openssl/doc/man3/SSL_get_error.pod

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=pod
=head1 NAME
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SSL_get_error - obtain result code for TLS/SSL I/O operation
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=head1 SYNOPSIS
#include <openssl/ssl.h>
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int SSL_get_error(const SSL *ssl, int ret);
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=head1 DESCRIPTION
SSL_get_error() returns a result code (suitable for the C "switch"
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statement) for a preceding call to SSL_connect(), SSL_accept(), SSL_do_handshake(),
SSL_read_ex(), SSL_read(), SSL_peek_ex(), SSL_peek(), SSL_write_ex() or
SSL_write() on B<ssl>. The value returned by that TLS/SSL I/O function must be
passed to SSL_get_error() in parameter B<ret>.
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In addition to B<ssl> and B<ret>, SSL_get_error() inspects the
current thread's OpenSSL error queue. Thus, SSL_get_error() must be
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used in the same thread that performed the TLS/SSL I/O operation, and no
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other OpenSSL function calls should appear in between. The current
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thread's error queue must be empty before the TLS/SSL I/O operation is
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attempted, or SSL_get_error() will not work reliably.
=head1 RETURN VALUES
The following return values can currently occur:
=over 4
=item SSL_ERROR_NONE
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The TLS/SSL I/O operation completed. This result code is returned
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if and only if B<ret E<gt> 0>.
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=item SSL_ERROR_ZERO_RETURN
The TLS/SSL peer has closed the connection for writing by sending the
close_notify alert.
No more data can be read.
Note that B<SSL_ERROR_ZERO_RETURN> does not necessarily
indicate that the underlying transport has been closed.
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=item SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE
The operation did not complete and can be retried later.
B<SSL_ERROR_WANT_READ> is returned when the last operation was a read
operation from a non-blocking B<BIO>.
It means that not enough data was available at this time to complete the
operation.
If at a later time the underlying B<BIO> has data available for reading the same
function can be called again.
SSL_read() and SSL_read_ex() can also set B<SSL_ERROR_WANT_READ> when there is
still unprocessed data available at either the B<SSL> or the B<BIO> layer, even
for a blocking B<BIO>.
See L<SSL_read(3)> for more information.
B<SSL_ERROR_WANT_WRITE> is returned when the last operation was a write
to a non-blocking B<BIO> and it was unable to sent all data to the B<BIO>.
When the B<BIO> is writeable again, the same function can be called again.
Note that the retry may again lead to an B<SSL_ERROR_WANT_READ> or
B<SSL_ERROR_WANT_WRITE> condition.
There is no fixed upper limit for the number of iterations that
may be necessary until progress becomes visible at application
protocol level.
It is safe to call SSL_read() or SSL_read_ex() when more data is available
even when the call that set this error was an SSL_write() or SSL_write_ex().
However if the call was an SSL_write() or SSL_write_ex(), it should be called
again to continue sending the application data.
For socket B<BIO>s (e.g. when SSL_set_fd() was used), select() or
poll() on the underlying socket can be used to find out when the
TLS/SSL I/O function should be retried.
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Caveat: Any TLS/SSL I/O function can lead to either of
B<SSL_ERROR_WANT_READ> and B<SSL_ERROR_WANT_WRITE>.
In particular,
SSL_read_ex(), SSL_read(), SSL_peek_ex(), or SSL_peek() may want to write data
and SSL_write() or SSL_write_ex() may want to read data.
This is mainly because
TLS/SSL handshakes may occur at any time during the protocol (initiated by
either the client or the server); SSL_read_ex(), SSL_read(), SSL_peek_ex(),
SSL_peek(), SSL_write_ex(), and SSL_write() will handle any pending handshakes.
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=item SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT
The operation did not complete; the same TLS/SSL I/O function should be
called again later. The underlying BIO was not connected yet to the peer
and the call would block in connect()/accept(). The SSL function should be
called again when the connection is established. These messages can only
appear with a BIO_s_connect() or BIO_s_accept() BIO, respectively.
In order to find out, when the connection has been successfully established,
on many platforms select() or poll() for writing on the socket file descriptor
can be used.
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=item SSL_ERROR_WANT_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.
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The TLS/SSL I/O function should be called again later.
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Details depend on the application.
=item SSL_ERROR_WANT_ASYNC
The operation did not complete because an asynchronous engine is still
processing data. This will only occur if the mode has been set to SSL_MODE_ASYNC
using L<SSL_CTX_set_mode(3)> or L<SSL_set_mode(3)> and an asynchronous capable
engine is being used. An application can determine whether the engine has
completed its processing using select() or poll() on the asynchronous wait file
descriptor. This file descriptor is available by calling
L<SSL_get_all_async_fds(3)> or L<SSL_get_changed_async_fds(3)>. The TLS/SSL I/O
function should be called again later. The function B<must> be called from the
same thread that the original call was made from.
