Don't try to call read, if len i 0.

runtime/bin/socket.cc

 // 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.
 
 #include "bin/io_buffer.h"
 #include "bin/isolate_data.h"
 #include "bin/socket.h"
 #include "bin/dartutils.h"
 #include "bin/thread.h"
 #include "bin/utils.h"
@@ skipping 93 matching lines @@
     if (short_socket_reads) {
       length = (length + 1) / 2;
     }
     uint8_t* buffer = NULL;
     Dart_Handle result = IOBuffer::Allocate(length, &buffer);
     if (Dart_IsError(result)) Dart_PropagateError(result);
     ASSERT(buffer != NULL);
     intptr_t bytes_read = Socket::Read(socket, buffer, length);
     if (bytes_read == length) {
       Dart_SetReturnValue(args, result);
-    } else if (bytes_read < length) {
+    } else if (bytes_read > 0) {
+      uint8_t* new_buffer = NULL;
+      Dart_Handle new_result = IOBuffer::Allocate(bytes_read, &new_buffer);
+      if (Dart_IsError(new_result)) Dart_PropagateError(new_result);
+      ASSERT(new_buffer != NULL);
+      memmove(new_buffer, buffer, bytes_read);
+      Dart_SetReturnValue(args, new_result);
+    } else if (bytes_read == 0) {
       // On MacOS when reading from a tty Ctrl-D will result in reading one
       // less byte then reported as available.
-      if (bytes_read == 0) {
-        Dart_SetReturnValue(args, Dart_Null());
-      } else {
-        uint8_t* new_buffer = NULL;
-        Dart_Handle new_result = IOBuffer::Allocate(bytes_read, &new_buffer);
-        if (Dart_IsError(new_result)) Dart_PropagateError(new_result);
-        ASSERT(new_buffer != NULL);
-        memmove(new_buffer, buffer, bytes_read);
-        Dart_SetReturnValue(args, new_result);
-      }
+      Dart_SetReturnValue(args, Dart_Null());
     } else {
       ASSERT(bytes_read == -1);
       Dart_SetReturnValue(args, DartUtils::NewDartOSError());
     }
   } else {
     OSError os_error(-1, "Invalid argument", OSError::kUnknown);
     Dart_Handle err = DartUtils::NewDartOSError(&os_error);
     if (Dart_IsError(err)) Dart_PropagateError(err);
     Dart_SetReturnValue(args, err);
   }
@@ skipping 551 matching lines @@
 intptr_t Socket::GetSocketIdNativeField(Dart_Handle socket_obj) {
   intptr_t socket = 0;
   Dart_Handle err =
       Dart_GetNativeInstanceField(socket_obj, kSocketIdNativeField, &socket);
   if (Dart_IsError(err)) Dart_PropagateError(err);
   return socket;
 }
 
 }  // namespace bin
 }  // namespace dart