@middy/http-header-normalizer/index.js

Http header normalizer middleware for the middy framework

const exceptionsList = [
  'ALPN',
  'C-PEP',
  'C-PEP-Info',
  'CalDAV-Timezones',
  'Content-ID',
  'Content-MD5',
  'DASL',
  'DAV',
  'DNT',
  'ETag',
  'GetProfile',
  'HTTP2-Settings',
  'Last-Event-ID',
  'MIME-Version',
  'Optional-WWW-Authenticate',
  'Sec-WebSocket-Accept',
  'Sec-WebSocket-Extensions',
  'Sec-WebSocket-Key',
  'Sec-WebSocket-Protocol',
  'Sec-WebSocket-Version',
  'SLUG',
  'TCN',
  'TE',
  'TTL',
  'WWW-Authenticate',
  'X-ATT-DeviceId',
  'X-DNSPrefetch-Control',
  'X-UIDH'
]

const exceptions = exceptionsList.reduce((acc, curr) => {
  acc[curr.toLowerCase()] = curr
  return acc
}, {})

const normalizeHeaderKey = (key, canonical) => {
  const lowerCaseKey = key.toLowerCase()
  if (!canonical) {
    return lowerCaseKey
  }

  if (exceptions[lowerCaseKey]) {
    return exceptions[lowerCaseKey]
  }

  return lowerCaseKey
    .split('-')
    .map((text) => (text[0] || '').toUpperCase() + text.substr(1))
    .join('-')
}

const defaults = {
  canonical: false,
  defaultHeaders: {},
  normalizeHeaderKey
}

const httpHeaderNormalizerMiddleware = (opts = {}) => {
  const options = { ...defaults, ...opts }

  const defaultHeaders = {}
  const defaultMultiValueHeaders = {}
  for (const key of Object.keys(options.defaultHeaders)) {
    const newKey = options.normalizeHeaderKey(key, options.canonical)
    const isArray = Array.isArray(options.defaultHeaders[key])
    defaultHeaders[newKey] = isArray
      ? options.defaultHeaders[key].join(',')
      : options.defaultHeaders[key]
    defaultMultiValueHeaders[newKey] = isArray
      ? options.defaultHeaders[key]
      : options.defaultHeaders[key].split(',')
  }

  const httpHeaderNormalizerMiddlewareBefore = async (request) => {
    if (request.event.headers) {
      const headers = { ...defaultHeaders }

      for (const key of Object.keys(request.event.headers)) {
        headers[options.normalizeHeaderKey(key, options.canonical)] =
          request.event.headers[key]
      }

      request.event.headers = headers
    }

    if (request.event.multiValueHeaders) {
      const headers = { ...defaultMultiValueHeaders }

      for (const key of Object.keys(request.event.multiValueHeaders)) {
        headers[options.normalizeHeaderKey(key, options.canonical)] =
          request.event.multiValueHeaders[key]
      }

      request.event.multiValueHeaders = headers
    }
  }

  return {
    before: httpHeaderNormalizerMiddlewareBefore
  }
}

export default httpHeaderNormalizerMiddleware