SSL_GET_ERROR(3)          BSD Library Functions Manual          SSL_GET_ERROR(3)

     SSL_get_error — obtain result code for TLS/SSL I/O operation

     #include <openssl/ssl.h>

     SSL_get_error(const SSL *ssl, int ret);

     SSL_get_error() returns a result code (suitable for the C “switch”
     statement) for a preceding call to SSL_connect(3), SSL_accept(3),
     SSL_do_handshake(3), SSL_read(3), SSL_peek(3), or SSL_write(3) 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.

     The following return values can currently occur:

             The TLS/SSL I/O operation completed.  This result code is returned
             if and only if ret > 0.

             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.

             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 a 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(2) or
             poll(2) 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(3) or SSL_peek(3) may want to write data and SSL_write(3)
             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(3), SSL_peek(3), and SSL_write(3)
             will handle any pending handshakes.

             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(2)/accept(2).
             The SSL function should be called again when the connection is
             established.  These messages can only appear with a
             BIO_s_connect(3) or BIO_s_accept(3) BIO, respectively.  In order to
             find out when the connection has been successfully established, on
             many platforms select(2) or poll(2) for writing on the socket file
             descriptor can be used.

             The operation did not complete because an application callback set
             by SSL_CTX_set_client_cert_cb(3) has asked to be called again.  The
             TLS/SSL I/O function should be called again later.  Details depend
             on the application.

             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).

             A failure in the SSL library occurred, usually a protocol error.
             The OpenSSL error queue contains more information on the error.

     err(3), ssl(3)

     SSL_get_error() first appeared in SSLeay 0.8.0 and have been available
     since OpenBSD 2.4.

BSD                              April 29, 2018                              BSD