lambder

Lambder - Serverless NodeJS Web Framework (v2.0)

Lambder is a highly opinionated dynamic serverless framework designed to facilitate the management and implementation of routes and APIs within AWS Lambda functions, specifically tailored for TypeScript projects. It provides a streamlined approach to handling HTTP requests, managing sessions, and defining API routes, making serverless application development more intuitive and structured.

New in v2.0: Full type safety with Zod schemas and runtime validation!

Features

• Type-Safe APIs with Zod: Define inputs and outputs with Zod schemas. Get automatic runtime validation and compile-time type inference.
• Method Chaining: Build your API contract incrementally with a fluent interface.
• Simple API & Route Declaration: Define your APIs and routes using concise and expressive syntax.
• Session Management: Built-in session management to secure and personalize user experiences.
• Flexible Hooks System: Employ hooks to execute code at different stages of the request lifecycle.
• Error Handling: Comprehensive error handling capabilities, including global error handlers and route-specific fallbacks.
• Seamless Integration: Designed to work effortlessly with AWS Lambda and API Gateway.

Installation

npm install lambder zod
# or
yarn add lambder zod

Backend Usage

Basic Setup

import Lambder from 'lambder';
import { z } from 'zod';
import * as path from 'path';

const lambder = new Lambder({
    apiPath: "/api",
    publicPath: path.resolve(`./public`),
});

// Enable session and CORS
lambder
    .enableDdbSession({
        tableName: "website-session",
        tableRegion: "us-east-1",
        sessionSalt: "CHANGE-THIS-TO-A-SECURE-RANDOM-STRING"
    })
    .enableCors(true);

// Define type-safe APIs with Zod schemas
lambder
    .addApi("getCompanyPage", {
        input: z.object({ companyName: z.string() }),
        output: z.object({ id: z.string(), name: z.string(), description: z.string() })
    }, async ({ apiPayload }, res) => {
        // apiPayload is automatically typed and validated!
        const data = await fetchDataSomehow(apiPayload.companyName);
        return res.api(data); // Return value is type-checked
    })
    .addApi("loginUser", {
        input: z.object({ email: z.string().email(), password: z.string() }),
        output: z.object({ success: z.boolean(), token: z.string().optional() })
    }, async (ctx, res) => {
        const user = await authenticateUser(ctx.apiPayload.email, ctx.apiPayload.password);
        if (!user) {
            return res.api({ success: false });
        }
        
        await lambder.getSessionController(ctx).createSession(user.id);
        return res.api({ success: true, token: "session-token" });
    });

// Export the inferred contract for the frontend
export type ApiContractType = typeof lambder.ApiContract;

// Export the handler
export const handler = lambder.getHandler();

Adding Routes

lambder
    // Define a simple route
    .addRoute("/hello-world", (ctx, res) => {
        return res.html("Hello World");
    })
    // Route with parameters
    .addRoute("/user/:userId", async (ctx, res) => {
        const user = await getUser(ctx.pathParams.userId);
        if(!user) return res.status404("Not found");
        return res.html(`Hello ${user.name}`);
    })
    // Define a regex route
    .addRoute(/\/hello-regex/, (ctx, res) => {
        return res.html("Hello Regex");
    })
    // Function routes allows routing on any context variable
    .addRoute((ctx)=>ctx.path === '/hello-fn-route', (ctx, res) => {
        return res.html("Hello from a function route");
    })
    // Match all other paths and serve static files from publicPath
    .addRoute("/(.*)", (ctx, res)=>{
        return res.file(ctx.path, {}, "index.html");
    })
    // Set a fallback handler for unmatched routes
    .setRouteFallbackHandler((ctx, res) => {
        return res.status404("Not Found");
    })
    // Set a fallback handler for unmatched APIs
    .setApiFallbackHandler((ctx, res) => {
        return res.api(null, { errorMessage: "API not found" });
    })
    // Handle Zod validation errors for API inputs
    .setApiInputValidationErrorHandler((ctx, res, zodError) => {
        return res.api(null, { errorMessage: zodError.errors });
    })
    // Global error handler
    .setGlobalErrorHandler((err, ctx, res) => {
        console.error("Error:", err);
        return res.raw({ statusCode: 500, body: "Internal Server Error" });
    });

