Blong Layer

Implementing a Layer

Overview

Layers are named groups of handlers that organize code by functional concern within a realm. They enable clear separation of responsibilities and support the framework's modular architecture.

Key Pattern: Layers are self-contained — each layer file defines its own configuration and validation, co-located with its implementation. No need to maintain configuration in a central server.ts.

Purpose

• Separation of Concerns: Group related functionality together
• Co-located Config: Each layer owns its configuration and validation
• Code Organization: Clear folder structure for handlers
• Deployment Control: Layers can be activated/deactivated per environment
• Team Coordination: Different teams can work on different layers

Recommended Layer Names

Server-Side Layers (auto-detected)

• gateway - API gateway: routes, validation, documentation (minimal business logic)
• adapter - External system communication: SQL, HTTP, FTP, mail protocols
• orchestrator - Business process coordination between adapters
• error - Domain-specific error definitions
• test - Test automation (dev/build only)
• eft - Electronic Funds Transfer (high TPS OLTP requirements)

Browser-Side Layers (auto-detected)

• backend - Browser adapter talking to server
• component - React UI components
• browser - Server-side code serving browser assets

Folder Structure

Typical Realm with Layers

Well-known layer folders are auto-discovered — no layer.server.ts needed:

realmname/
├── server.ts            # Optional — only for realm-level config/validation
├── error/               # Auto-activated (well-known name)
│   └── error.ts
├── adapter/             # Auto-activated (well-known name)
│   ├── db.ts            # Self-contained database adapter (with config)
│   ├── http.ts          # Self-contained HTTP adapter (with config)
│   └── db/              # Handler group: realmname.db
│       ├── userUserAdd.ts
│       └── userUserFind.ts
├── orchestrator/        # Auto-activated (well-known name)
│   └── dispatch.ts      # Self-contained orchestrator (with config)
└── gateway/             # Auto-activated (well-known name)
    └── api/
        └── user.yaml

Custom (non-well-known) layer folders need a layer.server.ts or layer.browser.ts:

realmname/
└── myCustomLayer/
    └── layer.server.ts  # Required: declares activation for non-well-known folder

layer.server.ts / layer.browser.ts

For folders with non-standard names, add a layer.server.ts or layer.browser.ts to declare activation. This eliminates the need for an explicit children array or activation config in the parent server.ts.

// myCustomLayer/layer.server.ts
import {layer} from '@feasibleone/blong';

export default layer({
    default: true, // active in all environments
    microservice: true, // additionally active in microservice deployment
});

// myBrowserLayer/layer.browser.ts
import {layer} from '@feasibleone/blong';

export default layer({
    integration: true, // only active during integration testing
});

Well-Known Layer Default Activations

Self-Contained Layer Pattern

Adapter Layer Definition

// adapter/db.ts - self-contained with config and validation
import {adapter} from '@feasibleone/blong';

export default adapter(blong => ({
    extends: 'adapter.knex',

    // Layer's own validation schema
    validation: blong.type.Object({
        namespace: blong.type.Union([blong.type.String(), blong.type.Array(blong.type.String())]),
        imports: blong.type.Union([blong.type.String(), blong.type.Array(blong.type.String())]),
        logLevel: blong.type.Optional(blong.type.String()),
    }),

    // Layer's own configuration per environment
    activation: {
        default: {
            namespace: 'db/$subject',
            imports: '$subject.db',
        },
        dev: {
            logLevel: 'trace',
        },
        prod: {
            logLevel: 'warn',
        },
    },
}));

Orchestrator Layer Definition

// orchestrator/dispatch.ts - self-contained with config and validation
import {orchestrator} from '@feasibleone/blong';

export default orchestrator(blong => ({
    extends: 'orchestrator.dispatch',

    validation: blong.type.Object({
        namespace: blong.type.Union([blong.type.String(), blong.type.Array(blong.type.String())]),
        imports: blong.type.Union([
            blong.type.String(),
            blong.type.Array(blong.type.String()),
            blong.type.Array(blong.type.RegExp()),
        ]),
        validations: blong.type.Optional(
            blong.type.Array(blong.type.Union([blong.type.String(), blong.type.RegExp()])),
        ),
        destination: blong.type.Optional(blong.type.String()),
    }),

    activation: {
        default: {
            destination: 'db',
            namespace: ['$subject'],
            imports: [/^$subject\./],
            validations: [/^$subject\.\w+\.validation$/],
        },
    },
}));

Realm Entry Point (Only When Needed)

server.ts is optional. It is only needed when there is realm-level config or validation shared across layers.

