Common API Utilities

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This is a lightweight library containing a few commonly used methods for creating API's with Express.js. It is ideally suited for prototyping API's.

There's a short walk-thru/guide/example available on Quora

Installation:

npm install @butlerlogic/common-api -S

Usage

const express = require('express')
const API = require('@butlerlogic/common-api')
const app = express()

app.post('/endpoint', API.validateJsonBody(), (req, res) => { ... })

const server = app.listen(() => console.log('Server is running.'))

Shortcuts

Request Middleware

• log()
• logRequestHeaders()
• logRedirects([bool])
• litmusTest([message]))
• validateJsonBody
• validNumericId
• validId
• validResult(res, callback)
• basicauth(user, password)
• bearer(token)
• applyCommonConfiguration(app, [autolog])
• applySimpleCORS(app, host='*')
• allowHeaders('Origin', 'X-Requested-With')
• allowMethods('GET', 'POST', 'OPTIONS')
• allowOrigins('a.domain.com', 'b.domain.com')
• allowPreflight()
• allowAll('host')

Responses

• 200
• OK
• 201
• CREATED
• 401
• UNAUTHORIZED
• 404
• NOT_FOUND
• 501
• NOT_IMPLEMENTED
• Other HTTP Status Codes
• redirect(url, [permanent, moved])
• reply(anything)
• replyWithError(res, [status, message]|error)
• replyWithMaskedError(res, [status, message]|error)

Utilities

• createUUID
• atob(value)
• applyBaseUrl (req, route = '/' [, forceTLS = false])
• applyRelativeUrl (req, route = '/' [, forceTLS = false])
• errorType
• commonHeaders
• httpMethods

Middleware

The following static methods are available:

log

Configures a simple console logging utility (with colorized output). This can be used as middleware for all requests or individual requests.

app.use(API.log)

app.post('/endpoint', API.log, ...)

logRequestHeaders

Configures a simple console logging utility (with colorized output), which will log the request headers of the request. This can be used as middleware for all requests or individual requests.

app.use(API.logRequestHeaders)

app.post('/endpoint', API.logRequestHeaders, ...)

logRedirects([bool])

Toggle redirect logging. This is not middleware. It is just a function to determine whether redirected requests should be logged to the console or not.

API.logRedirects() // Defaults to `true`
API.logRedirects(true)
API.logRedirects(false)

When active, this will log a message like:

Redirect GET /redirect → http://domain.com/endpoint

litmusTest([message])

This pass-thru middleware component is useful for determining whether a route or responder is reachable or not. A message (LITMUS TEST by default) is logged to the console/stdout, without affecting the network request/response.

app.use('/endpoint', API.litmusTest('endpoint reachable'), ...)

validateJsonBody

app.post('/endpoint', API.validateJsonBody(), ...)

Validates a request body exists and consists of valid JSON.

It is also possible to verify that the JSON body contains specific "top level" attributes (i.e. nesting is not supported).

For example,

app.post('/endpoint', API.validateJsonBody('a', 'b', 'c'), ...)

The code above will verify that the request body is valid JSON containing attributes a, b, and c.

Valid JSON

{
  "a": "text",
  "b": "text",
  "c": "text",
  "d": "extra is ok"
}

Invalid JSON

{
  "a": "text",
  "c": "text",
  "d": "extra is ok"
}

Produces:

400 - Missing parameters: b

validNumericId

app.post('/endpoint/:id', API.validNumericId(), ...)

Assures :id is a valid numeric value. This also supports a query parameter, such as /endpoint?id=12345. This will add an attribute to the request object (req.id).

An alternative argument name can be provided, such as:

app.post('/endpoint/:userid', API.validNumericId('userid'), ...)

validId

app.post('/endpoint/:id', API.validId(), ...)

Assures :id exists, as a string. This also supports a query parameter, such as /endpoint?id=some_id. This will add an attribute to the request object (req.id).

An alternative argument name can be provided, such as:

app.post('/endpoint/:userid', API.validId('userid'), ...)

validResult(res, callback)

Inspects the result and returns a function that will throw an error or return results.

let checkResult = API.validResult(res, results => res.send(results))

app.get('/endpoint', (req, res) => { ...processing... }, checkResult)

basicauth(user, password)

This method will perform basic authentication. It will compare the authentication header credentials with the username and password.

