AWS Lambda wrapper library
This documentation is for v3 of the library - go here for v1 and here for v2
Feedback appreciated! If you have an idea for how this library can be improved please open an issue.
Overview
TL;DR
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.
Rationale and motivation
AWS Lambda supports a wide variety of event triggers, each with unique payloads and expected responses. The Lambda execution environment, however, only provides the raw events and has no included mechanisms for simplifying 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. Given the standard nature of these kinds of concerns, this library exposes helpful abstractions like parsed HTTP bodies based on content-type headers, and success response functions which create response objects with the correct status codes and headers for returning.
Installation and setup
Install and save the package to package.json as a dependency:
npm i --save @manwaring/lambda-wrapper
yarn add @manwaring/lambda-wrapper
Optional configuration
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, environment/, and Git revision simply set environment variables for each: 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)
Supported events
All of the events bellow have a corresponding wrapper which provides a deconstructed method signature exposing parsed/unmarshalled request parameters and helper response methods.
- API Gateway with support for cors headers and 200, 302, 400, and 500 responses
- CloudFormation Custom Resource with support for CloudFormation successes and failures
- DynamoDB Stream with support for success and failure responses
- Lambda Authorizer with support for creating access policies for successfully authorized requests
- SNS with support for success and failure responses
- Generic event wrapper with support for success and failure responses
API Gateway
Sample implementation
import { api } from '@manwaring/lambda-wrapper';
export const handler = api(async ({ body, path, success, error }) => {
try {
const { pathParam1, pathParam2 } = path;
const results = await doSomething(body, pathParam1, pathParam2);
return success(results);
} catch (err) {
return error(err);
}
});Properties and methods available on wrapper signature
interface ApiSignature {
event: APIGatewayEvent; // original event
body: any; // JSON or form parsed body payload if exists (based on content-type headers), otherwise the raw body object
path: { [name: string]: string }; // path param payload as key-value pairs
query: { [name: string]: string }; // query param payload as key-value pairs
headers: { [name: string]: string }; // headers param payload as key-value pairs
testRequest: boolean; // indicates if this is a test request, based on presence of headers matching 'Test-Request' or process.env.TEST_REQUEST_HEADER
auth: any; // auth context from custom authorizer
success(payload?: any, replacer?: (this: any, key: string, value: any) => any): ApiResponse; // returns 200 status with payload
invalid(errors?: string[]): ApiResponse; // returns 400 status with errors
notFound(message?: string): ApiResponse; // returns 404 status with message
redirect(url: string): ApiResponse; // returns 302 redirect with new url
error(error?: any): ApiResponse; // returns 500 status with error
}
interface ApiResponse {
statusCode: number;
headers: { [name: string]: string | boolean };
body?: string;
}*Note that each callback helper functions (success, invalid, redirect, error) includes CORS-enabling header information
CloudFormation Custom Resource
Sample implementation
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
Properties and methods available on wrapper signature
interface CloudFormationSignature {
event: CloudFormationCustomResourceEvent; // original event
success(payload?: any): void; // sends CloudFormation success event
failure(message?: any): void; // sends CloudFormation failure event
}DynamoDB Stream
Sample implementation
import { dynamodbStream } from '@manwaring/lambda-wrapper';
export const handler = dynamodbStream(async ({ newVersions, success, error }) => {
try {
newVersions.forEach(version => console.log(version));
return success(newVersions);
} catch (err) {
return error(err);
}
});Properties and methods available on wrapper signature
interface DynamoDBStreamSignature {
event: DynamoDBStreamEvent; // original event
newVersions: any[]; // array of all unmarshalled javascript objects of new images
oldVersions: any[]; // array of all unmarshalled javascript objects of old images
versions: Version[]; // 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 {
newVersion: any; // unmarshalled javascript object of new image (if exists) or null
oldVersion: any; // 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: string; // name of the event (INSERT || MODIFY || REMOVE)
}Lambda Authorizer
Sample implementation
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);
}
});Properties and methods available on wrapper signature
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;
}[];
};
}SNS
Sample implementation
import { sns } from '@manwaring/lambda-wrapper';
export const handler = sns(async ({ message, success, error }) => {
try {
console.log(message);
return success();
} catch (err) {
return error(err);
}
});Properties and methods available on wrapper signature
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
}Generic event
Sample implementation
import { wrapper } from '@manwaring/lambda-wrapper';
export const handler = wrapper(async ({ event, success, error }) => {
try {
const { value1, value2 } = event;
const results = await doSomething(value1, value2);
return success(results);
} catch (err) {
return error(err);
}
});Properties and methods available on wrapper signature
interface WrapperSignature {
event: any; // original event
success(message?: any): any; // logs and returns the message
error(error?: any): void; // logs the error and throws
}Example projects
THere is one working example of how this package can be used in a simple 'hello world' serverless application:
![dependabot-preview[bot]](https://avatars.githubusercontent.com/u/27856297?size=120)