This library provides custom Lambda function wrappers which expose standard, abstracted functionality so that developers can focus on writing business logic instead of parsing event payloads and crafting response objects.
AWS Lambda supports a wide variety of event triggers, each with unique payloads and expected response objects. The Lambda method signature, however, only provides a raw event object and has no included mechanisms for simplifying payload parsing or response object creation. For example API Gateway events include only the raw request body, leaving it up to developers to implement parsing themselves. Similarly the developer is responsible for creating a response object which includes the correct HTTP status code and headers. This library exposes helpful abstractions like parsed HTTP bodies based on content-type headers, and success functions which create response objects with the correct status codes and headers for returning to API Gateway.
Feedback is appreciated! If you have an idea for how this library can be improved (or just a complaint/criticism) then please open an issue.
Install and save the package:
npm i -S @manwaring/lambda-wrapper
yarn add @manwaring/lambda-wrapper
If you want the wrapper to log request and response messages (helpful for debugging) set an environemnt variable for LAMBDA_WRAPPER_LOG=true.
If you want each invocation to be tagged with the AWS region, stage/environment, and Git revision simply set environment variables for each and the library will pick them up, for example REGION=us-east-1, STAGE=prod, REVISION=f4ba682. See git-rev-sync and serverless-plugin-git-variables for libraries that can help you set git revision automatically.
Each event listed here has a wrapper which provides a deconstructable method signature exposing parsed/unmarshalled request parameters and helper response methods.
- API Gateway
- API Gateway HTTP API
- CloudFormation Custom Resource
- DynamoDB Stream
- Lambda Authorizer
- SNS
- Generic event (a basic wrapper with support for success and failure responses)
import { api } from '@manwaring/lambda-wrapper';
import { CustomInterface } from './custom-interface';
import { doSomething } from './you-code';
export const handler = api<CustomInterface>(async ({ body, path, success, invalid, error }) => {
try {
const { pathParam1, pathParam2 } = path;
if (!pathParam1) {
return invalid();
}
const results = await doSomething(body, pathParam1, pathParam2);
return success({ body: results });
} catch (err) {
return error({ err });
}
});By passing in CustomInterface as a generic type the method signature will cast the body object as an instance of CustomInterface, making TypeScript development easier. Note that the type is not required and the body property defaults to type any.
Sample implementation without generic
import { api } from '@manwaring/lambda-wrapper';
import { doSomething } from './you-code';
export const handler = api(async ({ body, path, success, invalid, error }) => {
try {
const { pathParam1, pathParam2 } = path;
if (!pathParam1) {
return invalid();
}
const results = await doSomething(body, pathParam1, pathParam2);
return success({ body: results });
} catch (err) {
return error({ err });
}
});Deconstructable wrapper signature
Note that all properties are undefined if not present on the original request.
export interface ApiSignature<T = any> {
event: APIGatewayEvent; // original event provided by AWS
body: T; // body payload parsed according to content-type headers (or raw if no content-type headers found) and cast as T if provided (defaults to `any`)
websocket: WebsocketRequest; // websocket connection payload
path: { [name: string]: string }; // path params as key-value pairs
query: { [name: string]: string }; // query params as key-value pairs
headers: { [name: string]: string }; // headers as key-value pairs
testRequest: boolean; // indicates if this is a test request - looks for a header matching process.env.TEST_REQUEST_HEADER (dynamic from application) or 'Test-Request' (default)
auth: any; // auth context from custom authorizer
success(params?: ResponseParameters): ApiResponse;
invalid(params?: ResponseParameters): ApiResponse;
notFound(params?: ResponseParameters): ApiResponse;
notAuthorized(params?: ResponseParameters): ApiResponse;
redirect(params: RedirectParameters): ApiResponse;
error(params?: ErrorParameters): ApiResponse;
custom(params: CustomParameters): ApiResponse;
}ApiResponse
interface ApiResponse {
statusCode: number;
headers: { [name: string]: any };
body?: string;
}ResponseParameters
interface ResponseParameters {
body?: any; // response body
json?: boolean; // indicates if body should be JSON-stringified and content-type header set to application/json, defaults to true
cors?: boolean; // indicates if CORS headers should be added, defaults to true
statusCode?: number; // status code to return, defaults by callback (success: 200, invalid: 400, notFound: 404, notAuthorized: 401, redirect: 302, error: 500)
headers?: { [key: string]: any }; // custom headers to include
}RedirectParameters
interface RedirectParameters {
url: string; // url to redirect to
