treat 410 as error if we already have a token (#6538)

* treat 410 as error if we already have a token

Relates to: https://elixirforum.com/t/handling-channels-liveview-longpoll-fallback-unmatched-topic/72378

On mobile Safari (e.g. iOS) the following could happen when using LongPoll:

1. user connects to a channel
2. device goes to sleep
3. Phoenix shuts down long poll server
4. client connects again, server responds with 410
5. LongPoll continues as usual, but channels are not joined any more
6. client sends messages for previous channel
7. channel errors with "unmatched topic" but does not rejoin

We handle this by checking if we already have a LongPoll token when
receiving a 410 code and instead trigger an error which will cause a
proper rejoin.

* add unit test

Author: SteffenDE

assets/js/phoenix/longpoll.js

@@ -71,6 +71,13 @@ export default class LongPoll {
     this.ajax("GET", headers, null, () => this.ontimeout(), resp => {
       if(resp){
         var {status, token, messages} = resp
+        if(status === 410 && this.token !== null){
+          // In case we already have a token, this means that our existing session
+          // is gone. We fail so that the client rejoins its channels.
+          this.onerror(410)
+          this.closeAndRetry(3410, "session_gone", false)
+          return
+        }
         this.token = token
       } else {
         status = 0

assets/test/longpoll_test.js

@@ -83,11 +83,11 @@ describe("LongPoll", () => {
       const authToken = "my-auth-token"
       const encodedToken = btoa(authToken)
       const protocols = ["phoenix", `${AUTH_TOKEN_PREFIX}${encodedToken}`]
-      
+
       const longpoll = new LongPoll("http://localhost/socket/longpoll", protocols)
       longpoll.timeout = 1000
       longpoll.poll()
-      
+
       // Verify Ajax.request was called with the correct headers
       expect(Ajax.request).toHaveBeenCalledWith(
         "GET",
@@ -104,7 +104,7 @@ describe("LongPoll", () => {
       const longpoll = new LongPoll("http://localhost/socket/longpoll", undefined)
       longpoll.timeout = 1000
       longpoll.poll()
-      
+
       // Verify Ajax.request was called without auth token header
       expect(Ajax.request).toHaveBeenCalledWith(
         "GET",
@@ -116,6 +116,27 @@ describe("LongPoll", () => {
         expect.any(Function)
       )
     })
+
+    it("should treat 410 as error when token already exists", () => {
+      const longpoll = new LongPoll("http://localhost/socket/longpoll", undefined)
+      longpoll.timeout = 1000
+      longpoll.token = "existing-token"
+
+      const mockOnerror = jest.fn()
+      const mockCloseAndRetry = jest.fn()
+      longpoll.onerror = mockOnerror
+      longpoll.closeAndRetry = mockCloseAndRetry
+
+      Ajax.request.mockImplementation((method, url, headers, body, timeout, ontimeout, callback) => {
+        callback({status: 410, token: "new-token", messages: []})
+        return {abort: jest.fn()}
+      })
+
+      longpoll.poll()
+
+      expect(mockOnerror).toHaveBeenCalledWith(410)
+      expect(mockCloseAndRetry).toHaveBeenCalledWith(3410, "session_gone", false)
+    })
   })
 
   describe("batchSend", () => {