From 206b7c712d08723010d74cc2322c1a0c47472c3c Mon Sep 17 00:00:00 2001
From: George Barnett <gbarnett@apple.com>
Date: Thu, 2 Jul 2026 10:40:46 +0100
Subject: [PATCH] Avoid allocating in FrameArray empty init

`FrameArray()` sets the minimum capacity to one which allocates a
backing storage. This is a foot gun which is already triggered on many
code paths: an empty `FrameArray()` is initialized only to be assigned
over shortly after, resulting in an avoidable temporary allocation.
This pattern is avoidable but takes care, however a simpler solution
which removes the foot gun altogether is to not request capacity in
`FrameArray()`. When capacity is known users should use
`FrameArray(capacity:)` instead.

This change reduces allocations by ~7% and CPU cycles by ~5% in the QUIC
benchmarks I ran.
---
 Sources/SwiftNetwork/Protocols/FrameArray.swift | 2 +-
 Sources/SwiftNetwork/QUIC/QUICConnection.swift  | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/Sources/SwiftNetwork/Protocols/FrameArray.swift b/Sources/SwiftNetwork/Protocols/FrameArray.swift
index 5bbb353..90e59cd 100644
--- a/Sources/SwiftNetwork/Protocols/FrameArray.swift
+++ b/Sources/SwiftNetwork/Protocols/FrameArray.swift
@@ -36,7 +36,7 @@ public struct FrameArray: ~Copyable {
     }
 
     public init() {
-        self.frames = NetworkUniqueDeque<Frame>(minimumCapacity: 1)
+        self.frames = NetworkUniqueDeque<Frame>()
     }
 
     public init(capacity: Int) {
diff --git a/Sources/SwiftNetwork/QUIC/QUICConnection.swift b/Sources/SwiftNetwork/QUIC/QUICConnection.swift
index 8ff817c..557315d 100644
--- a/Sources/SwiftNetwork/QUIC/QUICConnection.swift
+++ b/Sources/SwiftNetwork/QUIC/QUICConnection.swift
@@ -3196,11 +3196,14 @@ public final class QUICConnection: ManyToManyApplicationStreamProtocol,
         else {
             return false
         }
-        var datagramBatch = FrameArray()
+
+        var datagramBatch: FrameArray
         if self.flowControlState.pendingOutboundBytesToSend > 0 && availableCongestionWindow > 0 {
             datagramBatch = buildOutboundFrameBatch(
                 availableCongestionWindow: (availableCongestionWindow - totalSendBytes)
             )
+        } else {
+            datagramBatch = FrameArray()
         }
 
         // Sending on the current path.