Be able to synchronize the TTL of cache-control header to expire in a coherent way

lib/api/middlewares/cache-control.js

@@ -1,14 +1,36 @@
 'use strict';
 
-const ONE_YEAR_IN_SECONDS = 31536000; // ttl in cache provider
-const FIVE_MINUTES_IN_SECONDS = 60 * 5; // ttl in cache provider
+const ONE_MINUTE_IN_SECONDS = 60;
+const THREE_MINUTE_IN_SECONDS = 60 * 3;
+const FIVE_MINUTES_IN_SECONDS = ONE_MINUTE_IN_SECONDS * 5;
+const TEN_MINUTES_IN_SECONDS = ONE_MINUTE_IN_SECONDS * 10;
+const FIFTEEN_MINUTES_IN_SECONDS = ONE_MINUTE_IN_SECONDS * 15;
+const THIRTY_MINUTES_IN_SECONDS = ONE_MINUTE_IN_SECONDS * 30;
+const ONE_HOUR_IN_SECONDS = ONE_MINUTE_IN_SECONDS * 60;
+const ONE_YEAR_IN_SECONDS = ONE_HOUR_IN_SECONDS * 24 * 365;
+
 const defaultCacheTTL = {
     ttl: ONE_YEAR_IN_SECONDS,
     fallbackTtl: FIVE_MINUTES_IN_SECONDS
 };
-const cacheControl = Object.assign(defaultCacheTTL, global.settings.cache);
+
+const validFallbackTTL = [
+    ONE_MINUTE_IN_SECONDS,
+    THREE_MINUTE_IN_SECONDS,
+    FIVE_MINUTES_IN_SECONDS,
+    TEN_MINUTES_IN_SECONDS,
+    FIFTEEN_MINUTES_IN_SECONDS,
+    THIRTY_MINUTES_IN_SECONDS,
+    ONE_HOUR_IN_SECONDS
+];
+
+const { ttl, fallbackTtl } = Object.assign(defaultCacheTTL, global.settings.cache);
 
 module.exports = function cacheControlHeader () {
+    if (!validFallbackTTL.includes(fallbackTtl)) {
+        throw new Error(`Invalid fallback TTL value for Cache-Control header. Got ${fallbackTtl}, expected ${validFallbackTTL.join(', ')}`);
+    }
+
     return function cacheControlHeaderMiddleware (req, res, next) {
         const { cachePolicy } = res.locals.params;
         const { affectedTables, mayWrite } = res.locals;
@@ -20,15 +42,23 @@ module.exports = function cacheControlHeader () {
         }
 
         if (affectedTables && affectedTables.getTables().every(table => table.updated_at !== null)) {
-            const maxAge = mayWrite ? 0 : cacheControl.ttl;
+            const maxAge = mayWrite ? 0 : ttl;
             res.header('Cache-Control', `no-cache,max-age=${maxAge},must-revalidate,public`);
 
             return next();
         }
 
-        const maxAge = cacheControl.fallbackTtl;
-        res.header('Cache-Control', `no-cache,max-age=${maxAge},must-revalidate,public`);
+        const maxAge = fallbackTtl;
+        res.header('Cache-Control', `no-cache,max-age=${computeNextTTL({ ttlInSeconds: maxAge })},must-revalidate,public`);
 
         return next();
     };
 };
+
+function computeNextTTL ({ ttlInSeconds } = {}) {
+    const nowInSeconds = Math.ceil(Date.now() / 1000);
+    const secondsAfterPreviousTTLStep = nowInSeconds % ttlInSeconds;
+    const secondsToReachTheNextTTLStep = ttlInSeconds - secondsAfterPreviousTTLStep;
+
+    return secondsToReachTheNextTTLStep;
+}

test/acceptance/app-test.js

@@ -246,7 +246,14 @@ it('TRUNCATE TABLE with GET and auth', function(done){
         assert.equal(res.statusCode, 200, res.statusCode + ': ' + res.body);
         // table should not get a cache channel as it won't get invalidated
         assert.ok(!res.headers.hasOwnProperty('x-cache-channel'));
-        assert.equal(res.headers['cache-control'], 'no-cache,max-age=300,must-revalidate,public');
+
+        const fallbackTtl = global.settings.cache.fallbackTtl || 300;
+        const cacheControl = res.headers['cache-control'];
+        const [ , maxAge ] = cacheControl.split(',');
+        const [ , value ] = maxAge.split('=');
+
+        assert.ok(Number(value) <= fallbackTtl);
+
         var pbody = JSON.parse(res.body);
         assert.equal(pbody.total_rows, 1);
         assert.equal(pbody.rows[0].count, 0);

test/acceptance/cache-headers-test.js

@@ -55,7 +55,12 @@ describe('cache headers', function () {
                 method: 'GET'
             }, {},
             function(err, res) {
-                assert.equal(res.headers['cache-control'], `no-cache,max-age=${fallbackTtl},must-revalidate,public`);
+                const fallbackTtl = global.settings.cache.fallbackTtl || 300;
+                const cacheControl = res.headers['cache-control'];
+                const [ , maxAge ] = cacheControl.split(',');
+                const [ , value ] = maxAge.split('=');
+
+                assert.ok(Number(value) <= fallbackTtl);
 
                 assert.response(server, {
                     url: `/api/v1/sql?${qs.encode({