I was writing an iOS app to connect to a socket server. When I ran on the simulator, I kept getting error and disconnected immediately. The Error Code was 57, and Error Domain is NSPOSIXErrorDomain. I was scratching my head for awhile because I knew that I tested it and it was working when I first time running it.
After an hour of research, I found out the reason. When changing the network, I have to restart the iOS simulator. After I restarted the simulator, the socket connection was working again. FML! LOL!