SSL_get_error - obtain result code for TLS/SSL I/O operation
#include <openssl/ssl.h>
int 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(),
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.
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).
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.
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.
SSL_ERROR_WANT_WRITE is returned when the last operation was a write
to a nonblocking BIO and it was unable to sent 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.
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.
ssl(7)
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.
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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>.