Add an endpoint to restart Grist with a new config

Dockerfile

@@ -113,6 +113,7 @@ ADD bower_components /grist/bower_components
 ADD sandbox /grist/sandbox
 ADD plugins /grist/plugins
 ADD static /grist/static
+ADD docker-runner.mjs /grist/docker-runner.mjs
 
 # Make optional pyodide sandbox available
 COPY --from=builder /grist/sandbox/pyodide /grist/sandbox/pyodide
@@ -152,4 +153,4 @@ ENV \
 EXPOSE 8484
 
 ENTRYPOINT ["/usr/bin/tini", "-s", "--"]
-CMD ["./sandbox/run.sh"]
+CMD ["node", "./sandbox/supervisor.mjs"]

app/server/lib/FlexServer.ts

@@ -1883,6 +1883,22 @@ export class FlexServer implements GristServer {
     const probes = new BootProbes(this.app, this, '/api', adminMiddleware);
     probes.addEndpoints();
 
+    this.app.post('/api/admin/restart', requireInstallAdmin, expressWrap(async (req, resp) => {
+      const newConfig = req.body.newConfig;
+      resp.on('finish', () => {
+        // If we have IPC with parent process (e.g. when running under
+        // Docker) tell the parent that we have a new environment so it
+        // can restart us.
+        if (process.send) {
+          process.send({ action: 'restart', newConfig });
+        }
+      });
+      // On the topic of http response codes, thus spake MDN:
+      // "409: This response is sent when a request conflicts with the current state of the server."
+      const status = process.send ? 200 : 409;
+      return resp.status(status).send();
+    }));
+
     // Restrict this endpoint to install admins
     this.app.get('/api/install/prefs', requireInstallAdmin, expressWrap(async (_req, resp) => {
       const activation = await this._activations.current();

sandbox/supervisor.mjs

@@ -0,0 +1,35 @@
+import {spawn} from 'child_process';
+
+let grist;
+
+function startGrist(newConfig={}) {
+  saveNewConfig(newConfig);
+  // H/T https://stackoverflow.com/a/36995148/11352427
+  grist = spawn('./sandbox/run.sh', {
+    stdio: ['inherit', 'inherit', 'inherit', 'ipc']
+  });
+  grist.on('message', function(data) {
+    if (data.action === 'restart') {
+      console.log('Restarting Grist with new environment');
+
+      // Note that we only set this event handler here, after we have
+      // a new environment to reload with. Small chance of a race here
+      // in case something else sends a SIGINT before we do it
+      // ourselves further below.
+      grist.on('exit', () => {
+        grist = startGrist(data.newConfig);
+      });
+
+      grist.kill('SIGINT');
+    }
+  });
+  return grist;
+}
+
+// Stub function
+function saveNewConfig(newConfig) {
+  // TODO: something here to actually persist the new config before
+  // restarting Grist.
+}
+
+startGrist();