[Event Hubs] Improve prefetching (Azure#27647)

### Packages impacted by this PR
@azure/event-hubs

### Issues associated with this PR
Azure#27253

### Describe the problem that is addressed by this PR

Azure#27253 (comment)

### What are the possible designs available to address the problem? If
there are more than one possible design, why was the one in this PR
chosen?


### Are there test cases added in this PR? _(If not, why?)_
To be tested using stress testing framework.

UPDATE: The results are in and it is confirmed there is no more space
leak!

### Provide a list of related PRs _(if any)_
Azure#26065

### Command used to generate this PR:**_(Applicable only to SDK release
request PRs)_

### Checklists
- [x] Added impacted package name to the issue description
- [ ] Does this PR needs any fixes in the SDK Generator?** _(If so,
create an Issue in the
[Autorest/typescript](https://github.com/Azure/autorest.typescript)
repository and link it here)_
- [x] Added a changelog (if necessary)

Author: deyaaeldeen

sdk/eventhub/event-hubs/CHANGELOG.md

@@ -7,6 +7,7 @@
 ### Breaking Changes
 
 ### Bugs Fixed
+- Improve event prefetching to not overload the internal queue.
 
 ### Other Changes
 

sdk/eventhub/event-hubs/src/partitionReceiver.ts

@@ -94,7 +94,6 @@ export interface PartitionReceiver {
 interface ConnectOptions {
   abortSignal: AbortSignalLike | undefined;
   timeoutInMs: number;
-  prefetchCount: number;
 }
 
 interface ReceiverState {
@@ -156,7 +155,7 @@ export function createReceiver(
       logger.verbose(`is open? -> ${isOpen}`);
       return isOpen;
     },
-    async connect({ abortSignal, timeoutInMs, prefetchCount }: ConnectOptions): Promise<void> {
+    async connect({ abortSignal, timeoutInMs }: ConnectOptions): Promise<void> {
       if (state.isConnecting || obj.isOpen()) {
         return;
       }
@@ -174,7 +173,6 @@ export function createReceiver(
               obj,
               state,
               queue,
-              prefetchCount,
               eventPosition,
               logger,
               options,
@@ -203,6 +201,7 @@ export function createReceiver(
       maxWaitTimeInSeconds: number = 60,
       abortSignal?: AbortSignalLike
     ) => {
+      const prefetchCount = options.prefetchCount ?? maxMessageCount * 3;
       const cleanupBeforeAbort = (): Promise<void> => {
         logger.info(abortLogMessage);
         return obj.close();
@@ -224,10 +223,10 @@ export function createReceiver(
                 .connect({
                   abortSignal,
                   timeoutInMs: getRetryAttemptTimeoutInMs(options.retryOptions),
-                  prefetchCount: options.prefetchCount ?? maxMessageCount * 3,
                 })
                 .then(() => {
-                  logger.verbose(`setting the wait timer for ${maxWaitTimeInSeconds} seconds`);
+                  addCredits(state.link, Math.max(prefetchCount, maxMessageCount) - queue.length);
+                  logger.verbose(`setting the max wait time to ${maxWaitTimeInSeconds} seconds`);
                   return waitForEvents(
                     maxMessageCount,
                     maxWaitTimeInSeconds * 1000,
@@ -504,7 +503,6 @@ function createRheaOptions(
   obj: PartitionReceiver,
   state: ReceiverState,
   queue: ReceivedEventData[],
-  prefetchCount: number,
   eventPosition: EventPosition,
   logger: SimpleLogger,
   options: PartitionReceiverOptions
@@ -516,7 +514,7 @@ function createRheaOptions(
     source: {
       address,
     },
-    credit_window: prefetchCount,
+    credit_window: 0,
     properties: {
       [receiverIdPropertyName]: consumerId,
     },
@@ -550,7 +548,6 @@ async function setupLink(
   obj: PartitionReceiver,
   state: ReceiverState,
   queue: ReceivedEventData[],
-  prefetchCount: number,
   eventPosition: EventPosition,
   logger: SimpleLogger,
   options: PartitionReceiverOptions,
@@ -563,7 +560,6 @@ async function setupLink(
     obj,
     state,
     queue,
-    prefetchCount,
     eventPosition,
     logger,
     options
@@ -577,3 +573,9 @@ async function setupLink(
   logger.verbose("is created successfully");
   ctx.receivers[name] = obj;
 }
+
+function addCredits(receiver: Link | undefined, creditsToAdd: number): void {
+  if (creditsToAdd > 0) {
+    receiver?.addCredit(creditsToAdd);
+  }
+}

sdk/eventhub/event-hubs/test/internal/cancellation.spec.ts

@@ -98,7 +98,7 @@ testWithServiceTypes((serviceVersion) => {
         it(`initialize supports cancellation (${caseType})`, async () => {
           const abortSignal = getSignal();
           try {
-            await client.connect({ abortSignal, timeoutInMs: 60000, prefetchCount: 1 });
+            await client.connect({ abortSignal, timeoutInMs: 60000 });
             throw new Error(TEST_FAILURE);
           } catch (err: any) {
             should.equal(err.name, "AbortError");
@@ -119,7 +119,7 @@ testWithServiceTypes((serviceVersion) => {
 
         it(`receiveBatch supports cancellation when connection already exists (${caseType})`, async () => {
           // Open the connection.
-          await client.connect({ abortSignal: undefined, timeoutInMs: 60000, prefetchCount: 1 });
+          await client.connect({ abortSignal: undefined, timeoutInMs: 60000 });
           try {
             const abortSignal = getSignal();
             await client.receiveBatch(10, undefined, abortSignal);

sdk/eventhub/event-hubs/test/internal/node/disconnect.spec.ts

@@ -131,12 +131,10 @@ testWithServiceTypes((serviceVersion) => {
           await receiver1.connect({
             abortSignal: undefined,
             timeoutInMs: 60000,
-            prefetchCount: 1,
           });
           await receiver2.connect({
             abortSignal: undefined,
             timeoutInMs: 60000,
-            prefetchCount: 1,
           });
 
           // We are going to override sender1's close method so that it also invokes receiver2's close method.
@@ -199,12 +197,10 @@ testWithServiceTypes((serviceVersion) => {
           await receiver1.connect({
             abortSignal: undefined,
             timeoutInMs: 60000,
-            prefetchCount: 1,
           });
           await receiver2.connect({
             abortSignal: undefined,
             timeoutInMs: 60000,
-            prefetchCount: 1,
           });
 
           // We are going to override sender1's close method so that it also invokes receiver2's close method.