Gracefully handle missing config file in watcher

.github/workflows/test.yml

@@ -12,3 +12,18 @@ jobs:
       - uses: actions/checkout@v4
       - name: Run Docker build and test
         run: bash test.sh
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Log in to Docker Hub
+        if: github.ref == 'refs/heads/main' && github.event_name == 'push'
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKER_USER }}
+          password: ${{ secrets.DOCKER_PASS }}
+      - name: Build and push Docker image
+        if: github.ref == 'refs/heads/main' && github.event_name == 'push'
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: ${{ secrets.DOCKER_USER }}/${{ github.event.repository.name }}:latest

README.md

@@ -2,6 +2,42 @@
 
 This container runs a cron daemon configured by environment variables or an optional `config.json` file.
 
+## Defining jobs with environment variables
+
+Jobs can be scheduled directly with pairs of `CMD_n` and `INTERVAL_n` variables. Each pair defines one job:
+
+```sh
+docker run \
+  -e CMD_1="echo hello" -e INTERVAL_1="*/5 * * * *" \
+  -e CMD_2="date"      -e INTERVAL_2="0 1 * * *" image
+```
+
+The index `n` starts at 1 and must increase sequentially with no gaps; the parser stops at the first missing pair.
+Both variables of a pair are required. `INTERVAL_n` expects a standard five-field cron expression, and `CMD_n`
+is any shell command.
+
+### Overriding values from `config.json`
+
+If a `CONFIG_FILE` is supplied, jobs from that file populate unset `CMD_n`/`INTERVAL_n` variables. Explicit
+environment values override those from the file:
+
+```json
+# config.json
+{
+  "jobs": [
+    {"cmd": "echo from file", "interval": "*/5 * * * *"}
+  ]
+}
+```
+
+```sh
+docker run -v $(pwd)/config.json:/app/config.json -e CONFIG_FILE=/app/config.json \
+  -e CMD_1="echo from env" -e INTERVAL_1="*/10 * * * *" image
+```
+
+In this example the job runs `echo from env` every ten minutes, ignoring the `cmd` and `interval` from
+`config.json`.
+
 ## Using a configuration file
 
 1. Create a `config.json` containing jobs with a `cmd` and `interval`:

run.sh

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
-set -e
+set -euo pipefail
+# Enable strict error handling: exit on errors, undefined variables, and
+# failures within pipelines.
 
 generate_cron() {
   bash /app/config_parser.sh
@@ -12,16 +14,36 @@ reload_crond() {
 watch_config() {
   local file="$1"
   if command -v inotifywait >/dev/null 2>&1; then
-    inotifywait -m -e close_write,move,delete "$file" | while read -r _; do
-      generate_cron
-      reload_crond
-    done
+    local dir="$(dirname "$file")"
+    local base="$(basename "$file")"
+    inotifywait -m -e close_write,move,create,delete "$dir" --format '%e %f' |
+      while read -r events fname; do
+        [ "$fname" = "$base" ] || continue
+        if echo "$events" | grep -qE 'DELETE|MOVED_FROM'; then
+          echo "Warning: configuration file '$file' missing, skipping cron generation" >&2
+        elif [ -f "$file" ]; then
+          generate_cron
+          reload_crond
+        fi
+      done || true
   else
     local prev
-    prev="$(md5sum "$file" 2>/dev/null | awk '{print $1}')"
+    if [ -f "$file" ]; then
+      prev="$(md5sum "$file" 2>/dev/null | awk '{print $1}' || true)"
+    else
+      prev="missing"
+      echo "Warning: configuration file '$file' missing, skipping cron generation" >&2
+    fi
     while sleep 5; do
+      if [ ! -f "$file" ]; then
+        if [ "$prev" != "missing" ]; then
+          prev="missing"
+          echo "Warning: configuration file '$file' missing, skipping cron generation" >&2
+        fi
+        continue
+      fi
       local curr
-      curr="$(md5sum "$file" 2>/dev/null | awk '{print $1}')"
+      curr="$(md5sum "$file" 2>/dev/null | awk '{print $1}' || true)"
       if [ "$curr" != "$prev" ]; then
         prev="$curr"
         generate_cron
@@ -32,13 +54,21 @@ watch_config() {
 }
 
 # Generate cron entries from environment/config
-generate_cron
+if [ -n "${CONFIG_FILE:-}" ]; then
+  if [ -f "$CONFIG_FILE" ]; then
+    generate_cron
+  else
+    echo "Warning: configuration file '$CONFIG_FILE' missing, skipping cron generation" >&2
+  fi
+else
+  generate_cron
+fi
 
 crond -f -l 2 &
 CROND_PID=$!
 
