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 (SSL_R_UNEXPECTED_EOF_WHILE_READING). This error reason 36code may be used for control flow decisions (see the man page for 37L<ERR_GET_REASON(3)> for further details on this). 38 39=head1 RETURN VALUES 40 41The following return values can currently occur: 42 43=over 4 44 45=item SSL_ERROR_NONE 46 47The TLS/SSL I/O operation completed. This result code is returned 48if and only if B<ret E<gt> 0>. 49 50=item SSL_ERROR_ZERO_RETURN 51 52The TLS/SSL peer has closed the connection for writing by sending the 53close_notify alert. 54No more data can be read. 55Note that B<SSL_ERROR_ZERO_RETURN> does not necessarily 56indicate that the underlying transport has been closed. 57 58This error can also appear when the option B<SSL_OP_IGNORE_UNEXPECTED_EOF> 59is set. See L<SSL_CTX_set_options(3)> for more details. 60 61=item SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE 62 63The operation did not complete and can be retried later. 64 65B<SSL_ERROR_WANT_READ> is returned when the last operation was a read 66operation from a nonblocking B<BIO>. 67It means that not enough data was available at this time to complete the 68operation. 69If at a later time the underlying B<BIO> has data available for reading the same 70function can be called again. 71 72SSL_read() and SSL_read_ex() can also set B<SSL_ERROR_WANT_READ> when there is 73still unprocessed data available at either the B<SSL> or the B<BIO> layer, even 74for a blocking B<BIO>. 75See L<SSL_read(3)> for more information. 76 77B<SSL_ERROR_WANT_WRITE> is returned when the last operation was a write 78to a nonblocking B<BIO> and it was unable to sent all data to the B<BIO>. 79When the B<BIO> is writable again, the same function can be called again. 80 81Note that the retry may again lead to an B<SSL_ERROR_WANT_READ> or 82B<SSL_ERROR_WANT_WRITE> condition. 83There is no fixed upper limit for the number of iterations that 84may be necessary until progress becomes visible at application 85protocol level. 86 87It is safe to call SSL_read() or SSL_read_ex() when more data is available 88even when the call that set this error was an SSL_write() or SSL_write_ex(). 89However, if the call was an SSL_write() or SSL_write_ex(), it should be called 90again to continue sending the application data. If you get B<SSL_ERROR_WANT_WRITE> 91from SSL_write() or SSL_write_ex() then you should not do any other operation 92that could trigger B<IO> other than to repeat the previous SSL_write() call. 93 94For socket B<BIO>s (e.g. when SSL_set_fd() was used), select() or 95poll() on the underlying socket can be used to find out when the 96TLS/SSL I/O function should be retried. 97 98Caveat: Any TLS/SSL I/O function can lead to either of 99B<SSL_ERROR_WANT_READ> and B<SSL_ERROR_WANT_WRITE>. 100In particular, 101SSL_read_ex(), SSL_read(), SSL_peek_ex(), or SSL_peek() may want to write data 102and SSL_write() or SSL_write_ex() may want to read data. 103This is mainly because 104TLS/SSL handshakes may occur at any time during the protocol (initiated by 105either the client or the server); SSL_read_ex(), SSL_read(), SSL_peek_ex(), 106SSL_peek(), SSL_write_ex(), and SSL_write() will handle any pending handshakes. 107 108=item SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT 109 110The operation did not complete; the same TLS/SSL I/O function should be 111called again later. The underlying BIO was not connected yet to the peer 112and the call would block in connect()/accept(). The SSL function should be 113called again when the connection is established. These messages can only 114appear with a BIO_s_connect() or BIO_s_accept() BIO, respectively. 115In order to find out, when the connection has been successfully established, 116on many platforms select() or poll() for writing on the socket file descriptor 117can be used. 118 119=item SSL_ERROR_WANT_X509_LOOKUP 120 121The operation did not complete because an application callback set by 122SSL_CTX_set_client_cert_cb() has asked to be called again. 123The TLS/SSL I/O function should be called again later. 124Details depend on the application. 125 126=item SSL_ERROR_WANT_ASYNC 127 128The operation did not complete because an asynchronous engine is still 129processing data. This will only occur if the mode has been set to SSL_MODE_ASYNC 130using L<SSL_CTX_set_mode(3)> or L<SSL_set_mode(3)> and an asynchronous capable 131engine is being used. An application can determine whether the engine has 132completed its processing using select() or poll() on the asynchronous wait file 133descriptor. This file descriptor is available by calling 134L<SSL_get_all_async_fds(3)> or L<SSL_get_changed_async_fds(3)>. The TLS/SSL I/O 135function should be called again later. The function B<must> be called from the 136same thread that the original call was made from. 137 138=item SSL_ERROR_WANT_ASYNC_JOB 139 140The asynchronous job could not be started because there were no async jobs 141available in the pool (see ASYNC_init_thread(3)). This will only occur if the 142mode has been set to SSL_MODE_ASYNC using L<SSL_CTX_set_mode(3)> or 143L<SSL_set_mode(3)> and a maximum limit has been set on the async job pool 144through a call to L<ASYNC_init_thread(3)>. The application should retry the 145operation after a currently executing asynchronous operation for the current 146thread has completed. 147 148=item SSL_ERROR_WANT_CLIENT_HELLO_CB 149 150The operation did not complete because an application callback set by 151SSL_CTX_set_client_hello_cb() has asked to be called again. 152The TLS/SSL I/O function should be called again later. 153Details depend on the application. 154 155=item SSL_ERROR_SYSCALL 156 157Some non-recoverable, fatal I/O error occurred. The OpenSSL error queue may 158contain more information on the error. For socket I/O on Unix systems, consult 159B<errno> for details. If this error occurs then no further I/O operations should 160be performed on the connection and SSL_shutdown() must not be called. 161 162This value can also be returned for other errors, check the error queue for 163details. 164 165=item SSL_ERROR_SSL 166 167A non-recoverable, fatal error in the SSL library occurred, usually a protocol 168error. The OpenSSL error queue contains more information on the error. If this 169error occurs then no further I/O operations should be performed on the 170connection and SSL_shutdown() must not be called. 171 172=back 173 174=head1 SEE ALSO 175 176L<ssl(7)> 177 178=head1 HISTORY 179 180The SSL_ERROR_WANT_ASYNC error code was added in OpenSSL 1.1.0. 181The SSL_ERROR_WANT_CLIENT_HELLO_CB error code was added in OpenSSL 1.1.1. 182 183=head1 COPYRIGHT 184 185Copyright 2000-2024 The OpenSSL Project Authors. All Rights Reserved. 186 187Licensed under the Apache License 2.0 (the "License"). You may not use 188this file except in compliance with the License. You can obtain a copy 189in the file LICENSE in the source distribution or at 190L<https://www.openssl.org/source/license.html>. 191 192=cut 193