1=pod
2
3=head1 NAME
4
5SSL_get_error - obtain result code for TLS/SSL I/O operation
6
7=head1 SYNOPSIS
8
9 #include <openssl/ssl.h>
10
11 int SSL_get_error(const SSL *ssl, int ret);
12
13=head1 DESCRIPTION
14
15SSL_get_error() returns a result code (suitable for the C "switch"
16statement) for a preceding call to SSL_connect(), SSL_accept(), SSL_do_handshake(),
17SSL_read_ex(), SSL_read(), SSL_peek_ex(), SSL_peek(), SSL_shutdown(),
18SSL_write_ex() or SSL_write() on B<ssl>.  The value returned by that TLS/SSL I/O
19function must be passed to SSL_get_error() in parameter B<ret>.
20
21In addition to B<ssl> and B<ret>, SSL_get_error() inspects the
22current thread's OpenSSL error queue.  Thus, SSL_get_error() must be
23used in the same thread that performed the TLS/SSL I/O operation, and no
24other OpenSSL function calls should appear in between.  The current
25thread's error queue must be empty before the TLS/SSL I/O operation is
26attempted, or SSL_get_error() will not work reliably.
27
28=head1 NOTES
29
30Some TLS implementations do not send a close_notify alert on shutdown.
31
32On an unexpected EOF, versions before OpenSSL 3.0 returned
33B<SSL_ERROR_SYSCALL>, nothing was added to the error stack, and errno was 0.
34Since OpenSSL 3.0 the returned error is B<SSL_ERROR_SSL> with a meaningful
35error on the error stack.
36
37=head1 RETURN VALUES
38
39The following return values can currently occur:
40
41=over 4
42
43=item SSL_ERROR_NONE
44
45The TLS/SSL I/O operation completed.  This result code is returned
46if and only if B<ret E<gt> 0>.
47
48=item SSL_ERROR_ZERO_RETURN
49
50The TLS/SSL peer has closed the connection for writing by sending the
51close_notify alert.
52No more data can be read.
53Note that B<SSL_ERROR_ZERO_RETURN> does not necessarily
54indicate that the underlying transport has been closed.
55
56This error can also appear when the option B<SSL_OP_IGNORE_UNEXPECTED_EOF>
57is set. See L<SSL_CTX_set_options(3)> for more details.
58
59=item SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE
60
61The operation did not complete and can be retried later.
62
63B<SSL_ERROR_WANT_READ> is returned when the last operation was a read
64operation from a nonblocking B<BIO>.
65It means that not enough data was available at this time to complete the
66operation.
67If at a later time the underlying B<BIO> has data available for reading the same
68function can be called again.
69
70SSL_read() and SSL_read_ex() can also set B<SSL_ERROR_WANT_READ> when there is
71still unprocessed data available at either the B<SSL> or the B<BIO> layer, even
72for a blocking B<BIO>.
73See L<SSL_read(3)> for more information.
74
75B<SSL_ERROR_WANT_WRITE> is returned when the last operation was a write
76to a nonblocking B<BIO> and it was unable to sent all data to the B<BIO>.
77When the B<BIO> is writable again, the same function can be called again.
78
79Note that the retry may again lead to an B<SSL_ERROR_WANT_READ> or
80B<SSL_ERROR_WANT_WRITE> condition.
81There is no fixed upper limit for the number of iterations that
82may be necessary until progress becomes visible at application
83protocol level.
84
85It is safe to call SSL_read() or SSL_read_ex() when more data is available
86even when the call that set this error was an SSL_write() or SSL_write_ex().
87However, if the call was an SSL_write() or SSL_write_ex(), it should be called
88again to continue sending the application data. If you get B<SSL_ERROR_WANT_WRITE>
89from SSL_write() or SSL_write_ex() then you should not do any other operation
90that could trigger B<IO> other than to repeat the previous SSL_write() call.
91
92For socket B<BIO>s (e.g. when SSL_set_fd() was used), select() or
93poll() on the underlying socket can be used to find out when the
94TLS/SSL I/O function should be retried.
