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Lightweight web framework for your serverless applications

Lambda API is a lightweight web framework for use with AWS API Gateway and AWS Lambda using Lambda Proxy Integration. This closely mirrors (and is based on) other web frameworks like Express.js and Fastify, but is significantly stripped down to maximize performance with Lambda's stateless, single run executions.

Simple Example

// Require the framework and instantiate it
const api = require('lambda-api')()
 
// Define a route
api.get('/status', async (req,res) => {
  return { status: 'ok' }
})
 
// Declare your Lambda handler
exports.handler = async (event, context) => {
  // Run the request
  return await api.run(event, context)
}

For a full tutorial see How To: Build a Serverless API with Serverless, AWS Lambda and Lambda API.

Why Another Web Framework?

Express.js, Fastify, Koa, Restify, and Hapi are just a few of the many amazing web frameworks out there for Node.js. So why build yet another one when there are so many great options already? One word: DEPENDENCIES.

These other frameworks are extremely powerful, but that benefit comes with the steep price of requiring several additional Node.js modules. Not only is this a bit of a security issue (see Beware of Third-Party Packages in Securing Serverless), but it also adds bloat to your codebase, filling your node_modules directory with a ton of extra files. For serverless applications that need to load quickly, all of these extra dependencies slow down execution and use more memory than necessary. Express.js has 30 dependencies, Fastify has 12, and Hapi has 17! These numbers don't even include their dependencies' dependencies.

Lambda API has ZERO dependencies. None. Zip. Zilch.

Lambda API was written to be extremely lightweight and built specifically for SERVERLESS applications using AWS Lambda and API Gateway. It provides support for API routing, serving up HTML pages, issuing redirects, serving binary files and much more. Worried about observability? Lambda API has a built-in logging engine that can even periodically sample requests for things like tracing and benchmarking. It has a powerful middleware and error handling system, allowing you to implement just about anything you can dream of. Best of all, it was designed to work with Lambda's Proxy Integration, automatically handling all the interaction with API Gateway for you. It parses REQUESTS and formats RESPONSES, allowing you to focus on your application's core functionality, instead of fiddling with inputs and outputs.

Single Purpose Functions

You may have heard that a serverless "best practice" is to keep your functions small and limit them to a single purpose. I generally agree since building monolith applications is not what serverless was designed for. However, what exactly is a "single purpose" when it comes to building serverless APIs and web services? Should we create a separate function for our "create user" POST endpoint and then another one for our "update user" PUT endpoint? Should we create yet another function for our "delete user" DELETE endpoint? You certainly could, but that seems like a lot of repeated boilerplate code. On the other hand, you could create just one function that handled all your user management features. It may even make sense (in certain circumstances) to create one big serverless function handling several related components that can share your VPC database connections.

Whatever you decide is best for your use case, Lambda API is there to support you. Whether your function has over a hundred routes, or just one, Lambda API's small size and lightning fast load time has virtually no impact on your function's performance. Yet despite its small footprint, it gives you the power of a full-featured web framework.

Table of Contents

• Installation
• Requirements
• Configuration
• Recent Updates
• Routes and HTTP Methods
• Returning Responses
  • Async/Await
  • Promises
• Route Prefixing
• Debugging Routes
• REQUEST
• RESPONSE
  • attachment()
  • cache()
  • clearCookie()
  • cookie()
  • cors()
  • download()
  • error()
  • etag()
  • getHeader()
  • getLink()
  • hasHeader()
  • header()
  • html()
  • json()
  • jsonp()
  • location
  • modified()
  • redirect()
  • removeHeader()
  • send()
  • sendFile()
  • status()
  • type()
• Enabling Binary Support
• Path Parameters
• Wildcard Routes
• Logging
  • Logging Configuration
  • Log Format
  • Access Logs
  • Logging Levels
  • Custom Logging Levels
  • Adding Additional Detail
  • Serializers
  • Sampling
• Middleware
• Clean Up
• Error Handling
• Namespaces
• CORS Support
• Lambda Proxy Integration
• Configuring Routes in API Gateway
• Contributions

Installation

npm i lambda-api --save

Requirements

• AWS Lambda running Node 8.10+
• AWS API Gateway using Proxy Integration

Configuration

Require the lambda-api module into your Lambda handler script and instantiate it. You can initialize the API with the following options:

