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- =pod
- =head1 NAME
- SSL_CTX_set_async_callback,
- SSL_CTX_set_async_callback_arg,
- SSL_set_async_callback,
- SSL_set_async_callback_arg,
- SSL_get_async_status,
- SSL_async_callback_fn
- - manage asynchronous operations
- =head1 SYNOPSIS
- =for comment multiple includes
- #include <openssl/ssl.h>
- typedef int (*SSL_async_callback_fn)(SSL *s, void *arg);
- int SSL_CTX_set_async_callback(SSL_CTX *ctx, SSL_async_callback_fn callback);
- int SSL_CTX_set_async_callback_arg(SSL_CTX *ctx, void *arg);
- int SSL_set_async_callback(SSL *s, SSL_async_callback_fn callback);
- int SSL_set_async_callback_arg(SSL *s, void *arg);
- int SSL_get_async_status(SSL *s, int *status);
- =head1 DESCRIPTION
- SSL_CTX_set_async_callback() sets an asynchronous callback function. All SSL
- objects generated based on this SSL_CTX will get this callback. If an engine
- supports the callback mechanism, it will be automatically called if
- SSL_MODE_ASYNC has been set and an asynchronous capable engine completes a
- cryptography operation to notify the application to resume the paused work flow.
- SSL_CTX_set_async_callback_arg() sets the callback argument.
- SSL_set_async_callback() allows an application to set a callback in an
- asynchronous SSL object, so that when an engine completes a cryptography
- operation, the callback will be called to notify the application to resume the
- paused work flow.
- SSL_set_async_callback_arg() sets an argument for the SSL object when the above
- callback is called.
- SSL_get_async_status() returns the engine status. This function facilitates the
- communication from the engine to the application. During an SSL session,
- cryptographic operations are dispatched to an engine. The engine status is very
- useful for an application to know if the operation has been successfully
- dispatched. If the engine does not support this additional callback method,
- "ASYNC_STATUS_UNSUPPORTED" will be returned. See ASYNC_WAIT_CTX_set_status() for
- a description of all of the status values.
- An example of the above functions would be the following.
- 1. Application sets the async callback and callback data on an SSL connection
- by calling SSL_set_async_callback().
- 2. Application sets SSL_MODE_ASYNC and makes an asynchronous SSL call
- 3. OpenSSL submits the asynchronous request to the engine. If a retry occurs at
- this point then the status within the ASYNC_WAIT_CTX would be set and the async
- callback function would be called (goto Step 7).
- 4. The OpenSSL engine pauses the current job and returns, so that the
- application can continue processing other connections.
- 5. At a future point in time (probably via a polling mechanism or via an
- interrupt) the engine will become aware that the asynchronous request has
- finished processing.
- 6. The engine will call the application's callback passing the callback data as
- a parameter.
- 7. The callback function should then run. Note: it is a requirement that the
- callback function is small and non-blocking as it will be run in the context of
- a polling mechanism or an interrupt.
- 8. It is the application's responsibility via the callback function to schedule
- recalling the OpenSSL asynchronous function and to continue processing.
- 9. The callback function has the option to check the status returned via
- SSL_get_async_status() to determine whether a retry happened instead of the
- request being submitted, allowing different processing if required.
- =head1 RETURN VALUES
- SSL_CTX_set_async_callback(), SSL_set_async_callback(),
- SSL_CTX_set_async_callback_arg(), SSL_CTX_set_async_callback_arg() and
- SSL_get_async_status() return 1 on success or 0 on error.
- =head1 HISTORY
- SSL_CTX_set_async_callback(), SSL_CTX_set_async_callback_arg(),
- SSL_set_async_callback(), SSL_set_async_callback_arg() and
- SSL_get_async_status() were first added to OpenSSL 3.0.0.
- =head1 COPYRIGHT
- Copyright 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
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