fix(rum): keep remote settings across app upgrades

README.md

@@ -490,7 +490,8 @@ await init({
 - **Kept on disk.** The last configuration accepted is kept in the application's `userData`
   directory. A graceful exit retries pending or failed writes; a forced termination can leave an
   older cache. New sessions use it before the network answers, or without the network at all. It
-  applies only to the same intake, application, `env` and `version`.
+  applies only to the same intake, application and `env`; an application upgrade keeps it, so the
+  first session after one is drawn on the previous release's settings until a new answer is stored.
 - **Resumed sessions.** A valid session resumed from the previous launch keeps its original draw,
   subject to immediate activation: when what was kept asks to apply immediately, the session is
   judged by it at startup, as below, unless it was drawn under a newer version than the one kept —

src/domain/RemoteConfiguration.spec.ts

@@ -65,7 +65,7 @@ function storedFile(overrides: Record<string, unknown> = {}) {
   return JSON.stringify({
     format: 1,
     sdkVersion: 'test',
-    identity: JSON.stringify(['http://proxy.test', 'test-app-id', 'prod', '1.2.3']),
+    identity: JSON.stringify(['http://proxy.test', 'test-app-id', 'prod']),
     version: 2,
     values: { sessionSampleRate: 0, sessionOnError: true },
     custom: { flag: 'cached' },
@@ -473,7 +473,7 @@ describe('RemoteConfiguration', () => {
         {
           format: 1,
           sdkVersion: 'test',
-          identity: JSON.stringify(['http://proxy.test', 'test-app-id', 'prod', '1.2.3']),
+          identity: JSON.stringify(['http://proxy.test', 'test-app-id', 'prod']),
           version: 3,
           values: { sessionSampleRate: 25, sessionOnError: true },
           custom: { flag: 1 },
@@ -497,9 +497,13 @@ describe('RemoteConfiguration', () => {
     });
 
     it.each([
-      ['another env', { identity: JSON.stringify(['http://proxy.test', 'test-app-id', 'staging', '1.2.3']) }],
-      ['another app version', { identity: JSON.stringify(['http://proxy.test', 'test-app-id', 'prod', '1.2.2']) }],
-      ['another application', { identity: JSON.stringify(['http://proxy.test', 'other-app', 'prod', '1.2.3']) }],
+      ['another env', { identity: JSON.stringify(['http://proxy.test', 'test-app-id', 'staging']) }],
+      ['another intake', { identity: JSON.stringify(['http://other-proxy.test', 'test-app-id', 'prod']) }],
+      [
+        'a build that keyed it on the app version',
+        { identity: JSON.stringify(['http://proxy.test', 'test-app-id', 'prod', '1.2.3']) },
+      ],
+      ['another application', { identity: JSON.stringify(['http://proxy.test', 'other-app', 'prod']) }],
       ['another file format', { format: 2 }],
       ['a rate out of range', { values: { sessionSampleRate: 200 } }],
       ['a switch that is not a boolean', { values: { sessionOnError: 'true' } }],
@@ -516,6 +520,34 @@ describe('RemoteConfiguration', () => {
       expect(requestHeaders()).toEqual({});
     });
 
+    it('applies a file written under another app version', async () => {
+      config = { ...config, version: '2.0.0' };
+      mfs.readFile.mockResolvedValue(storedFile());
+      fetchMock.mockReturnValue(new Promise(() => undefined));
+
+      const configuration = await start();
+
+      expect(configuration.getSampling()).toEqual({ sessionSampleRate: 0, sessionOnError: true, rcVersion: 2 });
+      expect(requestedUrl().searchParams.get('app_version')).toBe('2.0.0');
+      expect(requestedUrl().searchParams.get('applied_version')).toBe('2');
+    });
+
+    it('writes the same identity whatever the app version', async () => {
+      fetchMock.mockImplementation(() => Promise.resolve(ok(configurationBody())));
+      const identityWritten = async (version: string | undefined) => {
+        writtenFiles().length = 0;
+        mfs.writeFile.mockClear();
+        config = { ...config, version };
+        remote?.stop();
+        await start();
+        return (writtenFiles()[0] as { identity: string }).identity;
+      };
+
+      const first = await identityWritten('1.2.3');
+      expect(await identityWritten('2.0.0')).toBe(first);
+      expect(await identityWritten(undefined)).toBe(first);
+    });
+
     it('reads a kept version 0 as no configuration, whatever it holds', async () => {
       mfs.readFile.mockResolvedValue(storedFile({ version: 0, values: { sessionSampleRate: 0 } }));
       fetchMock.mockReturnValue(new Promise(() => undefined));

src/domain/RemoteConfiguration.ts

@@ -105,7 +105,7 @@ interface StoredConfiguration extends Omit<Delivered, 'activation' | 'refreshOnF
    * console's values rather than back on the init ones.
    */
   sdkVersion: string;
-  /** Who the answer was for: it only applies to the same endpoint, application, env and version. */
+  /** Who the answer was for: it only applies to the same endpoint, application and env, whatever the application version. */
   identity: string;
   etag?: string;
 }
@@ -153,9 +153,12 @@ export class RemoteConfiguration {
   private stopped = false;
 
   private constructor(private readonly config: Configuration) {
-    // The client token is not part of it: the configuration belongs to the application, so a token
-    // rotated for the same application, env and version is answered the same.
-    this.identity = JSON.stringify([config.proxy ?? config.site, config.applicationId, config.env, config.version]);
+    // Neither the client token nor the application version is part of it. The configuration belongs
+    // to the application, so a token rotated for the same application and env is answered the same.
+    // An installed application runs one version at a time, and keying on it would put the first
+    // session after every upgrade back on the init values: until the new fetch is stored, the
+    // previous release's settings are the better answer.
+    this.identity = JSON.stringify([config.proxy ?? config.site, config.applicationId, config.env]);
   }
 
   /** Reads the configuration the previous launch kept, if remote configuration is on. */