// Require the framework and instantiate it with optional version and base parameters
const api = require('lambda-api')({ version: 'v1.0', base: 'v1' });

Recent Updates

For detailed release notes see Releases.

v0.8: Logging Support with Sampling

Lambda API has added a powerful (and customizable) logging engine that utilizes native JSON support for CloudWatch Logs. Log entries can be manually added using standard severities like info and warn. In addition, "access logs" can be automatically generated with detailed information about each requests. See Logging for more information about logging and auto sampling for request tracing.

v0.7: Restrict middleware execution to certain paths

Middleware now supports an optional path parameter that supports multiple paths, wildcards, and parameter matching to better control middleware execution. See middleware for more information.

v0.6: Support for both callback-style and async-await

In additional to res.send(), you can now simply return the body from your route and middleware functions. See Returning Responses for more information.

v0.5: Remove Bluebird Promises Dependency

Now that AWS Lambda supports Node v8.10, asynchronous operations can be handled more efficiently with async/await rather than with promises. The core Lambda API execution engine has been rewritten to take advantage of async/await, which means we no longer need to depend on Bluebird. We now have ZERO dependencies.

v0.4: Binary Support

Binary support has been added! This allows you to both send and receive binary files from API Gateway. For more information, see Enabling Binary Support.

v0.3: New Instantiation Method

Please note that the invocation method has been changed. You no longer need to use the new keyword to instantiate Lambda API. It can now be instantiated in one line:

const api = require('lambda-api')()

lambda-api returns a function now instead of a class, so options can be passed in as its only argument:

const api = require('lambda-api')({ version: 'v1.0', base: 'v1' });

IMPORTANT: Upgrading from <v0.3.0 requires either removing the new keyword or switching to the one-line format. This provides more flexibility for instantiating Lambda API in future releases.

Routes and HTTP Methods

Routes are defined by using convenience methods or the METHOD method. There are currently eight convenience route methods: get(), post(), put(), patch(), delete(), head(), options() and any(). Convenience route methods require two parameters, a route and a function that accepts two arguments. A route is simply a path such as /users. The second parameter must be a function that accepts a REQUEST and a RESPONSE argument. These arguments can be named whatever you like, but convention dictates req and res. Examples using convenience route methods:

api.get('/users', (req,res) => {
  // do something
})
 
api.post('/users', (req,res) => {
  // do something
})
 
api.delete('/users', (req,res) => {
  // do something
})

Additional methods are support by calling the METHOD method with three arguments. The first argument is the HTTP method (or array of methods), a route, and a function that accepts a REQUEST and a RESPONSE argument.

api.METHOD('trace','/users', (req,res) => {
  // do something on TRACE
})
 
api.METHOD(['post','put'],'/users', (req,res) => {
  // do something on POST -or- PUT
})

All GET methods have a HEAD alias that executes the GET request but returns a blank body. GET requests should be idempotent with no side effects. The head() convenience method can be used to set specific paths for HEAD requests or to override default GET aliasing.

Routes that use the any() method or pass ANY to api.METHOD will respond to all HTTP methods. Routes that specify a specific method (such as GET or POST), will override the route for that method. For example:

api.any('/users', (req,res) => { res.send('any') })
api.get('/users', (req,res) => { res.send('get') })

A POST to /users will return "any", but a GET request would return "get". Please note that routes defined with an ANY method will override default HEAD aliasing for GET routes.

Returning Responses

Lambda API supports both callback-style and async-await for returning responses to users. The RESPONSE object has several callbacks that will trigger a response (send(), json(), html(), etc.) You can use any of these callbacks from within route functions and middleware to send the response:

api.get('/users', (req,res) => {
  res.send({ foo: 'bar' })
})

You can also return data from route functions and middleware. The contents will be sent as the body:

api.get('/users', (req,res) => {
  return { foo: 'bar' }
})

Async/Await

If you prefer to use async/await, you can easily apply this to your route functions.

