Pass WebSocket subprotocol to upstream (#256)

README.md

@@ -165,6 +165,7 @@ A few things are missing:
 1. forwarding headers as well as `rewriteHeaders`. Note: Only cookie headers are being forwarded
 2. request id logging
 3. support `ignoreTrailingSlash`
+4. forwarding more than one subprotocols. Note: Only the first subprotocol is being forwarded
 
 Pull requests are welcome to finish this feature.
 

index.js

@@ -90,6 +90,11 @@ function setupWebSocketProxy (fastify, options, rewritePrefix) {
       return
     }
 
+    const subprotocols = []
+    if (source.protocol) {
+      subprotocols.push(source.protocol)
+    }
+
     let optionsWs = {}
     if (request.headers.cookie) {
       const headers = { cookie: request.headers.cookie }
@@ -100,7 +105,7 @@ function setupWebSocketProxy (fastify, options, rewritePrefix) {
 
     const url = createWebSocketUrl(request)
 
-    const target = new WebSocket(url, optionsWs)
+    const target = new WebSocket(url, subprotocols, optionsWs)
 
     fastify.log.debug({ url: url.href }, 'proxy websocket')
     proxyWebSockets(source, target)

test/websocket.js

@@ -8,16 +8,18 @@ const { createServer } = require('http')
 const { promisify } = require('util')
 const { once } = require('events')
 const cookieValue = 'foo=bar'
+const subprotocolValue = 'foo-subprotocol'
 
 test('basic websocket proxy', async (t) => {
-  t.plan(3)
+  t.plan(4)
 
   const origin = createServer()
   const wss = new WebSocket.Server({ server: origin })
   t.teardown(wss.close.bind(wss))
   t.teardown(origin.close.bind(origin))
 
   wss.on('connection', (ws, request) => {
+    t.equal(ws.protocol, subprotocolValue)
     t.equal(request.headers.cookie, cookieValue)
     ws.on('message', (message) => {
       t.equal(message.toString(), 'hello')
@@ -38,7 +40,7 @@ test('basic websocket proxy', async (t) => {
   t.teardown(server.close.bind(server))
 
   const options = { headers: { cookie: cookieValue } }
-  const ws = new WebSocket(`ws://localhost:${server.server.address().port}`, options)
+  const ws = new WebSocket(`ws://localhost:${server.server.address().port}`, [subprotocolValue], options)
 
   await once(ws, 'open')
 
@@ -47,7 +49,6 @@ test('basic websocket proxy', async (t) => {
   stream.write('hello')
 
   const [buf] = await once(stream, 'data')
-
   t.equal(buf.toString(), 'hello')
 
   await Promise.all([