cronprobe

#!/usr/bin/env bash
# cronprobe - A minimal-dependency bash wrapper to catch and alert on failing cron jobs.

set -o pipefail

WEBHOOK_URL="${CRONPROBE_WEBHOOK:-}"
DESTINATION=""

show_help() {
    cat << EOF
Usage: cronprobe [options] -- <command> [args...]

Options:
  --webhook URL    Webhook URL for Slack, Discord, Ntfy, or any generic webhook
  --slack          Force Slack formatting
  --discord        Force Discord formatting
  --ntfy           Force Ntfy formatting (plain-text)
  --generic        Force generic JSON webhook formatting
  -h, --help       Show this help message

SECURITY WARNING & DATA LEAKAGE:
  On failure, cronprobe sends the target command string and its last 50 lines 
  of stdout/stderr directly to the configured webhook. 
  - Do NOT pass plaintext secrets (passwords, tokens) as command arguments. Use environment variables.
  - cronprobe alters native cron behavior: it swallows output on success, but prints it on failure.

Example:
  cronprobe --webhook="https://hooks.slack.com/..." -- python3 scraper.py
EOF
}

# Parse arguments cleanly
while [[ "$#" -gt 0 ]]; do
    case "$1" in
        --webhook=*) 
            WEBHOOK_URL="${1#*=}"
            if [[ -z "$WEBHOOK_URL" ]]; then
                echo "cronprobe error: --webhook requires a URL argument." >&2
                exit 1
            fi
            shift ;;
        --webhook) 
            if [[ -z "$2" || "$2" == -* ]]; then
                echo "cronprobe error: --webhook requires a URL argument." >&2
                exit 1
            fi
            WEBHOOK_URL="$2"; shift 2 ;;
        --slack) DESTINATION="slack"; shift ;;
        --discord) DESTINATION="discord"; shift ;;
        --ntfy) DESTINATION="ntfy"; shift ;;
        --generic) DESTINATION="generic"; shift ;;
        -h|--help) show_help; exit 0 ;;
        --) shift; break ;;
        -*) echo "cronprobe error: Unknown option: $1" >&2; show_help >&2; exit 1 ;;
        *) break ;; # Found start of command
    esac
done

if [[ "$#" -eq 0 ]]; then
    echo "cronprobe error: No command provided." >&2
    show_help >&2
    exit 1
fi

COMMAND=("$@")
# Clean quoting for array print to prevent log misdirection
printf -v COMMAND_STR '%q ' "${COMMAND[@]}"
COMMAND_STR="${COMMAND_STR% }"

# If no webhook is configured, execute transparently avoiding overhead proxying
if [[ -z "$WEBHOOK_URL" ]]; then
    exec "${COMMAND[@]}"
fi

# Auto-detect webhook type
if [[ -z "$DESTINATION" ]]; then
    if [[ "$WEBHOOK_URL" == *"discord.com"* ]]; then
        DESTINATION="discord"
    elif [[ "$WEBHOOK_URL" == *"ntfy.sh"* ]]; then
        DESTINATION="ntfy"
    elif [[ "$WEBHOOK_URL" == *"hooks.slack.com"* ]]; then
        DESTINATION="slack"
    else
        DESTINATION="generic"
    fi
fi

# Set up bounded ephemeral storage that cleans itself up safely cross-platform
TMP_OUT=$(mktemp "${TMPDIR:-/tmp}/cronprobe.XXXXXX") || exit 1
trap 'rm -f "$TMP_OUT"' EXIT

START_TIME=$(date +%s)

# Execute the target command, capturing all output 
"${COMMAND[@]}" > "$TMP_OUT" 2>&1
EXIT_CODE=$?

END_TIME=$(date +%s)
DURATION=$((END_TIME - START_TIME))

# We only care if it failed. Exit 0 -> exit 0 quietly.
if [[ $EXIT_CODE -ne 0 ]]; then
    # Re-emit the captured output so the native cron daemon can still email it
    cat "$TMP_OUT"
    
    HOSTNAME=$(hostname)
    
    # Grab the last 50 lines cleanly
    if [[ -s "$TMP_OUT" ]]; then
        OUTPUT=$(tail -n 50 "$TMP_OUT")
        # Trim payload to a reasonable size for webhook delivery
        OUTPUT="${OUTPUT:0:2000}"
    else
        OUTPUT="Process exited with code $EXIT_CODE and produced no output."
    fi

