From 53af412dd244c202ea16d3ba1bf7d99d2c511ae0 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 11:31:48 -0700
Subject: [PATCH 01/19] feat: Implement support for browser requests.

---
 packages/sdk/browser/src/platform/Backoff.ts  | 27 ++++++
 .../src/platform/BrowserEventSourceShim.ts    | 91 +++++++++++++++++++
 .../browser/src/platform/BrowserPlatform.ts   |  4 +-
 .../browser/src/platform/BrowserRequests.ts   | 18 ++++
 .../src/platform/PlatformRequests.ts          |  9 ++
 .../server-node/src/platform/NodeRequests.ts  |  9 ++
 .../common/src/api/platform/Requests.ts       | 20 ++++
 7 files changed, 177 insertions(+), 1 deletion(-)
 create mode 100644 packages/sdk/browser/src/platform/Backoff.ts
 create mode 100644 packages/sdk/browser/src/platform/BrowserEventSourceShim.ts
 create mode 100644 packages/sdk/browser/src/platform/BrowserRequests.ts

diff --git a/packages/sdk/browser/src/platform/Backoff.ts b/packages/sdk/browser/src/platform/Backoff.ts
new file mode 100644
index 0000000000..30d272e128
--- /dev/null
+++ b/packages/sdk/browser/src/platform/Backoff.ts
@@ -0,0 +1,27 @@
+const maxRetryDelay = 30 * 1000; // Maximum retry delay 30 seconds.
+const jitterRatio = 0.5; // Delay should be 50%-100% of calculated time.
+
+function jitter(computedDelayMillis: number): number {
+  return computedDelayMillis - Math.trunc(Math.random() * jitterRatio * computedDelayMillis);
+}
+
+export default class Backoff {
+  private retryCount: number = 0;
+
+  constructor(private readonly initialRetryDelayMillis: number) {}
+
+  reset(): void {
+    this.retryCount = 0;
+  }
+
+  backoff(): number {
+    const delay = this.initialRetryDelayMillis * 2 ** this.retryCount;
+    return delay > maxRetryDelay ? maxRetryDelay : delay;
+  }
+
+  getNextRetryDelay(): number {
+    const delay = jitter(this.backoff());
+    this.retryCount += 1;
+    return delay;
+  }
+}
diff --git a/packages/sdk/browser/src/platform/BrowserEventSourceShim.ts b/packages/sdk/browser/src/platform/BrowserEventSourceShim.ts
new file mode 100644
index 0000000000..c479a34e11
--- /dev/null
+++ b/packages/sdk/browser/src/platform/BrowserEventSourceShim.ts
@@ -0,0 +1,91 @@
+import {
+  EventListener,
+  EventName,
+  EventSourceInitDict,
+  HttpErrorResponse,
+  EventSource as LDEventSource,
+} from '@launchdarkly/js-client-sdk-common';
+
+import Backoff from './Backoff';
+
+/**
+ * Implementation Notes:
+ *
+ * This event source does not support a read-timeout.
+ * This event source does not support customized verbs.
+ * This event source does not support headers.
+ */
+
+export default class BrowserEventSourceShim implements LDEventSource {
+  private es?: EventSource;
+  private backoff: Backoff;
+  private errorFilter: (err: HttpErrorResponse) => boolean;
+
+  // The type of the handle can be platform specific and we treat is opaquely.
+  private reconnectTimeoutHandle?: any;
+
+  constructor(
+    private readonly url: string,
+    options: EventSourceInitDict,
+  ) {
+    this.backoff = new Backoff(options.initialRetryDelayMillis);
+    this.errorFilter = options.errorFilter;
+    this.createEventSource();
+  }
+
+  onclose: (() => void) | undefined;
+
+  onerror: ((err?: HttpErrorResponse) => void) | undefined;
+
+  onopen: (() => void) | undefined;
+
+  onretrying: ((e: { delayMillis: number }) => void) | undefined;
+
+  private createEventSource() {
+    this.es = new EventSource(this.url);
+    this.es.onopen = () => {
+      this.backoff.reset();
+      this.onopen?.();
+    };
+    // The error could be from a polyfill, or from the browser event source, so we are loose on the
+    // typing.
+    this.es.onerror = (err: any) => {
+      this.handleError(err);
+    };
+  }
+
+  addEventListener(type: EventName, listener: EventListener): void {
+    // TODO: Cache listeners so they can be re-added.
+    this.es?.addEventListener(type, listener);
+  }
+
+  close(): void {
+    // Ensure any pending retry attempts are not done.
+    clearTimeout(this.reconnectTimeoutHandle);
+    this.reconnectTimeoutHandle = undefined;
+    this.es?.close();
+  }
+
+  private tryConnect(delayMs: number) {
+    this.reconnectTimeoutHandle = setTimeout(() => {
+      this.createEventSource();
+    }, delayMs);
+  }
+
+  private handleError(err: any): void {
+    // The event source may not produce a status. But the LaunchDarkly
+    // polyfill can. If we can get the status, then we should stop retrying
+    // on certain error codes.
+    if (err.status && typeof err.status === 'number' && !this.errorFilter(err)) {
+      // If we encounter an unrecoverable condition, then we do not want to
+      // retry anymore.
+      this.close();
+      return;
+    }
+
+    const delay = this.backoff.getNextRetryDelay();
+
+    this.close();
+    this.tryConnect(delay);
+  }
+}
diff --git a/packages/sdk/browser/src/platform/BrowserPlatform.ts b/packages/sdk/browser/src/platform/BrowserPlatform.ts
index 8865ebc3c8..dc9d7054d9 100644
--- a/packages/sdk/browser/src/platform/BrowserPlatform.ts
+++ b/packages/sdk/browser/src/platform/BrowserPlatform.ts
@@ -2,10 +2,12 @@ import {
   Crypto,
   /* platform */
   LDOptions,
+  Requests,
   Storage,
 } from '@launchdarkly/js-client-sdk-common';
 
 import BrowserCrypto from './BrowserCrypto';
+import BrowserRequests from './BrowserRequests';
 import LocalStorage, { isLocalStorageSupported } from './LocalStorage';
 
 export default class BrowserPlatform /* implements platform.Platform */ {
@@ -13,7 +15,7 @@ export default class BrowserPlatform /* implements platform.Platform */ {
   // info: Info;
   // fileSystem?: Filesystem;
   crypto: Crypto = new BrowserCrypto();
-  // requests: Requests;
+  requests: Requests = new BrowserRequests();
   storage?: Storage;
 
   constructor(options: LDOptions) {
diff --git a/packages/sdk/browser/src/platform/BrowserRequests.ts b/packages/sdk/browser/src/platform/BrowserRequests.ts
new file mode 100644
index 0000000000..917b6ac4aa
--- /dev/null
+++ b/packages/sdk/browser/src/platform/BrowserRequests.ts
@@ -0,0 +1,18 @@
+import {
+  EventSourceInitDict,
+  EventSource as LDEventSource,
+  Options,
+  Requests,
+  Response,
+} from '@launchdarkly/js-client-sdk-common';
+
+import BrowserEventSourceShim from './BrowserEventSourceShim';
+
+export default class BrowserRequests implements Requests {
+  fetch(url: string, options?: Options): Promise<Response> {
+    return this.fetch(url, options);
+  }
+  createEventSource(url: string, eventSourceInitDict: EventSourceInitDict): LDEventSource {
+    return new BrowserEventSourceShim(url, eventSourceInitDict);
+  }
+}
diff --git a/packages/sdk/react-native/src/platform/PlatformRequests.ts b/packages/sdk/react-native/src/platform/PlatformRequests.ts
index 5b345d2950..6651a7bb1c 100644
--- a/packages/sdk/react-native/src/platform/PlatformRequests.ts
+++ b/packages/sdk/react-native/src/platform/PlatformRequests.ts
@@ -1,6 +1,7 @@
 import type {
   EventName,
   EventSource,
+  EventSourceCapabilities,
   EventSourceInitDict,
   LDLogger,
   Options,
@@ -21,6 +22,14 @@ export default class PlatformRequests implements Requests {
     });
   }
 
