Overview
The file-read node reads the contents of a file from the local
filesystem. It supports multiple output formats including plain text, binary buffers, parsed JSON,
and line-by-line streaming. The filename can be set statically in the node configuration or
dynamically via msg.filename.
Properties
| Property | Type | Default | Description |
|---|---|---|---|
| filename | string | "" | Path to the file. Can be overridden by msg.filename. |
| format | string | "text" | Output format: text, binary, json, or lines |
| encoding | string | "utf-8" | Character encoding: utf-8, ascii, or base64 |
Output Formats
text
Returns the file content as a single string in msg.payload. Best for configuration files, templates, and small text files.
binary
Returns the raw file content as a Node.js Buffer. Use for images, firmware binaries, or compressed archives.
json
Reads the file and parses it as JSON. Returns a JavaScript object in msg.payload. Errors if the file is not valid JSON.
lines
Reads the file line by line, emitting one message per line. The msg.parts property tracks sequence for later reassembly.
Example: Read CSV Sensor Log
Read a CSV file containing temperature sensor readings and process each line. Uses the lines format to stream large files without loading everything into memory.
// file-read node configuration
{
"filename": "/data/sensors/temperature-log.csv",
"format": "lines",
"encoding": "utf-8"
}
// CSV file contents:
// timestamp,sensor_id,temperature,humidity
// 2024-01-15T10:00:00Z,dht22-01,23.5,65
// 2024-01-15T10:05:00Z,dht22-01,23.7,64
// Each line emitted as a separate msg:
{
"payload": "2024-01-15T10:00:00Z,dht22-01,23.5,65",
"parts": {
"id": "read001",
"index": 1,
"count": 3,
"type": "string",
"ch": "\n"
},
"filename": "/data/sensors/temperature-log.csv"
}Example: Load JSON Configuration
Load a JSON configuration file and store it in flow context so other nodes can access the settings. Pair with file-watch for automatic reload on changes.
// file-read node configuration
{
"filename": "/etc/edgeflow/sensors.json",
"format": "json",
"encoding": "utf-8"
}
// JSON file contents:
// {
// "sensors": [
// { "id": "dht22-01", "pin": 4, "interval": 5000 },
// { "id": "bme280-01", "bus": 1, "interval": 10000 }
// ],
// "mqtt_topic_prefix": "home/sensors"
// }
// Output msg.payload (auto-parsed):
{
"sensors": [
{ "id": "dht22-01", "pin": 4, "interval": 5000 },
{ "id": "bme280-01", "bus": 1, "interval": 10000 }
],
"mqtt_topic_prefix": "home/sensors"
}
// In a function node downstream:
// flow.set('config', msg.payload);
// node.status({ text: msg.payload.sensors.length + " sensors" });Example: Read Firmware Binary for OTA
Read a firmware binary file and prepare it for over-the-air updates to connected devices.
// file-read node configuration
{
"filename": "/data/firmware/esp32-v2.1.bin",
"format": "binary",
"encoding": "utf-8"
}
// Output msg:
{
"payload": "",
"filename": "/data/firmware/esp32-v2.1.bin",
"_msgid": "fr003"
}
// msg.payload is a Buffer containing raw bytes
// msg.payload.length gives the file size in bytes Common Use Cases
Load Configuration
Read JSON or YAML config files at startup or on change
Process Data Files
Read CSV, JSON, or text data files for batch processing
Serve Static Content
Read HTML templates or static assets for HTTP responses
Firmware Distribution
Read binary firmware files for OTA device updates