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 RETURN VALUES
29
30The following return values can currently occur:
31
32=over 4
33
34=item SSL_ERROR_NONE
35
36The TLS/SSL I/O operation completed.  This result code is returned
37if and only if B<ret E<gt> 0>.
38
39=item SSL_ERROR_ZERO_RETURN
40
41The TLS/SSL peer has closed the connection for writing by sending the
42close_notify alert.
43No more data can be read.
44Note that B<SSL_ERROR_ZERO_RETURN> does not necessarily
45indicate that the underlying transport has been closed.
46
47=item SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE
48
49The operation did not complete and can be retried later.
50
51B<SSL_ERROR_WANT_READ> is returned when the last operation was a read
52operation from a nonblocking B<BIO>.
53It means that not enough data was available at this time to complete the
54operation.
55If at a later time the underlying B<BIO> has data available for reading the same
56function can be called again.
57
58SSL_read() and SSL_read_ex() can also set B<SSL_ERROR_WANT_READ> when there is
59still unprocessed data available at either the B<SSL> or the B<BIO> layer, even
60for a blocking B<BIO>.
61See L<SSL_read(3)> for more information.
62
63B<SSL_ERROR_WANT_WRITE> is returned when the last operation was a write
64to a nonblocking B<BIO> and it was unable to sent all data to the B<BIO>.
65When the B<BIO> is writable again, the same function can be called again.
66
67Note that the retry may again lead to an B<SSL_ERROR_WANT_READ> or
68B<SSL_ERROR_WANT_WRITE> condition.
69There is no fixed upper limit for the number of iterations that
70may be necessary until progress becomes visible at application
71protocol level.
72
73It is safe to call SSL_read() or SSL_read_ex() when more data is available
74even when the call that set this error was an SSL_write() or SSL_write_ex().
75However, if the call was an SSL_write() or SSL_write_ex(), it should be called
76again to continue sending the application data.
77
78For socket B<BIO>s (e.g. when SSL_set_fd() was used), select() or
79poll() on the underlying socket can be used to find out when the
80TLS/SSL I/O function should be retried.
81
82Caveat: Any TLS/SSL I/O function can lead to either of
83B<SSL_ERROR_WANT_READ> and B<SSL_ERROR_WANT_WRITE>.
84In particular,
85SSL_read_ex(), SSL_read(), SSL_peek_ex(), or SSL_peek() may want to write data
86and SSL_write() or SSL_write_ex() may want to read data.
87This is mainly because
88TLS/SSL handshakes may occur at any time during the protocol (initiated by
89either the client or the server); SSL_read_ex(), SSL_read(), SSL_peek_ex(),
90SSL_peek(), SSL_write_ex(), and SSL_write() will handle any pending handshakes.
91
92=item SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT
93
94The operation did not complete; the same TLS/SSL I/O function should be
95called again later. The underlying BIO was not connected yet to the peer
96and the call would block in connect()/accept(). The SSL function should be
97called again when the connection is established. These messages can only
98appear with a BIO_s_connect() or BIO_s_accept() BIO, respectively.
99In order to find out, when the connection has been successfully established,
100on many platforms select() or poll() for writing on the socket file descriptor
101can be used.
102
103=item SSL_ERROR_WANT_X509_LOOKUP
104
105The operation did not complete because an application callback set by
106SSL_CTX_set_client_cert_cb() has asked to be called again.
107The TLS/SSL I/O function should be called again later.
108Details depend on the application.
109
110=item SSL_ERROR_WANT_ASYNC
111
112The operation did not complete because an asynchronous engine is still
113processing data. This will only occur if the mode has been set to SSL_MODE_ASYNC
114using L<SSL_CTX_set_mode(3)> or L<SSL_set_mode(3)> and an asynchronous capable
115engine is being used. An application can determine whether the engine has
116completed its processing using select() or poll() on the asynchronous wait file
117descriptor. This file descriptor is available by calling
118L<SSL_get_all_async_fds(3)> or L<SSL_get_changed_async_fds(3)>. The TLS/SSL I/O
119function should be called again later. The function B<must> be called from the
120same thread that the original call was made from.
121
122=item SSL_ERROR_WANT_ASYNC_JOB
123
124The asynchronous job could not be started because there were no async jobs
125available in the pool (see ASYNC_init_thread(3)). This will only occur if the
126mode has been set to SSL_MODE_ASYNC using L<SSL_CTX_set_mode(3)> or
127L<SSL_set_mode(3)> and a maximum limit has been set on the async job pool
128through a call to L<ASYNC_init_thread(3)>. The application should retry the
129operation after a currently executing asynchronous operation for the current
130thread has completed.
131
132=item SSL_ERROR_WANT_CLIENT_HELLO_CB
133
134The operation did not complete because an application callback set by
135SSL_CTX_set_client_hello_cb() has asked to be called again.
136The TLS/SSL I/O function should be called again later.
137Details depend on the application.
138
139=item SSL_ERROR_SYSCALL
140
141Some non-recoverable, fatal I/O error occurred. The OpenSSL error queue may
142contain more information on the error. For socket I/O on Unix systems, consult
143B<errno> for details. If this error occurs then no further I/O operations should
144be performed on the connection and SSL_shutdown() must not be called.
145
146This value can also be returned for other errors, check the error queue for
147details.
148
149=item SSL_ERROR_SSL
150
151A non-recoverable, fatal error in the SSL library occurred, usually a protocol
152error.  The OpenSSL error queue contains more information on the error. If this
153error occurs then no further I/O operations should be performed on the
154connection and SSL_shutdown() must not be called.
155
156=back
157
158=head1 BUGS
159
160The B<SSL_ERROR_SYSCALL> with B<errno> value of 0 indicates unexpected EOF from
161the peer. This will be properly reported as B<SSL_ERROR_SSL> with reason
162code B<SSL_R_UNEXPECTED_EOF_WHILE_READING> in the OpenSSL 3.0 release because
163it is truly a TLS protocol error to terminate the connection without
164a SSL_shutdown().
165
166The issue is kept unfixed in OpenSSL 1.1.1 releases because many applications
167which choose to ignore this protocol error depend on the existing way of
168reporting the error.
169
170=head1 SEE ALSO
171
172L<ssl(7)>
173
174=head1 HISTORY
175
176The SSL_ERROR_WANT_ASYNC error code was added in OpenSSL 1.1.0.
177The SSL_ERROR_WANT_CLIENT_HELLO_CB error code was added in OpenSSL 1.1.1.
178
179=head1 COPYRIGHT
180
181Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
182
183Licensed under the OpenSSL license (the "License").  You may not use
184this file except in compliance with the License.  You can obtain a copy
185in the file LICENSE in the source distribution or at
186L<https://www.openssl.org/source/license.html>.
187
188=cut
189