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. Emptying the 27current thread's error queue is done with L<ERR_clear_error(3)>. 28 29=head1 NOTES 30 31Some TLS implementations do not send a close_notify alert on shutdown. 32 33On an unexpected EOF, versions before OpenSSL 3.0 returned 34B<SSL_ERROR_SYSCALL>, nothing was added to the error stack, and errno was 0. 35Since OpenSSL 3.0 the returned error is B<SSL_ERROR_SSL> with a meaningful 36error on the error stack (SSL_R_UNEXPECTED_EOF_WHILE_READING). This error reason 37code may be used for control flow decisions (see the man page for 38L<ERR_GET_REASON(3)> for further details on this). 39 40=head1 RETURN VALUES 41 42The following return values can currently occur: 43 44=over 4 45 46=item SSL_ERROR_NONE 47 48The TLS/SSL I/O operation completed. This result code is returned 49if and only if B<ret E<gt> 0>. 50 51=item SSL_ERROR_ZERO_RETURN 52 53The TLS/SSL peer has closed the connection for writing by sending the 54close_notify alert. 55No more data can be read. 56Note that B<SSL_ERROR_ZERO_RETURN> does not necessarily 57indicate that the underlying transport has been closed. 58 59This error can also appear when the option B<SSL_OP_IGNORE_UNEXPECTED_EOF> 60is set. See L<SSL_CTX_set_options(3)> for more details. 61 62=item SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE 63 64The operation did not complete and can be retried later. 65 66For non-QUIC SSL objects, B<SSL_ERROR_WANT_READ> is returned when the last 67operation was a read operation from a nonblocking B<BIO>. 68It means that not enough data was available at this time to complete the 69operation. 70If at a later time the underlying B<BIO> has data available for reading the same 71function can be called again. 72 73SSL_read() and SSL_read_ex() can also set B<SSL_ERROR_WANT_READ> when there is 74still unprocessed data available at either the B<SSL> or the B<BIO> layer, even 75for a blocking B<BIO>. 76See L<SSL_read(3)> for more information. 77 78For non-QUIC SSL objects, B<SSL_ERROR_WANT_WRITE> is returned when the last 79operation was a write to a nonblocking B<BIO> and it was unable to send all data 80to the B<BIO>. When the B<BIO> is writable again, the same function can be 81called again. 82 83Note that the retry may again lead to an B<SSL_ERROR_WANT_READ> or 84B<SSL_ERROR_WANT_WRITE> condition. 85There is no fixed upper limit for the number of iterations that 86may be necessary until progress becomes visible at application 87protocol level. 88 89For QUIC SSL objects, the meaning of B<SSL_ERROR_WANT_READ> and 90B<SSL_ERROR_WANT_WRITE> have different but largely compatible semantics. Since 91QUIC implements its own flow control and uses UDP datagrams, backpressure 92conditions in terms of the underlying BIO providing network I/O are not directly 93relevant to the circumstances in which these errors are produced. In particular, 94B<SSL_ERROR_WANT_WRITE> indicates that the OpenSSL internal send buffer for a 95given QUIC stream has been filled. Likewise, B<SSL_ERROR_WANT_READ> indicates 96that the OpenSSL internal receive buffer for a given QUIC stream is empty. 97 98It is safe to call SSL_read() or SSL_read_ex() when more data is available 99even when the call that set this error was an SSL_write() or SSL_write_ex(). 100However, if the call was an SSL_write() or SSL_write_ex(), it should be called 101again to continue sending the application data. If you get B<SSL_ERROR_WANT_WRITE> 102from SSL_write() or SSL_write_ex() then you should not do any other operation 103that could trigger B<IO> other than to repeat the previous SSL_write() call. 104 105For socket B<BIO>s (e.g. when SSL_set_fd() was used), select() or 106poll() on the underlying socket can be used to find out when the 107TLS/SSL I/O function should be retried. 108 109Caveat: Any TLS/SSL I/O function can lead to either of 110B<SSL_ERROR_WANT_READ> and B<SSL_ERROR_WANT_WRITE>. 111In particular, 112SSL_read_ex(), SSL_read(), SSL_peek_ex(), or SSL_peek() may want to write data 113and SSL_write() or SSL_write_ex() may want to read data. 114This is mainly because 115TLS/SSL handshakes may occur at any time during the protocol (initiated by 116either the client or the server); SSL_read_ex(), SSL_read(), SSL_peek_ex(), 117SSL_peek(), SSL_write_ex(), and SSL_write() will handle any pending handshakes. 