+  getEventSourceCapabilities(): EventSourceCapabilities {
+    return {
+      readTimeout: false,
+      headers: true,
+      customVerb: true,
+    };
+  }
+
   fetch(url: string, options?: Options): Promise<Response> {
     // @ts-ignore
     return fetch(url, options);
diff --git a/packages/sdk/server-node/src/platform/NodeRequests.ts b/packages/sdk/server-node/src/platform/NodeRequests.ts
index c951185195..3e83278b67 100644
--- a/packages/sdk/server-node/src/platform/NodeRequests.ts
+++ b/packages/sdk/server-node/src/platform/NodeRequests.ts
@@ -7,6 +7,7 @@ import { HttpsProxyAgentOptions } from 'https-proxy-agent';
 import { EventSource as LDEventSource } from 'launchdarkly-eventsource';
 
 import {
+  EventSourceCapabilities,
   LDLogger,
   LDProxyOptions,
   LDTLSOptions,
@@ -158,6 +159,14 @@ export default class NodeRequests implements platform.Requests {
     return new LDEventSource(url, expandedOptions);
   }
 
+  getEventSourceCapabilities(): EventSourceCapabilities {
+    return {
+      readTimeout: true,
+      headers: true,
+      customVerb: true,
+    };
+  }
+
   usingProxy(): boolean {
     return this.hasProxy;
   }
diff --git a/packages/shared/common/src/api/platform/Requests.ts b/packages/shared/common/src/api/platform/Requests.ts
index 96168012b6..32ef8149e8 100644
--- a/packages/shared/common/src/api/platform/Requests.ts
+++ b/packages/shared/common/src/api/platform/Requests.ts
@@ -78,11 +78,31 @@ export interface Options {
   timeout?: number;
 }
 
+export interface EventSourceCapabilities {
+  /**
+   * If true the event source supports read timeouts.
+   */
+  readTimeout: boolean;
+
+  /**
+   * If true the event source supports customized verbs POST/REPORT instead of
+   * only the default GET.
+   */
+  customVerb: boolean;
+
+  /**
+   * If true the event source supports setting HTTP headers.
+   */
+  headers: boolean;
+}
+
 export interface Requests {
   fetch(url: string, options?: Options): Promise<Response>;
 
   createEventSource(url: string, eventSourceInitDict: EventSourceInitDict): EventSource;
 
+  getEventSourceCapabilities(): EventSourceCapabilities;
+
   /**
    * Returns true if a proxy is configured.
    */

From bf164dd8dc75bfc6e33ce28ca07b1ac64d6c3e43 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 12:46:26 -0700
Subject: [PATCH 02/19] feat: Add support for conditional event source
 capabilities.

---
 .../src/platform/PlatformRequests.ts          |  9 +++++++++
 .../server-node/src/platform/NodeRequests.ts  |  9 +++++++++
 .../common/src/api/platform/Requests.ts       | 20 +++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/packages/sdk/react-native/src/platform/PlatformRequests.ts b/packages/sdk/react-native/src/platform/PlatformRequests.ts
index 5b345d2950..6add1e7be3 100644
--- a/packages/sdk/react-native/src/platform/PlatformRequests.ts
+++ b/packages/sdk/react-native/src/platform/PlatformRequests.ts
@@ -1,6 +1,7 @@
 import type {
   EventName,
   EventSource,
+  EventSourceCapabilities,
   EventSourceInitDict,
   LDLogger,
   Options,
@@ -21,6 +22,14 @@ export default class PlatformRequests implements Requests {
     });
   }
 
+  getEventSourceCapabilities(): EventSourceCapabilities {
+    return {
+      readTimeout: false,
+      headers: true,
+      customMethod: true,
+    };
+  }
+
   fetch(url: string, options?: Options): Promise<Response> {
     // @ts-ignore
     return fetch(url, options);
diff --git a/packages/sdk/server-node/src/platform/NodeRequests.ts b/packages/sdk/server-node/src/platform/NodeRequests.ts
index c951185195..ede410b63e 100644
--- a/packages/sdk/server-node/src/platform/NodeRequests.ts
+++ b/packages/sdk/server-node/src/platform/NodeRequests.ts
@@ -7,6 +7,7 @@ import { HttpsProxyAgentOptions } from 'https-proxy-agent';
 import { EventSource as LDEventSource } from 'launchdarkly-eventsource';
 
 import {
+  EventSourceCapabilities,
   LDLogger,
   LDProxyOptions,
   LDTLSOptions,
@@ -158,6 +159,14 @@ export default class NodeRequests implements platform.Requests {
     return new LDEventSource(url, expandedOptions);
   }
 
+  getEventSourceCapabilities(): EventSourceCapabilities {
+    return {
+      readTimeout: true,
+      headers: true,
+      customMethod: true,
+    };
+  }
+
   usingProxy(): boolean {
     return this.hasProxy;
   }
diff --git a/packages/shared/common/src/api/platform/Requests.ts b/packages/shared/common/src/api/platform/Requests.ts
index 96168012b6..a771dcc454 100644
--- a/packages/shared/common/src/api/platform/Requests.ts
+++ b/packages/shared/common/src/api/platform/Requests.ts
@@ -78,11 +78,31 @@ export interface Options {
   timeout?: number;
 }
 
+export interface EventSourceCapabilities {
+  /**
+   * If true the event source supports read timeouts.
+   */
+  readTimeout: boolean;
+
+  /**
+   * If true the event source supports customized verbs POST/REPORT instead of
+   * only the default GET.
+   */
+  customMethod: boolean;
+
+  /**
+   * If true the event source supports setting HTTP headers.
+   */
+  headers: boolean;
+}
+
 export interface Requests {
   fetch(url: string, options?: Options): Promise<Response>;
 
   createEventSource(url: string, eventSourceInitDict: EventSourceInitDict): EventSource;
 
+  getEventSourceCapabilities(): EventSourceCapabilities;
+
   /**
    * Returns true if a proxy is configured.
    */

From 8307b032231bc054b312f7a4383a9d129a8bf76a Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 12:57:59 -0700
Subject: [PATCH 03/19] Add more comments.

---
 packages/shared/common/src/api/platform/Requests.ts | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/packages/shared/common/src/api/platform/Requests.ts b/packages/shared/common/src/api/platform/Requests.ts
index a771dcc454..219d775f41 100644
--- a/packages/shared/common/src/api/platform/Requests.ts
+++ b/packages/shared/common/src/api/platform/Requests.ts
@@ -80,7 +80,14 @@ export interface Options {
 
 export interface EventSourceCapabilities {
   /**
-   * If true the event source supports read timeouts.
+   * If true the event source supports read timeouts. A read timeout for an
+   * event source represents the maximum time between receiving any data.
+   * If you receive 1 byte, and then a period of time greater than the read
+   * time out elapses, and you do not receive a second byte, then that would
+   * cause the event source to timeout.
+   *
+   * It is not a timeout for the read of the entire body, which should be
+   * indefinite.
    */
   readTimeout: boolean;
 

From c23bf45842403573711925ed0fc9eb11c4453948 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 13:03:53 -0700
Subject: [PATCH 04/19] Implement for edge SDKs.

---
 .../sdk/react-native/src/platform/PlatformRequests.ts    | 4 ++--
 .../akamai-edgeworker-sdk/src/platform/requests.ts       | 9 +++++++++
 packages/shared/sdk-server-edge/src/platform/requests.ts | 9 +++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/packages/sdk/react-native/src/platform/PlatformRequests.ts b/packages/sdk/react-native/src/platform/PlatformRequests.ts
index 6add1e7be3..ae5c3ab2c7 100644
--- a/packages/sdk/react-native/src/platform/PlatformRequests.ts
+++ b/packages/sdk/react-native/src/platform/PlatformRequests.ts
@@ -25,8 +25,8 @@ export default class PlatformRequests implements Requests {
   getEventSourceCapabilities(): EventSourceCapabilities {
     return {
       readTimeout: false,
-      headers: true,
-      customMethod: true,
+      headers: false,
+      customMethod: false,
     };
   }
 
diff --git a/packages/shared/akamai-edgeworker-sdk/src/platform/requests.ts b/packages/shared/akamai-edgeworker-sdk/src/platform/requests.ts
index 5a6b728b00..453344e13c 100644
--- a/packages/shared/akamai-edgeworker-sdk/src/platform/requests.ts
+++ b/packages/shared/akamai-edgeworker-sdk/src/platform/requests.ts
@@ -6,6 +6,7 @@ import type {
   Options,
   Requests,
   Response,
+  EventSourceCapabilities,
 } from '@launchdarkly/js-server-sdk-common';
 
