Cow-box WebSocketFrame.

Motivation:

WebSocketFrameDecoder makes an allocation due to WebSocketFrame not fitting in a
existential. We should reduce this overhead.

Modifications:

Moved data and extensionData into a cow-box and reorder fields to more efficiently
pack them.

Result:

WebSocketFrame is now 14 bytes, down from 55.

Sources/NIOWebSocket/WebSocketFrame.swift

@@ -106,6 +106,19 @@ extension WebSocketMaskingKey: Collection {
 
 /// A structured representation of a single WebSocket frame.
 public struct WebSocketFrame {
+    private var _storage: WebSocketFrame._Storage
+
+    /// The masking key, if any.
+    ///
+    /// A masking key is used to prevent specific byte sequences from appearing in the network
+    /// stream. This is primarily used by entities like browsers, but should be used any time it
+    /// is possible for a malicious user to control the data that appears in a websocket stream.
+    ///
+    /// If this value is `nil`, and this frame was *received from* the network, the data in `data`
+    /// is not masked. If this value is `nil`, and this frame is being *sent to* the network, the
+    /// data in `data` will not be masked.
+    public var maskKey: WebSocketMaskingKey? = nil
+
     /// Rather than unpack all the fields from the first byte, and thus take up loads
     /// of storage in the structure, we keep them in their packed form in this byte and
     /// use computed properties to unpack them.
@@ -170,30 +183,39 @@ public struct WebSocketFrame {
         return data.readableBytes + (extensionData?.readableBytes ?? 0)
     }
 
-    /// The masking key, if any.
-    ///
-    /// A masking key is used to prevent specific byte sequences from appearing in the network
-    /// stream. This is primarily used by entities like browsers, but should be used any time it
-    /// is possible for a malicious user to control the data that appears in a websocket stream.
-    ///
-    /// If this value is `nil`, and this frame was *received from* the network, the data in `data`
-    /// is not masked. If this value is `nil`, and this frame is being *sent to* the network, the
-    /// data in `data` will not be masked.
-    public var maskKey: WebSocketMaskingKey? = nil
-
     /// The application data.
     ///
     /// On frames received from the network, this data is not necessarily unmasked. This is to provide as much
     /// information as possible. If unmasked data is desired, either use the computed `unmaskedData` property to
     /// obtain it, or transform this data directly by calling `data.unmask(maskKey)`.
-    public var data: ByteBuffer
+    public var data: ByteBuffer {
+        get {
+            return self._storage.data
+        }
+        set {
+            if !isKnownUniquelyReferenced(&self._storage) {
+                self._storage = _Storage(copying: self._storage)
+            }
+            self._storage.data = newValue
+        }
+    }
 
     /// The extension data, if any.
     ///
     /// On frames received from the network, this data is not necessarily unmasked. This is to provide as much
     /// information as possible. If unmasked data is desired, either use the computed `unmaskedExtensionData` property to
     /// obtain it, or transform this data directly by calling `extensionData.unmask(maskKey)`.
-    public var extensionData: ByteBuffer? = nil
+    public var extensionData: ByteBuffer? {
+        get {
+            return self._storage.extensionData
+        }
+        set {
+            if !isKnownUniquelyReferenced(&self._storage) {
+                self._storage = _Storage(copying: self._storage)
+            }
+            self._storage.extensionData = newValue
+        }
+    }
 
     /// The unmasked application data.
     ///
@@ -234,7 +256,7 @@ public struct WebSocketFrame {
     /// - parameters:
     ///     - allocator: The `ByteBufferAllocator` to use when editing the empty buffers.
     public init(allocator: ByteBufferAllocator) {
-        self.data = allocator.buffer(capacity: 0)
+        self._storage = .init(data: allocator.buffer(capacity: 0), extensionData: nil)
     }
 
     /// Create a `WebSocketFrame` with the given properties.
@@ -251,8 +273,7 @@ public struct WebSocketFrame {
     public init(fin: Bool = false, rsv1: Bool = false, rsv2: Bool = false, rsv3: Bool = false,
                 opcode: WebSocketOpcode = .continuation, maskKey: WebSocketMaskingKey? = nil,
                 data: ByteBuffer, extensionData: ByteBuffer? = nil) {
-        self.data = data
-        self.extensionData = extensionData
+        self._storage = .init(data: data, extensionData: extensionData)
         self.fin = fin
         self.rsv1 = rsv1
         self.rsv2 = rsv2
@@ -263,10 +284,33 @@ public struct WebSocketFrame {
 
     /// Create a `WebSocketFrame` from the underlying data representation.
     internal init(firstByte: UInt8, maskKey: WebSocketMaskingKey?, applicationData: ByteBuffer) {
+        self._storage = .init(data: applicationData, extensionData: nil)
         self.firstByte = firstByte
         self.maskKey = maskKey
-        self.data = applicationData
     }
 }
 
 extension WebSocketFrame: Equatable {}
+
+extension WebSocketFrame {
+    fileprivate class _Storage {
+        var data: ByteBuffer
+        var extensionData: ByteBuffer?
+
+        fileprivate init(data: ByteBuffer, extensionData: ByteBuffer?) {
+            self.data = data
+            self.extensionData = extensionData
+        }
+
+        fileprivate init(copying original: WebSocketFrame._Storage) {
+            self.data = original.data
+            self.extensionData = original.extensionData
+        }
+    }
+}
+
+extension WebSocketFrame._Storage: Equatable {
+    static func ==(lhs: WebSocketFrame._Storage, rhs: WebSocketFrame._Storage) -> Bool {
+        return lhs.data == rhs.data && lhs.extensionData == rhs.extensionData
+    }
+}

docker/docker-compose.1604.51.yaml

@@ -30,7 +30,7 @@ services:
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_holding_buffer_with_space=2010
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_new_buffer=4010
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_new_buffer_with_space=4010
-      - MAX_ALLOCS_ALLOWED_decode_1000_ws_frames=2000
+      - MAX_ALLOCS_ALLOWED_decode_1000_ws_frames=1000
       - SANITIZER_ARG=--sanitize=thread
 
   performance-test:

docker/docker-compose.1804.50.yaml

@@ -30,7 +30,7 @@ services:
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_holding_buffer_with_space=2010
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_new_buffer=4010
       - MAX_ALLOCS_ALLOWED_encode_1000_ws_frames_new_buffer_with_space=4010
-      - MAX_ALLOCS_ALLOWED_decode_1000_ws_frames=2000
+      - MAX_ALLOCS_ALLOWED_decode_1000_ws_frames=1000
 
   performance-test:
     image: swift-nio:18.04-5.0