AWS Lambda Router

A small library for AWS Lambda providing routing for API Gateway, Proxy Integrations, SNS and S3 Events.

Features

• Easy Handling of ANY method in API Gateways
• Simplifies writing lambda handlers (in nodejs > 8)
• Lambda Proxy Resource support for AWS API Gateway
• Enable CORS for requests
• No external dependencies - well, almost, only types of aws-lambda :-)
• Currently there are four processors (callers for Lambda) implemented:
  • API Gateway ANY method (called proxyIntegration)
  • SNS
  • SQS
  • S3
• Compatibility with Typescript >= 3.5

Installation

Install via npm

$ npm install aws-lambda-router

or yarn

$ yarn add aws-lambda-router

Getting Started

This is a simple example of aws-lambda-router in conjunction with ANY method and the API Gateway proxy integration. The following code will respond with a message when executed using an AWS API Gateway with a GET request on URL path <base-url-of-gateway>/gateway-mapping/article/123. The corresponding AWS API Gateway Resource is /article/{articleId}.

import * as router from 'aws-lambda-router'

export const handler = router.handler({
    proxyIntegration: {
        routes: [
            {
                // request-path-pattern with a path variable:
                path: '/article/:id',
                method: 'GET',
                // we can use the path param 'id' in the action call:
                action: (request, context) => {
                    return "You called me with: " + request.paths.id;
                }
            },
            {
                // request-path-pattern with a path variable in Open API style:
                path: '/section/{id}',
                method: 'GET',
                // we can use the path param 'id' in the action call:
                action: (request, context) => {
                    return "You called me with: " + request.paths.id;
                }
            }
        ]
    }
})

Proxy path support (work in progress)

The proxy integration usually works using a path configured in the API gateway. For example: /article/{id}.

If you use the WIP proxy path support, the complete path will be used to match a route config in proxyIntegration. This can be used to build an Simple Proxy with API Gateway

Example:

• Resource in API Gateway : /{proxy+} see Proxy Integration with a Proxy Resource
• Method: ANY

With the lambda configuration shown below the following paths are matched:

• api-gateway-host/article/list
• api-gateway-host/api/json/v1/schema

const router = require('aws-lambda-router');

exports.handler = router.handler({
    proxyIntegration: {
        proxyPath: proxy,
        routes: [
            {
                path: '/article/list',
                method: 'GET',
                action: (request, context) => {
                    return "You called me with: " + request.path;
                }
            },
            {
                path: '/api/json/v1/schema',
                method: 'GET',
                action: (request, context) => {
                    return "You called me with: " + request.path;
                }
            }
        ]
    }
})

Typescript example:

import * as router from 'aws-lambda-router'
import { ProxyIntegrationEvent } from 'aws-lambda-router/lib/proxyIntegration'

export const handler = router.handler({
    proxyIntegration: {
        routes: [
            {
                path: '/saveExample',
                method: 'POST',
                // request.body needs type assertion, because it defaults to type unknown (user input should be checked):
                action: (request, context) => {
                    const { text } = request.body as { text: string }
                    return `You called me with: ${text}`
                }
            },
            {
                path: '/saveExample2',
                method: 'POST',
                // it's also possible to set a type (no type check):
                action: (request: ProxyIntegrationEvent<{ text: string }>, context) => {
                    return `You called me with: ${request.body.text}`
                }
            }
        ]
    }
}

Enable CORS

To activate CORS on all http methods (OPTIONS requests are handled automatically) you only need to set the parameter cors to true on the proxyIntegration rule.

See the following example:

import * as router from 'aws-lambda-router'

export const handler = router.handler({
    // for handling an http-call from an AWS Apigateway proxyIntegration we provide the following config:
    proxyIntegration: {
        cors: true,
        routes: [
            {
                path: '/graphql',
                method: 'POST',
                // provide a function to be called with the appropriate data
                action: (request, context) => doAnything(request.body)
            }
        ]
    }
})

If CORS is activated, these default headers will be sent on every response:

"Access-Control-Allow-Origin" = "'*'"
"Access-Control-Allow-Methods" = "'GET,POST,PUT,DELETE,HEAD,PATCH'"
"Access-Control-Allow-Headers" = "'Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token'"

Customizing CORS

To customize CORS for all routes pass any of the following options to the proxyIntegration cors property. If a property is not set then it will default to the above default CORS headers.

