DRP Go SDK

The official Go SDK for integrating the Digital Receipt Protocol into Go applications, microservices, and high-performance backends.

Installation

go get github.com/digitalreceiptprotocol/drp-go

Requirements:

Go 1.19 or higher

Quick Start

Merchant Integration

package main

import (
    "context"
    "fmt"
    "log"
    "os"
    
    "github.com/digitalreceiptprotocol/drp-go"
)

func main() {
    // Initialize client
    client := drp.NewClient(
        os.Getenv("DRP_API_KEY"),
        "issuer-bank.com",
        drp.Production, // or drp.Sandbox
    )
    
    // Load merchant private key
    if err := client.LoadPrivateKeyFromFile("./merchant-private-key.pem"); err != nil {
        log.Fatal(err)
    }
    
    ctx := context.Background()
    
    // Send a receipt
    if err := sendReceipt(ctx, client, "tok_card_abc123", "txn_auth_456"); err != nil {
        log.Printf("Error sending receipt: %v", err)
    }
}

func sendReceipt(ctx context.Context, client *drp.Client, cardToken, txnID string) error {
    // 1. Get customer's public key
    keyData, err := client.PublicKeys.Get(ctx, cardToken, &drp.PublicKeyOptions{
        TransactionID: txnID,
    })
    if err != nil {
        return fmt.Errorf("failed to get public key: %w", err)
    }
    
    // 2. Build receipt data
    receipt := buildReceiptData() // Your receipt JSON-LD
    
    // 3. Send encrypted receipt (SDK handles signing and encryption)
    result, err := client.Receipts.Send(ctx, &drp.SendReceiptParams{
        ReceiptID:           fmt.Sprintf("rcpt_%d", time.Now().Unix()),
        Receipt:             receipt,
        CustomerPublicKey:   keyData.PublicKey,
        CustomerPublicKeyID: keyData.KeyID,
        CardLastFour:        cardToken[len(cardToken)-4:],
        TransactionID:       txnID,
        MerchantID:          "mch_coffee_shop_001",
        Amount:              12.50,
        Currency:            "USD",
    })
    if err != nil {
        if drp.IsCustomerNotEnrolled(err) {
            log.Println("Customer not enrolled - skip DRP receipt")
            return nil
        }
        return fmt.Errorf("failed to send receipt: %w", err)
    }
    
    log.Printf("Receipt sent: %s", result.DeliveryConfirmation)
    return nil
}

func buildReceiptData() map[string]interface{} {
    return map[string]interface{}{
        "@context": "https://schema.org",
        "@type":    "Receipt",
        "totalPaymentDue": map[string]interface{}{
            "@type":         "PriceSpecification",
            "price":         12.50,
            "priceCurrency": "USD",
        },
        // ... rest of receipt
    }
}

HTTP Server Integration

package main

import (
    "encoding/json"
    "log"
    "net/http"
    "os"
    
    "github.com/digitalreceiptprotocol/drp-go"
)

var drpClient *drp.Client

func init() {
    drpClient = drp.NewClient(
        os.Getenv("DRP_API_KEY"),
        "issuer-bank.com",
        drp.Production,
    )
    drpClient.LoadPrivateKeyFromFile("./merchant-private-key.pem")
}

type CheckoutRequest struct {
    CardToken     string                 `json:"card_token"`
    TransactionID string                 `json:"transaction_id"`
    Receipt       map[string]interface{} `json:"receipt"`
    Amount        float64                `json:"amount"`
}

func handleCheckout(w http.ResponseWriter, r *http.Request) {
    var req CheckoutRequest
    if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }
    
    ctx := r.Context()
    
    // Get public key
    keyData, err := drpClient.PublicKeys.Get(ctx, req.CardToken, nil)
    if err != nil {
        log.Printf("DRP error: %v", err)
        json.NewEncoder(w).Encode(map[string]interface{}{
            "success": true,
            "drp":     false,
        })
        return
    }
    
    // Send receipt
    result, err := drpClient.Receipts.Send(ctx, &drp.SendReceiptParams{
        ReceiptID:           generateReceiptID(),
        Receipt:             req.Receipt,
        CustomerPublicKey:   keyData.PublicKey,
        CustomerPublicKeyID: keyData.KeyID,
        CardLastFour:        req.CardToken[len(req.CardToken)-4:],
        TransactionID:       req.TransactionID,
        MerchantID:          os.Getenv("MERCHANT_ID"),
        Amount:              req.Amount,
        Currency:            "USD",
    })
    if err != nil {
        log.Printf("DRP error: %v", err)
        json.NewEncoder(w).Encode(map[string]interface{}{
            "success": true,
            "drp":     false,
        })
        return
    }
    
    json.NewEncoder(w).Encode(map[string]interface{}{
        "success":      true,
        "confirmation": result.DeliveryConfirmation,
    })
}

func main() {
    http.HandleFunc("/checkout", handleCheckout)
    log.Fatal(http.ListenAndServe(":8080", nil))
}