Using return:

api.get('/users', async (req,res) => {
  let users = await getUsers()
  return users
})

Or using callbacks:

api.get('/users', async (req,res) => {
  let users = await getUsers()
  res.send(users)
})

Promises

If you like promises, you can either use a callback like res.send() at the end of your promise chain, or you can simply return the resolved promise:

api.get('/users', (req,res) => {
  getUsers().then(users => {
    res.send(users)
  })
})

OR

api.get('/users', (req,res) => {
  return getUsers().then(users => {
    return users
  })
})

IMPORTANT: You must either use a callback like res.send() OR return a value. Otherwise the execution will hang and no data will be sent to the user. Also, be sure not to return undefined, otherwise it will assume no response.

Route Prefixing

Lambda API makes it easy to create multiple versions of the same api without changing routes by hand. The register() method allows you to load routes from an external file and prefix all of those routes using the prefix option. For example:

// handler.js
const api = require('lambda-api')()
 
api.register(require('./routes/v1/products'), { prefix: '/v1' })
api.register(require('./routes/v2/products'), { prefix: '/v2' })
 
module.exports.handler = (event, context, callback) => {
  api.run(event, context, callback)
}

// routes/v1/products.js
module.exports = (api, opts) => {
  api.get('/product', handler_v1)
}

// routes/v2/products.js
module.exports = (api, opts) => {
  api.get('/product', handler_v2)
}

Even though both modules create a /product route, Lambda API will add the prefix to them, creating two unique routes. Your users can now access:

• /v1/product
• /v2/product

You can use register() as many times as you want AND it is recursive, so if you nest register() methods, the routes will build upon each other. For example:

module.exports = (api, opts) => {
  api.get('/product', handler_v1)
  api.register(require('./v2/products.js'), { prefix: '/v2'} )
}

This would create a /v1/product and /v1/v2/product route. You can also use register() to load routes from an external file without the prefix. This will just add routes to your base path. NOTE: Prefixed routes are built off of your base path if one is set. If your base was set to /api, then the first example above would produce the routes: /api/v1/product and /api/v2/product.

Debugging Routes

Lambda API has a routes() method that can be called on the main instance that will return an array containing the METHOD and full PATH of every configured route. This will include base paths and prefixed routes. This is helpful for debugging your routes.

 const api = require('lambda-api')()
 
 api.get('/', (req,res) => {})
 api.post('/test', (req,res) => {})
 
 api.routes() // => [ [ 'GET', '/' ], [ 'POST', '/test' ] ]

You can also log the paths in table form to the console by passing in true as the only parameter.

 const api = require('lambda-api')()
 
 api.get('/', (req,res) => {})
 api.post('/test', (req,res) => {})
 
 api.routes(true)
 
// Outputs to console
╔═══════════╤═════════════════╗
║  METHOD   │  ROUTE          ║
╟───────────┼─────────────────╢
║  GET      │  /              ║
╟───────────┼─────────────────╢
║  POST     │  /test          ║
╚═══════════╧═════════════════╝

REQUEST

The REQUEST object contains a parsed and normalized request from API Gateway. It contains the following values by default:

• app: A reference to an instance of the app
• version: The version set at initialization
• id: The awsRequestId from the Lambda context
• params: Dynamic path parameters parsed from the path (see path parameters)
• method: The HTTP method of the request
• path: The path passed in by the request including the base and any prefix assigned to routes
• query: Querystring parameters parsed into an object
• headers: An object containing the request headers (properties converted to lowercase for HTTP/2, see rfc7540 8.1.2. HTTP Header Fields)
• rawHeaders: An object containing the original request headers (property case preserved)
• body: The body of the request. If the isBase64Encoded flag is true, it will be decoded automatically.
  • If the content-type header is application/json, it will attempt to parse the request using JSON.parse()
  • If the content-type header is application/x-www-form-urlencoded, it will attempt to parse a URL encoded string using querystring
  • Otherwise it will be plain text.
• rawBody: If the isBase64Encoded flag is true, this is a copy of the original, base64 encoded body
• route: The matched route of the request
• requestContext: The requestContext passed from the API Gateway
• auth: An object containing the type and value of an authorization header. Currently supports Bearer, Basic, OAuth, and Digest schemas. For the Basic schema, the object is extended with additional fields for username/password. For the OAuth schema, the object is extended with key/value pairs of the supplied OAuth 1.0 values.
• namespace or ns: A reference to modules added to the app's namespace (see namespaces)
• cookies: An object containing cookies sent from the browser (see the cookie RESPONSE method)
• context: Reference to the context passed into the Lambda handler function
• coldStart: Boolean that indicates whether or not the current invocation was a cold start
• requestCount: Integer representing the total number of invocations of the current function container (how many times it has been reused)
• ip: The IP address of the client making the request
• userAgent: The User-Agent header sent by the client making the request
• clientType: Either desktop, mobile, tv, tablet or unknown based on CloudFront's analysis of the User-Agent header
• clientCountry: Two letter country code representing the origin of the requests as determined by CloudFront

