Use Int32x4List to optimize mask/unmask websockets.

sdk/lib/io/websocket_impl.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 const String _webSocketGUID = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
 
 // Matches _WebSocketOpcode.
 class _WebSocketMessageType {
@@ skipping 151 matching lines @@
         }
       } else {
         if (_state == MASK) {
           _maskingBytes[4 - _remainingMaskingKeyBytes--] = byte;
           if (_remainingMaskingKeyBytes == 0) {
             _maskDone();
           }
         } else {
           assert(_state == PAYLOAD);
           // The payload is not handled one byte at a time but in blocks.
-          int payload = min(lastIndex - index, _remainingPayloadBytes);
-          _remainingPayloadBytes -= payload;
+          int payloadLength = min(lastIndex - index, _remainingPayloadBytes);
+          _remainingPayloadBytes -= payloadLength;
           // Unmask payload if masked.
           if (_masked) {
-            for (int i = index; i < index + payload; i++) {
-              buffer[i] ^= _maskingBytes[_unmaskingIndex++ & 3];
-            }
+            _unmask(index, payloadLength, buffer);
           }
           // Control frame and data frame share _payload builder.
-          _payload.add(new Uint8List.view(buffer.buffer, index, payload));
-          index += payload;
+          _payload.add(new Uint8List.view(buffer.buffer, index, payloadLength));
+          index += payloadLength;
           if (_isControlFrame()) {
             if (_remainingPayloadBytes == 0) _controlFrameEnd();
           } else {
             if (_currentMessageType != _WebSocketMessageType.TEXT &&
                 _currentMessageType != _WebSocketMessageType.BINARY) {
                 throw new WebSocketException("Protocol error");
             }
             if (_remainingPayloadBytes == 0) _messageFrameEnd();
           }
 
           // Hack - as we always do index++ below.
           index--;
         }
       }
 
       // Move to the next byte.
       index++;
     }
   }
 
+  void _unmask(int index, int payload, Uint8List buffer) {

[kasperl, 2014/01/29 09:47:37]

payload -> length

[Anders Johnsen, 2014/01/29 10:19:04]

Done.

+    const int BLOCK_SIZE = 16;
+    // Start by alligning to 16 bytes.

[kasperl, 2014/01/29 09:47:37]

alligning -> aligning

[Anders Johnsen, 2014/01/29 10:19:04]

Done.

+    final int startOffset = min(BLOCK_SIZE - (index & 15), payload);

[kasperl, 2014/01/29 09:47:37]

Maybe replace this whole min computation by checking if the length is less than
BLOCK_SIZE. If it is, you can skip the alignment part and the block handling
part completely.

[Anders Johnsen, 2014/01/29 10:19:04]

Done.

+    int end = index + startOffset;
+    for (int i = index; i < end; i++) {
+      buffer[i] ^= _maskingBytes[_unmaskingIndex++ & 3];
+    }
+    index += startOffset;
+    payload -= startOffset;
+    final int blockCount = payload ~/ BLOCK_SIZE;
+    if (blockCount > 0) {
+      // Create mask block.
+      int mask = 0;
+      for (int i = 3; i >= 0; i--) {

[kasperl, 2014/01/29 09:47:37]

Here's an idea: Why don't you turn masking bytes into a Uint8List and make it
contain the following bytes:

   [ m0, m1, m2, m3,
     m0, m1, m2, m3,
     m0, m1, m2, m3,
     m0, m1, m2, m3,
     
     m1, m2, m3, m0,
     m1, m2, m3, m0,
     m1, m2, m3, m0,
     m1, m2, m3, m0,

     m2, m3, m0, m1,
     m2, m3, m0, m1,
     m2, m3, m0, m1,
     m2, m3, m0, m1,

     m3, m0, m1, m2,
     m3, m0, m1, m2,
     m3, m0, m1, m2,
     m3, m0, m1, m2 ]

You can fill this information in when you read the masking bytes before calling
maskDone(). If you create a Int32x4List view of these bytes and fetch the block
mask from it using:

   Int32x4 blockMask = _maskingBlocks[_unmaskingIndex];

Feel free to experiment with this in another CL.

[Anders Johnsen, 2014/01/29 10:19:04]

While the idea is very cool, I'm afraid the build-overhead may be too expensive
in the case of small packages. I'll keep as is, and investigate further in
another Cl.

+        mask = (mask << 8) | _maskingBytes[(_unmaskingIndex + i) & 3];
+      }
+      Int32x4 blockMask = new Int32x4(mask, mask, mask, mask);
+      Int32x4List blockBuffer = new Int32x4List.view(
+          buffer.buffer, index, blockCount);
+      for (int i = 0; i < blockBuffer.length; i++) {
+        blockBuffer[i] ^= blockMask;
+      }
+      final int bytes = blockCount * BLOCK_SIZE;
+      index += bytes;
+      payload -= bytes;
+    }
+    // Handle end.
+    end = index + payload;
+    for (int i = index; i < end; i++) {
+      buffer[i] ^= _maskingBytes[_unmaskingIndex++ & 3];
+    }
+  }
+
   void _lengthDone() {
     if (_masked) {
       if (!_serverSide) {
         throw new WebSocketException("Received masked frame from server");
       }
       _state = MASK;
     } else {
       if (_serverSide) {
         throw new WebSocketException("Received unmasked frame from client");
       }
@@ skipping 310 matching lines @@
     // Write the length in network byte order into the header.
     for (int i = 0; i < lengthBytes; i++) {
       header[index++] = dataLength >> (((lengthBytes - 1) - i) * 8) & 0xFF;
     }
     if (mask) {
       header[1] |= 1 << 7;
       var maskBytes = _IOCrypto.getRandomBytes(4);
       header.setRange(index, index + 4, maskBytes);
       index += 4;
       if (data != null) {
-        var list;
+        Uint8List list;
         // If this is a text message just do the masking inside the
         // encoded data.
-        if (opcode == _WebSocketOpcode.TEXT) {
+        if (opcode == _WebSocketOpcode.TEXT && data is Uint8List) {
           list = data;
         } else {
-          list = new Uint8List(data.length);
+          if (data is Uint8List) {
+            list = new Uint8List.fromList(data);
+          } else {
+            list = new Uint8List(data.length);
+            for (int i = 0; i < data.length; i++) {
+              if (data[i] < 0 || 255 < data[i]) {
+                throw new ArgumentError(
+                    "List element is not a byte value "
+                    "(value ${data[i]} at index $i)");
+              }
+              list[i] = data[i];
+            }
+          }
         }
-        if (data is Uint8List) {
-          for (int i = 0; i < data.length; i++) {
-            list[i] = data[i] ^ maskBytes[i & 3];
+        const int BLOCK_SIZE = 16;
+        int blockCount = list.length ~/ BLOCK_SIZE;
+        if (blockCount > 0) {
+          // Create mask block.
+          int mask = 0;
+          for (int i = 3; i >= 0; i--) {
+            mask = (mask << 8) | maskBytes[i];
           }
-        } else {
-          for (int i = 0; i < data.length; i++) {
-            if (data[i] < 0 || 255 < data[i]) {
-              throw new ArgumentError(
-                  "List element is not a byte value "
-                  "(value ${data[i]} at index $i)");
-            }
-            list[i] = data[i] ^ maskBytes[i & 3];
+          Int32x4 blockMask = new Int32x4(mask, mask, mask, mask);
+          Int32x4List blockBuffer = new Int32x4List.view(
+              list.buffer, 0, blockCount);
+          for (int i = 0; i < blockBuffer.length; i++) {
+            blockBuffer[i] ^= blockMask;
           }
         }
+        // Handle end.
+        for (int i = blockCount * BLOCK_SIZE; i < list.length; i++) {
+          list[i] ^= maskBytes[i & 3];
+        }
         data = list;
       }
     }
     assert(index == headerSize);
     if (data == null) {
       return [header];
     } else {
       return [header, data];
     }
   }
@@ skipping 335 matching lines @@
            (code < WebSocketStatus.NORMAL_CLOSURE ||
             code == WebSocketStatus.RESERVED_1004 ||
             code == WebSocketStatus.NO_STATUS_RECEIVED ||
             code == WebSocketStatus.ABNORMAL_CLOSURE ||
             (code > WebSocketStatus.INTERNAL_SERVER_ERROR &&
              code < WebSocketStatus.RESERVED_1015) ||
             (code >= WebSocketStatus.RESERVED_1015 &&
              code < 3000));
   }
 }