sc-templates/python/README.md

# Python Smart Contract Template

A Python-based smart contract client for Dragonchain Prime that connects via gRPC.

## Prerequisites

- Python 3.10 or later
- pip

## Quick Start

1. **Copy this template** to create your smart contract:
   ```bash
   cp -r python /path/to/my-smart-contract
   cd /path/to/my-smart-contract
   ```

2. **Set up the environment**:
   ```bash
   make setup
   source venv/bin/activate
   ```

   Or without make:
   ```bash
   python3 -m venv venv
   source venv/bin/activate
   pip install -r requirements.txt
   ```

3. **Generate the protobuf code**:
   ```bash
   make proto
   ```

4. **Configure your connection** by editing `config.yaml`:
   ```yaml
   server_address: "your-dragonchain-server:50051"
   chain_id: "your-chain-public-id"
   smart_contract_id: "your-smart-contract-id"
   api_key: "your-api-key"
   ```

5. **Implement your smart contract logic** in `process.py` by modifying the `process` function.

6. **Run**:
   ```bash
   python main.py --config config.yaml
   ```

## Configuration

| Field | Description | Default |
|-------|-------------|---------|
| `server_address` | gRPC server address | Required |
| `chain_id` | Public chain id the SC is registered on (sent as `x-chain-id` metadata) | Required |
| `smart_contract_id` | Your smart contract ID | Required |
| `api_key` | API key for authentication | Required |
| `use_tls` | Enable TLS encryption | `false` |
| `tls_cert_path` | Path to TLS certificate | - |
| `num_workers` | Concurrent transaction processors | `10` |
| `reconnect_delay_seconds` | Base delay for exponential backoff between reconnect attempts | `3` |
| `max_backoff_seconds` | Ceiling for the exponential backoff | `120` |
| `max_reconnect_attempts` | Max reconnect attempts (0 = infinite, recommended) | `0` |

## Durability guarantees (provided by `main.py`, no work for you)

- **Server restart, update, crash, or network blip** → the client auto-reconnects and resumes processing. Transactions observed while the stream was down stay queued on the Dragonchain Prime side and are delivered (oldest first) on reconnect.
- **Client restart or long outage** → when this process comes back up (minutes, hours, months later), it rejoins the stream and prime re-delivers every still-pending transaction that should have invoked it.
- **Half-open TCP** (silent peer, resumed laptop, corporate NAT dropping idle flows) is detected within ~13 seconds via gRPC keepalive and triggers a reconnect. No dangling ghost streams.
- **Reconnect storms** are avoided: exponential backoff with jitter means many clients reconnecting after a server restart don't all slam `accept()` at the same instant. The timer resets after a stream has been healthy for 60 seconds.

These are invariants of the template — you do not add any of this in `process.py`.

## Implementing Your Smart Contract

Edit the `process` function in `process.py`:

```python
def process(
    tx_json: str,
    env_vars: dict[str, str],
    secrets: dict[str, str],
) -> ProcessResult:
    # Parse the transaction
    tx = Transaction.from_json(tx_json)

    # Access transaction data
    txn_id = tx.header.txn_id
    txn_type = tx.header.txn_type
    payload = tx.payload

    # Access environment variables
    sc_name = env_vars.get("SMART_CONTRACT_NAME")
    dc_id = env_vars.get("DRAGONCHAIN_ID")

    # Access secrets
    my_secret = secrets.get("SC_SECRET_MY_SECRET")

    # Implement your logic here
    result = {
        "status": "success",
        "data": "your result data",
    }

    return ProcessResult(
        data=result,
        output_to_chain=True,  # Set to True to persist result on chain
        error=None,
    )
```

### Transaction Structure

The `Transaction` class in `process.py` matches the Dragonchain transaction format:

```python
@dataclass
class Transaction:
    version: str
    header: TransactionHeader
    payload: dict[str, Any]

@dataclass
class TransactionHeader:
    tag: str
    dc_id: str
    txn_id: str
    block_id: str
    txn_type: str
    timestamp: str
    invoker: str
```

### Available Environment Variables

| Variable | Description |
|----------|-------------|
| `TZ` | Timezone |
| `ENVIRONMENT` | Deployment environment |
| `INTERNAL_ID` | Internal identifier |
| `DRAGONCHAIN_ID` | Dragonchain ID |
| `DRAGONCHAIN_ENDPOINT` | Dragonchain API endpoint |
| `SMART_CONTRACT_ID` | This smart contract's ID |
| `SMART_CONTRACT_NAME` | This smart contract's name |
| `SC_ENV_*` | Custom environment variables |

### Secrets

Secrets are provided in the `secrets` dict with keys prefixed by `SC_SECRET_`.

## Project Structure

```
.
├── main.py              # Client infrastructure (do not modify)
├── process.py           # Your smart contract logic (modify this)
├── proto/
│   └── remote_sc.proto  # gRPC service definition
├── config.yaml          # Configuration file
├── requirements.txt     # Python dependencies
├── Makefile             # Build commands
└── README.md            # This file
```

### File Descriptions

- **`process.py`** - Contains the `process` function where you implement your smart contract logic. This is the only file you need to modify for most use cases.
- **`main.py`** - Contains the gRPC client infrastructure, connection handling, and worker pool. You typically don't need to modify this file.

## Make Commands

```bash
make setup   # Create venv and install dependencies
make proto   # Generate Python code from proto files
make run     # Run with default config
make test    # Run tests
make clean   # Remove generated files and venv
make deps    # Install dependencies (no venv)
make format  # Format code with black and isort
```

## Concurrent Processing

The client uses a thread pool to process multiple transactions concurrently. The number of workers is configurable via `num_workers` in the config file.

## Error Handling

- Return errors from the `process` function via `ProcessResult.error` to report failures
- The client automatically handles reconnection on connection failures
- Logs are captured and sent back with the response

## Docker

Example `Dockerfile`:

```dockerfile
FROM python:3.11-slim

WORKDIR /app

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

COPY . .
RUN python -m grpc_tools.protoc \
    -I./proto \
    --python_out=. \
    --grpc_python_out=. \
    proto/remote_sc.proto

CMD ["python", "main.py", "--config", "config.yaml"]
```

## License

[Your License Here]