1=pod
2
3=head1 NAME
4
5SSL_CTX_set_async_callback,
6SSL_CTX_set_async_callback_arg,
7SSL_set_async_callback,
8SSL_set_async_callback_arg,
9SSL_get_async_status,
10SSL_async_callback_fn
11- manage asynchronous operations
12
13=head1 SYNOPSIS
14
15=for openssl multiple includes
16
17 #include <openssl/ssl.h>
18
19 typedef int (*SSL_async_callback_fn)(SSL *s, void *arg);
20 int SSL_CTX_set_async_callback(SSL_CTX *ctx, SSL_async_callback_fn callback);
21 int SSL_CTX_set_async_callback_arg(SSL_CTX *ctx, void *arg);
22 int SSL_set_async_callback(SSL *s, SSL_async_callback_fn callback);
23 int SSL_set_async_callback_arg(SSL *s, void *arg);
24 int SSL_get_async_status(SSL *s, int *status);
25
26=head1 DESCRIPTION
27
28SSL_CTX_set_async_callback() sets an asynchronous callback function. All B<SSL>
29objects generated based on this B<SSL_CTX> will get this callback. If an engine
30supports the callback mechanism, it will be automatically called if
31B<SSL_MODE_ASYNC> has been set and an asynchronous capable engine completes a
32cryptography operation to notify the application to resume the paused work flow.
33
34SSL_CTX_set_async_callback_arg() sets the callback argument.
35
36SSL_set_async_callback() allows an application to set a callback in an
37asynchronous B<SSL> object, so that when an engine completes a cryptography
38operation, the callback will be called to notify the application to resume the
39paused work flow.
40
41SSL_set_async_callback_arg() sets an argument for the B<SSL> object when the
42above callback is called.
43
44SSL_get_async_status() returns the engine status. This function facilitates the
45communication from the engine to the application. During an SSL session,
46cryptographic operations are dispatched to an engine. The engine status is very
47useful for an application to know if the operation has been successfully
48dispatched. If the engine does not support this additional callback method,
49B<ASYNC_STATUS_UNSUPPORTED> will be returned. See ASYNC_WAIT_CTX_set_status()
50for a description of all of the status values.
51
52An example of the above functions would be the following:
53
54=over 4
55
56=item 1.
57
58Application sets the async callback and callback data on an SSL connection
59by calling SSL_set_async_callback().
60
61=item 2.
62
63Application sets B<SSL_MODE_ASYNC> and makes an asynchronous SSL call
64
65=item 3.
66
67OpenSSL submits the asynchronous request to the engine. If a retry occurs at
68this point then the status within the B<ASYNC_WAIT_CTX> would be set and the
69async callback function would be called (goto Step 7).
70
71=item 4.
72
73The OpenSSL engine pauses the current job and returns, so that the
74application can continue processing other connections.
75
76=item 5.
77
78At a future point in time (probably via a polling mechanism or via an
79interrupt) the engine will become aware that the asynchronous request has
80finished processing.
81
82=item 6.
83
84The engine will call the application's callback passing the callback data as
85a parameter.
86
87=item 7.
88
89The callback function should then run. Note: it is a requirement that the
90callback function is small and nonblocking as it will be run in the context of
91a polling mechanism or an interrupt.
92
93=item 8.
94
95It is the application's responsibility via the callback function to schedule
96recalling the OpenSSL asynchronous function and to continue processing.
97
98=item 9.
99
100The callback function has the option to check the status returned via
101SSL_get_async_status() to determine whether a retry happened instead of the
102request being submitted, allowing different processing if required.
103
104=back
105
106=head1 RETURN VALUES
107
108SSL_CTX_set_async_callback(), SSL_set_async_callback(),
109SSL_CTX_set_async_callback_arg(), SSL_CTX_set_async_callback_arg() and
110SSL_get_async_status() return 1 on success or 0 on error.
111
112=head1 SEE ALSO
113
114L<ssl(7)>
115
116=head1 HISTORY
117
118SSL_CTX_set_async_callback(), SSL_CTX_set_async_callback_arg(),
119SSL_set_async_callback(), SSL_set_async_callback_arg() and
120SSL_get_async_status() were first added to OpenSSL 3.0.
121
122=head1 COPYRIGHT
123
124Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.
125
126Licensed under the Apache License 2.0 (the "License").  You may not use
127this file except in compliance with the License.  You can obtain a copy
128in the file LICENSE in the source distribution or at
129L<https://www.openssl.org/source/license.html>.
130
131=cut
132