Common mistakes

Common mistakes

Table 9.4 lists the mistakes most often made when programming sockets.

Table 9.4. Common mistakes when working with sockets

Problem	Cause	Fix
the client and server "hang", no data arrives	a StreamWriter without AutoFlush keeps the line in its buffer	AutoFlush = true or await writer.FlushAsync()
the first line on the server starts with an invisible character	Encoding.UTF8 in a StreamWriter sends a BOM	new UTF8Encoding(false)
messages "stick together" or arrive in pieces	TCP is a byte stream without message boundaries	a \n delimiter, a length prefix, ReadExactlyAsync
SocketException 10061 actively refused	the server is not running, or the port or address is different	start the server, check the port with Get-NetTCPConnection
cannot connect from another computer	the server listens on 127.0.0.1 or the firewall blocks it	IPAddress.Any, a firewall rule for the private network
the server serves only one client	the accept loop waits for the exchange with the client to finish	a separate ServeAsync task for each client
interleaved messages in a broadcast	several tasks write to the stream simultaneously	SemaphoreSlim or a per-client message queue
the Windows Forms window does not respond	synchronous Read, Accept on the UI thread	asynchronous methods with await