needed --noconfirm
+echo -e '+ su builder'
+su builder
+echo -e '+ git clone --single-branch --depth 1 --branch main https://examplerepo.com repo'
+git clone --single-branch --depth 1 --branch main https://examplerepo.com repo
+echo -e '+ cd repo'
+cd repo
+echo -e '+ makepkg --nobuild --syncdeps --needed --noconfirm'
+makepkg --nobuild --syncdeps --needed --noconfirm
+echo -e '+ source PKGBUILD'
+source PKGBUILD
+echo -e '+ curl -s --head --fail https://example.com/vieter/x86_64/$pkgname-$pkgver-$pkgrel && exit 0'
+curl -s --head --fail https://example.com/vieter/x86_64/$pkgname-$pkgver-$pkgrel && exit 0
+echo -e '+ [ "$(id -u)" == 0 ] && exit 0'
+[ "$(id -u)" == 0 ] && exit 0
+echo -e '+ MAKEFLAGS="-j$(nproc)" makepkg -s --noconfirm --needed && for pkg in $(ls -1 *.pkg*); do curl -XPOST -T "$pkg" -H "X-API-KEY: $API_KEY" https://example.com/vieter/publish; done'
+MAKEFLAGS="-j$(nproc)" makepkg -s --noconfirm --needed && for pkg in $(ls -1 *.pkg*); do curl -XPOST -T "$pkg" -H "X-API-KEY: $API_KEY" https://example.com/vieter/publish; done
+```
+
+This script:
+
+1. Adds the target repository as a repository in the build container
+2. Updates mirrors & packages
+3. Clones the Git repository
+4. Runs `makepkg` without building to calculate `pkgver`
+5. Checks whether the package version is already present on the server
+6. If not, run makepkg & publish any generated package archives to the server