fix: use CNB_TARGET_* environment variables (#151)

Closes #148.

Removes os and arch detection in `build` scripts and instead use the
`CNB_TARGET_OS` and the `CNB_TARGET_ARCH` environment variables.

Also, print a warning if the detected architecture (from `uname`) is
different from the target architecture: at the moment, cross-platform
builds with pack will very likely create an image with incompatible
binaries (as many buildpacks use `uname` and not target platform
metadata).

Author: leafty

buildpacks/conda-nodefaults/bin/build

@@ -19,14 +19,8 @@ cp environment.yml "$TMPDIR/original.yml"
 cache_layer_dir="${CNB_LAYERS_DIR}"/cache
 mkdir -p "${cache_layer_dir}"
 
-OS=$(uname -s | tr '[:upper:]' '[:lower:]')
-ARCH=$(uname -m)
-
-case "$ARCH" in
-  x86_64) ARCH=amd64 ;;
-  arm64|aarch64) ARCH=arm64 ;;
-  *) >&2 echo "Unsupported architecture: $ARCH"; exit 1 ;;
-esac
+OS="${CNB_TARGET_OS:-unknown}"
+ARCH="${CNB_TARGET_ARCH:-unknown}"
 
 YQ_FILENAME="yq_${OS}_${ARCH}"
 YQ_VERSION=v4.47.1

buildpacks/renku-variables/bin/build

@@ -3,6 +3,22 @@ set -eo pipefail
 
 echo -e "=== 🔧 \033[1mRenku Environment Variables buildpack\033[0m ==="
 
+# NOTE: we run platform mismatch check here as this buildpack is always selected
+CURRENT_ARCH="$(uname -m)"
+case "${CURRENT_ARCH}" in
+  "aarch64"|"arm64") CURRENT_ARCH="arm64" ;;
+  "amd64"|"x86_64") CURRENT_ARCH="amd64" ;;
+  *) >&2 echo "ERROR: Unsupported architecture: ${CURRENT_ARCH}" ;;
+esac
+
+if [ -n "${CNB_TARGET_ARCH:-}" ]; then
+  if [ "${CNB_TARGET_ARCH}" != "${CURRENT_ARCH}" ]; then
+    >&2 echo "ERROR: current architecture ${CURRENT_ARCH} does not match target architecture ${CNB_TARGET_ARCH}!"
+    exit 1
+  fi
+fi
+
+
 layers_dir="$1"
 layer_dir="${layers_dir}"/renku-env
 env_dir="${layer_dir}"/env.launch

buildpacks/rstudio/bin/build

@@ -18,13 +18,7 @@ RSTUDIO_VERSION="2025.09.2-418"
 OS_CODENAME=jammy # https://posit.co/download/rstudio-server gives jammy regardless of ubuntu version
 FNAME="rstudio-$RSTUDIO_VERSION.deb"
 
-ARCH=$(uname -m)
-
-case "$ARCH" in
-  x86_64) ARCH=amd64 ;;
-  arm64|aarch64) ARCH=arm64 ;;
-  *) >&2 echo "Unsupported architecture: $ARCH"; exit 1 ;;
-esac
+ARCH="${CNB_TARGET_ARCH:-unknown}"
 
 if [ -f "$cache_layer_dir/$FNAME" ]; then
 	echo "Found rstudio $RSTUDIO_VERSION in $cache_layer_dir skipping download"

buildpacks/ttyd/bin/build

@@ -12,7 +12,12 @@ ttyd_layer_dir="${layers_dir}"/ttyd
 ttyd_bin_dir="${ttyd_layer_dir}"/bin
 mkdir -p "${ttyd_bin_dir}"
 
-ARCH=$(uname -i)
+ARCH="${CNB_TARGET_ARCH:-unknown}"
+case "${ARCH}" in
+  "arm64") ARCH="aarch64" ;;
+  "amd64") ARCH="x86_64" ;;
+esac
+
 TTYD_VERSION="1.7.7"
 TTYD_URL="https://github.com/tsl0922/ttyd/releases/download/${TTYD_VERSION}/ttyd.${ARCH}"
 

buildpacks/vscodium/bin/build

@@ -22,12 +22,9 @@ mkdir -p "${execd_layer_dir}"
 mkdir -p "${cache_layer_dir}"
 
 
-ARCH=$(uname -m)
-
-case "$ARCH" in
-  x86_64) ARCH=x64 ;;
-  arm64|aarch64) ARCH=arm64 ;;
-  *) >&2 echo "Unsupported architecture: $ARCH"; exit 1 ;;
+ARCH="${CNB_TARGET_ARCH:-unknown}"
+case "${ARCH}" in
+  "amd64") ARCH="x64" ;;
 esac
 
 VSCODIUM_DEFAULT_VERSION="1.104.36664"

scripts/install_shellcheck.sh

@@ -8,21 +8,13 @@ LOCATION=$2
 
 OS="linux"
 case "$(uname)" in
-  'Darwin')
-    OS='darwin'
-    ;;
-  *) ;;
+  'Darwin') OS='darwin' ;;
 esac
 
 ARCH="x86_64"
 case "$(uname -m)" in
-  'aarch64')
-	ARCH='aarch64'
-    ;;
-  'arm64')
-    ARCH='aarch64'
-    ;;
-  *) ;;
+  'aarch64') ARCH='aarch64' ;;
+  'arm64') ARCH='aarch64' ;;
 esac
 
 if [[ -z $VERSION ]]; then