BIAN Go

Banking Industry Architecture Network interfaces for Go

A Go library providing BIAN-compliant banking interfaces with dual API layer (REST + GraphQL). Built for developers creating fintech applications with open banking integration.

Repository: github.com/serverlesscloud/bian-go

🎆 Key Features

• 🌍 Cloud-portable - Deploy anywhere (Docker, Kubernetes, serverless)
• 🔄 Provider-agnostic - Swap between CDR, Plaid, Open Banking implementations
• 🚀 Dual API - Both REST and GraphQL on single server
• 🔒 Type-safe - Compile-time guarantees with Go's type system
• 💰 Decimal precision - No floating-point errors in financial calculations
• 🏦 BIAN v13.0.0 aligned - Standardized banking operations
• 🧪 Mock provider - Development without external dependencies
• ⚙️ Zero dependencies - REST API uses only Go standard library

🚀 Quick Start

go get github.com/serverlesscloud/bian-go

import (
    "github.com/serverlesscloud/bian-go/providers/mock"
    "github.com/serverlesscloud/bian-go/server"
)

provider := mock.NewProvider()
config := server.DefaultConfig()
srv := server.NewServer(provider, provider, provider, provider, config)
srv.Start() // Starts both REST and GraphQL APIs

Server URLs:

• REST API: http://localhost:8080/
• GraphQL API: http://localhost:8080/graphql
• GraphQL Playground: http://localhost:8080/playground
• Health Check: http://localhost:8080/health

See examples/ directory for complete working implementations.

🏢 Architecture

Three-Layer Design

API Layer (REST + GraphQL)
    ↓
Domain Layer (BIAN Interfaces)
    ↓
Provider Layer (CDR/Plaid/Open Banking)

Key principle: Business logic lives in domain layer, transport is swappable.

Dual API Support

Both REST and GraphQL APIs call domain interfaces directly (parallel implementations):

• Zero coupling between REST and GraphQL
• No performance overhead (both call domain directly)
• Independent evolution of each API

Supported Standards

Region	Standard	Provider Package	Status
🇦🇺 Australia	Consumer Data Right (CDR)	providers/cdr	Planned
🇺🇸 🇨🇦 US/Canada	Plaid	providers/plaid	Planned
🇬🇧 UK	Open Banking	providers/obuk	Planned
🇪🇺 EU	PSD2	providers/psd2	Planned
🧪 Testing	Mock	providers/mock	Available

📁 Project Structure

bian-go/
├── domains/              # BIAN service interfaces
│   ├── accounts.go
│   ├── transactions.go
│   ├── consents.go
│   └── balance.go
│
├── models/               # Canonical data types
│   ├── account.go
│   ├── transaction.go
│   ├── money.go
│   └── enums.go
│
├── rest/                 # REST API layer
│   ├── handlers.go
│   ├── middleware.go
│   └── server.go
│
├── graphql/              # GraphQL API layer
│   ├── schema.graphql
│   ├── resolver.go
│   ├── server.go
│   └── generated/        # gqlgen output
│
├── providers/            # Banking implementations
│   └── mock/            # Testing provider
│
├── server/               # Unified server
└── examples/            # Working examples

🔌 Core Interfaces

See domains/ for complete interface definitions. Key patterns:

• AccountService - Account lifecycle and balance queries (BIAN Current Account Fulfillment)
• TransactionService - Payment execution and transaction history (BIAN Payment Execution)
• BalanceService - Balance information (BIAN Account Balance Management)
• ConsentService - OAuth consent management (BIAN Customer Consent Management)

All interfaces accept context.Context as first parameter for cancellation/timeouts.

🌐 REST API

Base URL: http://localhost:8080/

Account Endpoints

# Get account details
GET /accounts/{id}

# Get current balance
GET /accounts/{id}/balance

# Get all balance types
GET /accounts/{id}/balances

# Get transaction history
GET /accounts/{id}/transactions?fromDate=2024-01-01&limit=10

Transaction Endpoints

# Get transaction details
GET /transactions/{id}

Consent Endpoints

# Get consent details
GET /consents/{id}

# Get consent status
GET /consents/{id}/status

🔍 GraphQL API

Endpoint: http://localhost:8080/graphql
Playground: http://localhost:8080/playground

Example Queries

# Get account with balance
query {
  account(id: "acc-001") {
    id
    accountNumber
    accountType
    productName
    status
  }
  
  balance(accountId: "acc-001") {
    balanceType
    amount {
      amount
      currency
    }
  }
}

# Get transaction history
query {
  transactions(accountId: "acc-001", input: {
    limit: 10
    fromDate: "2024-01-01"
  }) {
    id
    transactionType
    amount {
      amount
      currency
    }
    description
    postingDate
  }
}

Configuration via gqlgen.yml. Run go generate ./... to regenerate after schema changes.

📦 Provider Implementation

Implement domain interfaces to create new providers:

type MyProvider struct {
    client *BankingAPIClient
}

func (p *MyProvider) RetrieveCurrentAccount(ctx context.Context, id string) (*models.Account, error) {
    // 1. Call external banking API
    // 2. Normalize to BIAN canonical model
    // 3. Return standardized Account
}

See providers/mock/ for reference implementation.

💰 Money Model

Precise decimal arithmetic for financial calculations:

// Create money amounts
aud, _ := models.NewMoney(decimal.NewFromFloat(123.45), "AUD")
usd, _ := models.NewMoney(decimal.NewFromFloat(100.00), "USD")

// Arithmetic operations
sum, _ := aud.Add(otherAUD)
product := aud.Multiply(decimal.NewFromFloat(1.5))

// Comparisons
equal := aud.Equal(otherAUD)
greater, _ := aud.GreaterThan(otherAUD)

// JSON serialization (string format for precision)
// {"amount": "123.45", "currency": "AUD"}

Supported Currencies: AUD, USD, GBP, EUR, CAD, JPY, CHF, CNY, SEK, NZD

🧪 Mock Provider

Includes realistic sample data for development:

Sample Accounts

• acc-001: Checking Account (AUD $2,547.83)
• acc-002: Savings Account (AUD $15,420.50)
• acc-003: Credit Card (USD -$1,250.75)

Sample Transactions

• 11 transactions across accounts
• Various types: debit, credit, transfer, payment, fee
• Realistic merchants: Woolworths, Energy Australia, Amazon

Sample Consents

• consent-001: Active (account:read, transaction:read, balance:read)
• consent-002: Expired
• consent-003: Revoked

🔧 Development

# Install dependencies
go mod download

# Generate GraphQL code
go generate ./...

# Run tests
go test ./...

# Run example server
cd examples/basic && go run main.go

# Build Docker image
docker build -t bian-go .

# Run in Docker
docker run -p 8080:8080 bian-go

Environment Variables

• PORT: Server port (default: 8080)
• ENABLE_PLAYGROUND: Enable GraphQL Playground (default: true)

🔄 BIAN Spec Synchronization

Automated workflow syncs with BIAN releases:

• Weekly checks for new Service Landscape versions
• Auto-generates PRs with updated OpenAPI specs
• Validates breaking changes

See .github/workflows/bian-sync.yml

📝 Contributing

See CONTRIBUTING.md

Key areas for contribution:

• New provider implementations (regional banking standards)
• Performance optimizations
• Documentation improvements
• Test coverage expansion

👥 Contributors

• Amazon Q Developer - 3 Musketeers build system implementation, DevOps automation

📋 License

Apache License 2.0 - See LICENSE

Patent protection, corporate-friendly, permissive for commercial use.