cors?: boolean; // indicates if CORS headers should be added, defaults to true
statusCode?: number; // status code to return, defaults to 302
headers?: { [key: string]: any }; // custom headers to include
}ErrorParameters
interface ErrorParameters {
body?: any; // response body
json?: boolean; // indicates if body should be JSON-stringified and content-type header set to application/json, defaults to true
cors?: boolean; // indicates if CORS headers should be added, defaults to true
statusCode?: number; // status code to return, defaults to 500
headers?: { [key: string]: any }; // custom headers to include
err?: Error; // optional Error object for automatic logging
}CustomParameters
interface CustomParameters {
body?: any; // response body
json?: boolean; // indicates if body should be JSON-stringified and content-type header set to application/json, defaults to true
cors?: boolean; // indicates if CORS headers should be added, defaults to true
statusCode: number; // status code to return
headers?: { [key: string]: any }; // custom headers to include
err?: Error; // optional Error object for automatic logging
}WebsocketRequest
export interface WebsocketRequest {
accountId: string;
apiId: string;
connectedAt?: number;
connectionId?: string;
domainName?: string;
domainPrefix?: string;
eventType?: string;
extendedRequestId?: string;
protocol: string;
httpMethod: string;
identity: APIGatewayEventIdentity;
messageDirection?: string;
messageId?: string | null;
path: string;
stage: string;
requestId: string;
requestTime?: string;
requestTimeEpoch: number;
resourceId: string;
resourcePath: string;
routeKey?: string;
}Success
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
json: true,
cors: true,
statusCode: 200
}const response = { hello: 'world' };
return success({ body: response });
// returns
{
body: "{\"hello\":\"world\"}",
statusCode: 200,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
'Content-Type': 'application/json'
}
}const response = '<svg xmlns="http://www.w3.org/2000/svg"></svg>';
const headers = { 'Content-Type': 'image/svg+xml' };
return success({ body: response, json: false, cors: false, headers });
// returns
{
body: "<svg xmlns=\"http://www.w3.org/2000/svg\"></svg>",
statusCode: 200,
headers: { 'Content-Type': 'image/svg+xml' }
}Invalid
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
json: true,
cors: true,
statusCode: 400
}return invalid();
// returns
{
statusCode: 400,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}const response = { invalid: 'properties' };
return invalid({ body: response, cors: false });
// returns
{
body: "{\"invalid\":\"properties\"}",
statusCode: 400,
headers: { 'Content-Type': 'application/json' }
}Not found
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
json: true,
cors: true,
statusCode: 404
}return notFound();
// returns
{
statusCode: 404,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}const response = 'Not found';
return notFound({ body: response, cors: false });
// returns
{
body: "Not found",
statusCode: 404,
}Not authorized
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
json: true,
cors: true,
statusCode: 401
}return notAuthorized();
// returns
{
statusCode: 401,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}const response = 'Not authorized';
return notAuthorized({ body: response, cors: false });
// returns
{
body: "Not Authorized",
statusCode: 401,
}Redirect
{
url: string,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
cors: true,
statusCode: 302
}const url = 'https://github.com/manwaring/lambda-wrapper';
return redirect({ url });
// returns
{
statusCode: 302,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
'Location': 'https://github.com/manwaring/lambda-wrapper'
}
}const url = 'https://github.com/manwaring/lambda-wrapper';
return redirect({ url, statusCode: 308, cors: false });
// returns
{
statusCode: 308,
headers: {
'Location': 'https://github.com/manwaring/lambda-wrapper'
}
}Error
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any},
err?: Error
}{
json: true,
cors: true,
statusCode: 500
}return error();
// returns
{
statusCode: 500,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}catch (err) {
const body = { error: 'Unexpected error' };
return error({ body, err });
}
// logs
console.debug(err);
// returns
{
body: "{\"error\": \"Unexpected error\"}",
statusCode: 500,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}Custom
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode: number,
headers?: { [key: string]: any},
err?: Error
}{
json: true,
cors: true,
}return custom({ statusCode: 418 });
// returns
{
statusCode: 418,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}const body = { message: 'Custom response' };
return custom({ body, statusCode: 418 });
// returns
{
body: "{\"message\": \"Custom response\"}",
statusCode: 418,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}Other than the raw payload from AWS the HTTP API method signature and response functions match the API Gateway signature and functions. Hooray for wrappers! Note that you still need to provide the correct wrapper function so that the library can parse the AWS event correctly.
