From 07b80b1110b2bb7dd04ff924855fa2293116fd6c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jordi=20Guti=C3=A9rrez=20Hermoso?= <jordigh@octave.org>
Date: Thu, 9 May 2024 16:46:25 -0400
Subject: [PATCH] BootProbes: add a websocket probe

This self-test isn't perfect because we're running it from the backend
instead of the frontend. Conceivably the backend might have trouble
resolving its own url. Eventually we should move this test or
something like it to something that executes in the frontend.
---
 app/client/models/AdminChecks.ts |  9 +++++++++
 app/common/BootProbe.ts          |  3 ++-
 app/server/lib/BootProbes.ts     | 33 ++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/app/client/models/AdminChecks.ts b/app/client/models/AdminChecks.ts
index 51ff8b2bd7..bd5a8cee49 100644
--- a/app/client/models/AdminChecks.ts
+++ b/app/client/models/AdminChecks.ts
@@ -163,6 +163,15 @@ It is good practice not to run Grist as the root user.
   'reachable': {
     info: `
 The main page of Grist should be available.
+`
+  },
+
+  'websockets': {
+    // TODO: add a link to https://support.getgrist.com/self-managed/#how-do-i-run-grist-on-a-server
+    info: `
+Websocket connections need HTTP 1.1 and the ability to pass a few
+extra headers in order to work. Sometimes a reverse proxy can
+interfere with these requirements.
 `
   },
 };
diff --git a/app/common/BootProbe.ts b/app/common/BootProbe.ts
index dd86704937..0da3c859fc 100644
--- a/app/common/BootProbe.ts
+++ b/app/common/BootProbe.ts
@@ -7,7 +7,8 @@ export type BootProbeIds =
     'host-header' |
     'sandboxing' |
     'system-user' |
-    'authentication'
+    'authentication' |
+    'websockets'
 ;
 
 export interface BootProbeResult {
diff --git a/app/server/lib/BootProbes.ts b/app/server/lib/BootProbes.ts
index b1186c51a4..8145f2a2ce 100644
--- a/app/server/lib/BootProbes.ts
+++ b/app/server/lib/BootProbes.ts
@@ -4,6 +4,7 @@ import { removeTrailingSlash } from 'app/common/gutil';
 import { expressWrap, jsonErrorHandler } from 'app/server/lib/expressWrap';
 import { GristServer } from 'app/server/lib/GristServer';
 import * as express from 'express';
+import WS from 'ws';
 import fetch from 'node-fetch';
 
 /**
@@ -59,6 +60,7 @@ export class BootProbes {
     this._probes.push(_hostHeaderProbe);
     this._probes.push(_sandboxingProbe);
     this._probes.push(_authenticationProbe);
+    this._probes.push(_webSocketsProbe);
     this._probeById = new Map(this._probes.map(p => [p.id, p]));
   }
 }
@@ -105,6 +107,37 @@ const _homeUrlReachableProbe: Probe = {
   }
 };
 
+const _webSocketsProbe: Probe = {
+  id: 'websockets',
+  name: 'Can we open a websocket with the server',
+  apply: async (server, req) => {
+    return new Promise((resolve) => {
+      const url = new URL(server.getHomeUrl(req));
+      url.protocol = (url.protocol === 'https:') ? 'wss:' : 'ws:';
+      const ws = new WS.WebSocket(url.href);
+      const details: Record<string, any> = {
+        url,
+      };
+      ws.on('open', () => {
+        ws.send('Just nod if you can hear me.');
+        resolve({
+          success: true,
+          details,
+        });
+        ws.close();
+      });
+      ws.on('error', (ev) => {
+        details.error = ev.message;
+        resolve({
+          success: false,
+          details,
+        });
+        ws.close();
+      });
+    });
+  }
+};
+
 const _statusCheckProbe: Probe = {
   id: 'health-check',
   name: 'Is an internal health check passing',