CODEWITHSUNDEEP
c++linuxsocketstcp
jpoulsen
jpoulsen

Reputation: 23

c++ check for TCP window full?

I am writing a c++ server application running on Linux. An iOS client app opens a TCP connection to the server, and the server starts sending messages on the connection. When the iOS app is put in the background, e.g. by the user switching to another app, the app stops reading data from the socket, but the socket is still open in iOS. The server keeps sending until the buffer window is full, and then hangs in the send() call. Is there a way to detect that the send() call will hang before calling? Or a way to get out of the call, when it hangs, e.g. setting a timeout?

Upvotes: 1

Views: 639

Answers (3)

Sam Varshavchik
Sam Varshavchik

Reputation: 118300

You can put the sending socket in non-blocking mode.

Use fcntl() to F_SETFL the O_NONBLOCK flag on the socket.

Your properly-written code should already be checking the return value from send(), since even with blocking sockets send() may indicate that fewer bytes were written than were requested.

In non-blocking mode, send() will simply return immediately, with a return value of -1 and errno equal to EAGAIN or EWOULDBLOCK. Then, use poll() or select() to check when the socket can be written to next.

Upvotes: 1

doron
doron

Reputation: 28872

You can use a simple select or poll with a zero timeout and your single socket as a write file descriptor/handle.

Upvotes: 0

user207421
user207421

Reputation: 310869

Put the socket into non-blocking mode and detect EAGAIN/EWOULDBLOCK.

Upvotes: 0

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