import { httpApi } from '@manwaring/lambda-wrapper';
import { CustomInterface } from './custom-interface';
import { doSomething } from './you-code';
export const handler = httpApi<CustomInterface>(async ({ body, path, success, invalid, error }) => {
try {
const { pathParam1, pathParam2 } = path;
if (!pathParam1) {
return invalid();
}
const results = await doSomething(body, pathParam1, pathParam2);
return success({ body: results });
} catch (err) {
return error({ err });
}
});By passing in CustomInterface as a generic type the method signature will cast the body object as an instance of CustomInterface, making TypeScript development easier. Note that the type is not required and the body property defaults to type any.
Sample implementation without generic
import { httpApi } from '@manwaring/lambda-wrapper';
import { doSomething } from './you-code';
export const handler = httpApi(async ({ body, path, success, invalid, error }) => {
try {
const { pathParam1, pathParam2 } = path;
if (!pathParam1) {
return invalid();
}
const results = await doSomething(body, pathParam1, pathParam2);
return success({ body: results });
} catch (err) {
return error({ err });
}
});Deconstructable wrapper signature
Note that all properties are undefined if not present on the original request.
export interface HttpApiSignature<T = any> {
event: HttpApiEvent; // original event provided by AWS
body: T; // body payload parsed according to content-type headers (or raw if no content-type headers found) and cast as T if provided (defaults to `any`)
rawPath: string; // the endpoint path used to invoke this Lambda
path: { [name: string]: string }; // path params as key-value pairs
query: { [name: string]: string }; // query params as key-value pairs
rawQueryString: string // the raw query string from the request
headers: { [name: string]: string }; // headers as key-value pairs
testRequest: boolean; // indicates if this is a test request - looks for a header matching process.env.TEST_REQUEST_HEADER (dynamic from application) or 'Test-Request' (default)
auth: any; // auth context from JWT authorizer
success(params?: ResponseParameters): ApiResponse;
invalid(params?: ResponseParameters): ApiResponse;
notFound(params?: ResponseParameters): ApiResponse;
notAuthorized(params?: ResponseParameters): ApiResponse;
redirect(params: RedirectParameters): ApiResponse;
error(params?: ErrorParameters): ApiResponse;
custom(params: CustomParameters): ApiResponse;
}ApiResponse
interface ApiResponse {
statusCode: number;
headers: { [name: string]: any };
body?: string;
}ResponseParameters
interface ResponseParameters {
body?: any; // response body
json?: boolean; // indicates if body should be JSON-stringified and content-type header set to application/json, defaults to true
cors?: boolean; // indicates if CORS headers should be added, defaults to true
statusCode?: number; // status code to return, defaults by callback (success: 200, invalid: 400, notFound: 404, notAuthorized: 401, redirect: 302, error: 500)
headers?: { [key: string]: any }; // custom headers to include
}RedirectParameters
interface RedirectParameters {
url: string; // url to redirect to
cors?: boolean; // indicates if CORS headers should be added, defaults to true
statusCode?: number; // status code to return, defaults to 302
headers?: { [key: string]: any }; // custom headers to include
}ErrorParameters
interface ErrorParameters {
body?: any; // response body
json?: boolean; // indicates if body should be JSON-stringified and content-type header set to application/json, defaults to true
cors?: boolean; // indicates if CORS headers should be added, defaults to true
statusCode?: number; // status code to return, defaults to 500
headers?: { [key: string]: any }; // custom headers to include
err?: Error; // optional Error object for automatic logging
}CustomParameters
interface CustomParameters {
body?: any; // response body
json?: boolean; // indicates if body should be JSON-stringified and content-type header set to application/json, defaults to true
cors?: boolean; // indicates if CORS headers should be added, defaults to true
statusCode: number; // status code to return
headers?: { [key: string]: any }; // custom headers to include
err?: Error; // optional Error object for automatic logging
}HttpApiEvent
AWS documentation of raw event
export interface HttpApiEvent {
version: string;
routeKey: string;
rawPath: string;