Configuration

Client Options

import "github.com/digitalreceiptprotocol/drp-go"

// Basic client
client := drp.NewClient(
    "mch_live_abc123def456",  // API key
    "issuer-bank.com",         // Issuer domain
    drp.Production,            // Environment (Production or Sandbox)
)

// With custom options
client := drp.NewClientWithOptions(&drp.ClientOptions{
    APIKey:        "mch_live_abc123def456",
    IssuerDomain:  "issuer-bank.com",
    Environment:   drp.Production,
    Timeout:       30 * time.Second,
    MaxRetries:    3,
    Logger:        customLogger,
})

// Load private key
if err := client.LoadPrivateKeyFromFile("./merchant-private-key.pem"); err != nil {
    log.Fatal(err)
}

// Or set private key directly
privateKeyPEM := []byte(`-----BEGIN PRIVATE KEY-----...`)
if err := client.SetPrivateKey(privateKeyPEM); err != nil {
    log.Fatal(err)
}

API Reference

PublicKeys Methods

`Get(ctx, cardToken, options)`

keyData, err := client.PublicKeys.Get(
    ctx,
    "tok_card_abc123",
    &drp.PublicKeyOptions{
        TransactionID: "txn_auth_456",
    },
)
if err != nil {
    return err
}

fmt.Println(keyData.PublicKey)  // PEM-formatted public key
fmt.Println(keyData.KeyID)      // Key identifier
fmt.Println(keyData.ExpiresAt)  // Expiration time

Returns: *PublicKeyData, error

Receipts Methods

`Send(ctx, params)`

result, err := client.Receipts.Send(ctx, &drp.SendReceiptParams{
    ReceiptID:           "rcpt_unique_123",
    Receipt:             receiptData,
    CustomerPublicKey:   keyData.PublicKey,
    CustomerPublicKeyID: keyData.KeyID,
    CardLastFour:        "1234",
    TransactionID:       "txn_auth_456",
    MerchantID:          "mch_coffee_shop_001",
    Amount:              12.50,
    Currency:            "USD",
})
if err != nil {
    return err
}

fmt.Println(result.DeliveryConfirmation)
fmt.Println(result.IssuerSignature)

Returns: *ReceiptResponse, error

`List(ctx, filters)` - User Client Only

userClient := drp.NewUserClient(
    userOAuthToken,
    "your-bank.com",
)

response, err := userClient.Receipts.List(ctx, &drp.ReceiptsListOptions{
    StartDate:  "2025-11-01",
    EndDate:    "2025-12-07",
    MerchantID: "mch_coffee_shop_001",
    Limit:      20,
    Offset:     0,
})
if err != nil {
    return err
}

for _, receipt := range response.Receipts {
    fmt.Printf("Receipt from %s: $%.2f\n", receipt.MerchantName, receipt.Amount)
}

Returns: *ReceiptsListResponse, error

Merchants Methods

`Register(ctx, data)`

registration, err := drp.RegisterMerchant(ctx, &drp.RegistrationParams{
    RegistrationKey: "reg_key_xyz789",
    IssuerDomain:    "issuer-bank.com",
    MerchantID:      "mch_coffee_shop_001",
    MerchantName:    "Joe's Coffee Shop",
    ContactEmail:    "[email protected]",
    CallbackURL:     "https://coffeeshop.com/drp/webhook",
    PublicKey:       publicKeyPEM,
    BusinessAddress: &drp.Address{
        Street:     "123 Main St",
        City:       "Seattle",
        State:      "WA",
        PostalCode: "98101",
        Country:    "US",
    },
})
if err != nil {
    return err
}

// IMPORTANT: Save these securely!
fmt.Println(registration.APIKey)
fmt.Println(registration.WebhookSecret)

Returns: *RegistrationResponse, error

Crypto Utilities

// Encrypt data
encrypted, err := client.Crypto.Encrypt(
    []byte(receiptJSON),
    customerPublicKey,
)

// Decrypt data
decrypted, err := client.Crypto.Decrypt(
    encryptedData,
    userPrivateKey,
)

