Fix classic snap (#81)

* use core22 and patchelf
* Consolidate agent wrapper script

make-classic.sh

@@ -1,11 +1,9 @@
 #!/bin/sh
 
-# The classic snap needs to be built on core20 because of libc6 dependency:
-# A core22 snap needs glibc 2.32+, but in a 20.04 charm we have glibc 2.31.
-sed -i 's/base: core22/base: core20/g' snap/snapcraft.yaml
 sed -i 's/confinement: strict/confinement: classic/g' snap/snapcraft.yaml
-sed -i 's/CRAFT_PART_INSTALL/SNAPCRAFT_PART_INSTALL/g' snap/snapcraft.yaml
-sed -i '/libbpfcc/d' snap/snapcraft.yaml
-sed -i '/bpfcc-tools/d' snap/snapcraft.yaml
 yq -i 'del(.apps.grafana-agent.plugs) | del(.plugs)' snap/snapcraft.yaml
-sed -i 's/agent-wrapper.strict/agent-wrapper.classic/g' snap/snapcraft.yaml
+
+# With the classic snap we need to patchelf for the core22 snap to run on a 20.04 charm,
+# because of the libc6 dependency, otherwise the app will fail to start, complaining
+# about needing glibc 2.32+.
+yq -i '.parts.grafana-agent."build-attributes" += ["enable-patchelf"]' snap/snapcraft.yaml

snap/local/agent-wrapper

@@ -0,0 +1,48 @@
+#!/bin/sh
+
+# Get config option
+if [ "$(snapctl get reporting-enabled)" = "0" ]
+then
+  echo "Launching with reporting disabled" | systemd-cat
+  REPORTING_ARG="-disable-reporting"
+else
+  echo "Launching with reporting enabled" | systemd-cat
+  REPORTING_ARG=""
+fi
+
+
+launch_classic() {
+
+  echo "Launching with config from the host filesystem" | systemd-cat
+  exec "${SNAP}/agent" -config.expand-env -config.file "/etc/grafana-agent.yaml" "${REPORTING_ARG}"  
+
+}
+
+
+launch_strict() {
+
+  IS_CONNECTED=$(snapctl is-connected etc-grafana-agent; echo $?)
+
+  if [ "${IS_CONNECTED}" = "0" ] && [ -r /etc/grafana-agent.yaml ]
+  then
+    echo "Launching with config from the host filesystem" | systemd-cat
+    CONFIG_FILE="/etc/grafana-agent.yaml"
+  else
+    echo "Launching with minimal default config from the snap" | systemd-cat
+    CONFIG_FILE="$SNAP_DATA/etc/grafana-agent.yaml"
+  fi
+
+  exec "${SNAP}/agent" -config.expand-env -config.file "${CONFIG_FILE}" "${REPORTING_ARG}"
+
+}
+
+
+# Detect confinement type
+# https://forum.snapcraft.io/t/reliable-way-of-detecting-snap-confinement-mode/8896/4
+IS_CLASSIC=$(grep -qxF "confinement: classic" "$SNAP/meta/snap.yaml"; echo $?)
+if [ "${IS_CLASSIC}" = "0" ]
+then
+  launch_classic
+else
+  launch_strict
+fi

snap/snapcraft.yaml

@@ -51,7 +51,7 @@ parts:
     source: ./snap/local
     source-type: local
     override-build: |
-      cp agent-wrapper.strict $CRAFT_PART_INSTALL/agent-wrapper
+      cp agent-wrapper $CRAFT_PART_INSTALL/
   grafana-agent:
     plugin: go
     source: https://github.com/grafana/agent