Session-Protected APIs

Use addSessionApi for endpoints that require authentication:

lambder.addSessionApi("getProfile", {
    input: z.void(),
    output: z.object({ userId: z.string(), username: z.string() })
}, async (ctx, res) => {
    // Session is automatically fetched and validated
    return res.api({
        userId: ctx.session.data.userId,
        username: ctx.session.data.username
    });
});

Modular APIs with .use()

For larger applications, split your APIs into separate modules:

// user-api.ts
import { z } from "zod";
import Lambder from "lambder";

export const userApi = <T>(l: Lambder<T>) => {
    return l
        .addApi("getUser", {
            input: z.object({ id: z.string() }),
            output: z.object({ id: z.string(), name: z.string() })
        }, async (ctx, res) => {
            return res.api({ id: ctx.apiPayload.id, name: "User" });
        })
        .addApi("createUser", {
            input: z.object({ name: z.string(), email: z.string() }),
            output: z.object({ id: z.string() })
        }, async (ctx, res) => {
            return res.api({ id: "123" });
        });
};

// index.ts
import { userApi } from "./user-api";

const lambder = new Lambder({ publicPath: './public' })
    .use(userApi);

export type ApiContractType = typeof lambder.ApiContract;

Hooks

Lambder provides hooks to execute code at different stages of the request lifecycle.

lambder
    // Before render hook
    .addHook("beforeRender", async (ctx, res) => {
        // Perform actions before rendering
        console.log("Request received:", ctx.path);
        return ctx; // Return modified context or throw an Error
    })
    // After render hook
    .addHook("afterRender", async (ctx, res, response) => {
        // Modify response before sending
        console.log("Response status:", response.statusCode);
        return response;
    })
    // Fallback hook - runs when no route/API matches
    .addHook("fallback", async (ctx, res) => {
        // Perform cleanup or logging for unmatched requests
        console.log("No handler matched for:", ctx.path);
    });

Session Management

Enable DynamoDB-based sessions with enableDdbSession(). Optional configuration:

lambder
    .enableDdbSession({
        tableName: "website-session",
        tableRegion: "us-east-1",
        sessionSalt: "CHANGE-THIS-TO-A-SECURE-RANDOM-STRING",
        enableSlidingExpiration: true // Optional: extend session on each access
    })
    // Optionally customize session cookie names (defaults: LMDRSESSIONTKID, LMDRSESSIONCSTK)
    .setSessionCookieKey("MY_SESSION_TOKEN", "MY_CSRF_TOKEN");

DynamoDB Session Table Structure

• Primary Key: "pk"
• Sort Key: "sk"
• TTL Key: "expiresAt" (optional, recommended)

See docs/DYNAMODB_SETUP.md for detailed setup instructions.

Session Controller

Access the session controller with lambder.getSessionController(ctx):

Method	Description
createSession(sessionKey, data?, ttlInSeconds?)	Start new session, persist to DDB
fetchSession()	Fetch & validate existing session (throws if not found)
fetchSessionIfExists()	Returns session or null
updateSessionData(newData)	Update session data in DDB
endSession()	End session, delete from DDB
endSessionAll()	End all sessions for this sessionKey (all devices)
regenerateSession()	Regenerate token (use after password change)

EJS Templates

EJS templates have the variables page and partial available:

• Template: The main file called with await res.ejsFile('template-file'). Has page variable.
• Partial: Included from a template with <%- await include('partial/header.html.ejs', partialData) -%>. Has both page and partial variables.

Example template:

<div>
    <%- await include('partial/header.html.ejs', partialData) -%>
    <div>Page Variable: <pre><%~ JSON.stringify(page, null, 2) %></pre></div>
    <%- await include('partial/footer.html.ejs', partialData) -%>
</div>

Example partial:

<div>
    <div>Page Variable: <pre><%~ JSON.stringify(page, null, 2) %></pre></div>
    <div>Partial Variable: <pre><%~ JSON.stringify(partial, null, 2) %></pre></div>
</div>

Render Context (ctx) Variables

The ctx object provides access to request data:

