SSL_get_error() returns a result code (suitable for the C ``switch''
statement) for a preceding call to SSL_connect(), SSL_accept(), SSL_do_handshake(),
SSL_read(), SSL_peek(), or SSL_write() on ssl. The value returned by
that TLS/SSL I/O function must be passed to SSL_get_error() in parameter
ret.
In addition to ssl and ret, SSL_get_error() inspects the
current thread's OpenSSL error queue. Thus, SSL_get_error() must be
used in the same thread that performed the TLS/SSL I/O operation, and no
other OpenSSL function calls should appear in between. The current
thread's error queue must be empty before the TLS/SSL I/O operation is
attempted, or SSL_get_error() will not work reliably.
RETURN VALUES
The following return values can currently occur:
SSL_ERROR_NONE
The TLS/SSL I/O operation completed. This result code is returned
if and only if ret > 0.
SSL_ERROR_ZERO_RETURN
The TLS/SSL connection has been closed. If the protocol version is SSL 3.0
or TLS 1.0, this result code is returned only if a closure
alert has occurred in the protocol, i.e. if the connection has been
closed cleanly. Note that in this case SSL_ERROR_ZERO_RETURN
does not necessarily indicate that the underlying transport
has been closed.
SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE
The operation did not complete; the same TLS/SSL I/O function should be
called again later. If, by then, the underlying BIO has data
available for reading (if the result code is SSL_ERROR_WANT_READ)
or allows writing data (SSL_ERROR_WANT_WRITE), then some TLS/SSL
protocol progress will take place, i.e. at least part of an TLS/SSL
record will be read or written. Note that the retry may again lead to
a SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE condition.
There is no fixed upper limit for the number of iterations that
may be necessary until progress becomes visible at application
protocol level.
For socket BIOs (e.g. when SSL_set_fd() was used), select() or
poll() on the underlying socket can be used to find out when the
TLS/SSL I/O function should be retried.
Caveat: Any TLS/SSL I/O function can lead to either of
SSL_ERROR_WANT_READ and SSL_ERROR_WANT_WRITE. In particular,
SSL_read() or SSL_peek() may want to write data and SSL_write() may want
to read data. This is mainly because TLS/SSL handshakes may occur at any
time during the protocol (initiated by either the client or the server);
SSL_read(), SSL_peek(), and SSL_write() will handle any pending handshakes.
SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT
The operation did not complete; the same TLS/SSL I/O function should be
called again later. The underlying BIO was not connected yet to the peer
and the call would block in connect()/accept(). The SSL function should be
called again when the connection is established. These messages can only
appear with a BIO_s_connect() or BIO_s_accept() BIO, respectively.
In order to find out, when the connection has been successfully established,
on many platforms select() or poll() for writing on the socket file descriptor
can be used.
SSL_ERROR_WANT_X509_LOOKUP
The operation did not complete because an application callback set by
SSL_CTX_set_client_cert_cb() has asked to be called again.
The TLS/SSL I/O function should be called again later.
Details depend on the application.
SSL_ERROR_SYSCALL
Some I/O error occurred. The OpenSSL error queue may contain more
information on the error. If the error queue is empty
(i.e. ERR_get_error() returns 0), ret can be used to find out more
about the error: If ret == 0, an EOF was observed that violates
the protocol. If ret == -1, the underlying BIO reported an
I/O error (for socket I/O on Unix systems, consult errno for details).
SSL_ERROR_SSL
A failure in the SSL library occurred, usually a protocol error. The
OpenSSL error queue contains more information on the error.