The request object can be used to pass additional information through the processing chain. For example, if you are using a piece of authentication middleware, you can add additional keys to the REQUEST object with information about the user. See middleware for more information.

RESPONSE

The RESPONSE object is used to send a response back to the API Gateway. The RESPONSE object contains several methods to manipulate responses. All methods are chainable unless they trigger a response.

status(code)

The status method allows you to set the status code that is returned to API Gateway. By default this will be set to 200 for normal requests or 500 on a thrown error. Additional built-in errors such as 404 Not Found and 405 Method Not Allowed may also be returned. The status() method accepts a single integer argument.

api.get('/users', (req,res) => {
  res.status(401).error('Not Authorized')
})

header(key, value)

The header method allows for you to set additional headers to return to the client. By default, just the content-type header is sent with application/json as the value. Headers can be added or overwritten by calling the header() method with two string arguments. The first is the name of the header and then second is the value.

api.get('/users', (req,res) => {
  res.header('content-type','text/html').send('<div>This is HTML</div>')
})

NOTE: Header keys are converted and stored as lowercase in compliance with rfc7540 8.1.2. HTTP Header Fields for HTTP/2. Header convenience methods (getHeader, hasHeader, and removeHeader) automatically ignore case.

getHeader([key])

Retrieve the current header object or pass the optional key parameter and retrieve a specific header value. key is case insensitive.

hasHeader(key)

Returns a boolean indicating the existence of key in the response headers. key is case insensitive.

removeHeader(key)

Removes header matching key from the response headers. key is case insensitive. This method is chainable.

getLink(s3Path [, expires] [, callback])

This returns a signed URL to the referenced file in S3 (using the s3://{my-bucket}/{path-to-file} format). You can optionally pass in an integer as the second parameter that will changed the default expiration time of the link. The expiration time is in seconds and defaults to 900. In order to ensure proper URL signing, the getLink() must be asynchronous, and therefore returns a promise. You must either await the result or use a .then to retrieve the value.

There is an optional third parameter that takes an error handler callback. If the underlying getSignedUrl() call fails, the error will be returned using the standard res.error() method. You can override this by providing your own callback.

// async/await
api.get('/getLink', async (req,res) => {
  let url = await res.getLink('s3://my-bucket/my-file.pdf')
  return { link: url }
})
 
// promises
api.get('/getLink', (req,res) => {
  res.getLink('s3://my-bucket/my-file.pdf').then(url => {
    res.json({ link: url })
  })
})

send(body)

The send methods triggers the API to return data to the API Gateway. The send method accepts one parameter and sends the contents through as is, e.g. as an object, string, integer, etc. AWS Gateway expects a string, so the data should be converted accordingly.

json(body)

There is a json convenience method for the send method that will set the headers to application/json as well as perform JSON.stringify() on the contents passed to it.

api.get('/users', (req,res) => {
  res.json({ message: 'This will be converted automatically' })
})

jsonp(body)

There is a jsonp convenience method for the send method that will set the headers to application/json, perform JSON.stringify() on the contents passed to it, and wrap the results in a callback function. By default, the callback function is named callback.

res.jsonp({ foo: 'bar' })
// => callback({ "foo": "bar" })
 
res.status(500).jsonp({ error: 'some error'})
// => callback({ "error": "some error" })

The default can be changed by passing in callback as a URL parameter, e.g. ?callback=foo.

