Use ArrayBuffer in SseParser, deduplicate more logic

src/libraries/Common/src/System/Net/ArrayBuffer.cs

@@ -59,8 +59,7 @@ public ArrayBuffer(byte[] buffer)
 
         public void Dispose()
         {
-            _activeStart = 0;
-            _availableStart = 0;
+            DiscardAll();
 
             byte[] array = _bytes;
             _bytes = null!;
@@ -77,8 +76,7 @@ public void ClearAndReturnBuffer()
             Debug.Assert(_usePool);
             Debug.Assert(_bytes is not null);
 
-            _activeStart = 0;
-            _availableStart = 0;
+            DiscardAll();
 
             byte[] bufferToReturn = _bytes;
             _bytes = Array.Empty<byte>();
@@ -112,6 +110,12 @@ public void Discard(int byteCount)
             }
         }
 
+        public void DiscardAll()
+        {
+            _activeStart = 0;
+            _availableStart = 0;
+        }
+
         public void Commit(int byteCount)
         {
             Debug.Assert(byteCount <= AvailableLength);

src/libraries/Common/src/System/Text/Json/PooledByteBufferWriter.cs

@@ -33,7 +33,7 @@ public PooledByteBufferWriter(int initialCapacity, Stream stream) : this(initial
 
         public int Capacity => _buffer.Capacity;
 
-        public void Clear() => _buffer.Discard(_buffer.ActiveLength);
+        public void Clear() => _buffer.DiscardAll();
 
         public void ClearAndReturnBuffers() => _buffer.ClearAndReturnBuffer();
 

src/libraries/System.IO.Compression/src/System/IO/Compression/Zstandard/ZstandardStream.Decompress.cs

@@ -436,7 +436,7 @@ private void TryRewindStream(Stream stream)
             {
                 // Rewind the stream to the exact end of the compressed data
                 stream.Seek(-unconsumedBytes, SeekOrigin.Current);
-                _buffer.Discard(unconsumedBytes);
+                _buffer.DiscardAll();
             }
         }
 

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs

@@ -409,7 +409,7 @@ private async Task FlushOutgoingBytesAsync()
                 }
 
                 _lastPendingWriterShouldFlush = false;
-                _outgoingBuffer.Discard(_outgoingBuffer.ActiveLength);
+                _outgoingBuffer.DiscardAll();
             }
         }
 

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3RequestStream.cs

@@ -558,7 +558,7 @@ private async ValueTask WriteRequestContentAsync(ReadOnlyMemory<byte> buffer, Ca
                     await _stream.WriteAsync(_sendBuffer.ActiveMemory, cancellationToken).ConfigureAwait(false);
                     await _stream.WriteAsync(buffer, cancellationToken).ConfigureAwait(false);
 
-                    _sendBuffer.Discard(_sendBuffer.ActiveLength);
+                    _sendBuffer.DiscardAll();
 
                     _singleDataFrameWritten = true;
                 }
@@ -577,14 +577,14 @@ private async ValueTask WriteRequestContentAsync(ReadOnlyMemory<byte> buffer, Ca
                 await _stream.WriteAsync(_sendBuffer.ActiveMemory, cancellationToken).ConfigureAwait(false);
                 await _stream.WriteAsync(buffer, cancellationToken).ConfigureAwait(false);
 
-                _sendBuffer.Discard(_sendBuffer.ActiveLength);
+                _sendBuffer.DiscardAll();
             }
         }
 
         private ValueTask FlushSendBufferAsync(bool endStream, CancellationToken cancellationToken)
         {
             ReadOnlyMemory<byte> toSend = _sendBuffer.ActiveMemory;
-            _sendBuffer.Discard(toSend.Length);
+            _sendBuffer.DiscardAll();
             return _stream.WriteAsync(toSend, endStream, cancellationToken);
         }
 

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

@@ -1552,7 +1552,7 @@ private void Flush()
             ReadOnlySpan<byte> bytes = _writeBuffer.ActiveSpan;
             if (bytes.Length > 0)
             {
-                _writeBuffer.Discard(bytes.Length);
+                _writeBuffer.DiscardAll();
                 WriteToStream(bytes);
             }
         }
@@ -1562,7 +1562,7 @@ private ValueTask FlushAsync(bool async)
             ReadOnlyMemory<byte> bytes = _writeBuffer.ActiveMemory;
             if (bytes.Length > 0)
             {
-                _writeBuffer.Discard(bytes.Length);
+                _writeBuffer.DiscardAll();
                 return WriteToStreamAsync(bytes, async);
             }
             return default;
@@ -2080,7 +2080,7 @@ private void CompleteResponse()
                     Trace("Unexpected data on connection after response read.");
                 }
 
-                _readBuffer.Discard(_readBuffer.ActiveLength);
+                _readBuffer.DiscardAll();
                 _connectionClose = true;
             }
 

src/libraries/System.Net.Security/src/System/Net/Security/Pal.Android/SafeDeleteSslContext.cs

@@ -186,7 +186,7 @@ internal void ReadPendingWrites(ref ProtocolToken token)
                 }
 
                 token.SetPayload(_outputBuffer.ActiveSpan);
-                _outputBuffer.Discard(_outputBuffer.ActiveLength);
+                _outputBuffer.DiscardAll();
             }
         }
 

src/libraries/System.Net.Security/src/System/Net/Security/Pal.OSX/SafeDeleteSslContext.cs

@@ -319,7 +319,7 @@ internal void ReadPendingWrites(ref ProtocolToken token)
                 }
 
                 token.SetPayload(_outputBuffer.ActiveSpan);
-                _outputBuffer.Discard(_outputBuffer.ActiveLength);
+                _outputBuffer.DiscardAll();
             }
         }
 

src/libraries/System.Net.Security/src/System/Net/Security/TlsSession.OpenSsl.cs

@@ -92,10 +92,7 @@ partial void OnServerContextSet()
             _pendingFdSocket = null;
 
             // Discard any managed pre-fetch bytes; ownership transfers to the native BIO now.
-            if (_socketInBuffer.ActiveLength > 0)
-            {
-                _socketInBuffer.Discard(_socketInBuffer.ActiveLength);
-            }
+            _socketInBuffer.DiscardAll();
 
             _useFdMode = true;
         }

src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/PooledByteBufferWriter.cs

@@ -28,7 +28,7 @@ public Span<byte> GetSpan(int sizeHint = 0)
         public ReadOnlyMemory<byte> WrittenMemory => _buffer.ActiveMemory;
         public int Capacity => _buffer.Capacity;
         public int WrittenCount => _buffer.ActiveLength;
-        public void Reset() => _buffer.Discard(_buffer.ActiveLength);
+        public void Reset() => _buffer.DiscardAll();
         public void Dispose() => _buffer.Dispose();
     }
 }