118 119=item SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT 120 121The operation did not complete; the same TLS/SSL I/O function should be 122called again later. The underlying BIO was not connected yet to the peer 123and the call would block in connect()/accept(). The SSL function should be 124called again when the connection is established. These messages can only 125appear with a BIO_s_connect() or BIO_s_accept() BIO, respectively. 126In order to find out, when the connection has been successfully established, 127on many platforms select() or poll() for writing on the socket file descriptor 128can be used. 129 130=item SSL_ERROR_WANT_X509_LOOKUP 131 132The operation did not complete because an application callback set by 133SSL_CTX_set_client_cert_cb() has asked to be called again. 134The TLS/SSL I/O function should be called again later. 135Details depend on the application. 136 137=item SSL_ERROR_WANT_ASYNC 138 139The operation did not complete because an asynchronous engine is still 140processing data. This will only occur if the mode has been set to SSL_MODE_ASYNC 141using L<SSL_CTX_set_mode(3)> or L<SSL_set_mode(3)> and an asynchronous capable 142engine is being used. An application can determine whether the engine has 143completed its processing using select() or poll() on the asynchronous wait file 144descriptor. This file descriptor is available by calling 145L<SSL_get_all_async_fds(3)> or L<SSL_get_changed_async_fds(3)>. The TLS/SSL I/O 146function should be called again later. The function B<must> be called from the 147same thread that the original call was made from. 148 149=item SSL_ERROR_WANT_ASYNC_JOB 150 151The asynchronous job could not be started because there were no async jobs 152available in the pool (see ASYNC_init_thread(3)). This will only occur if the 153mode has been set to SSL_MODE_ASYNC using L<SSL_CTX_set_mode(3)> or 154L<SSL_set_mode(3)> and a maximum limit has been set on the async job pool 155through a call to L<ASYNC_init_thread(3)>. The application should retry the 156operation after a currently executing asynchronous operation for the current 157thread has completed. 158 159=item SSL_ERROR_WANT_CLIENT_HELLO_CB 160 161The operation did not complete because an application callback set by 162SSL_CTX_set_client_hello_cb() has asked to be called again. 163The TLS/SSL I/O function should be called again later. 164Details depend on the application. 165 166=item SSL_ERROR_SYSCALL 167 168Some non-recoverable, fatal I/O error occurred. The OpenSSL error queue may 169contain more information on the error. For socket I/O on Unix systems, consult 170B<errno> for details. If this error occurs then no further I/O operations should 171be performed on the connection and SSL_shutdown() must not be called. 172 173This value can also be returned for other errors, check the error queue for 174details. 175 176=item SSL_ERROR_SSL 177 178A non-recoverable, fatal error in the SSL library occurred, usually a protocol 179error. The OpenSSL error queue contains more information on the error. If this 180error occurs then no further I/O operations should be performed on the 181connection and SSL_shutdown() must not be called. 182 183=back 184 185The OpenSSL error queue can be inspected with the B<ERR> family of functions, 186such as L<ERR_print_errors(3)> and L<ERR_peek_last_error_all(3)>. 187 188=head1 SEE ALSO 189 190L<ssl(7)>, 191L<ERR_clear_error(3)>, ERR_print_errors(3), ERR_peek_last_error_all(3) 192 193=head1 HISTORY 194 195The SSL_ERROR_WANT_ASYNC error code was added in OpenSSL 1.1.0. 196The SSL_ERROR_WANT_CLIENT_HELLO_CB error code was added in OpenSSL 1.1.1. 197 198=head1 COPYRIGHT 199 200Copyright 2000-2024 The OpenSSL Project Authors. All Rights Reserved. 201 202Licensed under the Apache License 2.0 (the "License"). You may not use 203this file except in compliance with the License. You can obtain a copy 204in the file LICENSE in the source distribution or at 205L<https://www.openssl.org/source/license.html>. 206 207=cut 208