feat: Warn users when they change the base URL

config/app/init/base/init.json

@@ -1,6 +1,7 @@
 {
   "@context": "https://linkedsoftwaredependencies.org/bundles/npm/@solid/community-server/^2.0.0/components/context.jsonld",
   "import": [
+    "files-scs:config/app/init/initializers/base-url.json",
     "files-scs:config/app/init/initializers/logger.json",
     "files-scs:config/app/init/initializers/server.json"
   ],
@@ -11,6 +12,7 @@
       "@type": "SequenceHandler",
       "handlers": [
         { "@id": "urn:solid-server:default:LoggerInitializer" },
+        { "@id": "urn:solid-server:default:BaseUrlVerifier" },
         { "@id": "urn:solid-server:default:ParallelInitializer" },
         { "@id": "urn:solid-server:default:ServerInitializer" }
       ]

config/app/init/initializers/base-url.json

@@ -0,0 +1,13 @@
+{
+  "@context": "https://linkedsoftwaredependencies.org/bundles/npm/@solid/community-server/^2.0.0/components/context.jsonld",
+  "@graph": [
+    {
+      "comment": "Logs a warning if the base URL changes.",
+      "@id": "urn:solid-server:default:BaseUrlVerifier",
+      "@type": "BaseUrlVerifier",
+      "baseUrl": { "@id": "urn:solid-server:default:variable:baseUrl" },
+      "storageKey": "current-base-url",
+      "storage": { "@id": "urn:solid-server:default:SetupStorage" }
+    }
+  ]
+}

src/index.ts

@@ -201,6 +201,7 @@ export * from './init/variables/SettingsResolver';
 // Init
 export * from './init/App';
 export * from './init/AppRunner';
+export * from './init/BaseUrlVerifier';
 export * from './init/CliResolver';
 export * from './init/ConfigPodInitializer';
 export * from './init/ContainerInitializer';

src/init/BaseUrlVerifier.ts

@@ -0,0 +1,32 @@
+import { getLoggerFor } from '../logging/LogUtil';
+import type { KeyValueStorage } from '../storage/keyvalue/KeyValueStorage';
+import { Initializer } from './Initializer';
+
+/**
+ * Stores the `baseUrl` value that was used to start the server
+ * and warns the user in case it differs from the previous one.
+ */
+export class BaseUrlVerifier extends Initializer {
+  private readonly baseUrl: string;
+  private readonly storageKey: string;
+  private readonly storage: KeyValueStorage<string, string>;
+
+  private readonly logger = getLoggerFor(this);
+
+  public constructor(baseUrl: string, storageKey: string, storage: KeyValueStorage<string, string>) {
+    super();
+    this.baseUrl = baseUrl;
+    this.storageKey = storageKey;
+    this.storage = storage;
+  }
+
+  public async handle(): Promise<void> {
+    const previousValue = await this.storage.get(this.storageKey);
+    if (previousValue && this.baseUrl !== previousValue) {
+      this.logger.warn(`The server is being started with a base URL of ${this.baseUrl
+      } while it was previously started with ${previousValue
+      }. Resources generated with the previous server instance, such as a WebID, might no longer work correctly.`);
+    }
+    await this.storage.set(this.storageKey, this.baseUrl);
+  }
+}

test/unit/init/BaseUrlVerifier.test.ts

@@ -0,0 +1,38 @@
+import { BaseUrlVerifier } from '../../../src/init/BaseUrlVerifier';
+import type { Logger } from '../../../src/logging/Logger';
+import { getLoggerFor } from '../../../src/logging/LogUtil';
+import type { KeyValueStorage } from '../../../src/storage/keyvalue/KeyValueStorage';
+
+jest.mock('../../../src/logging/LogUtil', (): any => {
+  const logger: Logger = { warn: jest.fn() } as any;
+  return { getLoggerFor: (): Logger => logger };
+});
+
+describe('A BaseUrlVerifier', (): void => {
+  const logger: jest.Mocked<Logger> = getLoggerFor(BaseUrlVerifier) as any;
+  const baseUrl1 = 'http://base1.example.com/';
+  const baseUrl2 = 'http://base2.example.com/';
+  const storageKey = 'uniqueKey';
+  let storage: KeyValueStorage<string, string>;
+
+  beforeEach(async(): Promise<void> => {
+    storage = new Map<string, string>() as any;
+    jest.clearAllMocks();
+  });
+
+  it('stores the value if no value was stored yet.', async(): Promise<void> => {
+    const initializer = new BaseUrlVerifier(baseUrl1, storageKey, storage);
+    await expect(initializer.handle()).resolves.toBeUndefined();
+    expect(logger.warn).toHaveBeenCalledTimes(0);
+  });
+
+  it('logs a warning in case the value changes.', async(): Promise<void> => {
+    let initializer = new BaseUrlVerifier(baseUrl1, storageKey, storage);
+    await expect(initializer.handle()).resolves.toBeUndefined();
+    expect(logger.warn).toHaveBeenCalledTimes(0);
+
+    initializer = new BaseUrlVerifier(baseUrl2, storageKey, storage);
+    await expect(initializer.handle()).resolves.toBeUndefined();
+    expect(logger.warn).toHaveBeenCalledTimes(1);
+  });
+});