geolocation api rate-limit: add per-provider prefix to cached response, refactor geocoding provider code

server/api/controller/geocoding.js

@@ -0,0 +1,135 @@
+const rateLimit = require('express-rate-limit');
+const log = require('../../log')
+const nominatim = require('../../services/geocoding/nominatim')
+const photon = require('../../services/geocoding/photon')
+const axios = require('axios')
+const { version } = require('../../../package.json')
+const cache = require('memory-cache');
+let d = 0 // departure time
+let h = 0 // hit geocoding provider time (aka Latency)
+
+const geocodingController = {
+  /**
+   * TODO: replace/merge with a general 'instance rate-limiter' or 'instance api-related rate-limiter' when this will be defined
+   */  
+  instanceApiRateLimiter: rateLimit({
+    windowMs: 15 * 60 * 1000, // 15 minutes
+    max: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes)
+    standardHeaders: true, // Return rate limit info in the `RateLimit-*` headers
+    legacyHeaders: false, // Disable the `X-RateLimit-*` headers
+  }),
+
+  /** 
+   * Limit provider api usage.
+   * From https://operations.osmfoundation.org/policies/nominatim/
+   * [Requirements] No heavy uses (an absolute maximum of 1 request per second).
+   * [Websites and Apps] 
+   * - Note that the usage limits above apply per website/application: the sum of traffic by all your users should not exceed the limits.
+   * - If at all possible, set up a proxy and also enable caching of requests. 
+   */
+  providerRateLimit (req, res, next, providerCommonName) {
+    let a = Date.now(); // arrival time
+    let dprev = d
+    d = dprev + 1000 + h
+
+    console.log('a: ' + a)
+    console.log('dprev: ' + dprev)
+    console.log('d: ' + d)
+
+    // if the same request was already cached skip the delay mechanism
+    if (cache.get(providerCommonName + '_' + req.params.place_details)) {
+      if (a < d) {
+        log.warn('More than 1 request per second to geocoding api. This from ' + req.ip + ' . The response data is served from memory-cache')
+      }
+      console.log('yet cached')
+      // reset departure time because there is no need to ask provider
+      d = dprev
+      return next()
+    }
+
+    if (d === 0 || a > d) {
+      // no-queue or old-queue
+      console.log('No queue or Old queue')
+      // arrival time + 10ms estimated computing time
+      d = a + 10 
+      next()
+    } else {
+      // fresh queue
+      console.log('Fresh queue')
+      let wait = d - a
+      console.log('Waiting '+ wait)
+      log.warn('More than 1 request per second to geocoding api. This from ' + req.ip + ' . Applying ToS padding before asking to provider. The response data is now cached.')
+      
+      setTimeout(() => {
+        next()
+      }, wait)
+    }
+    
+  },
+
+  async nominatimRateLimit(req, res, next) {
+    geocodingController.providerRateLimit(req, res, next, nominatim.commonName)
+  },
+
+  async photonRateLimit(req, res, next) {
+    geocodingController.providerRateLimit(req, res, next, photon.commonName)
+  },
+
+  async checkInCache (req, res, details, providerCommonName) {
+    if (cache.get(providerCommonName + '_' + details)) { 
+      const ret = await cache.get(providerCommonName + '_' + details) 
+      return ret
+    } else {
+      console.log('Not in cache')
+      return
+    }
+  },
+
+  async queryProvider(req, res, details, provider) {
+    let RTTstart = Date.now()
+    console.log('Asking Provider: ' + RTTstart)
+
+    const ret = await axios.get(`${provider.endpoint(req, res)}`, { 
+      params: provider.getParams(req, res),
+      headers: { 'User-Agent': `gancio ${version}` }
+    })
+
+    if (ret) {
+      let RTTend = Date.now()
+      console.log('Asking Provider: ' + RTTend)
+      // Save the hit time (aka Latency)
+      console.log('Saving latency h: ' + h)
+      h = (RTTend - RTTstart) / 2
+    }
+
+    // Cache the response data
+    cache.put(provider.commonName + '_' + details, ret.data, 1000 * 60 * 60 * 24);
+    console.log(cache.keys())
+    console.log(cache.exportJson())
+    return ret.data
+  },
+
+
+  async _nominatim (req, res) {
+    const details = req.params.place_details
+
+    const ret = await geocodingController.checkInCache(req, res, details, nominatim.commonName) ||
+      await geocodingController.queryProvider(req, res, details, nominatim)
+
+    return res.json(ret)
+
+  },
+
+  async _photon (req, res) {
+    const details = req.params.place_details
+
+    const ret = await geocodingController.checkInCache(req, res, details, photon.commonName) ||
+      await geocodingController.queryProvider(req, res, details, photon)
+
+    return res.json(ret)
+
+  },
+
+}
+
+module.exports = geocodingController