For example, basicauth('user', 'passwd') would compare the user-submitted username/password to user and passwd. If they do not match, a 401 (Not Authorized) response is sent. If authentication is successful, a user attribute will be appended to the request (i.e. req.user).

app.get('/secure', API.basicauth('user', 'passwd'), (req, res) => ...)
// req.user would be set "user" when authentication succeeds.

It is also possible to perform a more advanced authentication using a custom function. For example:

app.get('/secure', API.basicauth(function (username, password, grantedFn, deniedFn) {
  if (confirmWithDatabase(username, password)) {
    grantedFn()
  } else {
    deniedFn()
  }
}))

The username/password will be supplied in plain text. The grantedFn() should be run when user authentication succeeds, and the deniedFn() should be run when it fails. Any downstream middleware or other handlers will be able to access the username by referencing req.user.

bearer(token)

This method looks for a bearer token in the Authorization request header. If the token does not match, a 401 (Unauthorized) status is returned.

app.get('/secure/path', API.bearer('mytoken'), API.reply('authenticated'))

The code above would succeed for requests which contain the following request header:

Authorization: Bearer mytoken

The case-insensitive keyword "bearer" is required for this to work.

It is also possible to use a custom function to evaluate the request token. The function must by synchronous and return a boolean value (true or false).

app.get('/secure/path', API.bearer(function (token) {
  return isValidToken(token)
}), API.reply('authenticated'))

Tokens do not necessarily represent a unique user, but they are often used to lookup a user. To facilitate this, the req.user attribute is set to the value of the token so downstream middleware can perform lookups or further validate the token.

applyCommonConfiguration(app, [autolog])

const express = require('express')
const app = express()
const API = require('@butlerlogic/common-api')

API.applyCommonConfiguration(app)

This helper method is designed to rapidly implement common endpoints. This can be used throughout the testing phase or in production.

The common configuration consists of 3 basic endpoints:

• /ping: A simple responder that returns a 200 (OK) response.
• /version: Responds with a plaintext body containing the version of the API, as determined by the version attribute found in the package.json file of the server.
• /info: Responds with a JSON payload containing 3 attributes:
  • runningSince: The timestamp when the API server was launched.
  • version: Same as /version above.
  • routes: An array of all known routes/endpoints of the API.

This also disables the x-powered-by header used in Express.

By default, this method enables logging (using the log method). This can be turned off by passing false as a second argument:

API.applyCommonConfiguration(app, false)

applySimpleCORS(app, host='*')

const express = require('express')
const app = express()
const API = require('@butlerlogic/common-api')

API.applySimpleCORS(app)
// API.applySimpleCORS(app, 'localhost')

Implementing CORS support while prototyping/developing an API can consume more time than most people anticipate. This method applies a simple CORS configuration so you can "continue coding". It is unlikely this configuration will be used in production environments unless the API is behind a secure gateway, but it helps temporarily resolve the most common challenges of developing with CORS.

This method applies 3 response headers to all responses:

• Access-Control-Allow-Origin: By default, this is set to *, but the host can be modified by passing an optional 2nd argument to the function.
• Access-Control-Allow-Headers: Set to 'Origin, X-Requested-With, Content-Type, Accept'
• Access-Control-Allow-Methods: Set to GET, POST, PUT, PATCH, DELETE, OPTIONS

allowHeaders('Origin', 'X-Requested-With')

This CORS middleware feature can be used to specify/override which HTTP headers are allowed to be sent with requests to the server (by endpoint). This automatically handles setting the appopriate Access-Control-Allow-Headers HTTP header.

const express = require('express')
const app = express()
const API = require('@butlerlogic/common-api')

API.applySimpleCORS(app)

app.get('/special/endpoint, API.allowOrigins('a.domain.com', 'b.domain.com'), (req, res) => {...})

This can also be applied to all requests:

app.use(API.allowOrigins('a.domain.com', 'b.domain.com'))

allowMethods('GET', 'POST', 'OPTIONS')

This CORS middleware feature can be used to specify/override which methods are allowed to be used when making HTTP requests to a specific endpoint/route. This automatically handles setting the appopriate Access-Control-Allow-Methods HTTP header.

const express = require('express')
const app = express()
const API = require('@butlerlogic/common-api')