95
96Caveat: Any TLS/SSL I/O function can lead to either of
97B<SSL_ERROR_WANT_READ> and B<SSL_ERROR_WANT_WRITE>.
98In particular,
99SSL_read_ex(), SSL_read(), SSL_peek_ex(), or SSL_peek() may want to write data
100and SSL_write() or SSL_write_ex() may want to read data.
101This is mainly because
102TLS/SSL handshakes may occur at any time during the protocol (initiated by
103either the client or the server); SSL_read_ex(), SSL_read(), SSL_peek_ex(),
104SSL_peek(), SSL_write_ex(), and SSL_write() will handle any pending handshakes.
105
106=item SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT
107
108The operation did not complete; the same TLS/SSL I/O function should be
109called again later. The underlying BIO was not connected yet to the peer
110and the call would block in connect()/accept(). The SSL function should be
111called again when the connection is established. These messages can only
112appear with a BIO_s_connect() or BIO_s_accept() BIO, respectively.
113In order to find out, when the connection has been successfully established,
114on many platforms select() or poll() for writing on the socket file descriptor
115can be used.
116
117=item SSL_ERROR_WANT_X509_LOOKUP
118
119The operation did not complete because an application callback set by
120SSL_CTX_set_client_cert_cb() has asked to be called again.
121The TLS/SSL I/O function should be called again later.
122Details depend on the application.
123
124=item SSL_ERROR_WANT_ASYNC
125
126The operation did not complete because an asynchronous engine is still
127processing data. This will only occur if the mode has been set to SSL_MODE_ASYNC
128using L<SSL_CTX_set_mode(3)> or L<SSL_set_mode(3)> and an asynchronous capable
129engine is being used. An application can determine whether the engine has
130completed its processing using select() or poll() on the asynchronous wait file
131descriptor. This file descriptor is available by calling
132L<SSL_get_all_async_fds(3)> or L<SSL_get_changed_async_fds(3)>. The TLS/SSL I/O
133function should be called again later. The function B<must> be called from the
134same thread that the original call was made from.
135
136=item SSL_ERROR_WANT_ASYNC_JOB
137
138The asynchronous job could not be started because there were no async jobs
139available in the pool (see ASYNC_init_thread(3)). This will only occur if the
140mode has been set to SSL_MODE_ASYNC using L<SSL_CTX_set_mode(3)> or
141L<SSL_set_mode(3)> and a maximum limit has been set on the async job pool
142through a call to L<ASYNC_init_thread(3)>. The application should retry the
143operation after a currently executing asynchronous operation for the current
144thread has completed.
145
146=item SSL_ERROR_WANT_CLIENT_HELLO_CB
147
148The operation did not complete because an application callback set by
149SSL_CTX_set_client_hello_cb() has asked to be called again.
150The TLS/SSL I/O function should be called again later.
151Details depend on the application.
152
153=item SSL_ERROR_SYSCALL
154
155Some non-recoverable, fatal I/O error occurred. The OpenSSL error queue may
156contain more information on the error. For socket I/O on Unix systems, consult
157B<errno> for details. If this error occurs then no further I/O operations should
158be performed on the connection and SSL_shutdown() must not be called.
159
160This value can also be returned for other errors, check the error queue for
161details.
162
163=item SSL_ERROR_SSL
164
165A non-recoverable, fatal error in the SSL library occurred, usually a protocol
166error.  The OpenSSL error queue contains more information on the error. If this
167error occurs then no further I/O operations should be performed on the
168connection and SSL_shutdown() must not be called.
169
170=back
171
172=head1 SEE ALSO
173
174L<ssl(7)>
175
176=head1 HISTORY
177
178The SSL_ERROR_WANT_ASYNC error code was added in OpenSSL 1.1.0.
179The SSL_ERROR_WANT_CLIENT_HELLO_CB error code was added in OpenSSL 1.1.1.
180
181=head1 COPYRIGHT
182
183Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
184
185Licensed under the Apache License 2.0 (the "License").  You may not use
186this file except in compliance with the License.  You can obtain a copy
187in the file LICENSE in the source distribution or at
188L<https://www.openssl.org/source/license.html>.
189
190=cut
191