=item SSL_ERROR_WANT_ASYNC_JOB
The asynchronous job could not be started because there were no async jobs
available in the pool (see ASYNC_init_thread(3)). This will only occur if the
mode has been set to SSL_MODE_ASYNC using L<SSL_CTX_set_mode(3)> or
L<SSL_set_mode(3)> and a maximum limit has been set on the async job pool
through a call to L<ASYNC_init_thread(3)>. The application should retry the
operation after a currently executing asynchronous operation for the current
thread has completed.
=item SSL_ERROR_WANT_CLIENT_HELLO_CB
Add SSL_CTX early callback Provide a callback interface that gives the application the ability to adjust the nascent SSL object at the earliest stage of ClientHello processing, immediately after extensions have been collected but before they have been processed. This is akin to BoringSSL's "select_certificate_cb" (though it is not API compatible), and as the name indicates, one major use is to examine the supplied server name indication and select what certificate to present to the client. However, it can also be used to make more sweeping configuration changes to the SSL object according to the selected server identity and configuration. That may include adjusting the permitted TLS versions, swapping out the SSL_CTX object (as is traditionally done in a tlsext_servername_callback), changing the server's cipher list, and more. We also wish to allow an early callback to indicate that it needs to perform additional work asynchronously and resume processing later. To that effect, refactor the second half of tls_process_client_hello() into a subroutine to be called at the post-processing stage (including the early callback itself), to allow the callback to result in remaining in the same work stage for a later call to succeed. This requires allocating for and storing the CLIENTHELLO_MSG in the SSL object to be preserved across such calls, but the storage is reclaimed after ClientHello processing finishes. Information about the CliehtHello is available to the callback by means of accessor functions that can only be used from the early callback. This allows extensions to make use of the existing internal parsing machinery without exposing structure internals (e.g., of PACKET), so that applications do not have to write fragile parsing code. Applications are encouraged to utilize an early callback and not use a servername_callback, in order to avoid unexpected behavior that occurs due to the relative order of processing between things like session resumption and the historical servername callback. Also tidy up nearby style by removing unnecessary braces around one-line conditional bodies. Reviewed-by: Matt Caswell <matt@openssl.org> Reviewed-by: Richard Levitte <levitte@openssl.org> (Merged from https://github.com/openssl/openssl/pull/2279)
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The operation did not complete because an application callback set by
SSL_CTX_set_client_hello_cb() has asked to be called again.
Add SSL_CTX early callback Provide a callback interface that gives the application the ability to adjust the nascent SSL object at the earliest stage of ClientHello processing, immediately after extensions have been collected but before they have been processed. This is akin to BoringSSL's "select_certificate_cb" (though it is not API compatible), and as the name indicates, one major use is to examine the supplied server name indication and select what certificate to present to the client. However, it can also be used to make more sweeping configuration changes to the SSL object according to the selected server identity and configuration. That may include adjusting the permitted TLS versions, swapping out the SSL_CTX object (as is traditionally done in a tlsext_servername_callback), changing the server's cipher list, and more. We also wish to allow an early callback to indicate that it needs to perform additional work asynchronously and resume processing later. To that effect, refactor the second half of tls_process_client_hello() into a subroutine to be called at the post-processing stage (including the early callback itself), to allow the callback to result in remaining in the same work stage for a later call to succeed. This requires allocating for and storing the CLIENTHELLO_MSG in the SSL object to be preserved across such calls, but the storage is reclaimed after ClientHello processing finishes. Information about the CliehtHello is available to the callback by means of accessor functions that can only be used from the early callback. This allows extensions to make use of the existing internal parsing machinery without exposing structure internals (e.g., of PACKET), so that applications do not have to write fragile parsing code. Applications are encouraged to utilize an early callback and not use a servername_callback, in order to avoid unexpected behavior that occurs due to the relative order of processing between things like session resumption and the historical servername callback. Also tidy up nearby style by removing unnecessary braces around one-line conditional bodies. Reviewed-by: Matt Caswell <matt@openssl.org> Reviewed-by: Richard Levitte <levitte@openssl.org> (Merged from https://github.com/openssl/openssl/pull/2279)
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The TLS/SSL I/O function should be called again later.
Details depend on the application.
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=item SSL_ERROR_SYSCALL
Some non-recoverable, fatal I/O error occurred. The OpenSSL error queue may
contain more information on the error. For socket I/O on Unix systems, consult
B<errno> for details. If this error occurs then no further I/O operations should
be performed on the connection and SSL_shutdown() must not be called.
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This value can also be returned for other errors, check the error queue for
details.
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=item SSL_ERROR_SSL
A non-recoverable, fatal error in the SSL library occurred, usually a protocol
error. The OpenSSL error queue contains more information on the error. If this
error occurs then no further I/O operations should be performed on the
connection and SSL_shutdown() must not be called.
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=back
=head1 SEE ALSO
L<ssl(7)>
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=head1 HISTORY
The SSL_ERROR_WANT_ASYNC error code was added in OpenSSL 1.1.0.
The SSL_ERROR_WANT_CLIENT_HELLO_CB error code was added in OpenSSL 1.1.1.
=head1 COPYRIGHT
Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (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