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Update: Revise WebSocket API documentation for protobuf-based communication

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Signed-off-by: YoungSoo Shin <shinys000114@gmail.com>
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YoungSoo Shin
2025-09-02 16:02:22 +09:00
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@@ -6,46 +6,44 @@ This document outlines the HTTP REST and WebSocket APIs for communication betwee
## WebSocket API
The WebSocket API provides a full-duplex communication channel for real-time data, such as sensor metrics and the interactive serial console.
The WebSocket API provides a full-duplex communication channel for real-time data, such as sensor metrics and the
interactive serial console. All server-to-client communication is done via binary WebSocket frames containing Protocol
Buffers (protobuf) messages.
**Endpoint**: `/ws`
> **Note**: The server only accepts one WebSocket client at a time. Subsequent connection attempts will be rejected with a `403 Forbidden` error until the active client disconnects.
### Server-to-Client Messages
The server pushes messages to the client, which can be either JSON objects or raw binary data. JSON messages always contain a `type` field to identify the payload.
The server pushes binary messages to the client. Each message is a Protocol Buffers (protobuf) encoded `StatusMessage`.
This top-level message uses a `oneof` field to carry different payload types.
#### JSON Messages
The protobuf schema is defined in `proto/status.proto`.
| Type | Description | Payload Example |
|---------------|---------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------|
| `sensor_data` | Pushed periodically (e.g., every second) with the latest power metrics. | `{"type":"sensor_data", "voltage":12.01, "current":1.52, "power":18.25, "uptime_sec":3600, "timestamp": 1672531200}` |
| `wifi_status` | Pushed periodically or on change to update the current Wi-Fi connection status. | `{"type":"wifi_status", "connected":true, "ssid":"MyHome_WiFi", "rssi":-65}` |
```proto
// Top-level message for all websocket communication
message StatusMessage {
oneof payload {
SensorData sensor_data = 1;
WifiStatus wifi_status = 2;
UartData uart_data = 3;
}
}
```
**Field Descriptions:**
- `sensor_data`:
- `voltage` (float): The measured voltage in Volts (V).
- `current` (float): The measured current in Amperes (A).
- `power` (float): The calculated power in Watts (W).
- `uptime_sec` (integer): The system uptime in seconds.
- `timestamp` (integer): A Unix timestamp (seconds) of when the measurement was taken.
- `wifi_status`:
- `connected` (boolean): `true` if connected to a Wi-Fi network, `false` otherwise.
- `ssid` (string): The SSID of the connected network. Null if not connected.
- `rssi` (integer): The Received Signal Strength Indicator in dBm. Null if not connected.
The client decodes the `StatusMessage` and then handles the specific payload:
#### Raw Binary Data
- **Description**: Raw binary data from the ODROID's serial (UART) port is forwarded directly to the client. This is used to display the terminal output.
- **Payload**: `(binary data)`
| `oneof` payload field | Contained Message | Description |
|-----------------------|-------------------|-----------------------------------------------------------------------------------------|
| `sensor_data` | `SensorData` | Pushed periodically (e.g., every second) with the latest power metrics. |
| `wifi_status` | `WifiStatus` | Pushed periodically or on change to update the current Wi-Fi connection status. |
| `uart_data` | `UartData` | Forwards raw binary data from the ODROID's serial (UART) port to the client's terminal. |
### Client-to-Server Messages
The client primarily sends raw binary data, which is interpreted as terminal input.
The client sends raw binary/text data, which is interpreted as terminal input.
- **Description**: Raw binary data representing user input from the web terminal. This data is forwarded directly to the ODROID's serial (UART) port.
- **Payload**: `(binary data)`
- **Payload**: `(raw data)`
---