Connection
APM runs a WebSocket server on your local machine that accepts connections from web applications.
Endpoint
ws://localhost:7000/websocket/
Connection Example
const ws = new WebSocket('ws://localhost:7000/websocket/');
ws.onopen = () => {
console.log('Connected to APM');
};
ws.onmessage = (event) => {
const data = JSON.parse(event.data);
console.log('Received:', data);
};
ws.onerror = (error) => {
console.error('WebSocket error:', error);
};
ws.onclose = () => {
console.log('Disconnected from APM');
};
Message Types
APM WebSocket API supports different message types identified by the message structure:
Client to Server Messages
| Message Type | Description | Reference |
|---|
| Print Job Request | Send a print job to a thermal printer | Print Jobs |
| Template Update | Update or create a print template | Template Updates |
| Scale Control | Start/stop listening to scale data | Scale Data |
Server to Client Messages
| Message Type | Description | Reference |
|---|
| Print Job Result | Result of a print job operation | Print Jobs |
| Scale Reading | Real-time weight data from scale | Scale Data |
| Template Update Result | Result of template update operation | Template Updates |
Status Endpoint
Check if APM is running and get connected client information:
curl http://localhost:7000/websocket/status
Response
{
"IsRunning": true,
"ConnectedClients": 2,
"ScaleStatuses": [
{
"ScaleId": "scale_001",
"IsConnected": true,
"LastReading": "2024-01-15T10:30:00Z"
}
]
}
Error Handling
All responses include status information. For errors:
{
"JobId": "job_12345",
"Status": "ERROR",
"ErrorMessage": "Printer not found: PRINTER_001"
}
- Printer not found: The specified printer ID doesn’t exist in the configuration
- Template not found: The document type doesn’t have a corresponding template
- Connection failed: Unable to connect to the printer hardware
- Invalid JSON: Malformed message sent to the server
Client Identification
Each WebSocket connection is automatically assigned a client ID based on the remote endpoint (IP:Port). The server uses this ID to:
- Send responses to the specific client that made the request
- Track scale data subscriptions per client
- Manage connection lifecycle
Print job results and template update results are sent only to the requesting client (unicast), while scale data can be broadcast to all subscribed clients.