From 31bd2dd9ed9f3f90685158c985f0f10b80d40d92 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 f8ee5420213..f6b955653c6 100644
--- a/app/client/models/AdminChecks.ts
+++ b/app/client/models/AdminChecks.ts
@@ -162,6 +162,15 @@ 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 753af1c4b48..699d3515659 100644
--- a/app/common/BootProbe.ts
+++ b/app/common/BootProbe.ts
@@ -6,7 +6,8 @@ export type BootProbeIds =
     'reachable' |
     'host-header' |
     'sandboxing' |
-    'system-user'
+    'system-user' |
+    'websockets'
 ;
 
 export interface BootProbeResult {
diff --git a/app/server/lib/BootProbes.ts b/app/server/lib/BootProbes.ts
index 8e3ae366acd..ba928ce3ff0 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';
 
 /**
@@ -58,6 +59,7 @@ export class BootProbes {
     this._probes.push(_bootProbe);
     this._probes.push(_hostHeaderProbe);
     this._probes.push(_sandboxingProbe);
+    this._probes.push(_webSocketsProbe);
     this._probeById = new Map(this._probes.map(p => [p.id, p]));
   }
 }
@@ -104,6 +106,37 @@ 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',