 class NoopResponse implements Response {
@@ -41,4 +42,12 @@ export default class EdgeRequests implements Requests {
   createEventSource(url: string, eventSourceInitDict: EventSourceInitDict): EventSource {
     return new NullEventSource(url, eventSourceInitDict);
   }
+
+  getEventSourceCapabilities(): EventSourceCapabilities {
+    return {
+      readTimeout: false,
+      headers: false,
+      customMethod: false,
+    };
+  }
 }
diff --git a/packages/shared/sdk-server-edge/src/platform/requests.ts b/packages/shared/sdk-server-edge/src/platform/requests.ts
index 2bc8010dc5..413bbb6b32 100644
--- a/packages/shared/sdk-server-edge/src/platform/requests.ts
+++ b/packages/shared/sdk-server-edge/src/platform/requests.ts
@@ -1,6 +1,7 @@
 import { NullEventSource } from '@launchdarkly/js-server-sdk-common';
 import type {
   EventSource,
+  EventSourceCapabilities,
   EventSourceInitDict,
   Options,
   Requests,
@@ -16,4 +17,12 @@ export default class EdgeRequests implements Requests {
   createEventSource(url: string, eventSourceInitDict: EventSourceInitDict): EventSource {
     return new NullEventSource(url, eventSourceInitDict);
   }
+
+  getEventSourceCapabilities(): EventSourceCapabilities {
+    return {
+      readTimeout: false,
+      headers: false,
+      customMethod: false,
+    };
+  }
 }

From a084b9a5d1d3602acedbe665b446a46b1129d29a Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 13:20:54 -0700
Subject: [PATCH 05/19] Lint

---
 packages/sdk/react-native/src/platform/PlatformRequests.ts    | 4 ++--
 .../shared/akamai-edgeworker-sdk/src/platform/requests.ts     | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/sdk/react-native/src/platform/PlatformRequests.ts b/packages/sdk/react-native/src/platform/PlatformRequests.ts
index ae5c3ab2c7..6add1e7be3 100644
--- a/packages/sdk/react-native/src/platform/PlatformRequests.ts
+++ b/packages/sdk/react-native/src/platform/PlatformRequests.ts
@@ -25,8 +25,8 @@ export default class PlatformRequests implements Requests {
   getEventSourceCapabilities(): EventSourceCapabilities {
     return {
       readTimeout: false,
-      headers: false,
-      customMethod: false,
+      headers: true,
+      customMethod: true,
     };
   }
 
diff --git a/packages/shared/akamai-edgeworker-sdk/src/platform/requests.ts b/packages/shared/akamai-edgeworker-sdk/src/platform/requests.ts
index 453344e13c..69cbeeb5e6 100644
--- a/packages/shared/akamai-edgeworker-sdk/src/platform/requests.ts
+++ b/packages/shared/akamai-edgeworker-sdk/src/platform/requests.ts
@@ -2,11 +2,11 @@
 import { Headers, NullEventSource } from '@launchdarkly/js-server-sdk-common';
 import type {
   EventSource,
+  EventSourceCapabilities,
   EventSourceInitDict,
   Options,
   Requests,
   Response,
-  EventSourceCapabilities,
 } from '@launchdarkly/js-server-sdk-common';
 
 class NoopResponse implements Response {

From 6acc5f47aa8c4bb2f272bb8afce024a22cf79272 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 13:23:05 -0700
Subject: [PATCH 06/19] Add getEventSourceCapabilities to mocks.

---
 packages/shared/mocks/src/platform.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/packages/shared/mocks/src/platform.ts b/packages/shared/mocks/src/platform.ts
index ef138ebd56..e3b0b9ecc5 100644
--- a/packages/shared/mocks/src/platform.ts
+++ b/packages/shared/mocks/src/platform.ts
@@ -49,6 +49,7 @@ export const createBasicPlatform = () => ({
   requests: {
     fetch: jest.fn(),
     createEventSource: jest.fn(),
+    getEventSourceCapabilities: jest.fn(),
   },
   storage: {
     get: jest.fn(),

From b89e14e5eac45bd14825d7891357ce27d9c585a7 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 13:26:45 -0700
Subject: [PATCH 07/19] Test updates.

---
 ...{PollingProcessot.test.ts => PollingProcessor.test.ts} | 8 ++++++++
 1 file changed, 8 insertions(+)
 rename packages/shared/sdk-client/__tests__/polling/{PollingProcessot.test.ts => PollingProcessor.test.ts} (98%)

diff --git a/packages/shared/sdk-client/__tests__/polling/PollingProcessot.test.ts b/packages/shared/sdk-client/__tests__/polling/PollingProcessor.test.ts
similarity index 98%
rename from packages/shared/sdk-client/__tests__/polling/PollingProcessot.test.ts
rename to packages/shared/sdk-client/__tests__/polling/PollingProcessor.test.ts
index b6a98ae3eb..33cfa40771 100644
--- a/packages/shared/sdk-client/__tests__/polling/PollingProcessot.test.ts
+++ b/packages/shared/sdk-client/__tests__/polling/PollingProcessor.test.ts
@@ -2,6 +2,7 @@ import { waitFor } from '@testing-library/dom';
 
 import {
   EventSource,
+  EventSourceCapabilities,
   EventSourceInitDict,
   Info,
   PlatformData,
@@ -45,6 +46,13 @@ function makeRequests(): Requests {
     createEventSource(_url: string, _eventSourceInitDict: EventSourceInitDict): EventSource {
       throw new Error('Function not implemented.');
     },
+    getEventSourceCapabilities(): EventSourceCapabilities {
+      return {
+        readTimeout: false,
+        headers: false,
+        customMethod: false,
+      };
+    },
   };
 }
 

From 5becb5b410b5366c7ab82d9dda51775c9a4a990c Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 13:27:57 -0700
Subject: [PATCH 08/19] More test updates.

---
 .../sdk/react-native/__tests__/ReactNativeLDClient.test.ts | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/packages/sdk/react-native/__tests__/ReactNativeLDClient.test.ts b/packages/sdk/react-native/__tests__/ReactNativeLDClient.test.ts
index 7a4f594c68..56ddebcbfc 100644
--- a/packages/sdk/react-native/__tests__/ReactNativeLDClient.test.ts
+++ b/packages/sdk/react-native/__tests__/ReactNativeLDClient.test.ts
@@ -42,6 +42,7 @@ jest.mock('../src/platform', () => ({
     requests: {
       createEventSource: jest.fn(),
       fetch: jest.fn(),
+      getEventSourceCapabilities: jest.fn(),
     },
     encoding: new PlatformEncoding(),
     storage: new PlatformStorage(logger),
@@ -70,6 +71,7 @@ it('uses correct default diagnostic url', () => {
     requests: {
       createEventSource: jest.fn(),
       fetch: mockedFetch,
+      getEventSourceCapabilities: jest.fn(),
     },
     encoding: new PlatformEncoding(),
     storage: new PlatformStorage(logger),
@@ -97,6 +99,7 @@ it('uses correct default analytics event url', async () => {
     requests: {
       createEventSource: createMockEventSource,
       fetch: mockedFetch,
+      getEventSourceCapabilities: jest.fn(),
     },
     encoding: new PlatformEncoding(),
     storage: new PlatformStorage(logger),
@@ -128,6 +131,7 @@ it('uses correct default polling url', async () => {
     requests: {
       createEventSource: jest.fn(),
       fetch: mockedFetch,
+      getEventSourceCapabilities: jest.fn(),
     },
     encoding: new PlatformEncoding(),
     storage: new PlatformStorage(logger),
@@ -158,6 +162,7 @@ it('uses correct default streaming url', (done) => {
     requests: {
       createEventSource: mockedCreateEventSource,
       fetch: jest.fn(),
+      getEventSourceCapabilities: jest.fn(),
     },
     encoding: new PlatformEncoding(),
     storage: new PlatformStorage(logger),
@@ -197,6 +202,7 @@ it('includes authorization header for polling', async () => {
     requests: {
       createEventSource: jest.fn(),
       fetch: mockedFetch,
+      getEventSourceCapabilities: jest.fn(),
     },
     encoding: new PlatformEncoding(),
     storage: new PlatformStorage(logger),
@@ -231,6 +237,7 @@ it('includes authorization header for streaming', (done) => {
     requests: {
       createEventSource: mockedCreateEventSource,
       fetch: jest.fn(),
+      getEventSourceCapabilities: jest.fn(),
     },
     encoding: new PlatformEncoding(),
     storage: new PlatformStorage(logger),

From 8f63e45643ecdb78348b0a247547a287df24071d Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 13:30:23 -0700
Subject: [PATCH 09/19] More tests.

