feat: return 304 when If-None-Match matches ETag

Resolves #31

Author: Jakub Sarnowski

index.js

@@ -99,13 +99,16 @@ module.exports = ({
     } = result
 
     const etag = cachedEtag || getEtag(serialize(data))
+    const ifNoneMatch = req.headers['if-none-match']
+    const isModified = etag !== ifNoneMatch
 
     debug({
       key,
       isHit,
       cachedResult: !isEmpty(cachedResult),
       result: !isEmpty(result),
-      etag
+      etag,
+      ifNoneMatch
     })
 
     setHeaders({
@@ -117,13 +120,18 @@ module.exports = ({
       hasForce
     })
 
-    if (!isHit) {
-      const payload = { etag, createdAt, ttl, data, ...props }
-      const value = await compress(payload)
-      await cache.set(key, value, ttl)
+    if (isModified) {
+      if (!isHit) {
+        const payload = { etag, createdAt, ttl, data, ...props }
+        const value = await compress(payload)
+        await cache.set(key, value, ttl)
+      }
+
+      return send({ data, res, req, ...props })
+    } else {
+      res.statusCode = 304
+      res.end()
     }
-
-    return send({ data, res, req, ...props })
   }
 }
 

test/index.js

@@ -237,3 +237,25 @@ test('prevent send if data is undefined', async t => {
     t.false(isSendCalled)
   }
 })
+
+test('return empty 304 response when If-None-Match matches ETag', async t => {
+  const url = await createServer({
+    get: ({ req, res }) => {
+      return {
+        data: { foo: 'bar' },
+        ttl: 1000,
+        createdAt: Date.now(),
+        foo: { bar: true }
+      }
+    },
+    send: ({ data, headers, res, req, ...props }) => {
+      res.end('Welcome to Micro')
+    }
+  })
+  const { headers } = await got(`${url}/kikobeats`)
+  const { body, statusCode } = await got(`${url}/kikobeats`, {
+    headers: { 'If-None-Match': headers.etag }
+  })
+  t.is(statusCode, 304)
+  t.is(body, '')
+})