build: accept build args for extra packages to install

Dockerfile

@@ -7,9 +7,14 @@ ARG TARGETOS
 ARG TARGETARCH
 ARG TARGETVARIANT
 
+# The following three arg/env vars get used by the platform specific "install-packages" script
+ARG EXTRA_DEB_PACKAGES=""
+ARG EXTRA_DNF_PACKAGES=""
+ARG EXTRA_ALPINE_PACKAGES=""
 ARG FORCE_INSTALL_PACKAGES=1
 RUN --mount=target=/build,source=build \
- TARGET=${TARGETARCH}${TARGETVARIANT} /build/run.sh install-packages
+ TARGET=${TARGETARCH}${TARGETVARIANT} \
+ /build/run.sh install-packages
 
 RUN --mount=target=/build,source=build \
  /build/run.sh setup-user

build/alpine/install-packages.sh

@@ -4,6 +4,7 @@ set -e
 set -o pipefail
 
 # Install necessary packages
+# shellcheck disable=SC2086
 apk add --no-cache -U \
  openssl \
  imagemagick \
@@ -29,7 +30,8 @@ apk add --no-cache -U \
  nfs-utils \
  libpcap \
  libwebp \
- libcap
+ libcap \
+ ${EXTRA_ALPINE_PACKAGES}
 
 # Download and install patched knockd
 curl -fsSL -o /tmp/knock.tar.gz https://github.com/Metalcape/knock/releases/download/0.8.1/knock-0.8.1-alpine-amd64.tar.gz

build/ol/install-packages.sh

@@ -23,6 +23,7 @@ EOF
 dnf update -y
 
 # Install necessary packages
+# shellcheck disable=SC2086
 dnf install -y \
  ImageMagick \
  file \
@@ -44,7 +45,8 @@ dnf install -y \
  libpcap \
  libwebp \
  findutils \
- which
+ which \
+ ${EXTRA_DNF_PACKAGES}
 
 # Install Git LFS
 curl -s https://packagecloud.io/install/repositories/github/git-lfs/script.rpm.sh | sudo bash

build/ubuntu/install-packages.sh

@@ -6,6 +6,7 @@ set -euo pipefail
 
 # Update and install packages
 apt-get update
+# shellcheck disable=SC2086
 DEBIAN_FRONTEND=noninteractive \
 apt-get install -y \
  imagemagick \
@@ -26,7 +27,8 @@ apt-get install -y \
  zstd \
  lbzip2 \
  nfs-common \
- libpcap0.8
+ libpcap0.8 \
+ ${EXTRA_DEB_PACKAGES}
 
 # Install Git LFS
 curl -s https://packagecloud.io/install/repositories/github/git-lfs/script.deb.sh | sudo bash

docs/misc/contributing/building.md

@@ -26,3 +26,11 @@ or just a plain build
 ```shell
 docker build -t IMG_PREFIX/minecraft-server .
 ```
+
+## Installing extra packages
+
+The following build args can be set to install additional packages for the respective base image distro:
+
+- `EXTRA_DEB_PACKAGES`
+- `EXTRA_DNF_PACKAGES`
+- `EXTRA_ALPINE_PACKAGES`