Sean O'Dell <[EMAIL PROTECTED]> in ulf.openssl.users:
>[...] SSL_connect, SSL_accept, SSL_read and SSL_write. Apparently, when the
> underlying socket is in non-blocking mode, these functions can/may/tend to
> behave in a non-blocking way also. What I'd like to know is, how can I tell
> when these functions are completed without using a callback of some sort?
> With plain old sockets, you can use select() to tell when connect() and
> accept() have completed successfully. Similarly, with read() and write()
> it's possible to know when data is available/being sent or if the function
> would block and to try again. Can anyone describe the behavior of their
> OpenSSL-counterparts when the socket is non-blocking?
The sequence to use is
r = SSL_connect/accept/read/write(ssl);
err = SSL_get_error(ssl, r);
Then err is one of the following:
SSL_ERROR_NONE
Operation completed (this happens iff r > 0).
SSL_ERROR_ZERO_RETURN
The connection was closed (cleanly, i.e. using SSL/TLS closure alerts
unless you are using SSL version 2).
SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE
The operation did not complete; call the same function again later
when select() or poll() on the underlying socket (if you are using
the socket BIO, e.g. when you called SSL_set_fd) said that data is
available for reading or that writing is possible.
Note the SSL_read may want to write data and SSL_write may want to
read data!
SSL_ERROR_WANT_X509_LOOKUP
If you have not called SSL_CTX_set_client_cert_cb, this should not
happen. Otherwise this means that an application callback
could not complete.
SSL_ERROR_SYSCALL
Some I/O error. The OpenSSL error queue might contain more information
(call ERR_get_error or one of its variants until it returns 0,
ERR_error_string can be used to translate its return values into
strings; if the first call to ERR_get_error returns 0, then the
queue is empty). If the error queue is empty, then look at r:
0 means an EOF that should not have happened according to the protocol
(or you'd get SSL_ERROR_ZERO_RETURN). If it's -1, then for socket I/O
look at errno for details on the error.
SSL_ERROR_SSL
Protocol error. Look at the OpenSSL error queue.
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