• origin: Configures the Access-Control-Allow-Origin CORS header. Possible values:
  • Boolean - set origin to true to reflect the request origin or set it to false to disable CORS.
  • String - set origin to a specific origin. For example if you set it to "http://example.com" only requests from "http://example.com" will be allowed.
  • RegExp - set origin to a regular expression pattern which will be used to test the request origin. If it's a match, the request origin will be reflected. For example the pattern /example\.com$/ will reflect any request that is coming from an origin ending with "example.com".
  • Array - set origin to an array of valid origins. Each origin can be a String or a RegExp. For example ["http://example1.com", /\.example2\.com$/] will accept any request from "http://example1.com" or from a subdomain of "example2.com".
  • Function - set origin to a function to be evaluated. The function will get passed the APIGatewayProxyEvent and must return the allowed origin or false
• methods: Configures the Access-Control-Allow-Methods CORS header. Expects a comma-delimited string (ex: 'GET,PUT,POST') or an array (ex: ['GET', 'PUT', 'POST']).
• allowedHeaders: Configures the Access-Control-Allow-Headers CORS header. Expects a comma-delimited string (ex: 'Content-Type,Authorization') or an array (ex: ['Content-Type', 'Authorization']). If not specified, defaults to reflecting the headers specified in the request's Access-Control-Request-Headers header.
• exposedHeaders: Configures the Access-Control-Expose-Headers CORS header. Expects a comma-delimited string (ex: 'Content-Range,X-Content-Range') or an array (ex: ['Content-Range', 'X-Content-Range']). If not specified, no custom headers are exposed.
• credentials: Configures the Access-Control-Allow-Credentials CORS header. Set to true to pass the header, otherwise it is omitted.
• maxAge: Configures the Access-Control-Max-Age CORS header. Set to an integer to pass the header, otherwise it is omitted.

import * as router from 'aws-lambda-router'

export const handler = router.handler({
    // for handling an http-call from an AWS Apigateway proxyIntegration we provide the following config:
    proxyIntegration: {
        cors: {
          origin: 'https://test.example.com', // Only allow CORS request from this url
          methods: ['GET', 'POST', 'PUT']     // Only allow these HTTP methods to make requests
        },
        routes: [
            {
                path: '/graphql',
                method: 'POST',
                // provide a function to be called with the appropriate data
                action: (request, context) => doAnything(request.body)
            }
        ]
    }
})

Error mapping / handling

import * as router from 'aws-lambda-router'

export const handler = router.handler({
    // for handling an http-call from an AWS Apigateway proxyIntegration we provide the following config:
    proxyIntegration: {
        routes: [
            {
                path: '/graphql',
                method: 'POST',
                action: (request, context) => doThrowAnException(request.body)
            }
        ],
        debug: true,
        errorMapping: {
            'NotFound': 404,
            'MyCustomError': 429,
            'ServerError': 500
        }
    }
})

function doThrowAnException(body) {
    throw {reason: 'MyCustomError', message: 'Throw an error for this example'}
}

With the key word errorMapping shown in the example above you can adjust the assignment of thrown errors to http response code error. The action can throw an object like

"throw {reason: 'NotFound', message: 'object id not found'}"

and the http response then contains the configured value as response code and the message as the body.

Genereric error handler for proxyIntegration

Also there is implemented an generic error handler. The idea is to have a place for handling error logging and also return custom error messages.

onError: (error, event, context) => {
    // Global exceptions goes here, works for sns, s3 and sqs should end up here aswell
    console.log(error)
},
proxyIntegration: {
    onError: (error, request, context) => {
        // proxy integration exceptions goes here
        console.log('Error', error, request, context)
    },
    routes: ...
}

// Also support returning a response:
proxyIntegration: {
    onError: async (error) => {
        console.log('Error', error)
        await someAsyncMethod();
        return {
           statusCode: 401,
           body: Not allowed
        }
    },
    routes: ...
}

For more examples please look into the tests of proxyIntegration.

SNS to Lambda Integrations

SNS Event Structure: https://docs.aws.amazon.com/sns/latest/dg/sns-message-and-json-formats.html

For handling calls in Lambdas initiated from AWS-SNS you can use the following code snippet:

import * as router from 'aws-lambda-router'

export const handler = router.handler({
    sns: {
        routes: [
            {
                // a regex to match the content of the SNS-Subject:
                subject: /.*/,
                // Attention: the message is JSON-stringified
                action: (sns, context, records) => service.doSomething(JSON.parse(sns.Message))
            }
        ]
    }
})

The records parameter contains SNSEventRecord[]. An exampe event structure can be found here. For example you can parse now the message attributes of the SNS or reads the topic arn of SNS.