    # Robust pure-bash JSON string escaping (no jq dependency)
    # Replaces \, ", \n, \r, \t, and safely strips problematic ANSI/control chars except \n and \t
    escape_json() {
        local str="$1"
        str="${str//\\/\\\\}"         # backslashes
        str="${str//\"/\\\"}"         # quotes
        str="${str//$'\n'/\\n}"       # newlines
        str="${str//$'\r'/}"          # carriage returns
        str="${str//$'\t'/\\t}"       # tabs
        # Strip ASCII control chars (0x00-0x1F) safely while preserving UTF-8 (0x80-0xFF)
        printf '%s' "$str" | LC_ALL=C tr -d '\000-\010\013-\037\177'
    }

    SAFE_CMD=$(escape_json "$COMMAND_STR")
    SAFE_OUT=$(escape_json "$OUTPUT")
    SAFE_HOST=$(escape_json "$HOSTNAME")

    # Format the payload
    if [[ "$DESTINATION" == "discord" ]]; then
        PAYLOAD=$(cat <<EOF
{
  "embeds": [{
    "title": "🚨 [\`$SAFE_HOST\`] Job Failed",
    "color": 16711680,
    "description": "**Command:** \`$SAFE_CMD\`\n**Exit Code:** $EXIT_CODE | **Duration:** ${DURATION}s\n\n**Output (last 50 lines):**\n\`\`\`text\n$SAFE_OUT\n\`\`\`"
  }]
}
EOF
)
    elif [[ "$DESTINATION" == "slack" ]]; then
        PAYLOAD=$(cat <<EOF
{
  "blocks": [
    {
      "type": "header",
      "text": { "type": "plain_text", "text": "🚨 [$SAFE_HOST] Job Failed", "emoji": true }
    },
    {
      "type": "section",
      "text": { "type": "mrkdwn", "text": "*Command:* \`$SAFE_CMD\`\n*Exit Code:* $EXIT_CODE | *Duration:* ${DURATION}s" }
    },
    {
      "type": "section",
      "text": { "type": "mrkdwn", "text": "*Output (last 50 lines):*\n\`\`\`\n$SAFE_OUT\n\`\`\`" }
    }
  ]
}
EOF
)
    elif [[ "$DESTINATION" == "ntfy" ]]; then
        # ntfy takes regular plaintext formatting if POSTed directly
        PAYLOAD="🚨 [$HOSTNAME] Job Failed
Command: $COMMAND_STR
Exit Code: $EXIT_CODE | Duration: ${DURATION}s

Output (last 50 lines):
$OUTPUT"
    else
        # generic webhook endpoint
        PAYLOAD=$(cat <<EOF
{
  "status": "failed",
  "host": "$SAFE_HOST",
  "command": "$SAFE_CMD",
  "exit_code": $EXIT_CODE,
  "duration_seconds": $DURATION,
  "output": "$SAFE_OUT"
}
EOF
)
    fi

    if ! command -v curl >/dev/null 2>&1; then
        echo "cronprobe error: curl is required but not installed." >&2
        exit "$EXIT_CODE"
    fi

    CURL_HEADERS=(-H 'Content-Type: application/json')
    if [[ "$DESTINATION" == "ntfy" ]]; then
        CURL_HEADERS=(-H 'Content-Type: text/plain')
    fi

    # Deliver to webhook (surface network errors directly for rapid debugging)
    HTTP_CODE=$(curl --max-time 10 -s -w "%{http_code}" -X POST "${CURL_HEADERS[@]}" -d "$PAYLOAD" "$WEBHOOK_URL" -o /dev/null || echo "curl_failed")
    
    if [[ "$HTTP_CODE" == *"curl_failed"* ]]; then
        echo "cronprobe error: Webhook delivery failed (network or timeout error)" >&2
    elif [[ "$HTTP_CODE" -ge 400 ]]; then
        echo "cronprobe error: Webhook delivery failed with HTTP status $HTTP_CODE" >&2
    fi
fi

# Pass the original exit code completely unmodified
exit $EXIT_CODE