Property	Description	Example
host	Request host	"www.example.com"
path	Request path	"/api"
pathParams	Path parameters (routes)	{ userId: "123" }
method	HTTP method	"GET", "POST"
get	Query parameters	{ page: "1" }
post	POST body (parsed)	{ name: "John" }
cookie	Cookies	{ rememberMe: "true" }
headers	Request headers	{ "Content-Type": "..." }
event	Raw APIGatewayProxyEvent	-
lambdaContext	AWS Lambda Context	-
apiName	API name (for API calls)	"getUser"
apiPayload	Validated input	{ userId: "123" }
session	Session data	Available in addSessionApi

Resolver Methods

Header Manipulation (call before returning response):

• res.addHeader(key, value) - Adds a header value (can be called multiple times for same key)
• res.setHeader(key, value) - Sets a header (replaces existing values)
• res.logToApiResponse(data) - Adds data to logList in API responses (debugging)

Response Methods:

Method	Description
res.raw(param)	Custom HTTP response
res.json(data, headers?)	JSON response
res.xml(data)	XML response (base64 encoded)
res.html(data, headers?)	HTML response (base64 encoded)
res.redirect(url, statusCode?, headers?)	Redirect (default: 302)
res.status404(data, headers?)	404 Not Found response
res.cors()	200 OK with CORS headers (preflight)
res.fileBase64(base64, mimeType, headers?)	File from base64 content
res.file(path, headers?, fallbackPath?)	Serve file from public directory
await res.ejsFile(path, pageData, headers?)	Render EJS file
await res.ejsTemplate(template, pageData, headers?)	Render EJS template string
res.api(payload, config?, headers?)	Standardized API response
res.apiBinary(payload, config?, headers?)	Gzip-compressed API response

API Config Options: { notAuthorized, message, errorMessage, versionExpired, sessionExpired, logList }

Die Methods: res.die.* - Same as above but immediately returns, skipping afterRender hooks.

Frontend Usage with LambderCaller

LambderCaller is a frontend companion library for Lambder (only 2kb compressed) designed to simplify making type-safe API requests to your Lambder backend.

Basic Setup with Type Safety

import { LambderCaller } from "lambder";
import type { ApiContractType } from "./backend/handler"; // Import the inferred contract type

const lambderCaller = new LambderCaller<ApiContractType>({
    apiPath: "/api",
    isCorsEnabled: false,
    fetchStartedHandler: ({ fetchParams, activeFetchList }) => {
        console.log("API Called:", fetchParams.apiName);
    },
    fetchEndedHandler: ({ fetchParams, fetchResult, activeFetchList }) => {
        console.log("Ongoing calls:", activeFetchList.length);
    },
    errorMessageHandler: (message) => {
        console.error("LambderCaller:", message);
    },
});

// Fully typed API calls!
const user = await lambderCaller.api("getCompanyPage", { companyName: "Acme" });
// TypeScript knows:
// - Available API names (autocomplete)
// - Required input type
// - Expected output type

Benefits

No Manual Type Definitions - Types are inferred from your Zod schemas
Single Source of Truth - API contract comes from your backend code
Runtime Validation - Zod validates inputs automatically
Compile-Time Safety - TypeScript catches errors before runtime
Autocomplete - IDE suggests available APIs as you type
Zero Overhead - Type-only imports, no runtime code bloat

Read the Quick Start Guide for more details and examples!

Testing with LambderMSW

LambderMSW provides seamless integration with MSW (Mock Service Worker) for testing your APIs with full type safety.

import { LambderMSW } from 'lambder';
import { setupServer } from 'msw/node';
import type { ApiContractType } from './backend/handler';

const lambderMSW = new LambderMSW<ApiContractType>({
    apiPath: '/api',
});

const handlers = [
    // Mock API with full type safety! ✨
    lambderMSW.mockApi('getUser', async (payload) => {
        // payload is typed based on your Zod schema
        return {
            id: payload.userId,
            name: 'John Doe',
            email: 'john@example.com'
        };
    }),
    
    // Simulate delays and custom responses
    lambderMSW.mockApi('createUser', async (payload) => {
        return { id: '123', name: payload.name, email: payload.email };
    }, { 
        delay: 500,
        message: 'User created successfully'
    }),
    
    // Mock session expired
    lambderMSW.mockSessionExpired('protectedApi'),
];

const server = setupServer(...handlers);

Read the LambderMSW Guide for complete testing documentation!

Contributing

Contributions are welcome! Especially for documentation. If you have an idea for an improvement or have found a bug, please open an issue or submit a pull request.

License

This project is licensed under the MIT License.