---
 .../sdk-client/__tests__/polling/PollingProcessor.test.ts  | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/packages/shared/sdk-client/__tests__/polling/PollingProcessor.test.ts b/packages/shared/sdk-client/__tests__/polling/PollingProcessor.test.ts
index 33cfa40771..8e6a39c931 100644
--- a/packages/shared/sdk-client/__tests__/polling/PollingProcessor.test.ts
+++ b/packages/shared/sdk-client/__tests__/polling/PollingProcessor.test.ts
@@ -177,6 +177,13 @@ it('stops polling when stopped', (done) => {
     createEventSource(_url: string, _eventSourceInitDict: EventSourceInitDict): EventSource {
       throw new Error('Function not implemented.');
     },
+    getEventSourceCapabilities(): EventSourceCapabilities {
+      return {
+        readTimeout: false,
+        headers: false,
+        customMethod: false,
+      };
+    },
   };
   const dataCallback = jest.fn();
   const errorCallback = jest.fn();

From 1c5450f0a3d392584f1d2956b7632b6aa96f1efc Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 13:34:43 -0700
Subject: [PATCH 10/19] More test updates.

---
 .../sdk-client/__tests__/flag-manager/FlagPersistence.test.ts  | 1 +
 .../shared/sdk-server/__tests__/data_sources/Requestor.test.ts | 3 +++
 .../shared/sdk-server/__tests__/events/EventProcessor.test.ts  | 3 +++
 3 files changed, 7 insertions(+)

diff --git a/packages/shared/sdk-client/__tests__/flag-manager/FlagPersistence.test.ts b/packages/shared/sdk-client/__tests__/flag-manager/FlagPersistence.test.ts
index 6e90c10af3..cd31ef46c4 100644
--- a/packages/shared/sdk-client/__tests__/flag-manager/FlagPersistence.test.ts
+++ b/packages/shared/sdk-client/__tests__/flag-manager/FlagPersistence.test.ts
@@ -329,6 +329,7 @@ function makeMockPlatform(storage: Storage, crypto: Crypto): Platform {
     requests: {
       fetch: jest.fn(),
       createEventSource: jest.fn(),
+      getEventSourceCapabilities: jest.fn(),
     },
   };
 }
diff --git a/packages/shared/sdk-server/__tests__/data_sources/Requestor.test.ts b/packages/shared/sdk-server/__tests__/data_sources/Requestor.test.ts
index 1fb0558155..46a0640ac8 100644
--- a/packages/shared/sdk-server/__tests__/data_sources/Requestor.test.ts
+++ b/packages/shared/sdk-server/__tests__/data_sources/Requestor.test.ts
@@ -75,6 +75,9 @@ describe('given a requestor', () => {
       createEventSource(_url: string, _eventSourceInitDict: EventSourceInitDict): EventSource {
         throw new Error('Function not implemented.');
       },
+      getEventSourceCapabilities() {
+        throw new Error('Function not implemented.');
+      },
     };
 
     requestor = new Requestor(
diff --git a/packages/shared/sdk-server/__tests__/events/EventProcessor.test.ts b/packages/shared/sdk-server/__tests__/events/EventProcessor.test.ts
index 8aed40555f..41fa4135ef 100644
--- a/packages/shared/sdk-server/__tests__/events/EventProcessor.test.ts
+++ b/packages/shared/sdk-server/__tests__/events/EventProcessor.test.ts
@@ -111,6 +111,9 @@ function makePlatform(requestState: RequestState) {
     createEventSource(_url: string, _eventSourceInitDict: EventSourceInitDict): EventSource {
       throw new Error('Function not implemented.');
     },
+    getEventSourceCapabilities() {
+      throw new Error('Function not implemented.');
+    },
   };
   return {
     info,

From f0a51c6f452a455a7b6a2468ee9fa91343995aa6 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 13:37:46 -0700
Subject: [PATCH 11/19] feat: Implement browser platform.

---
 .../src/platform/BrowserEventSourceShim.ts    | 21 +++++++++++++++----
 .../browser/src/platform/BrowserRequests.ts   | 10 +++++++++
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/packages/sdk/browser/src/platform/BrowserEventSourceShim.ts b/packages/sdk/browser/src/platform/BrowserEventSourceShim.ts
index c479a34e11..b5e07b1a17 100644
--- a/packages/sdk/browser/src/platform/BrowserEventSourceShim.ts
+++ b/packages/sdk/browser/src/platform/BrowserEventSourceShim.ts
@@ -24,13 +24,15 @@ export default class BrowserEventSourceShim implements LDEventSource {
   // The type of the handle can be platform specific and we treat is opaquely.
   private reconnectTimeoutHandle?: any;
 
+  private listeners: Record<string, EventListener[]> = {};
+
   constructor(
     private readonly url: string,
     options: EventSourceInitDict,
   ) {
     this.backoff = new Backoff(options.initialRetryDelayMillis);
     this.errorFilter = options.errorFilter;
-    this.createEventSource();
+    this.openConnection();
   }
 
   onclose: (() => void) | undefined;
@@ -41,7 +43,7 @@ export default class BrowserEventSourceShim implements LDEventSource {
 
   onretrying: ((e: { delayMillis: number }) => void) | undefined;
 
-  private createEventSource() {
+  private openConnection() {
     this.es = new EventSource(this.url);
     this.es.onopen = () => {
       this.backoff.reset();
@@ -51,11 +53,18 @@ export default class BrowserEventSourceShim implements LDEventSource {
     // typing.
     this.es.onerror = (err: any) => {
       this.handleError(err);
+      this.onerror?.(err);
     };
+    Object.entries(this.listeners).forEach(([eventName, listeners]) => {
+      listeners.forEach((listener) => {
+        this.es?.addEventListener(eventName, listener);
+      });
+    });
   }
 
   addEventListener(type: EventName, listener: EventListener): void {
-    // TODO: Cache listeners so they can be re-added.
+    this.listeners[type] ??= [];
+    this.listeners[type].push(listener);
     this.es?.addEventListener(type, listener);
   }
 
@@ -63,12 +72,16 @@ export default class BrowserEventSourceShim implements LDEventSource {
     // Ensure any pending retry attempts are not done.
     clearTimeout(this.reconnectTimeoutHandle);
     this.reconnectTimeoutHandle = undefined;
+
+    // Close the event source and notify any listeners.
     this.es?.close();
+    this.onclose?.();
   }
 
   private tryConnect(delayMs: number) {
+    this.onretrying?.({ delayMillis: delayMs });
     this.reconnectTimeoutHandle = setTimeout(() => {
-      this.createEventSource();
+      this.openConnection();
     }, delayMs);
   }
 
diff --git a/packages/sdk/browser/src/platform/BrowserRequests.ts b/packages/sdk/browser/src/platform/BrowserRequests.ts
index 917b6ac4aa..ca4d42f51d 100644
--- a/packages/sdk/browser/src/platform/BrowserRequests.ts
+++ b/packages/sdk/browser/src/platform/BrowserRequests.ts
@@ -1,4 +1,5 @@
 import {
+  EventSourceCapabilities,
   EventSourceInitDict,
   EventSource as LDEventSource,
   Options,
@@ -12,7 +13,16 @@ export default class BrowserRequests implements Requests {
   fetch(url: string, options?: Options): Promise<Response> {
     return this.fetch(url, options);
   }
+
   createEventSource(url: string, eventSourceInitDict: EventSourceInitDict): LDEventSource {
     return new BrowserEventSourceShim(url, eventSourceInitDict);
   }
+
+  getEventSourceCapabilities(): EventSourceCapabilities {
+    return {
+      customMethod: false,
+      readTimeout: false,
+      headers: false,
+    };
+  }
 }

From d2597913b835b8c213df5e7b2323858fdae0a025 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 14:16:19 -0700
Subject: [PATCH 12/19] Rename browser event source.

