[openssl-users] Graceful shutdown of TLS connection for blocking sockets
Thomas J. Hruska
shinelight at shininglightpro.com
Sun Oct 8 20:55:36 UTC 2017
On 10/8/2017 7:28 AM, Michel wrote:
> While I understand that using non-blocking descriptors is a better practice,
> I still do not see why select() should NEVER be used for blocking sockets
> (except when combined/interfered with the internal OpenSSL state machine or
> equivalent mechanism).
> Could you please elaborate or give an example ?
Example: You call select(), it returns the descriptor as readable, you
pass it into SSL_read(), and SSL_read() blocks. You are worse off than
before you used select() since you made the incorrect assumption that
you could do something when select() returns and not have a blocking
Just because select() says that something is readable (or writable) does
not actually make it so. The function only makes sense for non-blocking
descriptors. The use of select() with a blocking descriptor is always
Non-blocking code is actually easier to implement than you think.
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