Error Dictionary Keys
Networking-related keys that may be available in a CFErrorRef object’s userInfo dictionary.
Overview
Many network functions return CFErrorRef objects. When the error object’s domain is kCFErrorDomainCFNetwork, you can query the object for additional information.
For example:
if (CFEqual(CFErrorGetDomain(err), kCFErrorDomainCFNetwork) && CFErrorGetCode(err) == kCFHostErrorUnknown) {
CFDictionaryRef userInfo = CFErrorCopyUserInfo(err);
CFNumberRef number = (CFNumberRef) CFDictionaryGetValue(userInfo, kCFGetAddrInfoFailureKey);
...
CFRelease(userInfo);
}