---
 packages/sdk/browser/src/platform/BrowserRequests.ts  |  4 ++--
 ...ventSourceShim.ts => DefaultBrowserEventSource.ts} | 11 +++++++----
 2 files changed, 9 insertions(+), 6 deletions(-)
 rename packages/sdk/browser/src/platform/{BrowserEventSourceShim.ts => DefaultBrowserEventSource.ts} (93%)

diff --git a/packages/sdk/browser/src/platform/BrowserRequests.ts b/packages/sdk/browser/src/platform/BrowserRequests.ts
index ca4d42f51d..52d4d0dbd4 100644
--- a/packages/sdk/browser/src/platform/BrowserRequests.ts
+++ b/packages/sdk/browser/src/platform/BrowserRequests.ts
@@ -7,7 +7,7 @@ import {
   Response,
 } from '@launchdarkly/js-client-sdk-common';
 
-import BrowserEventSourceShim from './BrowserEventSourceShim';
+import DefaultBrowserEventSource from './DefaultBrowserEventSource';
 
 export default class BrowserRequests implements Requests {
   fetch(url: string, options?: Options): Promise<Response> {
@@ -15,7 +15,7 @@ export default class BrowserRequests implements Requests {
   }
 
   createEventSource(url: string, eventSourceInitDict: EventSourceInitDict): LDEventSource {
-    return new BrowserEventSourceShim(url, eventSourceInitDict);
+    return new DefaultBrowserEventSource(url, eventSourceInitDict);
   }
 
   getEventSourceCapabilities(): EventSourceCapabilities {
diff --git a/packages/sdk/browser/src/platform/BrowserEventSourceShim.ts b/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts
similarity index 93%
rename from packages/sdk/browser/src/platform/BrowserEventSourceShim.ts
rename to packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts
index b5e07b1a17..be791ad9b4 100644
--- a/packages/sdk/browser/src/platform/BrowserEventSourceShim.ts
+++ b/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts
@@ -16,7 +16,11 @@ import Backoff from './Backoff';
  * This event source does not support headers.
  */
 
-export default class BrowserEventSourceShim implements LDEventSource {
+/**
+ * Browser event source implementation which extends the built-in event
+ * source with additional reconnection logic.
+ */
+export default class DefaultBrowserEventSource implements LDEventSource {
   private es?: EventSource;
   private backoff: Backoff;
   private errorFilter: (err: HttpErrorResponse) => boolean;
@@ -86,19 +90,18 @@ export default class BrowserEventSourceShim implements LDEventSource {
   }
 
   private handleError(err: any): void {
+    this.close();
+
     // The event source may not produce a status. But the LaunchDarkly
     // polyfill can. If we can get the status, then we should stop retrying
     // on certain error codes.
     if (err.status && typeof err.status === 'number' && !this.errorFilter(err)) {
       // If we encounter an unrecoverable condition, then we do not want to
       // retry anymore.
-      this.close();
       return;
     }
 
     const delay = this.backoff.getNextRetryDelay();
-
-    this.close();
     this.tryConnect(delay);
   }
 }

From 679b813640bd096425abb5a6e229e6fda3daf2e1 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 15:04:42 -0700
Subject: [PATCH 13/19] Add backoff tests.

---
 .../__tests__/platform/Backoff.test.ts        | 67 +++++++++++++++++
 packages/sdk/browser/src/platform/Backoff.ts  | 74 +++++++++++++++----
 .../src/platform/DefaultBrowserEventSource.ts |  5 +-
 3 files changed, 129 insertions(+), 17 deletions(-)
 create mode 100644 packages/sdk/browser/__tests__/platform/Backoff.test.ts

diff --git a/packages/sdk/browser/__tests__/platform/Backoff.test.ts b/packages/sdk/browser/__tests__/platform/Backoff.test.ts
new file mode 100644
index 0000000000..3d32614ae8
--- /dev/null
+++ b/packages/sdk/browser/__tests__/platform/Backoff.test.ts
@@ -0,0 +1,67 @@
+import Backoff from '../../src/platform/Backoff';
+
+const noJitter = (): number => 0;
+const maxJitter = (): number => 1;
+
+it.each([1, 1000, 5000])('has the correct starting delay', (initialDelay) => {
+  const backoff = new Backoff(initialDelay, noJitter);
+  expect(backoff.fail()).toEqual(initialDelay);
+});
+
+it.each([1, 1000, 5000])('doubles delay on consecutive failures', (initialDelay) => {
+  const backoff = new Backoff(initialDelay, noJitter);
+  expect(backoff.fail()).toEqual(initialDelay);
+  expect(backoff.fail()).toEqual(initialDelay * 2);
+  expect(backoff.fail()).toEqual(initialDelay * 4);
+});
+
+it('stops increasing delay when the max backoff is encountered', () => {
+  const backoff = new Backoff(5000, noJitter);
+  expect(backoff.fail()).toEqual(5000);
+  expect(backoff.fail()).toEqual(10000);
+  expect(backoff.fail()).toEqual(20000);
+  expect(backoff.fail()).toEqual(30000);
+
+  const backoff2 = new Backoff(1000, noJitter);
+  expect(backoff2.fail()).toEqual(1000);
+  expect(backoff2.fail()).toEqual(2000);
+  expect(backoff2.fail()).toEqual(4000);
+  expect(backoff2.fail()).toEqual(8000);
+  expect(backoff2.fail()).toEqual(16000);
+  expect(backoff2.fail()).toEqual(30000);
+});
+
+it('handles an initial retry delay longer than the maximum retry delay', () => {
+  const backoff = new Backoff(40000, noJitter);
+  expect(backoff.fail()).toEqual(30000);
+});
+
+it('jitters the backoff value', () => {
+  const backoff = new Backoff(1000, maxJitter);
+  expect(backoff.fail()).toEqual(500);
+  expect(backoff.fail()).toEqual(1000);
+  expect(backoff.fail()).toEqual(2000);
+  expect(backoff.fail()).toEqual(4000);
+  expect(backoff.fail()).toEqual(8000);
+  expect(backoff.fail()).toEqual(15000);
+});
+
+it('resets the delay when the last successful connection was connected greater than RESET_INTERVAL', () => {
+  const backoff = new Backoff(1000, noJitter);
+  expect(backoff.fail(1000)).toEqual(1000);
+  backoff.success(2000);
+  expect(backoff.fail(62001)).toEqual(1000);
+  expect(backoff.fail(62002)).toEqual(2000);
+  backoff.success(64002);
+  expect(backoff.fail(124003)).toEqual(1000);
+});
+
+it('does not reset the delay when the connection did not persist longer than the RESET_INTERVAL', () => {
+  const backoff = new Backoff(1000, noJitter);
+  expect(backoff.fail(1000)).toEqual(1000);
+  backoff.success(2000);
+  expect(backoff.fail(61000)).toEqual(2000);
+  expect(backoff.fail(120000)).toEqual(4000);
+  backoff.success(124000);
+  expect(backoff.fail(183000)).toEqual(8000);
+});
diff --git a/packages/sdk/browser/src/platform/Backoff.ts b/packages/sdk/browser/src/platform/Backoff.ts
index 30d272e128..59e28b5b82 100644
--- a/packages/sdk/browser/src/platform/Backoff.ts
+++ b/packages/sdk/browser/src/platform/Backoff.ts
@@ -1,26 +1,72 @@
-const maxRetryDelay = 30 * 1000; // Maximum retry delay 30 seconds.
-const jitterRatio = 0.5; // Delay should be 50%-100% of calculated time.
-
-function jitter(computedDelayMillis: number): number {
-  return computedDelayMillis - Math.trunc(Math.random() * jitterRatio * computedDelayMillis);
-}
+const MAX_RETRY_DELAY = 30 * 1000; // Maximum retry delay 30 seconds.
+const JITTER_RATIO = 0.5; // Delay should be 50%-100% of calculated time.
+const RESET_INTERVAL = 60 * 1000; // Reset interval in seconds.
 
