Fix problem with socket input stream on MacOS when reading from tty.

runtime/bin/socket_stream_impl.dart

 // Copyright (c) 2012, 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.
 
 class _SocketInputStream implements SocketInputStream {
   _SocketInputStream(Socket socket) : _socket = socket {
     _socket.closeHandler = _closeHandler;
   }
 
   List<int> read([int len]) {
     int bytesToRead = available();
     if (bytesToRead == 0) return null;
     if (len !== null) {
       if (len <= 0) {
         throw new StreamException("Illegal length $len");
       } else if (bytesToRead > len) {
         bytesToRead = len;
       }
     }
     ByteArray buffer = new ByteArray(bytesToRead);
     int bytesRead = _socket.readList(buffer, 0, bytesToRead);
-    if (bytesRead < bytesToRead) {
+    if (bytesRead == 0) {
+      // On MacOS when reading from a tty Ctrl-D will result in one
+      // byte reported as available. Attempting to read it out will
+      // result in zero bytes read. When that happens there is no data
+      // which is indicated by a null return value.
+      return null;
+    } else if (bytesRead < bytesToRead) {
       ByteArray newBuffer = new ByteArray(bytesRead);
       newBuffer.setRange(0, bytesRead, buffer);
       return newBuffer;
     } else {
       return buffer;
     }
   }
 
   int readInto(List<int> buffer, int offset, int len) {
     if (offset === null) offset = 0;
@@ skipping 147 matching lines @@
     if (_streamErrorHandler != null) _streamErrorHandler();
   }
 
   Socket _socket;
   _BufferList _pendingWrites;
   var _noPendingWriteHandler;
   var _streamErrorHandler;
   bool _closing = false;
   bool _closed = false;
 }