// ?callback=foo
res.jsonp({ foo: 'bar' })
// => foo({ "foo": "bar" })

You can change the default URL parameter using the optional callback option when initializing the API.

const api = require('lambda-api')({ callback: 'cb' });
 
// ?cb=bar
res.jsonp({ foo: 'bar' })
// => bar({ "foo": "bar" })

html(body)

There is also an html convenience method for the send method that will set the headers to text/html and pass through the contents.

api.get('/users', (req,res) => {
  res.html('<div>This is HTML</div>')
})

type(type)

Sets the content-type header for you based on a single String input. There are thousands of MIME types, many of which are likely never to be used by your application. Lambda API stores a list of the most popular file types and will automatically set the correct content-type based on the input. If the type contains the "/" character, then it sets the content-type to the value of type.

res.type('.html');              // => 'text/html'
res.type('html');               // => 'text/html'
res.type('json');               // => 'application/json'
res.type('application/json');   // => 'application/json'
res.type('png');                // => 'image/png'
res.type('.doc');               // => 'application/msword'
res.type('text/css');           // => 'text/css'

For a complete list of auto supported types, see mimemap.js. Custom MIME types can be added by using the mimeTypes option when instantiating Lambda API

location(path)

The location convenience method sets the Location: header with the value of a single string argument. The value passed in is not validated but will be encoded before being added to the header. Values that are already encoded can be safely passed in. Note that a valid 3xx status code must be set to trigger browser redirection. The value can be a relative/absolute path OR a FQDN.

api.get('/redirectToHome', (req,res) => {
  res.location('/home').status(302).html('<div>Redirect to Home</div>')
})
 
api.get('/redirectToGithub', (req,res) => {
  res.location('https://github.com').status(302).html('<div>Redirect to GitHub</div>')
})

redirect([status,] path)

The redirect convenience method triggers a redirection and ends the current API execution. This method is similar to the location() method, but it automatically sets the status code and calls send(). The redirection URL (relative/absolute path, a FQDN, or an S3 path reference) can be specified as the only parameter or as a second parameter when a valid 3xx status code is supplied as the first parameter. The status code is set to 302 by default, but can be changed to 300, 301, 302, 303, 307, or 308 by adding it as the first parameter.

api.get('/redirectToHome', (req,res) => {
  res.redirect('/home')
})
 
api.get('/redirectToGithub', (req,res) => {
  res.redirect(301,'https://github.com')
})
 
// This will redirect a signed URL using the getLink method
api.get('/redirectToS3File', (req,res) => {
  res.redirect('s3://my-bucket/someFile.pdf')
})

cors([options])

Convenience method for adding CORS headers to responses. An optional options object can be passed in to customize the defaults.

The six defined CORS headers are as follows:

• Access-Control-Allow-Origin (defaults to *)
• Access-Control-Allow-Methods (defaults to GET, PUT, POST, DELETE, OPTIONS)
• Access-Control-Allow-Headers (defaults to Content-Type, Authorization, Content-Length, X-Requested-With)
• Access-Control-Expose-Headers
• Access-Control-Max-Age
• Access-Control-Allow-Credentials

The options object can contain the following properties that correspond to the above headers:

• origin (string)
• methods (string)
• headers (string)
• exposeHeaders (string)
• maxAge (number in milliseconds)
• credentials (boolean)

Defaults can be set by calling res.cors() with no properties, or with any combination of the above options.

res.cors({
  origin: 'example.com',
  methods: 'GET, POST, OPTIONS',
  headers: 'content-type, authorization',
  maxAge: 84000000
})

You can override existing values by calling res.cors() with just the updated values:

res.cors({
  origin: 'api.example.com'
})

error([code], message [,detail])

An error can be triggered by calling the error method. This will cause the API to stop execution and return the message to the client. The status code can be set by optionally passing in an integer as the first parameter. Additional detail can be added as an optional third parameter (or second parameter if no status code is passed). This will add an additional detail property to error logs. Details accepts any value that can be serialized by JSON.stringify including objects, strings and arrays. Custom error handling can be accomplished using the Error Handling feature.

api.get('/users', (req,res) => {
  res.error('This is an error')
})
 
api.get('/users', (req,res) => {
  res.error(403,'Not authorized')
})
 
api.get('/users', (req,res) => {
  res.error('Error', { foo: 'bar' })
})
 
api.get('/users', (req,res) => {
  res.error(404, 'Page not found', 'foo bar')
})

cookie(name, value [,options])

Convenience method for setting cookies. This method accepts a name, value and an optional options object with the following parameters:

The name attribute should be a string (auto-converted if not), but the value attribute can be any type of value. The value will be serialized (if an object, array, etc.) and then encoded using encodeURIComponent for safely assigning the cookie value. Cookies are automatically parsed, decoded, and available via the REQUEST object (see REQUEST).