+/**
+ * Implements exponential backoff and jitter. This class tracks successful connections and failures
+ * and produces a retry delay.
+ *
+ * It does not start any timers or directly control a connection.
+ *
+ * The backoff follows an exponential backoff scheme with 50% jitter starting at
+ * initialRetryDelayMillis and capping at MAX_RETRY_DELAY.  If RESET_INTERVAL has elapsed after a
+ * success, without an intervening faulure, then the backoff is reset to initialRetryDelayMillis.
+ */
 export default class Backoff {
   private retryCount: number = 0;
+  private activeSince?: number;
+  private initialRetryDelayMillis: number;
+  /**
+   * The exponent at which the backoff delay will exceed the maximum.
+   * Beyond this limit the backoff can be set to the max.
+   */
+  private readonly maxExponent: number;
 
-  constructor(private readonly initialRetryDelayMillis: number) {}
+  constructor(
+    initialRetryDelayMillis: number,
+    private readonly random = Math.random,
+  ) {
+    // Initial retry delay cannot be 0.
+    this.initialRetryDelayMillis = Math.max(1, initialRetryDelayMillis);
+    this.maxExponent = Math.ceil(Math.log2(MAX_RETRY_DELAY / this.initialRetryDelayMillis));
+  }
+
+  private backoff(): number {
+    const exponent = Math.min(this.retryCount, this.maxExponent);
+    const delay = this.initialRetryDelayMillis * 2 ** exponent;
+    return Math.min(delay, MAX_RETRY_DELAY);
+  }
 
-  reset(): void {
-    this.retryCount = 0;
+  private jitter(computedDelayMillis: number): number {
+    return computedDelayMillis - Math.trunc(this.random() * JITTER_RATIO * computedDelayMillis);
   }
 
-  backoff(): number {
-    const delay = this.initialRetryDelayMillis * 2 ** this.retryCount;
-    return delay > maxRetryDelay ? maxRetryDelay : delay;
+  /**
+   * This function should be called when a connection attempt is successful.
+   *
+   * @param timeStampMs The time of the success. Used primarily for testing, when not provided
+   * the current time is used.
+   */
+  success(timeStampMs: number = Date.now()): void {
+    this.activeSince = timeStampMs;
   }
 
-  getNextRetryDelay(): number {
-    const delay = jitter(this.backoff());
+  /**
+   * This function should be called when a connection fails. It returns the a delay, in
+   * milliseconds, after which a reconnection attempt should be made.
+   *
+   * @param timeStampMs The time of the success. Used primarily for testing, when not provided
+   * the current time is used.
+   * @returns The delay before the next connection attempt.
+   */
+  fail(timeStampMs: number = Date.now()): number {
+    // If the last successful connection was active for more than the RESET_INTERVAL, then we
+    // return to the initial retry delay.
+    if (this.activeSince !== undefined && timeStampMs - this.activeSince > RESET_INTERVAL) {
+      this.retryCount = 0;
+    }
+    this.activeSince = undefined;
+    const delay = this.jitter(this.backoff());
     this.retryCount += 1;
     return delay;
   }
diff --git a/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts b/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts
index be791ad9b4..c560c86daf 100644
--- a/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts
+++ b/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts
@@ -50,7 +50,7 @@ export default class DefaultBrowserEventSource implements LDEventSource {
   private openConnection() {
     this.es = new EventSource(this.url);
     this.es.onopen = () => {
-      this.backoff.reset();
+      this.backoff.success();
       this.onopen?.();
     };
     // The error could be from a polyfill, or from the browser event source, so we are loose on the
@@ -101,7 +101,6 @@ export default class DefaultBrowserEventSource implements LDEventSource {
       return;
     }
 
-    const delay = this.backoff.getNextRetryDelay();
-    this.tryConnect(delay);
+    this.tryConnect(this.backoff.fail());
   }
 }

From 0434103da5fb5cf1f36097cbebfd87e5f0b6d3d3 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Tue, 10 Sep 2024 16:15:07 -0700
Subject: [PATCH 14/19] Enable encoding.

---
 packages/sdk/browser/src/platform/BrowserPlatform.ts | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/packages/sdk/browser/src/platform/BrowserPlatform.ts b/packages/sdk/browser/src/platform/BrowserPlatform.ts
index dc9d7054d9..827566d6a3 100644
--- a/packages/sdk/browser/src/platform/BrowserPlatform.ts
+++ b/packages/sdk/browser/src/platform/BrowserPlatform.ts
@@ -1,5 +1,6 @@
 import {
   Crypto,
+  Encoding,
   /* platform */
   LDOptions,
   Requests,
@@ -7,11 +8,12 @@ import {
 } from '@launchdarkly/js-client-sdk-common';
 
 import BrowserCrypto from './BrowserCrypto';
+import BrowserEncoding from './BrowserEncoding';
 import BrowserRequests from './BrowserRequests';
 import LocalStorage, { isLocalStorageSupported } from './LocalStorage';
 
 export default class BrowserPlatform /* implements platform.Platform */ {
-  // encoding?: Encoding;
+  encoding: Encoding = new BrowserEncoding();
   // info: Info;
   // fileSystem?: Filesystem;
   crypto: Crypto = new BrowserCrypto();

From 7c66b7ba7b171e202e93858d6b1040062475334d Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Wed, 11 Sep 2024 14:32:02 -0700
Subject: [PATCH 15/19] Move to rollup.

---
 packages/sdk/browser/package.json     | 13 +++---
 packages/sdk/browser/rollup.config.js | 61 +++++++++++++++++++++++++++
 packages/sdk/browser/src/index.ts     |  6 +++
 packages/sdk/browser/tsconfig.json    |  1 +
 packages/sdk/browser/vite.config.ts   | 18 --------
 5 files changed, 76 insertions(+), 23 deletions(-)
 create mode 100644 packages/sdk/browser/rollup.config.js
 delete mode 100644 packages/sdk/browser/vite.config.ts

diff --git a/packages/sdk/browser/package.json b/packages/sdk/browser/package.json
index 1d1c44388e..60ae7d9f05 100644
--- a/packages/sdk/browser/package.json
+++ b/packages/sdk/browser/package.json
@@ -27,7 +27,7 @@
   ],
   "scripts": {
     "clean": "rimraf dist",
-    "build": "tsc --noEmit && vite build",
+    "build": "rollup -c rollup.config.js",
     "lint": "eslint . --ext .ts,.tsx",
     "prettier": "prettier --write '**/*.@(js|ts|tsx|json|css)' --ignore-path ../../../.prettierignore",
     "test": "jest",
@@ -39,6 +39,10 @@
   },
   "devDependencies": {
     "@launchdarkly/private-js-mocks": "0.0.1",
+    "@rollup/plugin-commonjs": "^25.0.0",
+    "@rollup/plugin-node-resolve": "^15.0.2",
+    "@rollup/plugin-terser": "^0.4.3",
+    "@rollup/plugin-typescript": "^11.1.1",
     "@trivago/prettier-plugin-sort-imports": "^4.1.1",
     "@types/jest": "^29.5.11",
     "@typescript-eslint/eslint-plugin": "^6.20.0",
@@ -54,11 +58,10 @@
     "jest-environment-jsdom": "^29.7.0",
     "prettier": "^3.0.0",
     "rimraf": "^5.0.5",
+    "rollup": "^3.23.0",
+    "rollup-plugin-generate-package-json": "^3.2.0",
     "ts-jest": "^29.1.1",
-    "ts-node": "^10.9.2",
     "typedoc": "0.25.0",
-    "typescript": "^5.5.3",
-    "vite": "^5.4.1",
-    "vite-plugin-dts": "^4.0.3"
+    "typescript": "^5.5.3"
   }
 }
diff --git a/packages/sdk/browser/rollup.config.js b/packages/sdk/browser/rollup.config.js
new file mode 100644
index 0000000000..d395193e4a
--- /dev/null
+++ b/packages/sdk/browser/rollup.config.js
@@ -0,0 +1,61 @@
+import common from '@rollup/plugin-commonjs';
+import resolve from '@rollup/plugin-node-resolve';
+import terser from '@rollup/plugin-terser';
+import typescript from '@rollup/plugin-typescript';
+import generatePackageJson from 'rollup-plugin-generate-package-json';
+
+const getSharedConfig = (format, file) => ({
+  input: 'src/index.ts',
+  output: [
+    {
+      format: format,
+      sourcemap: true,
+      file: file,
+    },
+  ],
+  onwarn: (warning) => {
+    if (warning.code !== 'CIRCULAR_DEPENDENCY') {
+      console.error(`(!) ${warning.message}`);
+    }
+  },
+});
+
+export default [
+  {
+    ...getSharedConfig('es', 'dist/index.es.js'),
+    plugins: [
+      generatePackageJson({
+        baseContents: (pkg) => ({
+          name: pkg.name,
+          version: pkg.version,
+          type: 'module',
+        }),
+      }),
+      typescript({
+        module: 'esnext',
+      }),
+      common({
+        transformMixedEsModules: true,
+        esmExternals: true,
+      }),
+      resolve(),
+      terser(),
+    ],
+  },
+  {
+    ...getSharedConfig('cjs', 'dist/index.cjs.js'),
+    plugins: [
+      generatePackageJson({
+        baseContents: (pkg) => ({
+          name: pkg.name,
+          version: pkg.version,
+          type: 'commonjs',
+        }),
+      }),
+      typescript(),
+      common(),
+      resolve(),
+      terser(),
+    ],
+  },
+];
diff --git a/packages/sdk/browser/src/index.ts b/packages/sdk/browser/src/index.ts
index a31204dbd8..89e7f67b95 100644
--- a/packages/sdk/browser/src/index.ts
+++ b/packages/sdk/browser/src/index.ts
@@ -1,3 +1,9 @@
+import DefaultBrowserEventSource from './platform/DefaultBrowserEventSource';
+
+// Temporary exports for testing the events source in a browser.
+export { DefaultBrowserEventSource };
+export * from '@launchdarkly/js-client-sdk-common';
+
 export function Hello() {
   // eslint-disable-next-line no-console
   console.log('HELLO');
diff --git a/packages/sdk/browser/tsconfig.json b/packages/sdk/browser/tsconfig.json
index 79420d3d43..66b350fda3 100644
--- a/packages/sdk/browser/tsconfig.json
+++ b/packages/sdk/browser/tsconfig.json
@@ -11,6 +11,7 @@
     "resolveJsonModule": true,
     // Uses "." so it can load package.json.
     "rootDir": ".",
+    "outDir": "dist",
     "skipLibCheck": true,
     // enables importers to jump to source
     "sourceMap": true,
diff --git a/packages/sdk/browser/vite.config.ts b/packages/sdk/browser/vite.config.ts
deleted file mode 100644
index 74378ce665..0000000000
--- a/packages/sdk/browser/vite.config.ts
+++ /dev/null
@@ -1,18 +0,0 @@
-/* eslint-disable import/no-extraneous-dependencies */
-// This file intentionally uses dev dependencies as it is a build file.
-import { resolve } from 'path';
-import { defineConfig } from 'vite';
-import dts from 'vite-plugin-dts';
-
-export default defineConfig({
-  plugins: [dts()],
-  build: {
-    lib: {
-      entry: resolve(__dirname, 'src/index.ts'),
-      name: '@launchdarkly/js-client-sdk',
-      fileName: (format) => `index.${format}.js`,
-      formats: ['cjs', 'es'],
-    },
-    rollupOptions: {},
-  },
-});

