When compressing add accept-encoding to the Vary header, if the header exists concatenate it. (#120)

* When compressing add the Vary header, if exists concat to it

* support multiple headers

* updated tests

* preveted accept-encoding from being added twice

* shortened the code

Author: Arnovsky

index.js

@@ -371,6 +371,15 @@ function compress (params) {
       payload = intoStream(payload)
     }
 
+    if (this.hasHeader('Vary')) {
+      const varyHeader = Array.isArray(this.getHeader('Vary')) ? this.getHeader('Vary') : [this.getHeader('Vary')]
+      if (!varyHeader.some(h => h === 'accept-encoding')) {
+        this.header('Vary', [...varyHeader, 'accept-encoding'])
+      }
+    } else {
+      this.header('Vary', 'accept-encoding')
+    }
+
     this
       .header('Content-Encoding', encoding)
       .removeHeader('content-length')

test/test-global-compress.js

@@ -12,7 +12,7 @@ const Fastify = require('fastify')
 const compressPlugin = require('../index')
 
 test('should send a deflated data', t => {
-  t.plan(4)
+  t.plan(5)
   const fastify = Fastify()
   fastify.register(compressPlugin, { global: false })
 
@@ -29,6 +29,7 @@ test('should send a deflated data', t => {
   }, (err, res) => {
     t.error(err)
     t.strictEqual(res.headers['content-encoding'], 'deflate')
+    t.strictEqual(res.headers.vary, 'accept-encoding')
     t.notOk(res.headers['content-length'], 'no content length')
     const file = readFileSync('./package.json', 'utf8')
     const payload = zlib.inflateSync(res.rawPayload)
@@ -1735,3 +1736,42 @@ test('stream onEnd handler should log an error if exists', t => {
     t.equal(actual.msg, expect.message)
   })
 })
+
+test('should concat accept-encoding to vary header if present', t => {
+  t.plan(4)
+  const fastify = Fastify()
+
+  fastify.register(compressPlugin, { global: false })
+
+  fastify.get('/', (req, reply) => {
+    reply.header('vary', 'different-header')
+    reply.type('text/plain').compress(createReadStream('./package.json'))
+  })
+
+  fastify.get('/foo', (req, reply) => {
+    reply.header('vary', ['different-header', 'my-header'])
+    reply.type('text/plain').compress(createReadStream('./package.json'))
+  })
+
+  fastify.inject({
+    url: '/',
+    method: 'GET',
+    headers: {
+      'accept-encoding': 'deflate'
+    }
+  }, (err, res) => {
+    t.error(err)
+    t.deepEqual(res.headers.vary, ['different-header', 'accept-encoding'])
+  })
+
+  fastify.inject({
+    url: '/foo',
+    method: 'GET',
+    headers: {
+      'accept-encoding': 'deflate'
+    }
+  }, (err, res) => {
+    t.error(err)
+    t.deepEqual(res.headers.vary, ['different-header', 'my-header', 'accept-encoding'])
+  })
+})