SQS to Lambda Integrations

For handling calls in Lambdas initiated from AWS-SQS you can use the following code snippet:

import * as router from 'aws-lambda-router'

export const handler = router.handler({
    sqs: {
        routes: [
            {
                // match complete SQS ARN:
                source: 'arn:aws:sqs:us-west-2:594035263019:aticle-import',
                // Attention: the messages Array is JSON-stringified
                action: (messages, context, records) => messages.forEach(message => console.log(JSON.parse(message)))
            },
            {
                // a regex to match the source SQS ARN:
                source: /.*notification/,
                // Attention: the messages array is JSON-stringified
                action: (messages, context, records) => service.doNotify(messages)
            }
        ]
    }
})

An SQS message always contains an array of records. In each SQS record there is the message in the body JSON key. The action method gets all body elements from the router as an array.

If more than one route matches, only the first is used!

The records parameter contains the complete array of records, which handled by aws-lambda-router. An exampe can be found here. This gives you the possibility to read metadata from the event. For example, you can parse the message attributes of the SQS and use them for further processing.

S3 to Lambda Integrations

Lambdas can be triggered by S3 events. The router now supports these events. With the router it is very easy and flexible to connect a lambda to different s3 sources (different buckets). The following configurations are available:

• bucketName: By specifying a fixed bucketName all s3 records with this bucket name are forwarded to a certain action. Instead of a fixed bucket a RegExp is also possible.
• eventName: By configuring the S3 event name the routing can be further restricted. A RegExp is also possible here.
• objectKeyPrefix: fixed string as an prefix of an object key (but not an RegExp). Is useful if you want to organize your bucket in subfolder.

A combination of bucketName, eventName and objectKeyPrefix is possible. If no bucketName, eventName and objectKeyPrefix is configured, all records of s3 events are forwarded to the action.

The action method will be called with the records of the S3Event Structure

The following examples demonstrates the most use cases:

import * as router from 'aws-lambda-router'

export const handler = router.handler({
    s3: {
        routes: [
            {
                //match every s3 record to this action 
                action: (record, context) => console.log(record.s3.object.key, record.eventName)
            },
            {
                //match s3 events which created, bucket name is whitelisted here
                eventName: 'ObjectCreated:Put',
                action: (record, context) => console.log(record.s3.object.key, record.eventName)
            },
            {
                //event name is an regex: match 'ObjectCreated:Put' or 'ObjectCreated:Copy'
                eventName: /ObjectCreated:*/,
                action: (record, context) => console.log(record.s3.object.key, record.eventName)
            },
            {
                //exact name of bucket 'myBucket', event name is whitelisted and will not be checked
                bucketName: 'myBucket',
                action: (record, context) => console.log(record.s3.object.key, record.eventName)
            },
            {
                //regex of bucket name (all buckets started with 'bucket-dev-' will be machted
                bucketName: /^bucket-dev-.*/,
                action: (record, context) => console.log(record.s3.object.key, record.eventName)
            },
            { 
                //action only will be called if bucket and event matched to the given regex
                bucketName: /bucket-dev-.*/,
                eventName: /ObjectCreated:*/,
                action: (record, context) => console.log(event.s3.object.key, record.eventName)
            },
            { 
                //action only will be called if bucket and event matched to the given fixed string
                bucketName: 'bucket',
                eventName: 'ObjectRemoved:Delete',
                action: (record, context) => console.log(event.s3.object.key, record.eventName)
            },
            { 
                //match if s3 events comes from Bucket 'bucket' with event 'ObjectRemoved:Delete' 
                // and the object key starts with /upload
                objectKeyPrefix: '/upload',
                bucketName: 'bucket',
                eventName: 'ObjectRemoved:Delete',
                action: (record, context) => console.log(record.s3.object.key, record.eventName)
            }
        ],
        debug: true
    }
})

Per s3 event there can be several records per event. The action methods are called one after the other record. The result of the action method is an array with objects insides.

Custom response

Per default a status code 200 will be returned. This behavior can be overridden.

By providing a body property in the returned object you can modify the status code and response headers.

return {
        // Allow for custom status codes depending on execution.
        statusCode: 218,
        // Headers will merge with CORS headers when enabled.
        // Will merge with Content-Type: application/json
        headers: {
            'x-new-header': 'another-value'
        },
        // When returning a custom response object, a key of body is required
        // The value of body needs to be JSON stringified, this matches
        // the expected response for an AWS Lambda.
        body: JSON.stringify({
            foo: 'bar'
        })
    }

Local developement

The best is to work with yarn link

See here: https://yarnpkg.com/en/docs/cli/link

Releasing

It's simple.

Increase version in package.json (using semantic version syntax). After than create an new tag in github (with description, can be the same as of the release history below) with the same version (like v0.98.9). Our build pipeline at Travis CI will be started and release an new version at NPM Repository.

Thats all.

Release History

see CHANGELOG.md