From fd8d7d63e5e52646e57d521ea022683ed59542ec Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Wed, 11 Sep 2024 14:39:42 -0700
Subject: [PATCH 16/19] Validate package.json imports.

---
 packages/sdk/browser/package.json     |  2 +-
 packages/sdk/browser/rollup.config.js | 18 +++---------------
 packages/sdk/browser/src/index.ts     |  5 +++--
 3 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/packages/sdk/browser/package.json b/packages/sdk/browser/package.json
index 60ae7d9f05..3f6f646b60 100644
--- a/packages/sdk/browser/package.json
+++ b/packages/sdk/browser/package.json
@@ -40,6 +40,7 @@
   "devDependencies": {
     "@launchdarkly/private-js-mocks": "0.0.1",
     "@rollup/plugin-commonjs": "^25.0.0",
+    "@rollup/plugin-json": "^6.1.0",
     "@rollup/plugin-node-resolve": "^15.0.2",
     "@rollup/plugin-terser": "^0.4.3",
     "@rollup/plugin-typescript": "^11.1.1",
@@ -59,7 +60,6 @@
     "prettier": "^3.0.0",
     "rimraf": "^5.0.5",
     "rollup": "^3.23.0",
-    "rollup-plugin-generate-package-json": "^3.2.0",
     "ts-jest": "^29.1.1",
     "typedoc": "0.25.0",
     "typescript": "^5.5.3"
diff --git a/packages/sdk/browser/rollup.config.js b/packages/sdk/browser/rollup.config.js
index d395193e4a..d78a55a79d 100644
--- a/packages/sdk/browser/rollup.config.js
+++ b/packages/sdk/browser/rollup.config.js
@@ -2,7 +2,7 @@ import common from '@rollup/plugin-commonjs';
 import resolve from '@rollup/plugin-node-resolve';
 import terser from '@rollup/plugin-terser';
 import typescript from '@rollup/plugin-typescript';
-import generatePackageJson from 'rollup-plugin-generate-package-json';
+import json from '@rollup/plugin-json';
 
 const getSharedConfig = (format, file) => ({
   input: 'src/index.ts',
@@ -24,13 +24,6 @@ export default [
   {
     ...getSharedConfig('es', 'dist/index.es.js'),
     plugins: [
-      generatePackageJson({
-        baseContents: (pkg) => ({
-          name: pkg.name,
-          version: pkg.version,
-          type: 'module',
-        }),
-      }),
       typescript({
         module: 'esnext',
       }),
@@ -40,22 +33,17 @@ export default [
       }),
       resolve(),
       terser(),
+      json(),
     ],
   },
   {
     ...getSharedConfig('cjs', 'dist/index.cjs.js'),
     plugins: [
-      generatePackageJson({
-        baseContents: (pkg) => ({
-          name: pkg.name,
-          version: pkg.version,
-          type: 'commonjs',
-        }),
-      }),
       typescript(),
       common(),
       resolve(),
       terser(),
+      json(),
     ],
   },
 ];
diff --git a/packages/sdk/browser/src/index.ts b/packages/sdk/browser/src/index.ts
index 89e7f67b95..e736320369 100644
--- a/packages/sdk/browser/src/index.ts
+++ b/packages/sdk/browser/src/index.ts
@@ -1,7 +1,8 @@
+import BrowserInfo from './platform/BrowserInfo';
 import DefaultBrowserEventSource from './platform/DefaultBrowserEventSource';
 
-// Temporary exports for testing the events source in a browser.
-export { DefaultBrowserEventSource };
+// Temporary exports for testing in a browser.
+export { DefaultBrowserEventSource, BrowserInfo };
 export * from '@launchdarkly/js-client-sdk-common';
 
 export function Hello() {

From 61a36316bb3961dcc6a5ba45c1b00fb95ca5a3a9 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Wed, 11 Sep 2024 15:08:18 -0700
Subject: [PATCH 17/19] Configurable reset time.

---
 .../__tests__/platform/Backoff.test.ts        | 68 ++++++++++++-------
 packages/sdk/browser/src/platform/Backoff.ts  |  7 +-
 .../src/platform/DefaultBrowserEventSource.ts |  2 +-
 3 files changed, 50 insertions(+), 27 deletions(-)

diff --git a/packages/sdk/browser/__tests__/platform/Backoff.test.ts b/packages/sdk/browser/__tests__/platform/Backoff.test.ts
index 3d32614ae8..49cdd901cb 100644
--- a/packages/sdk/browser/__tests__/platform/Backoff.test.ts
+++ b/packages/sdk/browser/__tests__/platform/Backoff.test.ts
@@ -2,27 +2,28 @@ import Backoff from '../../src/platform/Backoff';
 
 const noJitter = (): number => 0;
 const maxJitter = (): number => 1;
+const defaultResetInterval = 60 * 1000;
 
 it.each([1, 1000, 5000])('has the correct starting delay', (initialDelay) => {
-  const backoff = new Backoff(initialDelay, noJitter);
+  const backoff = new Backoff(initialDelay, defaultResetInterval, noJitter);
   expect(backoff.fail()).toEqual(initialDelay);
 });
 
 it.each([1, 1000, 5000])('doubles delay on consecutive failures', (initialDelay) => {
-  const backoff = new Backoff(initialDelay, noJitter);
+  const backoff = new Backoff(initialDelay, defaultResetInterval, noJitter);
   expect(backoff.fail()).toEqual(initialDelay);
   expect(backoff.fail()).toEqual(initialDelay * 2);
   expect(backoff.fail()).toEqual(initialDelay * 4);
 });
 
 it('stops increasing delay when the max backoff is encountered', () => {
-  const backoff = new Backoff(5000, noJitter);
+  const backoff = new Backoff(5000, defaultResetInterval, noJitter);
   expect(backoff.fail()).toEqual(5000);
   expect(backoff.fail()).toEqual(10000);
   expect(backoff.fail()).toEqual(20000);
   expect(backoff.fail()).toEqual(30000);
 