// server.ts — only when realm-level config is needed
import {realm} from '@feasibleone/blong';

export default realm(blong => ({
    url: import.meta.url,
    validation: blong.type.Object({
        myService: blong.type.Object({url: blong.type.String()}),
    }),
    activation: {
        default: {
            myService: {url: 'http://localhost:8080'},
        },
    },
}));

Handler Group Pattern

Group Naming Convention

Groups are named in format: realmname.foldername

Example:

• Realm: user
• Folder: orchestrator/user/
• Group name: user.user

Referencing Groups

Groups are referenced in the imports property of the adapter/orchestrator:

// adapter/db.ts - imports declared inline
export default adapter(blong => ({
    extends: 'adapter.knex',
    activation: {
        default: {
            namespace: ['user', 'role'],
            imports: ['user.user', 'user.role'], // handler groups loaded
        },
    },
}));

Implementation Patterns

Error Layer

// realmname/error/error.ts
export default {
    userNotFound: 'User not found',
    userExists: 'User already exists',
    invalidEmail: 'Invalid email format',
    permissionDenied: 'Permission denied',
};

Adapter Layer Structure

adapter/
├── db.ts              # Self-contained database adapter
├── http.ts            # Self-contained HTTP adapter
├── db/                # Handler group for db operations
│   ├── userAdd.ts
│   └── userFind.ts
└── http/              # Handler group for HTTP operations
    ├── send.ts
    └── receive.ts

Orchestrator Layer Structure

orchestrator/
├── dispatch.ts        # Self-contained orchestrator definition
├── entity1/           # Handler group: realmname.entity1
│   ├── ~.schema.ts   # Auto-generated validation
│   ├── helper.ts     # Library function
│   └── realmEntity1Action.ts
└── entity2/           # Handler group: realmname.entity2
    ├── ~.schema.ts
    └── realmEntity2Action.ts

Gateway Layer Structure

gateway/
└── api/
    ├── entity1.yaml   # OpenAPI spec for entity1
    └── entity2.yaml   # OpenAPI spec for entity2

Or with custom validation:

gateway/
└── entity/
    ├── entityAction1.ts  # Manual validation
    └── entityAction2.ts

Test Layer Structure

test/
└── test/              # Handler group: test.test
    ├── testEntity1.ts
    ├── testEntity2.ts
    └── testWorkflow.ts

Layer Activation

In Realm Configuration (server.ts)

export default realm(blong => ({
    config: {
        // Activate for automated testing
        test: {
            error: true,
            adapter: true,
            orchestrator: true,
            gateway: true,
            test: true,
        },

        // Activate for microservice deployment
        microservice: {
            error: true,
            adapter: true,
            orchestrator: true,
            gateway: true,
        },

        // Activate for single realm dev focus
        realm: {
            adapter: true,
            orchestrator: true,
        },

        // Development with full stack
        dev: {
            error: true,
            adapter: true,
            orchestrator: true,
            gateway: true,
        },
    },
}));

One Handler Per File Pattern

Benefits

1. Fast Discovery: Use ctrl+p in VS Code to find handlers quickly
   • Example: ctrl+p uua finds userUserAdd.ts
2. Easier Code Review: Smaller files, less nesting
3. Better Isolation: Clear boundaries between handlers
4. Git-Friendly: Smaller diffs, fewer conflicts

Naming Convention

File name = handler name:

• Handler: userUserAdd → File: userUserAdd.ts
• Handler: mathNumberSum → File: mathNumberSum.ts
• Library: validateEmail → File: validateEmail.ts

Adding a New Adapter

Before (Old Pattern) - Touch 2 files

// 1. Create adapter/newadapter.ts
export default adapter(() => ({
    extends: 'adapter.http',
}));

// 2. Update server.ts validation + config + children
// (3 edits in server.ts)

After (New Pattern) - Touch 1 file

// 1. Create adapter/newadapter.ts - everything co-located
export default adapter(blong => ({
    extends: 'adapter.http',

    validation: blong.type.Object({
        url: blong.type.String(),
        timeout: blong.type.Number(),
    }),

    activation: {
        default: {
            url: 'http://api.example.com',
            timeout: 5000,
        },
    },
}));

// 2. Done! Framework uses the layer's own config.

Multi-Layer Example

Complete Realm Structure

payment/
├── server.ts           # Minimal - activation only
├── error/
│   └── error.ts
├── adapter/
│   ├── db.ts           # Self-contained: config + validation inside
│   ├── fspiop.ts       # Self-contained: config + validation inside
│   └── db/
│       ├── paymentCreate.ts
│       └── paymentFind.ts
├── orchestrator/
│   ├── dispatch.ts     # Self-contained: config + validation inside
│   ├── transfer/
│   │   ├── ~.schema.ts
│   │   ├── calculateFees.ts
│   │   ├── paymentTransferPrepare.ts
│   │   └── paymentTransferCommit.ts
│   └── quote/
│       ├── ~.schema.ts
│       └── paymentQuoteCreate.ts
├── gateway/
│   └── api/
│       ├── transfer.yaml
│       └── quote.yaml
└── test/
    └── test/
        ├── testTransfer.ts
        └── testQuote.ts

Best Practices

1. Co-locate Config: Put layer configuration in the layer file, not in server.ts
2. Clear Separation: Keep business logic in orchestrator, not gateway
3. Consistent Naming: Use lowercase single words for layer names
4. Group by Entity: Organize handlers by business entity within layers
5. Library Functions: Extract reusable code into library functions
6. Error Definitions: Always define errors in error layer first
7. Test Coverage: Create test layer with comprehensive test handlers
8. One File Per Handler: Follow the one handler per file pattern
9. Validation: Use ~.schema.ts for automatic validation generation
10. Import Order: Load layers in order: error → adapter → orchestrator → gateway → test

Examples from Codebase

• Complete realm: core/test/demo/
• Payment realm: ml/payment/
• Agreement realm: ml/agreement/