=pod

=head1 NAME

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

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 int SSL_get_error(const SSL *ssl, int ret);

=head1 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 B<ssl>.  The value returned by that TLS/SSL I/O

function must be passed to SSL_get_error() in parameter B<ret>.

In addition to B<ssl> and B<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.

=head1 RETURN VALUES

The following return values can currently occur:

=over 4

=item SSL_ERROR_NONE

The TLS/SSL I/O operation completed.  This result code is returned

if and only if B<ret E<gt> 0>.

=item 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 B<SSL_ERROR_ZERO_RETURN> does not necessarily

indicate that the underlying transport has been closed.

=item SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE

The operation did not complete and can be retried later.

B<SSL_ERROR_WANT_READ> is returned when the last operation was a read

operation from a non-blocking B<BIO>.

It means that not enough data was available at this time to complete the

operation.

If at a later time the underlying B<BIO> has data available for reading the same

function can be called again.

SSL_read() and SSL_read_ex() can also set B<SSL_ERROR_WANT_READ> when there is

still unprocessed data available at either the B<SSL> or the B<BIO> layer, even

for a blocking B<BIO>.

See L<SSL_read(3)> for more information.

B<SSL_ERROR_WANT_WRITE> is returned when the last operation was a write

to a non-blocking B<BIO> and it was unable to sent all data to the B<BIO>.

When the B<BIO> is writeable again, the same function can be called again.

Note that the retry may again lead to an B<SSL_ERROR_WANT_READ> or

B<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 B<BIO>s (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

B<SSL_ERROR_WANT_READ> and B<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.

=item 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.

=item 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.

=item 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 L<SSL_CTX_set_mode(3)> or L<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

L<SSL_get_all_async_fds(3)> or L<SSL_get_changed_async_fds(3)>. The TLS/SSL I/O

function should be called again later. The function B<must> be called from the

same thread that the original call was made from.

=item 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 L<SSL_CTX_set_mode(3)> or

L<SSL_set_mode(3)> and a maximum limit has been set on the async job pool

through a call to L<ASYNC_init_thread(3)>. The application should retry the

operation after a currently executing asynchronous operation for the current

thread has completed.

=item 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.

=item 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

B<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.

=item 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.

=back

=head1 BUGS

The B<SSL_ERROR_SYSCALL> with B<errno> value of 0 indicates unexpected EOF from

the peer. This will be properly reported as B<SSL_ERROR_SSL> with reason

code B<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.

=head1 SEE ALSO

L<ssl(7)>

=head1 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.

=head1 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

L<https://www.openssl.org/source/license.html>.

=cut