rawQueryString: string;
cookies: string[];
headers: { [key: string]: string };
queryStringParameters: { [key: string]: string };
requestContext: {
accountId: string;
apiId: string;
authorizer: {
jwt: {
claims: { [key: string]: string };
scopes: string[];
};
};
domainName: string;
domainPrefix: string;
http: {
method: string;
path: string;
protocol: string;
sourceIp: string;
userAgent: string;
};
requestId: string;
routeKey: string;
stage: string;
time: string;
timeEpoch: number;
};
body: string;
pathParameters: { [key: string]: string };
isBase64Encoded: boolean;
stageVariables: { [key: string]: string };
}Success
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
json: true,
cors: true,
statusCode: 200
}const response = { hello: 'world' };
return success({ body: response });
// returns
{
body: "{\"hello\":\"world\"}",
statusCode: 200,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
'Content-Type': 'application/json'
}
}const response = '<svg xmlns="http://www.w3.org/2000/svg"></svg>';
const headers = { 'Content-Type': 'image/svg+xml' };
return success({ body: response, json: false, cors: false, headers });
// returns
{
body: "<svg xmlns=\"http://www.w3.org/2000/svg\"></svg>",
statusCode: 200,
headers: { 'Content-Type': 'image/svg+xml' }
}Invalid
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
json: true,
cors: true,
statusCode: 400
}return invalid();
// returns
{
statusCode: 400,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}const response = { invalid: 'properties' };
return invalid({ body: response, cors: false });
// returns
{
body: "{\"invalid\":\"properties\"}",
statusCode: 400,
headers: { 'Content-Type': 'application/json' }
}Not found
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
json: true,
cors: true,
statusCode: 404
}return notFound();
// returns
{
statusCode: 404,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}const response = 'Not found';
return notFound({ body: response, cors: false });
// returns
{
body: "Not found",
statusCode: 404,
}Not authorized
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
json: true,
cors: true,
statusCode: 401
}return notAuthorized();
// returns
{
statusCode: 401,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}const response = 'Not authorized';
return notAuthorized({ body: response, cors: false });
// returns
{
body: "Not Authorized",
statusCode: 401,
}Redirect
{
url: string,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any}
}{
cors: true,
statusCode: 302
}const url = 'https://github.com/manwaring/lambda-wrapper';
return redirect({ url });
// returns
{
statusCode: 302,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
'Location': 'https://github.com/manwaring/lambda-wrapper'
}
}const url = 'https://github.com/manwaring/lambda-wrapper';
return redirect({ url, statusCode: 308, cors: false });
// returns
{
statusCode: 308,
headers: {
'Location': 'https://github.com/manwaring/lambda-wrapper'
}
}Error
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode?: number,
headers?: { [key: string]: any},
err?: Error;
}{
json: true,
cors: true,
statusCode: 500
}return error();
// returns
{
statusCode: 500,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}catch (err) {
const body = { error: 'Unexpected error' };
return error({ body, err });
}
// logs
console.debug(err);
// returns
{
body: "{\"error\": \"Unexpected error\"}",
statusCode: 500,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}Custom
{
body?: any,
json?: boolean,
cors?: boolean,
statusCode: number,
headers?: { [key: string]: any},
err?: Error
}{
json: true,
cors: true,
}return custom({ statusCode: 418 });
// returns
{
statusCode: 418,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}const body = { message: 'Custom response' };
return custom({ body, statusCode: 418 });
// returns
{
body: "{\"message\": \"Custom response\"}",
statusCode: 418,
headers: {
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Credentials': true,
}
}import { cloudFormation } from '@manwaring/lambda-wrapper';
export const handler = cloudFormation(({ event, success, failure }) => {
try {
const { BucketName } = event.ResourceProperties;
return success();
} catch (err) {
return failure(err);
}
});*Note that currently the method wrapped by cloudFormation cannot be async - for reasons that aren't entirely clear to me when the method is async the requests to update CloudFormation with the correct action status fail, leaving a stack in the 'pending' state