NOTE: The cookie() method only sets the header. A execution ending method like send(), json(), etc. must be called to send the response.

res.cookie('foo', 'bar', { maxAge: 3600*1000, secure: true }).send()
res.cookie('fooObject', { foo: 'bar' }, { domain: '.test.com', path: '/admin', httpOnly: true }).send()
res.cookie('fooArray', [ 'one', 'two', 'three' ], { path: '/', httpOnly: true }).send()

clearCookie(name [,options])

Convenience method for expiring cookies. Requires the name and optional options object as specified in the cookie method. This method will automatically set the expiration time. However, most browsers require the same options to clear a cookie as was used to set it. E.g. if you set the path to "/admin" when you set the cookie, you must use this same value to clear it.

res.clearCookie('foo', { secure: true }).send()
res.clearCookie('fooObject', { domain: '.test.com', path: '/admin', httpOnly: true }).send()
res.clearCookie('fooArray', { path: '/', httpOnly: true }).send()

NOTE: The clearCookie() method only sets the header. A execution ending method like send(), json(), etc. must be called to send the response.

etag([boolean])

Enables Etag generation for the response if at value of true is passed in. Lambda API will generate an Etag based on the body of the response and return the appropriate header. If the request contains an If-No-Match header that matches the generated Etag, a 304 Not Modified response will be returned with a blank body.

cache([age] [, private])

Adds cache-control header to responses. If the first parameter is an integer, it will add a max-age to the header. The number should be in milliseconds. If the first parameter is true, it will add the cache headers with max-age set to 0 and use the current time for the expires header. If set to false, it will add a cache header with no-cache, no-store, must-revalidate as the value. You can also provide a custom string that will manually set the value of the cache-control header. And optional second argument takes a boolean and will set the cache-control to private This method is chainable.

res.cache(false).send() // 'cache-control': 'no-cache, no-store, must-revalidate'
res.cache(1000).send() // 'cache-control': 'max-age=1'
res.cache(30000,true).send() // 'cache-control': 'private, max-age=30'

modified(date)

Adds a last-modified header to responses. A value of true will set the value to the current date and time. A JavaScript Date object can also be passed in. Note that it will be converted to UTC if not already. A string can also be passed in and will be converted to a date if JavaScript's Date() function is able to parse it. A value of false will prevent the header from being generated, but will not remove any existing last-modified headers.

attachment([filename])

Sets the HTTP response content-disposition header field to "attachment". If a filename is provided, then the content-type is set based on the file extension using the type() method and the "filename=" parameter is added to the content-disposition header.

res.attachment()
// content-disposition: attachment
 
res.attachment('path/to/logo.png')
// content-disposition: attachment; filename="logo.png"
// content-type: image/png

download(file [, filename] [, options] [, callback])

This transfers the file (either a local path, S3 file reference, or Javascript Buffer) as an "attachment". This is a convenience method that combines attachment() and sendFile() to prompt the user to download the file. This method optionally takes a filename as a second parameter that will overwrite the "filename=" parameter of the content-disposition header, otherwise it will use the filename from the file. An optional options object passes through to the sendFile() method and takes the same parameters. Finally, a optional callback method can be defined which is passed through to sendFile() as well.

res.download('./files/sales-report.pdf')
 
res.download('./files/sales-report.pdf', 'report.pdf')
 
res.download('s3://my-bucket/path/to/file.png', 'logo.png', { maxAge: 3600000 })
 
res.download(<Buffer>, 'my-file.docx', { maxAge: 3600000 }, (err) => {
  if (err) {
    res.error('Custom File Error')
  }
})

sendFile(file [, options] [, callback])

The sendFile() method takes up to three arguments. The first is the file. This is either a local filename (stored within your uploaded lambda code), a reference to a file in S3 (using the s3://{my-bucket}/{path-to-file} format), or a JavaScript Buffer. You can optionally pass an options object using the properties below as well as a callback function callback(err) that can handle custom errors or manipulate the response before sending to the client.

res.sendFile('./img/logo.png')
 
res.sendFile('./img/logo.png', { maxAge: 3600000 })
 
res.sendFile('s3://my-bucket/path/to/file.png', { maxAge: 3600000 })
 
res.sendFile(<Buffer>, 'my-file.docx', { maxAge: 3600000 }, (err) => {
  if (err) {
    res.error('Custom File Error')
  }
})

The callback function supports returning a promise, allowing you to perform additional tasks after the file is successfully loaded from the source. This can be used to perform additional synchronous tasks before returning control to the API execution.