API.applySimpleCORS(app)

app.get('/special/endpoint, API.allowMethods('PATCH', 'POST'), (req, res) => {...})

This can also be applied to all requests:

app.use(API.allowMethods('GET'))

allowOrigins('a.domain.com', 'b.domain.com')

This CORS middleware feature can be used to specify/override which hosts are allowed to send requests to the server (by endpoint). This automatically handles setting the appopriate Access-Control-Allow-Origin HTTP header.

const express = require('express')
const app = express()
const API = require('@butlerlogic/common-api')

API.applySimpleCORS(app)

app.get('/special/endpoint, API.allowOrigins('a.domain.com', 'b.domain.com'), (req, res) => {...})

This can also be applied to all requests:

app.use(API.allowOrigins('a.domain.com', 'b.domain.com'))

allowPreflight()

This middleware responds to OPTIONS requests with a 200 OK response. This method is useful because it automatically applies the appropriate CORS configurations to support any request headers submitted to the endpoint.

app.use(API.allowPreflight())

// or

app.any('/path', API.allowPreflight(), (req, res) => { ... })

allowAll(host)

This middleware uses CORS, allowing any request from the specified host(s). This should not be considered a secure or insecure method. Used appropriately, it can provide proper security at large scale. Used inappropriately, it can be insecure at any scale. Use with caution. Remember, this method is primarily useful for developing functional API's before locking them down with tighter security restrictions.

// Allow anything from any domain (insecure)
app.use(API.allowAll('*'))
app.use(API.allowAll()) // Equivalent of above

// Allow anything from my domain (semi-secure, limited to 1 domain)
app.use(API.allowAll('mydomain.com'))

// Applied to a specific endpoint (semi-secure, limited to 1 path on 1 domain)
app.get('/endpoint', this.allowAll('mydomain.com'), (req, res) => { ... })

// Applied to a specific endpoint for multiple sources
app.get('/endpoint', this.allowAll('mydomain.com', 'mypartner.com'), (req, res) => { ... })

Responses

200

app.post('/endpoint', API.200)

Sends a status code 200 response.

OK

app.post('/endpoint', API.OK)

Sends a status code 200 response.

201

app.post('/endpoint', API.201)

Sends a status code 201 response.

CREATED

app.post('/endpoint', API.CREATED)

Sends a status code 201 response.

401

app.post('/endpoint', API.401)

Sends a status code 401 response.

UNAUTHORIZED

app.post('/endpoint', API.UNAUTHORIZED)

Sends a status code 401 response.

404

app.post('/endpoint', API.404)

Sends a status code 404 response.

NOT_FOUND

app.post('/endpoint', API.NOT_FOUND)

Sends a status code 404 response.

501

app.post('/endpoint', API.501)

Sends a status code 501 response.

NOT_IMPLEMENTED

app.post('/endpoint', API.NOT_IMPLEMENTED)

Sends a status code 501 response.

OTHER_STATUS_CODES

All of the standard status codes have shortcut methods available. Each HTTP status code has two methods associated with it: HTTP### and a method named by replacing spaces and hyphens in the the status message with underscores, removing special characters, and converting the whole message to upper case.

For example, HTTP status 304 (Not Modified) would have a method HTTP304 and NOT_MODIFIED.

The joke status, 418 (I'm a Teapot) illustrates how special characters are removed.

• HTTP418()
• IM_A_TEAPOT()

redirect(url, [permanent, moved])

A helper method for redirecting requests to another location. This is not a proxy, it does not actually forward requests. It tells the client the URL being requested is outdated and/or has been moved permanently/temporarily.

This method exists since redirects have been used incorrectly in the past (by the entire industry). The redirect HTTP status codes changed in RFC 7231 (2014), but are still commonly disregarded. This method supplies the appropriate HTTP status codes without having to remember which code is proper for each circumstance.

app.get('/path', API.redirect('https://elsewhere.com')) // 307
// ^ equivalent of: app.get('/path', API.redirect('https://elsewhere.com', false, false))

app.get('/path', API.redirect('https://elsewhere.com', true, false)) // 308
app.get('/path', API.redirect('https://elsewhere.com', true, true)) // 301
app.get('/path', API.redirect('https://elsewhere.com', false, true)) // 303

