Start better error reporting for sockets

runtime/bin/utils.h

Index: runtime/bin/utils.h
diff --git a/runtime/bin/utils.h b/runtime/bin/utils.h
index f8f77661a257d194abb0265847fa88755b467a40..7f0e41fa61d080a08e1ebb556b5a2f8818c0958f 100644
--- a/runtime/bin/utils.h
+++ b/runtime/bin/utils.h
@@ -13,17 +13,27 @@
 
 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;
@@ -33,6 +43,7 @@ class OSError {
   }
 
  private:
+  SubSystem sub_system_;
   int code_;
   char* message_;