NOTE: In order to access S3 files, your Lambda function must have GetObject access to the files you're attempting to access.

See Enabling Binary Support for more information.

Enabling Binary Support

To enable binary support, you need to add */* under "Binary Media Types" in API Gateway -> APIs -> [ your api ] -> Settings. This will also base64 encode all body content, but Lambda API will automatically decode it for you.

Add */* to Binary Media Types

Path Parameters

Path parameters are extracted from the path sent in by API Gateway. Although API Gateway supports path parameters, the API doesn't use these values but insteads extracts them from the actual path. This gives you more flexibility with the API Gateway configuration. Path parameters are defined in routes using a colon : as a prefix.

api.get('/users/:userId', (req,res) => {
  res.send('User ID: ' + req.params.userId)
})

Path parameters act as wildcards that capture the value into the params object. The example above would match /users/123 and /users/test. The system always looks for static paths first, so if you defined paths for /users/test and /users/:userId, exact path matches would take precedence. Path parameters only match the part of the path they are defined on. E.g. /users/456/test would not match /users/:userId. You would either need to define /users/:userId/test as its own path, or create another path with an additional path parameter, e.g. /users/:userId/:anotherParam.

A path can contain as many parameters as you want. E.g. /users/:param1/:param2/:param3.

Wildcard Routes

Wildcard routes are supported for methods that match an existing route. E.g. options on an existing get route. Wildcards only work at the end of a route definition such as /* or /users/*. Wildcards within a path, e.g. /users/*/posts are not supported. Wildcard routes do support parameters, so /users/:id/* would capture the :id parameter in your wildcard handler.

Wildcard routes will match deep paths if the route exists. For example, an OPTIONS method for path /users/* would match /users/:id/posts/latest if that path was defined by another method.

The best use case is for the OPTIONS method to provide CORS headers. For more control over variable paths, use Path Parameters instead.

api.options('/users/*', (req,res) => {
  // Do something
  res.status(200).send({})
})

Logging

Lambda API includes a robust logging engine specifically designed to utilize native JSON support for CloudWatch Logs. Not only is it ridiculously fast, but it's also highly configurable. Logging is disabled by default, but can be enabled by passing { logger: true } when you create the Lambda API instance (or by passing a Logging Configuration definition).

The logger is attached to the REQUEST object and can be used anywhere the object is available (e.g. routes, middleware, and error handlers).

const api = require('lambda-api')({ logger: true })
 
api.get('/status', (req,res) => {
  req.log.info('Some info about this route')
  res.send({ status: 'ok' })
})

In addition to manual logging, Lambda API can also generate "access" logs for your API requests. API Gateway can also provide access logs, but they are limited to contextual information about your request (see here). Lambda API allows you to capture the same data PLUS additional information directly from within your application.

Logging Configuration

Logging can be enabled by setting the logger option to true when creating the Lambda API instance. Logging can be configured by setting logger to an object that contains configuration information. The following table contains available logging configuration properties.

Example:

const api = require('lambda-api')({
  logger: {
    level: 'debug',
    access: true,
    customKey: 'detail',
    messageKey: 'message',
    timestamp: () => new Date().toUTCString(), // custom timestamp
    stack: true
  }
})

Log Format

Logs are generated using Lambda API's standard JSON format. The log format can be customized using Serializers.

Standard log format (manual logging):

  {
    "level": "info", // log level
    "time": 1534724904910, // request timestamp
    "id": "41b45ea3-70b5-11e6-b7bd-69b5aaebc7d9", // awsRequestId
    "route": "/user/:userId", // route accessed
    "method": "GET", // request method
    "msg": "Some info about this route", // log message
    "timer": 2, // execution time up until log was generated
    "custom": "additional data", // addditional custom log detail
    "remaining": 2000, // remaining milliseconds until function timeout
    "function": "my-function-v1", // function name
    "memory": 2048, // allocated function memory
    "sample": true // is generated during sampling request?
  }

Access Logs

Access logs generate detailed information about the API request. Access logs are disabled by default, but can be enabled by setting the access property to true in the logging configuration object. If set to false, access logs will only be generated when other log entries (info, error, etc.) are created. If set to the string 'never', access logs will never be generated.

