SSL_GET_ERROR(3SSL) OpenSSL SSL_GET_ERROR(3SSL)
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. Emptying the current
thread's error queue is done with ERR_clear_error(3).
NOTES
Some TLS implementations do not send a close_notify alert on shutdown.
On an unexpected EOF, versions before OpenSSL 3.0 returned
SSL_ERROR_SYSCALL, nothing was added to the error stack, and errno was
0. Since OpenSSL 3.0 the returned error is SSL_ERROR_SSL with a
meaningful error on the error stack
(SSL_R_UNEXPECTED_EOF_WHILE_READING). This error reason code may be used
for control flow decisions (see the man page for ERR_GET_REASON(3) for
further details on this).
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.
This error can also appear when the option
SSL_OP_IGNORE_UNEXPECTED_EOF is set. See SSL_CTX_set_options(3) for
more details.
SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE
The operation did not complete and can be retried later.
For non-QUIC SSL objects, SSL_ERROR_WANT_READ is returned when the
last operation was a read operation from a nonblocking 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.
For non-QUIC SSL objects, SSL_ERROR_WANT_WRITE is returned when the
last operation was a write to a nonblocking BIO and it was unable to
send all data to the BIO. When the BIO is writable 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.
For QUIC SSL objects, the meaning of SSL_ERROR_WANT_READ and
SSL_ERROR_WANT_WRITE have different but largely compatible
semantics. Since QUIC implements its own flow control and uses UDP
datagrams, backpressure conditions in terms of the underlying BIO
providing network I/O are not directly relevant to the circumstances
in which these errors are produced. In particular,
SSL_ERROR_WANT_WRITE indicates that the OpenSSL internal send buffer
for a given QUIC stream has been filled. Likewise,
SSL_ERROR_WANT_READ indicates that the OpenSSL internal receive
buffer for a given QUIC stream is empty.
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. If you get SSL_ERROR_WANT_WRITE from SSL_write()
or SSL_write_ex() then you should not do any other operation that
could trigger IO other than to repeat the previous SSL_write() call.
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.
The OpenSSL error queue can be inspected with the ERR family of
functions, such as ERR_print_errors(3) and ERR_peek_last_error_all(3).
SEE ALSO
ssl(7), ERR_clear_error(3), ERR_print_errors(3),
ERR_peek_last_error_all(3)
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 2000-2024 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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>.
3.5.7 2026-06-09 SSL_GET_ERROR(3SSL)
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