From 581f76a6cc807532398c4233142b0b437987395d Mon Sep 17 00:00:00 2001
From: agnosticdev <agnosticdev@gmail.com>
Date: Wed, 10 Jun 2026 06:57:02 -0700
Subject: [PATCH] agnosticdev/AckBundling: SwiftQUIC: Improve ACK Bundling

---
 Sources/SwiftNetwork/QUIC/Ack.swift                 |  4 ++--
 Sources/SwiftNetwork/QUIC/QUICConnection.swift      | 13 ++++++++++---
 Tests/SwiftNetworkTests/QUICTestHarness.swift       |  2 +-
 .../SwiftNetworkQUICEarlyDataTests.swift            | 10 ++++++++--
 .../SwiftNetworkQUICHarnessTests.swift              | 11 +++++++++++
 5 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/Sources/SwiftNetwork/QUIC/Ack.swift b/Sources/SwiftNetwork/QUIC/Ack.swift
index 83c4f2f..9984f41 100644
--- a/Sources/SwiftNetwork/QUIC/Ack.swift
+++ b/Sources/SwiftNetwork/QUIC/Ack.swift
@@ -497,7 +497,7 @@ final class Ack: PrefixedLoggable, TimerUser {
                 setAckFrame: connection.scheduleAckFrame,
                 ecn: connection.ecn
             ) {
-                connection.sendFrames()
+                connection.sendFrames(delayedACK: true)
             }
         }
 
@@ -718,7 +718,7 @@ final class Ack: PrefixedLoggable, TimerUser {
         )
     }
 
-    private func scheduleDelayedAck() {
+    func scheduleDelayedAck() {
         // ACK timer is already scheduled
         if timerScheduled {
             return
diff --git a/Sources/SwiftNetwork/QUIC/QUICConnection.swift b/Sources/SwiftNetwork/QUIC/QUICConnection.swift
index e00d776..8d1d300 100644
--- a/Sources/SwiftNetwork/QUIC/QUICConnection.swift
+++ b/Sources/SwiftNetwork/QUIC/QUICConnection.swift
@@ -2923,14 +2923,21 @@ public final class QUICConnection: ManyToManyApplicationStreamProtocol,
     }
 
     @discardableResult
-    func sendFrames(ignoreCongestionWindow: Bool = false) -> Bool {
-        // Make sure there is something to send first
+    func sendFrames(ignoreCongestionWindow: Bool = false, delayedACK: Bool = false) -> Bool {
+        // Make sure there are packets to send
         guard
-            initialPendingItems.hasPendingItems || handshakePendingItems.hasPendingItems
+            initialPendingItems.hasPendingItems
+                || handshakePendingItems.hasPendingItems
                 || applicationPendingItems.hasPendingItems
         else {
             return false
         }
+        // For ACK bundling purposes make sure to rely on the ACK-delay timer as much as possible
+        guard !applicationPendingItems.isAckOnly || delayedACK else {
+            // Make sure the ack-delay timer is armed if returning early
+            ack.scheduleDelayedAck()
+            return false
+        }
         return withCurrentPath { path in
             var sentPackets = NetworkUniqueDeque<SentPacketRecord>(minimumCapacity: capacityForPacketNumberSpace())
             var discardInitialRecoveryState = false
diff --git a/Tests/SwiftNetworkTests/QUICTestHarness.swift b/Tests/SwiftNetworkTests/QUICTestHarness.swift
index 2b71a07..68dc568 100644
--- a/Tests/SwiftNetworkTests/QUICTestHarness.swift
+++ b/Tests/SwiftNetworkTests/QUICTestHarness.swift
@@ -990,7 +990,7 @@ final class QUICTestHarness {
                     generator = TestDataGenerator(
                         blockSize: blockSize,
                         numberOfBlocks: blockCount,
-                        uniqueBits: UInt8(index),
+                        uniqueBits: UInt8(clamping: index),
                         sendFIN: sendFIN
                     )
                 }
diff --git a/Tests/SwiftNetworkTests/SwiftNetworkQUICEarlyDataTests.swift b/Tests/SwiftNetworkTests/SwiftNetworkQUICEarlyDataTests.swift
index c04acd6..d004bb7 100644
--- a/Tests/SwiftNetworkTests/SwiftNetworkQUICEarlyDataTests.swift
+++ b/Tests/SwiftNetworkTests/SwiftNetworkQUICEarlyDataTests.swift
@@ -413,15 +413,21 @@ final class SwiftNetworkQUICEarlyDataTests: NetTestCase {
                 let receiveExpectation = XCTestExpectation()
                 context.async {
                     Logger.test.info("Trying to read data")
-                    for _ in 0..<10 {
+                    func attemptServerRead() {
                         if pairedPathsArray.first?.transferPackets() == 0 {
-                            break
+                            // Wait for new writes from the client to be sent
+                            context.async {
+                                attemptServerRead()
+                            }
+                            return
                         }
+                        Logger.test.info("Trying to read data")
                         if let readData = serverUpperHarness?.upperHarnesses.first?.read() {
                             XCTAssertEqual(readData, dataToSend)
                             receiveExpectation.fulfill()
                         }
                     }
+                    attemptServerRead()
                 }
                 wait(for: [receiveExpectation], timeout: 5.0)
             }
diff --git a/Tests/SwiftNetworkTests/SwiftNetworkQUICHarnessTests.swift b/Tests/SwiftNetworkTests/SwiftNetworkQUICHarnessTests.swift
index 056a78f..6dba7d0 100644
--- a/Tests/SwiftNetworkTests/SwiftNetworkQUICHarnessTests.swift
+++ b/Tests/SwiftNetworkTests/SwiftNetworkQUICHarnessTests.swift
@@ -293,6 +293,17 @@ final class SwiftNetworkQUICHarnessTests: NetTestCase {
         )
     }
 
+    func testQUIC1000BidirectionalStreamsEcho1k() {
+        let serverOptions = QUICProtocol.options()
+        serverOptions.connectionOptions.initialMaxStreamsBidirectional = 1000
+        QUICTestHarness().runQUICTest(
+            streamCount: 1000,
+            blockSize: 1000,
+            blockCount: 1,
+            serverOptions: serverOptions
+        )
+    }
+
     func testQUICConnectionCloseError() {
         QUICTestHarness().runQUICTest(
             streamCount: 2,