// Sign data
signature, err := client.Crypto.Sign(
    []byte(receiptJSON),
    merchantPrivateKey,
)

// Verify signature
valid, err := client.Crypto.Verify(
    []byte(receiptJSON),
    signature,
    merchantPublicKey,
)

Error Handling

import (
    "errors"
    "github.com/digitalreceiptprotocol/drp-go"
)

result, err := client.Receipts.Send(ctx, params)
if err != nil {
    // Check for specific error types
    var rateLimitErr *drp.RateLimitError
    var authErr *drp.AuthenticationError
    
    switch {
    case errors.As(err, &rateLimitErr):
        log.Printf("Rate limited. Retry after %d seconds", rateLimitErr.RetryAfter)
        time.Sleep(time.Duration(rateLimitErr.RetryAfter) * time.Second)
        // Retry logic
        
    case errors.As(err, &authErr):
        log.Fatal("Invalid API key")
        
    case drp.IsCustomerNotEnrolled(err):
        // Customer not enrolled - skip DRP receipt
        log.Println("Customer not enrolled")
        return nil
        
    case drp.IsValidationError(err):
        log.Printf("Validation error: %v", err)
        
    default:
        log.Printf("DRP error: %v", err)
        return err
    }
}

Error Types

type DRPError struct {
    Code    string
    Message string
    Details string
}

type RateLimitError struct {
    DRPError
    RetryAfter int
}

type AuthenticationError struct{ DRPError }
type ValidationError struct{ DRPError }
type NetworkError struct{ DRPError }
type EncryptionError struct{ DRPError }
type SignatureError struct{ DRPError }

Helper Functions

drp.IsCustomerNotEnrolled(err) bool
drp.IsRateLimitError(err) bool
drp.IsValidationError(err) bool
drp.IsAuthenticationError(err) bool

Context & Cancellation

All SDK methods accept context.Context for cancellation and timeouts:

import "context"

// With timeout
ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()

result, err := client.Receipts.Send(ctx, params)
if err != nil {
    if errors.Is(err, context.DeadlineExceeded) {
        log.Println("Request timed out")
    }
    return err
}

// With cancellation
ctx, cancel := context.WithCancel(context.Background())

go func() {
    time.Sleep(2 * time.Second)
    cancel() // Cancel after 2 seconds
}()

result, err := client.Receipts.Send(ctx, params)

Concurrency

The Go SDK is thread-safe and designed for concurrent use:

var wg sync.WaitGroup

for _, transaction := range transactions {
    wg.Add(1)
    
    go func(txn Transaction) {
        defer wg.Done()
        
        if err := sendReceipt(ctx, client, txn.CardToken, txn.ID); err != nil {
            log.Printf("Error sending receipt for %s: %v", txn.ID, err)
        }
    }(transaction)
}

wg.Wait()

Connection Pooling

The SDK automatically manages HTTP connection pooling. Configure if needed:

import "net/http"

transport := &http.Transport{
    MaxIdleConns:        100,
    MaxIdleConnsPerHost: 10,
    IdleConnTimeout:     90 * time.Second,
}

client := drp.NewClientWithOptions(&drp.ClientOptions{
    APIKey:       os.Getenv("DRP_API_KEY"),
    IssuerDomain: "issuer-bank.com",
    HTTPClient:   &http.Client{Transport: transport},
})

Webhooks

Handle webhook events from issuers:

package main

import (
    "encoding/json"
    "io"
    "log"
    "net/http"
    "os"
    
    "github.com/digitalreceiptprotocol/drp-go/webhooks"
)

func handleWebhook(w http.ResponseWriter, r *http.Request) {
    signature := r.Header.Get("X-DRP-Signature")
    webhookSecret := os.Getenv("DRP_WEBHOOK_SECRET")
    
    // Read body
    body, err := io.ReadAll(r.Body)
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }
    
    // Verify signature
    if !webhooks.Verify(body, signature, webhookSecret) {
        http.Error(w, "Invalid signature", http.StatusUnauthorized)
        return
    }
    
    // Parse event
    var event webhooks.Event
    if err := json.Unmarshal(body, &event); err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }
    
    // Handle event
    switch event.Type {
    case webhooks.ReceiptDelivered:
        log.Printf("Receipt %s delivered", event.ReceiptID)
        
    case webhooks.ReceiptDisputed:
        log.Printf("Receipt %s disputed: %s", 
            event.ReceiptID, 
            event.Details.DisputeReason,
        )
        // Handle dispute
    }
    
    w.WriteHeader(http.StatusOK)
    json.NewEncoder(w).Encode(map[string]bool{"received": true})
}

func main() {
    http.HandleFunc("/drp/webhook", handleWebhook)
    log.Fatal(http.ListenAndServe(":8080", nil))
}

