=pod

=head1 NAME

SSL_want, SSL_want_nothing, SSL_want_read, SSL_want_write,
SSL_want_x509_lookup, SSL_want_retry_verify, SSL_want_async, SSL_want_async_job,
SSL_want_client_hello_cb - obtain state information TLS/SSL I/O operation

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 int SSL_want(const SSL *ssl);
 int SSL_want_nothing(const SSL *ssl);
 int SSL_want_read(const SSL *ssl);
 int SSL_want_write(const SSL *ssl);
 int SSL_want_x509_lookup(const SSL *ssl);
 int SSL_want_retry_verify(const SSL *ssl);
 int SSL_want_async(const SSL *ssl);
 int SSL_want_async_job(const SSL *ssl);
 int SSL_want_client_hello_cb(const SSL *ssl);

=head1 DESCRIPTION

SSL_want() returns state information for the SSL object B<ssl>.

The other SSL_want_*() calls are shortcuts for the possible states returned
by SSL_want().

=head1 NOTES

SSL_want() examines the internal state information of the SSL object. Its
return values are similar to that of L<SSL_get_error(3)>.
Unlike L<SSL_get_error(3)>, which also evaluates the
error queue, the results are obtained by examining an internal state flag
only. The information must therefore only be used for normal operation under
nonblocking I/O. Error conditions are not handled and must be treated
using L<SSL_get_error(3)>.

The result returned by SSL_want() should always be consistent with
the result of L<SSL_get_error(3)>.

=head1 RETURN VALUES

The following return values can currently occur for SSL_want():

=over 4

=item SSL_NOTHING

There is no data to be written or to be read.

=item SSL_WRITING

There are data in the SSL buffer that must be written to the underlying
B<BIO> layer in order to complete the actual SSL_*() operation.
A call to L<SSL_get_error(3)> should return B<SSL_ERROR_WANT_WRITE>.

=item SSL_READING

More data must be read from the underlying B<BIO> layer in order to
complete the actual SSL_*() operation.
A call to L<SSL_get_error(3)> should return B<SSL_ERROR_WANT_READ>.

=item SSL_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.
A call to L<SSL_get_error(3)> should return B<SSL_ERROR_WANT_X509_LOOKUP>.

=item SSL_RETRY_VERIFY

The operation did not complete because a certificate verification callback
has asked to be called again via L<SSL_set_retry_verify(3)>.
A call to L<SSL_get_error(3)> should return B<SSL_ERROR_WANT_RETRY_VERIFY>.

=item SSL_ASYNC_PAUSED

An asynchronous operation partially completed and was then paused. See
L<SSL_get_all_async_fds(3)>. A call to L<SSL_get_error(3)> should return
B<SSL_ERROR_WANT_ASYNC>.

=item SSL_ASYNC_NO_JOBS

The asynchronous job could not be started because there were no async jobs
available in the pool (see ASYNC_init_thread(3)). A call to L<SSL_get_error(3)>
should return B<SSL_ERROR_WANT_ASYNC_JOB>.

=item SSL_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.
A call to L<SSL_get_error(3)> should return B<SSL_ERROR_WANT_CLIENT_HELLO_CB>.

=back

SSL_want_nothing(), SSL_want_read(), SSL_want_write(),
SSL_want_x509_lookup(), SSL_want_retry_verify(),
SSL_want_async(), SSL_want_async_job(), and SSL_want_client_hello_cb()
return 1 when the corresponding condition is true or 0 otherwise.

=head1 QUIC-SPECIFIC CONSIDERATIONS

For QUIC, these functions relate only to the TLS handshake layer.

=head1 SEE ALSO

L<ssl(7)>, L<SSL_get_error(3)>

=head1 HISTORY

The SSL_want_client_hello_cb() function and the SSL_CLIENT_HELLO_CB return value
were added in OpenSSL 1.1.1.

=head1 COPYRIGHT

Copyright 2001-2023 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
L<https://www.openssl.org/source/license.html>.

=cut
