From 6adc5a55e4b90c2206e4d31bcc170597530554db Mon Sep 17 00:00:00 2001
From: Stephen Toub <stoub@microsoft.com>
Date: Wed, 20 Nov 2024 18:27:27 -0500
Subject: [PATCH 1/2] Fix PooledByteBufferWriter handling of sizeHint <= 0

---
 .../PooledByteBufferWriter.cs                 |  4 +--
 .../tests/SseFormatterTests.cs                | 30 +++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/PooledByteBufferWriter.cs b/src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/PooledByteBufferWriter.cs
index 81e5070b765d0..3258ded10da37 100644
--- a/src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/PooledByteBufferWriter.cs
+++ b/src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/PooledByteBufferWriter.cs
@@ -14,13 +14,13 @@ internal sealed class PooledByteBufferWriter : IBufferWriter<byte>, IDisposable
 
         public Memory<byte> GetMemory(int sizeHint = 0)
         {
-            _buffer.EnsureAvailableSpace(sizeHint);
+            _buffer.EnsureAvailableSpace(Math.Max(sizeHint, 1));
             return _buffer.AvailableMemory;
         }
 
         public Span<byte> GetSpan(int sizeHint = 0)
         {
-            _buffer.EnsureAvailableSpace(sizeHint);
+            _buffer.EnsureAvailableSpace(Math.Max(sizeHint, 1));
             return _buffer.AvailableSpan;
         }
 
diff --git a/src/libraries/System.Net.ServerSentEvents/tests/SseFormatterTests.cs b/src/libraries/System.Net.ServerSentEvents/tests/SseFormatterTests.cs
index a21f74f8cacb2..a71acf2099848 100644
--- a/src/libraries/System.Net.ServerSentEvents/tests/SseFormatterTests.cs
+++ b/src/libraries/System.Net.ServerSentEvents/tests/SseFormatterTests.cs
@@ -4,6 +4,7 @@
 using System.Buffers;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Runtime.CompilerServices;
 using System.Text;
 using System.Text.Json;
@@ -117,6 +118,35 @@ async IAsyncEnumerable<SseItem<string>> GetItemsAsync([EnumeratorCancellation] C
             }
         }
 
+        [Fact]
+        public static async Task WriteLargeItems_DataWrittenSuccessfully()
+        {
+            const int NumberOfItems = 10;
+            byte[] expected = Encoding.UTF8.GetBytes(string.Concat(Enumerable.Repeat("This is a test. This is only a test.", 100)));
+
+            MemoryStream memoryStream = new();
+            await SseFormatter.WriteAsync(GetBuffersAsync(), memoryStream, (item, writer) => writer.Write(item.Data));
+
+            memoryStream.Position = 0;
+            int count = 0;
+            foreach (SseItem<byte[]> item in SseParser.Create(memoryStream, (eventType, data) => data.ToArray()).Enumerate())
+            {
+                Assert.Equal(expected, item.Data);
+                count++;
+            }
+
+            Assert.Equal(NumberOfItems, count);
+
+            async IAsyncEnumerable<SseItem<byte[]>> GetBuffersAsync()
+            {
+                await Task.Yield();
+                for (int i = 0; i < NumberOfItems; i++)
+                {
+                    yield return new SseItem<byte[]>(expected);
+                }
+            }
+        }
+
         [Fact]
         public static async Task WriteAsync_ParserCanRoundtripJsonEvents()
         {

From 87107e401583ba6d2ecd46931962dd14d7d43e0e Mon Sep 17 00:00:00 2001
From: Stephen Toub <stoub@microsoft.com>
Date: Wed, 20 Nov 2024 18:41:31 -0500
Subject: [PATCH 2/2] Add MinimumBufferSize constant and update usage

---
 .../System/Net/ServerSentEvents/PooledByteBufferWriter.cs  | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/PooledByteBufferWriter.cs b/src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/PooledByteBufferWriter.cs
index 3258ded10da37..15df82ba2f2ce 100644
--- a/src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/PooledByteBufferWriter.cs
+++ b/src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/PooledByteBufferWriter.cs
@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Buffers;
@@ -8,19 +8,20 @@ namespace System.Net.ServerSentEvents
 {
     internal sealed class PooledByteBufferWriter : IBufferWriter<byte>, IDisposable
     {
+        private const int MinimumBufferSize = 256;
         private ArrayBuffer _buffer = new(initialSize: 256, usePool: true);
 
         public void Advance(int count) => _buffer.Commit(count);
 
         public Memory<byte> GetMemory(int sizeHint = 0)
         {
-            _buffer.EnsureAvailableSpace(Math.Max(sizeHint, 1));
+            _buffer.EnsureAvailableSpace(Math.Max(sizeHint, MinimumBufferSize));
             return _buffer.AvailableMemory;
         }
 
         public Span<byte> GetSpan(int sizeHint = 0)
         {
-            _buffer.EnsureAvailableSpace(Math.Max(sizeHint, 1));
+            _buffer.EnsureAvailableSpace(Math.Max(sizeHint, MinimumBufferSize));
             return _buffer.AvailableSpan;
         }