-  const backoff2 = new Backoff(1000, noJitter);
+  const backoff2 = new Backoff(1000, defaultResetInterval, noJitter);
   expect(backoff2.fail()).toEqual(1000);
   expect(backoff2.fail()).toEqual(2000);
   expect(backoff2.fail()).toEqual(4000);
@@ -32,12 +33,12 @@ it('stops increasing delay when the max backoff is encountered', () => {
 });
 
 it('handles an initial retry delay longer than the maximum retry delay', () => {
-  const backoff = new Backoff(40000, noJitter);
+  const backoff = new Backoff(40000, defaultResetInterval, noJitter);
   expect(backoff.fail()).toEqual(30000);
 });
 
 it('jitters the backoff value', () => {
-  const backoff = new Backoff(1000, maxJitter);
+  const backoff = new Backoff(1000, defaultResetInterval, maxJitter);
   expect(backoff.fail()).toEqual(500);
   expect(backoff.fail()).toEqual(1000);
   expect(backoff.fail()).toEqual(2000);
@@ -46,22 +47,41 @@ it('jitters the backoff value', () => {
   expect(backoff.fail()).toEqual(15000);
 });
 
-it('resets the delay when the last successful connection was connected greater than RESET_INTERVAL', () => {
-  const backoff = new Backoff(1000, noJitter);
-  expect(backoff.fail(1000)).toEqual(1000);
-  backoff.success(2000);
-  expect(backoff.fail(62001)).toEqual(1000);
-  expect(backoff.fail(62002)).toEqual(2000);
-  backoff.success(64002);
-  expect(backoff.fail(124003)).toEqual(1000);
-});
+it.each([10 * 1000, 60 * 1000])(
+  'resets the delay when the last successful connection was connected greater than the retry reset interval',
+  (retryResetInterval) => {
+    let time = 1000;
+    const backoff = new Backoff(1000, retryResetInterval, noJitter);
+    expect(backoff.fail(time)).toEqual(1000);
+    time += 1;
+    backoff.success(time);
+    time = time + retryResetInterval + 1;
+    expect(backoff.fail(time)).toEqual(1000);
+    time += 1;
+    expect(backoff.fail(time)).toEqual(2000);
+    time += 1;
+    backoff.success(time);
+    time = time + retryResetInterval + 1;
+    expect(backoff.fail(time)).toEqual(1000);
+  },
+);
 
-it('does not reset the delay when the connection did not persist longer than the RESET_INTERVAL', () => {
-  const backoff = new Backoff(1000, noJitter);
-  expect(backoff.fail(1000)).toEqual(1000);
-  backoff.success(2000);
-  expect(backoff.fail(61000)).toEqual(2000);
-  expect(backoff.fail(120000)).toEqual(4000);
-  backoff.success(124000);
-  expect(backoff.fail(183000)).toEqual(8000);
-});
+it.each([10 * 1000, 60 * 1000])(
+  'does not reset the delay when the connection did not persist longer than the retry reset interval',
+  (retryResetInterval) => {
+    const backoff = new Backoff(1000, retryResetInterval, noJitter);
+
+    let time = 1000;
+    expect(backoff.fail(time)).toEqual(1000);
+    time += 1;
+    backoff.success(time);
+    time += retryResetInterval;
+    expect(backoff.fail(time)).toEqual(2000);
+    time += retryResetInterval;
+    expect(backoff.fail(time)).toEqual(4000);
+    time += 1;
+    backoff.success(time);
+    time += retryResetInterval;
+    expect(backoff.fail(time)).toEqual(8000);
+  },
+);
diff --git a/packages/sdk/browser/src/platform/Backoff.ts b/packages/sdk/browser/src/platform/Backoff.ts
index 59e28b5b82..f90bcd7c4d 100644
--- a/packages/sdk/browser/src/platform/Backoff.ts
+++ b/packages/sdk/browser/src/platform/Backoff.ts
@@ -1,6 +1,5 @@
 const MAX_RETRY_DELAY = 30 * 1000; // Maximum retry delay 30 seconds.
 const JITTER_RATIO = 0.5; // Delay should be 50%-100% of calculated time.
-const RESET_INTERVAL = 60 * 1000; // Reset interval in seconds.
 
 /**
  * Implements exponential backoff and jitter. This class tracks successful connections and failures
@@ -24,6 +23,7 @@ export default class Backoff {
 
   constructor(
     initialRetryDelayMillis: number,
+    private readonly retryResetIntervalMillis: number,
     private readonly random = Math.random,
   ) {
     // Initial retry delay cannot be 0.
@@ -62,7 +62,10 @@ export default class Backoff {
   fail(timeStampMs: number = Date.now()): number {
     // If the last successful connection was active for more than the RESET_INTERVAL, then we
     // return to the initial retry delay.
-    if (this.activeSince !== undefined && timeStampMs - this.activeSince > RESET_INTERVAL) {
+    if (
+      this.activeSince !== undefined &&
+      timeStampMs - this.activeSince > this.retryResetIntervalMillis
+    ) {
       this.retryCount = 0;
     }
     this.activeSince = undefined;
diff --git a/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts b/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts
index c560c86daf..b9084349bc 100644
--- a/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts
+++ b/packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts
@@ -34,7 +34,7 @@ export default class DefaultBrowserEventSource implements LDEventSource {
     private readonly url: string,
     options: EventSourceInitDict,
   ) {
-    this.backoff = new Backoff(options.initialRetryDelayMillis);
+    this.backoff = new Backoff(options.initialRetryDelayMillis, options.retryResetIntervalMillis);
     this.errorFilter = options.errorFilter;
     this.openConnection();
   }

From af341cb7a42e71d8253c822d920ade1aab26682a Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Wed, 11 Sep 2024 15:26:32 -0700
Subject: [PATCH 18/19] Implements platform.

---
 packages/sdk/browser/src/platform/BrowserPlatform.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/sdk/browser/src/platform/BrowserPlatform.ts b/packages/sdk/browser/src/platform/BrowserPlatform.ts
index 3267969c40..34dfccaefa 100644
--- a/packages/sdk/browser/src/platform/BrowserPlatform.ts
+++ b/packages/sdk/browser/src/platform/BrowserPlatform.ts
@@ -2,8 +2,8 @@ import {
   Crypto,
   Encoding,
   Info,
-  /* platform */
   LDOptions,
+  Platform,
   Requests,
   Storage,
 } from '@launchdarkly/js-client-sdk-common';
@@ -14,7 +14,7 @@ import BrowserInfo from './BrowserInfo';
 import BrowserRequests from './BrowserRequests';
 import LocalStorage, { isLocalStorageSupported } from './LocalStorage';
 
-export default class BrowserPlatform /* implements platform.Platform */ {
+export default class BrowserPlatform implements Platform {
   encoding: Encoding = new BrowserEncoding();
   info: Info = new BrowserInfo();
   // fileSystem?: Filesystem;

From ff1dc23d4bead265a92077e99424a04a269b3b57 Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Wed, 11 Sep 2024 15:58:35 -0700
Subject: [PATCH 19/19] Correct fetch.

---
 packages/sdk/browser/src/platform/BrowserRequests.ts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/sdk/browser/src/platform/BrowserRequests.ts b/packages/sdk/browser/src/platform/BrowserRequests.ts
index 52d4d0dbd4..5e73467843 100644
--- a/packages/sdk/browser/src/platform/BrowserRequests.ts
+++ b/packages/sdk/browser/src/platform/BrowserRequests.ts
@@ -11,7 +11,8 @@ import DefaultBrowserEventSource from './DefaultBrowserEventSource';
 
 export default class BrowserRequests implements Requests {
   fetch(url: string, options?: Options): Promise<Response> {
-    return this.fetch(url, options);
+    // @ts-ignore
+    return fetch(url, options);
   }
 
   createEventSource(url: string, eventSourceInitDict: EventSourceInitDict): LDEventSource {