sc-templates/go

Go Smart Contract Template

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

Prerequisites

• Go 1.21 or later
• Protocol Buffers compiler (protoc)
• Go protobuf plugins

Installing Tools

# Install protoc (Ubuntu/Debian)
sudo apt install -y protobuf-compiler

# Install protoc (macOS)
brew install protobuf

# Install Go protobuf plugins
make tools

Quick Start

1. Copy this template to create your smart contract:

   cp -r go /path/to/my-smart-contract
   cd /path/to/my-smart-contract
   

2. Initialize your Go module and update package names:

   go mod init github.com/your-org/your-project
   make fix-package-name
   

3. Generate the protobuf code:

   make proto
   

4. Configure your connection by editing config.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.go by modifying the Process function.

6. Build and run:

   make build
   ./smart-contract -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.go, 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.go.

Implementing Your Smart Contract

Edit the Process function in process.go:

func Process(ctx context.Context, txJSON string, envVars, secrets map[string]string) ProcessResult {
    // Parse the transaction
    var tx Transaction
    if err := json.Unmarshal([]byte(txJSON), &tx); err != nil {
        return ProcessResult{Error: fmt.Errorf("failed to parse transaction: %w", err)}
    }

    // Access transaction data
    txnId := tx.Header.TxnId
    txnType := tx.Header.TxnType
    payload := tx.Payload

    // Access environment variables
    scName := envVars["SMART_CONTRACT_NAME"]
    dcID := envVars["DRAGONCHAIN_ID"]

    // Access secrets
    mySecret := secrets["SC_SECRET_MY_SECRET"]

    // Implement your logic here
    result := map[string]any{
        "status": "success",
        "data":   "your result data",
    }

    return ProcessResult{
        Data:          result,
        OutputToChain: true,  // Set to true to persist result on chain
        Error:         nil,
    }
}

Transaction Structure

The Transaction struct in process.go matches the Dragonchain transaction format:

type Transaction struct {
    Version string            `json:"version"`
    Header  TransactionHeader `json:"header"`
    Payload map[string]any    `json:"payload"`
}

type TransactionHeader struct {
    Tag       string `json:"tag"`
    DcId      string `json:"dc_id"`
    TxnId     string `json:"txn_id"`
    BlockId   string `json:"block_id"`
    TxnType   string `json:"txn_type"`
    Timestamp string `json:"timestamp"`
    Invoker   string `json:"invoker"`
}

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 map with keys prefixed by SC_SECRET_.

Project Structure

.
├── main.go              # Client infrastructure (do not modify)
├── process.go           # Your smart contract logic (modify this)
├── proto/
│   └── remote_sc.proto  # gRPC service definition
├── config.yaml          # Configuration file
├── go.mod               # Go module definition
├── Makefile             # Build commands
└── README.md            # This file

File Descriptions

• process.go - 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.go - Contains the gRPC client infrastructure, connection handling, and worker pool. You typically don't need to modify this file.

Make Commands

make proto              # Generate Go code from proto files
make build              # Build the binary
make run                # Run with default config
make test               # Run tests
make clean              # Remove build artifacts
make tools              # Install required tools
make deps               # Download dependencies
make fix-package-name   # Update package name based on go.mod

Concurrent Processing

The client uses a worker pool pattern 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 to report failures to the server
• The client automatically handles reconnection on connection failures
• Logs are captured and sent back with the response

License

[Your License Here]