oracular (3) SSL_get_error.3ssl.gz
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.
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.
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 2000-2024 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>.