[fpc-pascal] How to detect connection status of a socket

Ewald ewald at yellowcouch.org
Sun Apr 28 23:58:43 CEST 2013

On 22 Apr 2013, at 15:10, Xiangrong Fang wrote:
> 1) fpsend() just pass data to the OS's socket layer without try to determine if the connection is still alive, right?

I suppose, but there exists an error code that might come in handy: ENotConn (see http://linux.die.net/man/2/send), which is returned by send().

> 2) is it normal that in BLOCK mode, recv returns 0?  i.e. if I receive a 0 from fprecv(), I can say that the connection is closed by the other end (if there is no detectable socketerror), right?

Yes, if recv() return 0, it mens the client disconnected. If it returns -1, errno will be set. From http://linux.die.net/man/2/recv (see `return value`):
	"These calls return the number of bytes received, or -1 if an error occurred. The return value will be 0 when the peer has performed an orderly shutdown."

Note that even in non-blocking mode, 0 means the socket is closed. If you received no data yet, you will get -1 as a return value and errno will be set to EAgain of EWouldBlock (see the link above).

Does this help or am I completely talking besides the point?


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