/**
 * Redirect the request to another location.
 * @param {string} url
 * The location to redirect to.
 * @param {boolean} [permanent=false]
 * Instruct the client that the redirect is permanent,
 * suggesting all future requests should be made directly
 * to the new location. When this is `false`, a HTTP `307`
 * code is returned. When `true`, a HTTP `308` is returned.
 * @param {boolean} [moved=false]
 * Inform the client that the destination has been moved.
 * When _moved_ is `true` and _permanent_ is `false`, an
 * HTTP `303` (Found) status is returned, informing the
 * client the request has been received and a `GET` request
 * should be issued to the new location to retrieve it. When
 * _permanent_ is `true`, a HTTP `301` is returned,
 * indicating all future requests should be made directly to
 * the new location.
 */

reply(anything)

A helper method to send objects as a JSON response, or to send plain text. This function attempts to automatically determine the appropriate response header type.

Example:

app.get('/path', API.reply(myJsonObject))

replyWithError(res, [status, message]|error)

Send an HTTP error response. This function accepts two different kinds of arguments. The response is always the first argument. The method will also accept a custom HTTP status code and/or a custom plaintext message, as shown here:

app.get('/myendpoint', (req, res) => {
  if (problem === true) {
    API.replyWithError(res, 400, 'There is a problem.')
  }
})

By default, an HTTP status code of 500 (Server Error) is used.

Another option it to pass a JavaScript error as the last argument.

app.get('/myendpoint', (req, res) => {
  someFunction((err, data) => {
    API.replyWithError(res, err)
  })
})

// A custom HTTP status code can be used
app.get('/myendpoint', (req, res) => {
  someFunction((err, data) => {
    API.replyWithError(res, 404, err)
  })
})

In the first example, an error is passed as the last argument. Using this approach, the response will have a 400 status and the message will be auto-extracted from the JavaScript error. The second example will do the same thing, but it will send a 404 status code instead of the default.

replyWithMaskedError(res, [status, message]|error)

This functions very similarly to replyWithError, but a non-descript error message is sent to the client with a reference ID. The message/error is written to the console, making it possible to lookup actual error in the server logs.

For example:

app.get('/myendpoint', (req, res) => {
  if (problem === true) {
    API.replyWithMaskedError(res, 400, 'There is a problem connecting to the database.')
  }
})

The response sent in the reply will actually look like:

400 An error occurred. Reference: eaac53bc-8b95-4e81-bc29-dead2a14c2ea

The logs would look like:

[ERROR:eaac53bc-8b95-4e81-bc29-dead2a14c2ea] (400) There was a problem connecting to the database.

Utilities

createUUID

This utility method helps generate unique ID's. This is used to generate the transaction ID for masked error output (replyWithMaskedError method).

atob(value)

ASCII to Binary: This mimics the window.atob function. It is commonly used to extract username/password from a request.

applyBaseUrl (req, route = '/', forceTLS = false)

Apply the base URL to the specified route. If forceTLS is set to true, the response will always use the https protocol.

app.get('/my/path', (req, res) => {
  res.json({
    id: API.applyBaseURL(req, 'myid')
  })
})

If a request was made to http://domain.com/my/path, this would return:

{
  "id": "http://domain.com/myid"
}

applyRelativeUrl (req, route = '/', forceTLS = false)

Apply the relative URL to the specified route. If forceTLS is set to true, the response will always use the https protocol.

app.get('/my/path', (req, res) => {
  res.json({
    id: API.applyBaseURL(req, 'myid')
  })
})

If a request was made to http://domain.com/my/path, this would return:

{
  "id": "http://domain.com/my/path/myid"
}

errorType

By default, using replyWithError or replyWithMaskedError will produce standard text-based error reponses, such as 401 (Unauthorized).

It is possible to produce JSON instead, resulting in:

{
  "status": 401,
  "message": "Unauthorized"
}

If JSON is needed, set the errorType to json.

API.errorType = 'json'

commonHeaders

This is an array of the most common request headers used by HTTP clients. This is useful when constructing your own list of CORS headers using the allowHeaders method.

console.log(API.commonHeaders)

Headers include: Origin, X-Requested-With, Content-Type, and Accept. This list may be updated from time to time.

httpMethods

An array of the official HTTP methods.

console.log(API.httpMethods)

Includes:

• GET
• HEAD
• POST
• PUT
• DELETE
• CONNECT
• OPTIONS
• TRACE
• PATCH