interface CloudFormationSignature {
event: CloudFormationCustomResourceEvent; // original event
success(payload?: any): void; // sends CloudFormation success event
failure(message?: any): void; // sends CloudFormation failure event
}import { dynamodbStream } from '@manwaring/lambda-wrapper';
import { CustomInterface } from './custom-interface';
// By passing in CustomInterface as a generic the async method signature will correctly identify newVersions as an array of CustomInterface, making TypeScript development easier (note that the generic is not required in JavaScript projects)
export const handler = dynamodbStream<CustomInterface>(async ({ newVersions, success, error }) => {
try {
newVersions.forEach((version) => console.log(version));
return success(newVersions);
} catch (err) {
return error(err);
}
});
interface CustomInterface {
id: number;
value: string;
}interface DynamoDBStreamSignature<T> {
event: DynamoDBStreamEvent; // original event
newVersions: T[]; // array of all unmarshalled javascript objects of new images
oldVersions: T[]; // array of all unmarshalled javascript objects of old images
versions: Version<T>[]; // array of full version object (new image, old image, etc - see Version interface)
success(message?: any): any; // logs and returns the message
error(error?: any): void; // logs the error and throws it
}
interface Version<T> {
newVersion: T; // unmarshalled javascript object of new image (if exists) or null
oldVersion: T; // unmarshalled javascript object of old image (if exists) or null
keys: any; // unmarshalled javascript object of keys (includes key values)
tableName: string; // name of the table the object came from
tableArn: string; // arn of the table the object came from
eventName: 'INSERT' | 'MODIFY' | 'REMOVE'; // name of the event (INSERT || MODIFY || REMOVE)
}import { authorizer } from '@manwaring/lambda-wrapper';
const verifier = new Verifier(); // setup and configure JWT validation library
export const handler = authorizer(async ({ token, valid, invalid }) => {
try {
if (!token) {
return invalid('Missing token');
}
const jwt = await verifier.verifyAccessToken(token);
return valid(jwt);
} catch (err) {
return invalid(err);
}
});interface AuthorizerSignature {
event: CustomAuthorizerEvent; // original event
token: string; // authorizer token from original event
valid(jwt: any): Policy; // returns AWS policy to authenticate request, and adds auth context if available
invalid(message?: any): void; // records invalid information and throws 401 unauthorized
error(error?: any): void; // records error information and throws 401 unauthorized
}
interface Policy {
principalId: string;
policyDocument: {
Version: string;
Statement: {
Action: string;
Effect: string;
Resource: string;
}[];
};
}import { sns } from '@manwaring/lambda-wrapper';
import { CustomInterface } from './custom-interface';
// By passing in CustomInterface as a generic the async method signature will correctly identify newVersions as an array of CustomInterface, making TypeScript development easier (note that the generic is not required in JavaScript projects)
export const handler = sns<CustomInterface>(async ({ message, success, error }) => {
try {
console.log(message);
return success();
} catch (err) {
return error(err);
}
});interface SnsSignature {
event: SNSEvent; // original event
message: any; // JSON-parsed message from event
success(message?: any): any; // logs and returns the message
error(error?: any): void; // logs the error and throws
}import { wrapper } from '@manwaring/lambda-wrapper';
import { CustomInterface } from './custom-interface';
// By passing in CustomInterface as a generic the async method signature will correctly identify newVersions as an array of CustomInterface, making TypeScript development easier (note that the generic is not required in JavaScript projects)
export const handler = wrapper<CustomInterface>(async ({ event, success, error }) => {
try {
const { value1, value2 } = event;
const results = await doSomething(value1, value2);
return success(results);
} catch (err) {
return error(err);
}
});interface WrapperSignature<T> {
event: T; // original event
success(message?: any): any; // logs and returns the message
error(error?: any): void; // logs the error and throws
}There is one working example of how this package can be used in a simple 'hello world' serverless application: