trjhtr

We're converting the City of Philadelphia's website to be served as static files. In order to support redirects and rewrites (URL masking), we decided to use a Lambda@edge function, which modifies (or responds to) the inbound request. I expect this will be maintained by other people so readability is very important. I would love your feedback on how this could be easier to understand and maintain.

const URL = require('url')
const inspect = require('util')
const TRAILING_SLASH = //$/
let compiledRegexes = 

exports.handler = createHandler(require('../rules.json')) // expose to lambda
exports.createHandler = createHandler // expose for testing

function createHandler (rules) 
 return async function (event) 
 const request = event.Records[0].cf.request
 const cleanPath = request.uri.toLowerCase().replace(TRAILING_SLASH, '')
 log(event)

 for (const rule of rules) 
 let newPath = null

 if (rule.regex) 
 if (!compiledRegexes.hasOwnProperty(rule.pattern)) 
 compiledRegexes[rule.pattern] = new RegExp(rule.pattern)
 

 const regex = compiledRegexes[rule.pattern]
 if (regex.test(cleanPath)) 
 newPath = cleanPath.replace(regex, rule.replacement)
 
 else if (cleanPath === rule.pattern) 
 newPath = rule.replacement
 

 if (newPath !== null) 
 if (rule.type === 'rewrite') else 
 const response = createRedirect(newPath)
 log(response)
 return response
 
 
 

 // If no matches, return unmodified request
 log('no match')
 return request
 


// Mutates request object
function setOrigin (request, origin) 
 const url = new URL(origin)
 const protocol = url.protocol.slice(0, -1) // remove trailing colon
 const path = url.pathname.replace(TRAILING_SLASH, '')

 request.origin = 
 custom: 
 domainName: url.hostname,
 protocol,
 port: (protocol === 'https') ? 443 : 80,
 path,
 sslProtocols: ['TLSv1.2', 'TLSv1.1'],
 readTimeout: 5,
 keepaliveTimeout: 5,
 customHeaders: 
 
 
 request.headers.host = [
 key: 'host', value: url.hostname 
 ]


function createRedirect (newUri) 
 return 
 status: '301',
 statusDescription: 'Moved Permanently',
 headers: 
 location: [
 key: 'Location', value: newUri 
 ]
 
 


function log (data) 
 if (process.env.NODE_ENV === 'test') return
 // use util.inspect so objects aren't collapsed
 console.log(inspect(data, false, 10))

A few example rules from rules.json:

redirects

 "pattern": "/old",
 "replacement": "https://example.com/new",
 "type": "redirect"

rewrites

 "pattern": "/old(/.+)?",
 "regex": true,
 "replacement": "$1",
 "origin": "https://example.com/new",
 "type": "rewrite"

(I definitely don't love the "API" of how these rules are configured, and I think they could be simplified or merged. Would love any ideas here too!)

Thanks so much for your time.