file-watch

Overview

The file-watch node monitors files and directories on the local filesystem. It emits a message whenever a watched file is created, modified, or deleted. Ideal for detecting configuration changes, monitoring upload directories, or triggering processing pipelines when new data files arrive.

Properties

Output Message

When a file event is detected, the node outputs a message with the following structure:

{
  "payload": "/data/uploads/sensor-log.csv",
  "topic": "/data/uploads",
  "file": "sensor-log.csv",
  "type": "file",
  "size": 2048,
  "event": "change",       // "change", "add", or "unlink"
  "_msgid": "fw001"
}

Example: Watch Config File for Changes

Monitor a configuration file and reload application settings whenever it is updated. Uses a single file path to watch one specific file.

// file-watch node configuration
{
  "path": "/etc/edgeflow/config.json",
  "recursive": false,
  "pattern": "*.json"
}

// When config.json is saved, output:
{
  "payload": "/etc/edgeflow/config.json",
  "file": "config.json",
  "event": "change",
  "size": 512
}

// Connect to a file-read node to reload the config
// then pass to a function node to apply changes:
// flow.set('config', JSON.parse(msg.payload));
// node.status({ text: "Config reloaded" });

Example: Monitor Upload Directory

Watch an upload directory for new CSV files arriving from connected sensors. Trigger processing only for newly added files matching the CSV pattern.

// file-watch node configuration
{
  "path": "/data/uploads",
  "recursive": true,
  "pattern": "*.csv"
}

// When a new CSV is dropped in, output:
{
  "payload": "/data/uploads/2024/temp-readings.csv",
  "file": "temp-readings.csv",
  "event": "add",
  "size": 8192
}

// Connect to a switch node to filter by event type:
// Rule 1: msg.event == "add"    -> process new files
// Rule 2: msg.event == "change" -> re-process updated files
// Rule 3: msg.event == "unlink" -> log deleted files

Example: Detect Log File Rotation

Monitor a log directory for new log files created by rotation, and archive them automatically.

// file-watch node configuration
{
  "path": "/var/log/edgeflow",
  "recursive": false,
  "pattern": "*.log"
}

// When logrotate creates a new file:
{
  "payload": "/var/log/edgeflow/app-2024-01-15.log",
  "file": "app-2024-01-15.log",
  "event": "add"
}

// Downstream: compress and move to archive storage
// using an exec node or file-write + gzip pipeline

Common Use Cases