5 SSL_CTX_set_async_callback,
6 SSL_CTX_set_async_callback_arg,
7 SSL_set_async_callback,
8 SSL_set_async_callback_arg,
11 - manage asynchronous operations
15 =for comment multiple includes
17 #include <openssl/ssl.h>
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);
28 SSL_CTX_set_async_callback() sets an asynchronous callback function. All SSL
29 objects generated based on this SSL_CTX will get this callback. If an engine
30 supports the callback mechanism, it will be automatically called if
31 SSL_MODE_ASYNC has been set and an asynchronous capable engine completes a
32 cryptography operation to notify the application to resume the paused work flow.
34 SSL_CTX_set_async_callback_arg() sets the callback argument.
36 SSL_set_async_callback() allows an application to set a callback in an
37 asynchronous SSL object, so that when an engine completes a cryptography
38 operation, the callback will be called to notify the application to resume the
41 SSL_set_async_callback_arg() sets an argument for the SSL object when the above
44 SSL_get_async_status() returns the engine status. This function facilitates the
45 communication from the engine to the application. During an SSL session,
46 cryptographic operations are dispatched to an engine. The engine status is very
47 useful for an application to know if the operation has been successfully
48 dispatched. If the engine does not support this additional callback method,
49 "ASYNC_STATUS_UNSUPPORTED" will be returned. See ASYNC_WAIT_CTX_set_status() for
50 a description of all of the status values.
52 An example of the above functions would be the following.
53 1. Application sets the async callback and callback data on an SSL connection
54 by calling SSL_set_async_callback().
55 2. Application sets SSL_MODE_ASYNC and makes an asynchronous SSL call
56 3. OpenSSL submits the asynchronous request to the engine. If a retry occurs at
57 this point then the status within the ASYNC_WAIT_CTX would be set and the async
58 callback function would be called (goto Step 7).
59 4. The OpenSSL engine pauses the current job and returns, so that the
60 application can continue processing other connections.
61 5. At a future point in time (probably via a polling mechanism or via an
62 interrupt) the engine will become aware that the asynchronous request has
64 6. The engine will call the application's callback passing the callback data as
66 7. The callback function should then run. Note: it is a requirement that the
67 callback function is small and non-blocking as it will be run in the context of
68 a polling mechanism or an interrupt.
69 8. It is the application's responsibility via the callback function to schedule
70 recalling the OpenSSL asynchronous function and to continue processing.
71 9. The callback function has the option to check the status returned via
72 SSL_get_async_status() to determine whether a retry happened instead of the
73 request being submitted, allowing different processing if required.
77 SSL_CTX_set_async_callback(), SSL_set_async_callback(),
78 SSL_CTX_set_async_callback_arg(), SSL_CTX_set_async_callback_arg() and
79 SSL_get_async_status() return 1 on success or 0 on error.
83 SSL_CTX_set_async_callback(), SSL_CTX_set_async_callback_arg(),
84 SSL_set_async_callback(), SSL_set_async_callback_arg() and
85 SSL_get_async_status() were first added to OpenSSL 3.0.
89 Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
91 Licensed under the OpenSSL license (the "License"). You may not use
92 this file except in compliance with the License. You can obtain a copy
93 in the file LICENSE in the source distribution or at
94 L<https://www.openssl.org/source/license.html>.