Access logs use the same format as the standard logs above, but include additional information about the request. The access log format can be customized using Serializers.

Access log format (automatic logging):

  {
    ... Standard Log Data ...,
    "path": "/user/123", // path accessed
    "ip": "12.34.56.78", // client ip address
    "ua": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6)...", // User-Agent
    "version": "v1", // specified API version
    "device": "mobile", // client device (as determined by CloudFront)
    "country": "US", // client country (as determined by CloudFront)
    "qs": { // query string parameters
      "foo": "bar"
    }
  }

Logging Levels

Logging "levels" allow you to add detailed logging to your functions based on severity. There are six standard log levels as specified in the table below along with their default priority.

Logs are written to CloudWatch Logs ONLY if they are the same or higher severity than specified in the level log configuration.

// Logging level set to "warn"
const api = require('lambda-api')({ logger: { level: 'warn' } })
 
api.get('/', (req,res) => {
  req.log.trace('trace log message') // ignored
  req.log.debug('debug log message') // ignored
  req.log.info('info log message') // ignored
  req.log.warn('warn log message') // write to CloudWatch
  req.log.error('error log message') // write to CloudWatch
  req.log.fatal('fatal log message') // write to CloudWatch
  res.send({ hello: 'world' })
})

Custom Logging Levels

Custom logging "levels" can be added by specifying an object containing "level names" as keys and their priorities as values. You can also adjust the priority of standard levels by adding it to the object.

const api = require('lambda-api')({
  logger: {
    levels: {
      'test': 5, // low priority 'test' level
      'customLevel': 35, // between info and warn
      'trace': 70 // set trace to the highest priority
    }
  }
})

In the example above, the test level would only generate logs if the priority was set to test. customLevel would generate logs if level was set to anything with the same or lower priority (e.g. info). trace now has the highest priority and would generate a log entry no matter what the level was set to.

Adding Additional Detail

Manual logging also allows you to specify additional detail with each log entry. Details can be added by suppling any variable type as a second parameter to the logger function.

req.log.info('This is the main log message','some other detail') // string
req.log.info('This is the main log message',{ foo: 'bar', isAuthorized: someVar }) // object
req.log.info('This is the main log message',25) // number
req.log.info('This is the main log message',['val1','val2','val3']) // array
req.log.info('This is the main log message',true) // boolean

If an object is provided, the keys will be merged into the main log entry's JSON. If any other type is provided, the value will be assigned to a key using the the customKey setting as its property name. If nested is set to true, objects will be nested under the value of customKey as well.

Serializers

Serializers allow you to customize log formats as well as add additional data from your application. Serializers can be defined by adding a serializers property to the logger configuration object. A property named for an available serializer (main, req, res, context or custom) needs to return an anonymous function that takes one argument and returns an object. The returned object will be merged into the main JSON log entry. Existing properties can be removed by returning undefined as their values.

const api = require('lambda-api')({
  logger: {
    serializers: {
      req: (req) => {
        return {
          apiId: req.requestContext.apiId, // add the apiId
          stage: req.requestContext.stage, // add the stage
          qs: undefined // remove the query string
        }
      }
    }
  }
})

Serializers are passed one argument that contains their corresponding object. req and main receive the REQUEST object, res receives the RESPONSE object, context receives the context object passed into the main run function, and custom receives custom data passed in to the logging methods. Note that only custom objects will trigger the custom serializer.

If the nested option is set to true in the logger configuration, then JSON log entries will be generated with properties for req, res, context and custom with their serialized data as nested objects.

Sampling

Sampling allows you to periodically generate log entries for all possible severities within a single request execution. All of the log entries will be written to CloudWatch Logs and can be used to trace an entire request. This can be used for debugging, metric samples, resource response time sampling, etc.

Sampling can be enabled by adding a sampling property to the logger configuration object. A value of true will enable the default sampling rule. The default can be changed by passing in a configuration object with the following available optional properties: