Ensure that only byte values are sent by sockets and web sockets

sdk/lib/io/common.dart

Index: sdk/lib/io/common.dart
diff --git a/sdk/lib/io/common.dart b/sdk/lib/io/common.dart
index 31ce72b6c9232096c18104b1a907dc6bc4204972..ba5f07d9908b39f1ef811a97624ec53c3b1ac38d 100644
--- a/sdk/lib/io/common.dart
+++ b/sdk/lib/io/common.dart
@@ -100,7 +100,7 @@ class _BufferAndStart {
 // Only builtin Lists can be serialized through. If user-defined Lists
 // get here, the contents is copied to a Uint8List. This has the added
 // benefit that it is faster to access from the C code as well.
-_BufferAndStart _ensureFastAndSerializableBuffer(
+_BufferAndStart _ensureFastAndSerializableData(
     List buffer, int start, int end) {
   if (buffer is Uint8List ||
       buffer is Int8List ||
@@ -131,6 +131,28 @@ _BufferAndStart _ensureFastAndSerializableBuffer(
 }
 
 
+_BufferAndStart _ensureFastAndSerializableByteData(
+    List buffer, int start, int end) {
+  if (buffer is Uint8List) {
+    return new _BufferAndStart(buffer, start);
+  }
+  int length = end - start;
+  var newBuffer = new Uint8List(length);
+  int j = start;
+  for (int i = 0; i < length; i++) {
+    int value = buffer[j];
+    if (value is! int ||
+        value < 0 || 255 < value) {
+      throw new ArgumentError(
+          "List element is not a byte value (value $value at index $j)");
+    }
+    newBuffer[i] = value;
+    j++;
+  }
+  return new _BufferAndStart(newBuffer, 0);
+}
+
+
 // TODO(ager): The only reason for the class here is that
 // we cannot patch a top-level function.
 class _BufferUtils {