Dynamic cache length overriding (#2755)

For the Endpoint badge: #2473.

`request-handler.js` is such a bear. I’m looking forward to being able to rewrite it when the service refactor is done.

lib/request-handler.js

@@ -89,19 +89,35 @@ function handleRequest(cacheHeaderConfig, handlerOptions) {
 
   const allowedKeys = flattenQueryParams(handlerOptions.queryParams)
   const {
-    cacheLength: serviceCacheLengthSeconds,
+    cacheLength: serviceDefaultCacheLengthSeconds,
     fetchLimitBytes,
   } = handlerOptions
 
   return (queryParams, match, end, ask) => {
     const reqTime = new Date()
 
-    setCacheHeaders({
-      cacheHeaderConfig,
-      serviceCacheLengthSeconds,
-      queryParams,
-      res: ask.res,
-    })
+    // `defaultCacheLengthSeconds` can be overridden by
+    // `serviceDefaultCacheLengthSeconds` (either by category or on a badge-
+    // by-badge basis). Then in turn that can be overridden by
+    // `serviceOverrideCacheLengthSeconds` (which we expect to be used only in
+    // the dynamic badge) but only if `serviceOverrideCacheLengthSeconds` is
+    // longer than `serviceDefaultCacheLengthSeconds` and then the `maxAge`
+    // query param can also override both of those but again only if `maxAge`
+    // is longer.
+    //
+    // When the legacy services have been rewritten, all the code in here
+    // will go away, which should achieve this goal in a simpler way.
+    //
+    // Ref: https://github.com/badges/shields/pull/2755
+    function setCacheHeadersOnResponse(res, serviceOverrideCacheLengthSeconds) {
+      setCacheHeaders({
+        cacheHeaderConfig,
+        serviceDefaultCacheLengthSeconds,
+        serviceOverrideCacheLengthSeconds,
+        queryParams,
+        res,
+      })
+    }
 
     analytics.noteRequest(queryParams, match)
 
@@ -123,6 +139,10 @@ function handleRequest(cacheHeaderConfig, handlerOptions) {
       const tooSoon = +reqTime - cached.time < cached.interval
       if (tooSoon || cached.dataChange / cached.reqs <= freqRatioMax) {
         const svg = makeBadge(cached.data.badgeData)
+        setCacheHeadersOnResponse(
+          ask.res,
+          cached.data.badgeData.cacheLengthSeconds
+        )
         makeSend(cached.data.format, ask.res, end)(svg)
         cachedVersionSent = true
         // We do not wish to call the vendor servers.
@@ -140,9 +160,13 @@ function handleRequest(cacheHeaderConfig, handlerOptions) {
         return
       }
       if (requestCache.has(cacheIndex)) {
-        const cached = requestCache.get(cacheIndex).data
-        const svg = makeBadge(cached.badgeData)
-        makeSend(cached.format, ask.res, end)(svg)
+        const cached = requestCache.get(cacheIndex)
+        const svg = makeBadge(cached.data.badgeData)
+        setCacheHeadersOnResponse(
+          ask.res,
+          cached.data.badgeData.cacheLengthSeconds
+        )
+        makeSend(cached.data.format, ask.res, end)(svg)
         return
       }
       ask.res.setHeader('Cache-Control', 'no-cache, no-store, must-revalidate')
@@ -155,6 +179,7 @@ function handleRequest(cacheHeaderConfig, handlerOptions) {
         extension = 'svg'
       }
       const svg = makeBadge(badgeData)
+      setCacheHeadersOnResponse(ask.res)
       makeSend(extension, ask.res, end)(svg)
     }, 25000)
 
@@ -256,6 +281,7 @@ function handleRequest(cacheHeaderConfig, handlerOptions) {
           requestCache.set(cacheIndex, updatedCache)
           if (!cachedVersionSent) {
             const svg = makeBadge(badgeData)
+            setCacheHeadersOnResponse(ask.res, badgeData.cacheLengthSeconds)
             makeSend(format, ask.res, end)(svg)
           }
         },

lib/request-handler.spec.js

@@ -25,6 +25,16 @@ function fakeHandler(queryParams, match, sendBadge, request) {
   sendBadge(format, badgeData)
 }
 
+function createFakeHandlerWithCacheLength(cacheLengthSeconds) {
+  return function fakeHandler(queryParams, match, sendBadge, request) {
+    const [, someValue, format] = match
+    const badgeData = getBadgeData('testing', queryParams)
+    badgeData.text[1] = someValue
+    badgeData.cacheLengthSeconds = cacheLengthSeconds
+    sendBadge(format, badgeData)
+  }
+}
+
 function fakeHandlerWithNetworkIo(queryParams, match, sendBadge, request) {
   const [, someValue, format] = match
   request('https://www.google.com/foo/bar', (err, res, buffer) => {
@@ -198,6 +208,62 @@ describe('The request handler', function() {
         expect(res.headers.get('cache-control')).to.equal('max-age=900')
       })
 
+      it('should set the expected cache headers on cached responses', async function() {
+        register({ cacheHeaderConfig: { defaultCacheLengthSeconds: 900 } })
+
+        // Make first request.
+        await fetch(`${baseUrl}/testing/123.json`)
+
+        const res = await fetch(`${baseUrl}/testing/123.json`)
+        const expectedExpiry = new Date(
+          +new Date(res.headers.get('date')) + 900000
+        ).toGMTString()
+        expect(res.headers.get('expires')).to.equal(expectedExpiry)
+        expect(res.headers.get('cache-control')).to.equal('max-age=900')
+      })
+
+      it('should let live service data override the default cache headers with longer value', async function() {
+        camp.route(
+          /^\/testing\/([^/]+)\.(svg|png|gif|jpg|json)$/,
+          handleRequest(
+            { defaultCacheLengthSeconds: 300 },
+            (queryParams, match, sendBadge, request) => {
+              ++handlerCallCount
+              createFakeHandlerWithCacheLength(400)(
+                queryParams,
+                match,
+                sendBadge,
+                request
+              )
+            }
+          )
+        )
+
+        const res = await fetch(`${baseUrl}/testing/123.json`)
+        expect(res.headers.get('cache-control')).to.equal('max-age=400')
+      })
+
+      it('should not let live service data override the default cache headers with shorter value', async function() {
+        camp.route(
+          /^\/testing\/([^/]+)\.(svg|png|gif|jpg|json)$/,
+          handleRequest(
+            { defaultCacheLengthSeconds: 300 },
+            (queryParams, match, sendBadge, request) => {
+              ++handlerCallCount
+              createFakeHandlerWithCacheLength(200)(
+                queryParams,
+                match,
+                sendBadge,
+                request
+              )
+            }
+          )
+        )
+
+        const res = await fetch(`${baseUrl}/testing/123.json`)
+        expect(res.headers.get('cache-control')).to.equal('max-age=300')
+      })
+
       it('should set the expires header to current time + maxAge', async function() {
         register({ cacheHeaderConfig: { defaultCacheLengthSeconds: 0 } })
         const res = await fetch(`${baseUrl}/testing/123.json?maxAge=3600`)