SSL_GET_ERROR
Section: OpenSSL (3)
Updated: 2020-07-28
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NAME
SSL_get_error - obtain result code for TLS/SSL I/O operation
SYNOPSIS
#include <openssl/ssl.h>
int SSL_get_error(const SSL *ssl, int ret);
DESCRIPTION
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_ex(),
SSL_read(),
SSL_peek_ex(),
SSL_peek(),
SSL_shutdown(),
SSL_write_ex() 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 peer has closed the connection for writing by sending the
close_notify alert.
No more data can be read.
Note that 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 and can be retried later.
SSL_ERROR_WANT_READ is returned when the last operation was a read
operation from a non-blocking BIO.
It means that not enough data was available at this time to complete the
operation.
If at a later time the underlying BIO has data available for reading the same
function can be called again.
SSL_read() and SSL_read_ex() can also set SSL_ERROR_WANT_READ when there is
still unprocessed data available at either the SSL or the BIO layer, even
for a blocking BIO.
See SSL_read(3) for more information.
SSL_ERROR_WANT_WRITE is returned when the last operation was a write
to a non-blocking BIO and it was unable to sent all data to the BIO.
When the BIO is writeable again, the same function can be called again.
Note that the retry may again lead to an 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.
It is safe to call SSL_read() or SSL_read_ex() when more data is available
even when the call that set this error was an SSL_write() or SSL_write_ex().
However if the call was an SSL_write() or SSL_write_ex(), it should be called
again to continue sending the application data.
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_ex(), SSL_read(), SSL_peek_ex(), or SSL_peek() may want to write data
and SSL_write() or SSL_write_ex() 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_ex(), SSL_read(), SSL_peek_ex(),
SSL_peek(), SSL_write_ex(), 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_WANT_ASYNC
-
The operation did not complete because an asynchronous engine is still
processing data. This will only occur if the mode has been set to SSL_MODE_ASYNC
using SSL_CTX_set_mode(3) or SSL_set_mode(3) and an asynchronous capable
engine is being used. An application can determine whether the engine has
completed its processing using select() or poll() on the asynchronous wait file
descriptor. This file descriptor is available by calling
SSL_get_all_async_fds(3) or SSL_get_changed_async_fds(3). The TLS/SSL I/O
function should be called again later. The function must be called from the
same thread that the original call was made from.
- SSL_ERROR_WANT_ASYNC_JOB
-
The asynchronous job could not be started because there were no async jobs
available in the pool (see ASYNC_init_thread(3)). This will only occur if the
mode has been set to SSL_MODE_ASYNC using SSL_CTX_set_mode(3) or
SSL_set_mode(3) and a maximum limit has been set on the async job pool
through a call to ASYNC_init_thread(3). The application should retry the
operation after a currently executing asynchronous operation for the current
thread has completed.
- SSL_ERROR_WANT_CLIENT_HELLO_CB
-
The operation did not complete because an application callback set by
SSL_CTX_set_client_hello_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 non-recoverable, fatal I/O error occurred. The OpenSSL error queue may
contain more information on the error. For socket I/O on Unix systems, consult
errno for details. If this error occurs then no further I/O operations should
be performed on the connection and SSL_shutdown() must not be called.
This value can also be returned for other errors, check the error queue for
details.
- SSL_ERROR_SSL
-
A non-recoverable, fatal error in the SSL library occurred, usually a protocol
error. The OpenSSL error queue contains more information on the error. If this
error occurs then no further I/O operations should be performed on the
connection and SSL_shutdown() must not be called.
BUGS
The
SSL_ERROR_SYSCALL with
errno value of 0 indicates unexpected
EOF from
the peer. This will be properly reported as
SSL_ERROR_SSL with reason
code
SSL_R_UNEXPECTED_EOF_WHILE_READING in the OpenSSL 3.0 release because
it is truly a
TLS protocol error to terminate the connection without
a
SSL_shutdown().
The issue is kept unfixed in OpenSSL 1.1.1 releases because many applications
which choose to ignore this protocol error depend on the existing way of
reporting the error.
SEE ALSO
ssl(7)
HISTORY
The
SSL_ERROR_WANT_ASYNC error code was added in OpenSSL 1.1.0.
The
SSL_ERROR_WANT_CLIENT_HELLO_CB error code was added in OpenSSL 1.1.1.
COPYRIGHT
Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the ``License''). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.