Testing

Mock Client

package main

import (
    "testing"
    
    "github.com/digitalreceiptprotocol/drp-go/mocks"
    "github.com/stretchr/testify/assert"
    "github.com/stretchr/testify/mock"
)

func TestSendReceipt(t *testing.T) {
    // Create mock client
    mockClient := new(mocks.Client)
    
    // Set expectations
    mockClient.On("Send", mock.Anything, mock.Anything).Return(
        &drp.ReceiptResponse{
            Status:               "accepted",
            ReceiptID:            "rcpt_123",
            DeliveryConfirmation: "conf_456",
        },
        nil,
    )
    
    // Use mock in test
    result, err := mockClient.Send(ctx, params)
    
    assert.NoError(t, err)
    assert.Equal(t, "accepted", result.Status)
    mockClient.AssertExpectations(t)
}

Best Practices

Use Context for Timeouts

Always pass context with timeout to prevent hanging requests:

ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()

result, err := client.Receipts.Send(ctx, params)

Handle Errors Properly

Check for CustomerNotEnrolled explicitly - it’s not an error:

if drp.IsCustomerNotEnrolled(err) {
    // Normal case - skip DRP receipt
    return nil
}

Reuse Client Instances

Create one client instance and reuse it across requests. It manages connection pooling internally.

Use Goroutines for Async Processing

Send receipts concurrently but limit concurrency:

semaphore := make(chan struct{}, 10) // Max 10 concurrent

for _, txn := range transactions {
    semaphore <- struct{}{}
    go func(t Transaction) {
        defer func() { <-semaphore }()
        sendReceipt(ctx, client, t)
    }(txn)
}

Store Keys Securely

Use environment variables or secret management (AWS Secrets Manager, HashiCorp Vault) for API keys and private keys.

Resources

GitHub Repository

Source code, examples, and issue tracking

Go Package

Package documentation

API Reference

Complete API documentation

Support

Get help with integration

Changelog

v1.0.0 (Latest)

Initial stable release
Full support for DRP API v1
Context support throughout
Thread-safe client
Connection pooling

v0.9.0 (Beta)

Beta release for testing
Core merchant and user APIs

See full changelog on GitHub.

Overview

Server SDKs

Go SDK

DRP Go SDK

Installation

Quick Start

Merchant Integration

HTTP Server Integration

Configuration

Client Options

API Reference

PublicKeys Methods

`Get(ctx, cardToken, options)`

Receipts Methods

`Send(ctx, params)`

`List(ctx, filters)` - User Client Only

Merchants Methods

`Register(ctx, data)`

Crypto Utilities

Error Handling

Error Types

Helper Functions

Context & Cancellation

Concurrency

Connection Pooling

Webhooks

Testing

Mock Client

Best Practices

Resources

GitHub Repository

Go Package

API Reference

Support

Changelog

v1.0.0 (Latest)

v0.9.0 (Beta)

Overview

Server SDKs

​DRP Go SDK

​Installation

​Quick Start

​Merchant Integration

​HTTP Server Integration

​Configuration

​Client Options

​API Reference

​PublicKeys Methods

​Get(ctx, cardToken, options)

​Receipts Methods

​Send(ctx, params)

​List(ctx, filters) - User Client Only

​Merchants Methods

​Register(ctx, data)

​Crypto Utilities

​Error Handling

​Error Types

​Helper Functions

​Context & Cancellation

​Concurrency

​Connection Pooling

​Webhooks

​Testing

​Mock Client

​Best Practices

​Resources

GitHub Repository

Go Package

API Reference

Support

​Changelog

​v1.0.0 (Latest)

​v0.9.0 (Beta)

DRP Go SDK

Installation

Quick Start

Merchant Integration

HTTP Server Integration

Configuration

Client Options

API Reference

PublicKeys Methods

`Get(ctx, cardToken, options)`

Receipts Methods

`Send(ctx, params)`

`List(ctx, filters)` - User Client Only

Merchants Methods

`Register(ctx, data)`

Crypto Utilities

Error Handling

Error Types

Helper Functions

Context & Cancellation

Concurrency

Connection Pooling

Webhooks

Testing

Mock Client

Best Practices

Resources

Changelog

v1.0.0 (Latest)

v0.9.0 (Beta)