-if [ -n "$CONFIG_FILE" ] && [ -f "$CONFIG_FILE" ]; then
+if [ -n "${CONFIG_FILE:-}" ]; then
   watch_config "$CONFIG_FILE" &
 fi
 
-wait $CROND_PID
+wait "$CROND_PID"

test.sh

@@ -1,31 +1,7 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-IMAGE_NAME=docker-cron-test
-LOG_FILE=test.log
-TEMP_CONFIG=config.json
+bash tests/config_parser_test.sh
+bash tests/watch_config_test.sh
 
-cleanup() {
-  rm -f "$TEMP_CONFIG" "$LOG_FILE"
-}
-trap cleanup EXIT
-
-# Build docker image
- docker build -t "$IMAGE_NAME" .
-
-# Create temporary config file
-cat > "$TEMP_CONFIG" <<'CFG'
-{
-  "jobs": [
-    {"cmd": "echo hello from cron", "interval": "* * * * *"}
-  ]
-}
-CFG
-
-# Run config parser inside container and display generated crontab
- docker run --rm -v "$(pwd)/$TEMP_CONFIG:/config.json" -e CONFIG_FILE=/config.json --entrypoint /bin/sh "$IMAGE_NAME" -c '/app/config_parser.sh; cat /etc/crontabs/root' | tee "$LOG_FILE"
-
-# Verify expected command is present in log
-grep -q "echo hello from cron" "$LOG_FILE"
-
-echo "Test completed successfully"
+echo "All tests passed"

tests/config_parser_test.sh

@@ -55,7 +55,37 @@ CFG
   rm -rf /etc/crontabs
 }
 
+test_env_overrides_config() {
+  local tmpdir
+  tmpdir=$(mktemp -d)
+  cat >"$tmpdir/config.json" <<'CFG'
+{
+  "jobs": [
+    {"cmd": "/bin/echo hi", "interval": "0 1 * * *"}
+  ]
+}
+CFG
+
+  CMD_1="/bin/date" INTERVAL_1="*/5 * * * *" CONFIG_FILE="$tmpdir/config.json" bash app/config_parser.sh
+
+  local expected=$'*/5 * * * * /bin/date'
+  local actual
+  actual=$(cat /etc/crontabs/root)
+  if [[ "$actual" != "$expected" ]]; then
+    echo "crontab content mismatch" >&2
+    echo "expected:" >&2
+    printf '%s\n' "$expected" >&2
+    echo "actual:" >&2
+    printf '%s\n' "$actual" >&2
+    exit 1
+  fi
+
+  rm -rf "$tmpdir"
+  rm -rf /etc/crontabs
+}
+
 test_writes_crontab_from_config
 test_errors_when_missing_pair
+test_env_overrides_config
 
 echo "All config_parser tests passed"

tests/watch_config_test.sh

@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Ensure crond is available
+if ! command -v crond >/dev/null 2>&1; then
+  if command -v busybox >/dev/null 2>&1; then
+    ln -sf "$(command -v busybox)" /usr/bin/crond
+  elif command -v apt-get >/dev/null 2>&1; then
+    apt-get update >/dev/null
+    apt-get install -y busybox >/dev/null
+    ln -sf /bin/busybox /usr/bin/crond
+  else
+    echo "crond not available, skipping watch_config test" >&2
+    exit 0
+  fi
+fi
+
+# Ensure config parser is accessible at /app
+if [ ! -e /app ]; then
+  ln -s "$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)/app" /app
+fi
+
+# busybox crond expects /var/spool/cron/crontabs; map it to /etc/crontabs
+if [ ! -e /var/spool/cron/crontabs ]; then
+  mkdir -p /var/spool/cron
+  mkdir -p /etc/crontabs
+  ln -s /etc/crontabs /var/spool/cron/crontabs
+fi
+
+TMPDIR=$(mktemp -d)
+CONFIG="$TMPDIR/config.json"
+LOG="$TMPDIR/run.log"
+RUN_PID=0
+
+cleanup() {
+  if [ "$RUN_PID" -ne 0 ]; then
+    pkill -P "$RUN_PID" >/dev/null 2>&1 || true
+    kill "$RUN_PID" >/dev/null 2>&1 || true
+  fi
+  rm -rf "$TMPDIR"
+}
+trap cleanup EXIT
+
+cat >"$CONFIG" <<'CFG'
+{
+  "jobs": [
+    {"cmd": "/bin/echo first", "interval": "* * * * *"}
+  ]
+}
+CFG
+
+CONFIG_FILE="$CONFIG" bash ./run.sh >"$LOG" 2>&1 &
+RUN_PID=$!
+
+# Allow initial generation
+sleep 2
+
+grep -q "echo first" /etc/crontabs/root
+
+# Remove config file and ensure watcher keeps running
+rm "$CONFIG"
+
+sleep 7
+
+kill -0 "$RUN_PID"
+
+grep -q "configuration file.*missing" "$LOG"
+
+# Recreate config file with different command
+cat >"$CONFIG" <<'CFG'
+{
+  "jobs": [
+    {"cmd": "/bin/echo second", "interval": "* * * * *"}
+  ]
+}
+CFG
+
+sleep 7
+
+grep -q "echo second" /etc/crontabs/root
+
+echo "watch_config test passed"