Flush keepalive batches past keepalive limit

.changeset/shaggy-dryers-press.md

@@ -0,0 +1,5 @@
+---
+'@segment/analytics-next': minor
+---
+
+Flush large keepalive requests

packages/browser/src/plugins/segmentio/__tests__/batched-dispatcher.test.ts

@@ -130,6 +130,31 @@ describe('Batching', () => {
     expect(fetch).toHaveBeenCalledTimes(1)
   })
 
+  it('sends requests if the size of events exceeds keepalive limits', async () => {
+    const { dispatch } = batch(`https://api.segment.io`, {
+      size: 600,
+      keepalive: true,
+    })
+
+    // fatEvent is about ~1kb in size
+    for (let i = 0; i < 250; i++) {
+      await dispatch(`https://api.segment.io/v1/t`, {
+        event: 'small event',
+      })
+    }
+    expect(fetch).not.toHaveBeenCalled()
+
+    for (let i = 0; i < 65; i++) {
+      await dispatch(`https://api.segment.io/v1/t`, {
+        event: 'fat event',
+        properties: fatEvent,
+      })
+    }
+
+    // still called, even though our batch limit is 600 events
+    expect(fetch).toHaveBeenCalledTimes(1)
+  })
+
   it('sends requests when the timeout expires', async () => {
     const { dispatch } = batch(`https://api.segment.io`, {
       size: 100,

packages/browser/src/plugins/segmentio/batched-dispatcher.ts

@@ -5,9 +5,11 @@ import { onPageChange } from '../../lib/on-page-change'
 export type BatchingDispatchConfig = {
   size?: number
   timeout?: number
+  keepalive?: boolean
 }
 
 const MAX_PAYLOAD_SIZE = 500
+const MAX_KEEPALIVE_SIZE = 64
 
 function kilobytes(buffer: unknown): number {
   const size = encodeURI(JSON.stringify(buffer)).split(/%..|./).length - 1
@@ -23,6 +25,15 @@ function approachingTrackingAPILimit(buffer: unknown): boolean {
   return kilobytes(buffer) >= MAX_PAYLOAD_SIZE - 50
 }
 
+/**
+ * Checks if payload is over or approaching the limit for keepalive
+ * requests. If keepalive is enabled we want to avoid
+ * going over this to prevent data loss.
+ */
+function passedKeepaliveLimit(buffer: unknown): boolean {
+  return kilobytes(buffer) >= MAX_KEEPALIVE_SIZE - 10
+}
+
 function chunks(batch: object[]): Array<object[]> {
   const result: object[][] = []
   let index = 0
@@ -67,7 +78,7 @@ export default function batch(
     })
 
     return fetch(`https://${apiHost}/b`, {
-      keepalive: pageUnloaded,
+      keepalive: config?.keepalive || pageUnloaded,
       headers: {
         'Content-Type': 'text/plain',
       },
@@ -114,7 +125,9 @@ export default function batch(
     buffer.push(body)
 
     const bufferOverflow =
-      buffer.length >= limit || approachingTrackingAPILimit(buffer)
+      buffer.length >= limit ||
+      approachingTrackingAPILimit(buffer) ||
+      (config?.keepalive && passedKeepaliveLimit(buffer))
 
     return bufferOverflow || pageUnloaded ? flush() : scheduleFlush()
   }