Use ArrayBuffer for write buffer management in HttpConnection (#79525)

Author: MihaZupan

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ChunkedEncodingWriteStream.cs

@@ -11,6 +11,7 @@ internal sealed partial class HttpConnection : IDisposable
     {
         private sealed class ChunkedEncodingWriteStream : HttpContentWriteStream
         {
+            private static readonly byte[] s_crlfBytes = "\r\n"u8.ToArray();
             private static readonly byte[] s_finalChunkBytes = "0\r\n\r\n"u8.ToArray();
 
             public ChunkedEncodingWriteStream(HttpConnection connection) : base(connection)
@@ -31,12 +32,14 @@ public override void Write(ReadOnlySpan<byte> buffer)
                 }
 
                 // Write chunk length in hex followed by \r\n
-                connection.WriteHexInt32Async(buffer.Length, async: false).GetAwaiter().GetResult();
-                connection.WriteTwoBytesAsync((byte)'\r', (byte)'\n', async: false).GetAwaiter().GetResult();
+                ValueTask writeTask = connection.WriteHexInt32Async(buffer.Length, async: false);
+                Debug.Assert(writeTask.IsCompleted);
+                writeTask.GetAwaiter().GetResult();
+                connection.Write(s_crlfBytes);
 
                 // Write chunk contents followed by \r\n
                 connection.Write(buffer);
-                connection.WriteTwoBytesAsync((byte)'\r', (byte)'\n', async: false).GetAwaiter().GetResult();
+                connection.Write(s_crlfBytes);
             }
 
             public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken ignored)
@@ -62,11 +65,11 @@ static async ValueTask WriteChunkAsync(HttpConnection connection, ReadOnlyMemory
                 {
                     // Write chunk length in hex followed by \r\n
                     await connection.WriteHexInt32Async(buffer.Length, async: true).ConfigureAwait(false);
-                    await connection.WriteTwoBytesAsync((byte)'\r', (byte)'\n', async: true).ConfigureAwait(false);
+                    await connection.WriteAsync(s_crlfBytes).ConfigureAwait(false);
 
                     // Write chunk contents followed by \r\n
-                    await connection.WriteAsync(buffer, async: true).ConfigureAwait(false);
-                    await connection.WriteTwoBytesAsync((byte)'\r', (byte)'\n', async: true).ConfigureAwait(false);
+                    await connection.WriteAsync(buffer).ConfigureAwait(false);
+                    await connection.WriteAsync(s_crlfBytes).ConfigureAwait(false);
                 }
             }
 
@@ -75,7 +78,16 @@ public override Task FinishAsync(bool async)
                 // Send 0 byte chunk to indicate end, then final CrLf
                 HttpConnection connection = GetConnectionOrThrow();
                 _connection = null;
-                return connection.WriteBytesAsync(s_finalChunkBytes, async);
+
+                if (async)
+                {
+                    return connection.WriteAsync(s_finalChunkBytes).AsTask();
+                }
+                else
+                {
+                    connection.Write(s_finalChunkBytes);
+                    return Task.CompletedTask;
+                }
             }
         }
     }

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ContentLengthWriteStream.cs

@@ -28,9 +28,6 @@ public override void Write(ReadOnlySpan<byte> buffer)
                     throw new HttpRequestException(SR.net_http_content_write_larger_than_content_length);
                 }
 
-                // Have the connection write the data, skipping the buffer. Importantly, this will
-                // force a flush of anything already in the buffer, i.e. any remaining request headers
-                // that are still buffered.
                 HttpConnection connection = GetConnectionOrThrow();
                 Debug.Assert(connection._currentRequest != null);
                 connection.Write(buffer);
@@ -45,12 +42,9 @@ public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationTo
                     return ValueTask.FromException(new HttpRequestException(SR.net_http_content_write_larger_than_content_length));
                 }
 
-                // Have the connection write the data, skipping the buffer. Importantly, this will
-                // force a flush of anything already in the buffer, i.e. any remaining request headers
-                // that are still buffered.
                 HttpConnection connection = GetConnectionOrThrow();
                 Debug.Assert(connection._currentRequest != null);
-                return connection.WriteAsync(buffer, async: true);
+                return connection.WriteAsync(buffer);
             }
 
             public override Task FinishAsync(bool async)