Timeout implementation for connections.

[Ali-Nasrolahi]

Objective

Automatically closing a connection, which becomes stalled for some reason. Fixes MortezaBashsiz/nipovpn#79

Implementation Details

Before every read/write operation, a timer (deadline_timer) gets started/reseted, and after each successful I/O; the timer gets cancelled. When timer's handlers called ,in case of an expiration, it closes associated socket with the connection; by doing so, any blocking I/O on respected socket will be interrupted.

This patch only addresses TCPConnection and TCPClient classes' read and write methods. The underlying implementation is identical for both classes.

Test

For testing, I did following scenarios while timeout is specified:

• Grabbing www.google.com using curl to check to ensure no data transfer issue.
• telnet to agent's socket and waiting to be closed by timeout.
• Using a simple python TCP socket as a destination server and never sending any data. Which caused the connection to be timeout-ed.

My tests are not addressing every block of read and write code, therefore this patch should be tested further to ensure stability.

About the diffs

Timeout configuration is identical to timeWait and uses similar value range.
I have implemented three main method to handle the timer: resetTimeout, cancelTimeout and onTimeout. And few other minor changes.

Please, let me know of any issue/suggestion :)

[Ali-Nasrolahi]

Sure!

I have modified the patch based on your requested changes.

Also, I believe the performance decrement is due to the frequency of start/reset-ing and cancel-ing the timeout's handler during each read/write operation. Which as you have mentioned, needs to be improved.