XML File Watcher Docker Container

A Nix flake that builds a Docker container which monitors a directory tree for new XML files and triggers webhooks when they appear. Written in Rust for performance and reliability.

Features

• Recursive directory monitoring using the notify Rust crate
• Triggers webhook on new XML files (created or moved into watched directory)
• Configurable webhook URL, method, and payload options
• Lightweight container built with Nix
• High-performance Rust implementation with async I/O

Building

# Build the Docker image
nix build .#docker

# Load the image into Docker
docker load < result

Running

Docker

docker run -d \
  -v /path/to/watch:/watch \
  -e WEBHOOK_URL="https://your-webhook.example.com/endpoint" \
  -e WEBHOOK_METHOD="POST" \
  -e INCLUDE_CONTENT="false" \
  xml-watcher:latest

Docker Compose

version: '3.8'
services:
  xml-watcher:
    image: xml-watcher:latest
    volumes:
      - ./watched-folder:/watch
    environment:
      - WEBHOOK_URL=https://your-webhook.example.com/endpoint
      - WEBHOOK_METHOD=POST
      - INCLUDE_CONTENT=false
    restart: unless-stopped

Environment Variables

Variable	Default	Description
WATCH_DIR	/watch	Directory to monitor for XML files
WEBHOOK_URL	(required)	URL to send webhook requests to
WEBHOOK_METHOD	POST	HTTP method for webhook requests
INCLUDE_CONTENT	false	Include full XML file content in payload
OVERWRITE_WITH_RESPONSE	false	Overwrite file with server response (requires INCLUDE_CONTENT=true)
RUST_LOG	-	Set log level (trace, debug, info, warn, error)

Webhook Payload

The webhook sends a JSON payload like this:

{
  "event": "new_xml_file",
  "filepath": "/watch/subdir/example.xml",
  "filename": "example.xml",
  "timestamp": "2024-01-15T10:30:00+00:00"
}

Note: The filename field is always included in the payload.

With INCLUDE_CONTENT=true:

{
  "event": "new_xml_file",
  "filepath": "/watch/subdir/example.xml",
  "filename": "example.xml",
  "content": "<?xml version=\"1.0\"?>...",
  "timestamp": "2024-01-15T10:30:00+00:00"
}

File Overwrite Feature

When OVERWRITE_WITH_RESPONSE=true is set (along with INCLUDE_CONTENT=true), the watcher will overwrite the original XML file with the response from the webhook server. This feature has the following requirements:

• The webhook must respond with a successful HTTP status code (2xx)
• The response Content-Type header must start with text/xml or application/xml
• The response body must not be empty

When these conditions are met, the watcher will:

1. Overwrite the original file with the response content
2. Temporarily ignore watch events for that file to prevent triggering a new webhook
3. Log the overwrite operation

This is useful for scenarios where the server processes the XML and returns a modified or transformed version.

Development

Run locally (without Docker)

# Enter dev shell
nix develop

# Build with cargo
cargo build --release

# Or run directly with Nix
RUST_LOG=info WATCH_DIR=/tmp/watch WEBHOOK_URL=http://localhost:8080/hook nix run

# Or run with cargo
RUST_LOG=info WATCH_DIR=/tmp/watch WEBHOOK_URL=http://localhost:8080/hook cargo run

Test the watcher

# Terminal 1: Start a simple webhook receiver
python3 -m http.server 8080

# Terminal 2: Run the watcher
RUST_LOG=info WATCH_DIR=/tmp/watch WEBHOOK_URL=http://localhost:8080/ nix run

# Terminal 3: Create a test XML file
mkdir -p /tmp/watch
echo '<?xml version="1.0"?><test/>' > /tmp/watch/test.xml

The RUST_LOG environment variable controls logging levels (trace, debug, info, warn, error).

License

MIT