root made optional if serve is false

index.js

@@ -19,7 +19,10 @@ send.mime.default_type = 'application/octet-stream'
 
 async function fastifyStatic (fastify, opts) {
   opts.root = normalizeRoot(opts.root)
-  checkRootPathForErrors(fastify, opts.root)
+
+  if (opts.serve !== false) {
+    checkRootPathForErrors(fastify, opts.root)
+  }
 
   const setHeaders = opts.setHeaders
   if (setHeaders !== undefined && typeof setHeaders !== 'function') {

test/static.test.js

@@ -901,6 +901,54 @@
   })
 })
 
+t.test('root optional if serving disabled', (t) => {
+  t.plan(3)
+
+  const pluginOptions = {
+    prefix: '/static/',
+    serve: false
+  }
+  const fastify = Fastify()
+  fastify.register(fastifyStatic, pluginOptions)
+
+  fastify.get('/foo/bar', (request, reply) => {
+    const file = path.join(__dirname, '/static/index.html');
+    reply.sendFile(file)
+  })
+
+  t.teardown(fastify.close.bind(fastify))
+
+  fastify.listen({ port: 0 }, (err) => {
+    t.error(err)
+
+    fastify.server.unref()
+
+    t.test('/static/index.html not found', (t) => {
+      t.plan(2)
+      simple.concat({
+        method: 'GET',
+        url: 'http://localhost:' + fastify.server.address().port + '/static/index.html'
+      }, (err, response, body) => {
+        t.error(err)
+        t.equal(response.statusCode, 404)
+      })
+    })
+
+    t.test('/static/index.html via sendFile found', (t) => {
+      t.plan(3 + GENERIC_RESPONSE_CHECK_COUNT)
+      simple.concat({
+        method: 'GET',
+        url: 'http://localhost:' + fastify.server.address().port + '/foo/bar'
+      }, (err, response, body) => {
+        t.error(err)
+        t.equal(response.statusCode, 200)
+        t.equal(body.toString(), indexContent)
+        genericResponseChecks(t, response)
+      })
+    })
+  })
+})
+
 t.test('sendFile', (t) => {
   t.plan(5)