server/middlewares/cache.ts


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import * as express from 'express'
import * as AsyncLock from 'async-lock'
import { Redis } from '../lib/redis'
import { logger } from '../helpers/logger'

const lock = new AsyncLock({ timeout: 5000 })

function cacheRoute (lifetime: number) {
  return async function (req: express.Request, res: express.Response, next: express.NextFunction) {
    const redisKey = Redis.Instance.buildCachedRouteKey(req)

    await lock.acquire(redisKey, async (done) => {
      const cached = await Redis.Instance.getCachedRoute(req)

      // Not cached
      if (!cached) {
        logger.debug('No cached results for route %s.', req.originalUrl)

        const sendSave = res.send.bind(res)

        res.send = (body) => {
          if (res.statusCode >= 200 && res.statusCode < 400) {
            const contentType = res.getHeader('content-type').toString()
            Redis.Instance.setCachedRoute(req, body, lifetime, contentType, res.statusCode)
                 .then(() => done())
                 .catch(err => {
                   logger.error('Cannot cache route.', { err })
                   return done(err)
                 })
          }

          return sendSave(body)
        }

        return next()
      }

      if (cached.contentType) res.contentType(cached.contentType)

      if (cached.statusCode) {
        const statusCode = parseInt(cached.statusCode, 10)
        if (!isNaN(statusCode)) res.status(statusCode)
      }

      logger.debug('Use cached result for %s.', req.originalUrl)
      res.send(cached.body).end()

      return done()
    })
  }
}

// ---------------------------------------------------------------------------

export {
  cacheRoute
}