Start better error reporting for sockets

runtime/bin/utils.h

 // 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.
 
 #ifndef BIN_UTILS_H_
 #define BIN_UTILS_H_
 
 #include <stdlib.h>
 #include <string.h>
 
 #include "include/dart_api.h"
 #include "platform/globals.h"
 
 class OSError {
  public:
+  enum SubSystem {
+    kSystem,
+    kGetAddressInfo,
+    kUnknown = -1
+  };
+
   OSError();
-  OSError(int code, char* message) {
+  OSError(int code, const char* message, SubSystem sub_system) {
+    sub_system_ = sub_system;
     code_ = code;
+    message_ = NULL;  // SetMessage will free existing message.
     SetMessage(message);
   }
   virtual ~OSError() { free(message_); }
 
+  SubSystem sub_system() { return sub_system_; }
+  void set_sub_system(SubSystem sub_system) { sub_system_ = sub_system; }
   int code() { return code_; }
   void set_code(int code) { code_ = code; }
   char* message() { return message_; }
-  void SetMessage(char* message) {
+  void SetMessage(const char* message) {
     free(message_);
     if (message == NULL) {
       message_ = NULL;
     } else {
       message_ = strdup(message);
     }
   }
 
  private:
+  SubSystem sub_system_;
   int code_;
   char* message_;
 
   DISALLOW_COPY_AND_ASSIGN(OSError);
 };
 
 #endif  // BIN_UTILS_H_