Updated: 2022/Sep/29

Please read Privacy Policy. It's for your privacy.

SSL_set_async_callback(3)           OpenSSL          SSL_set_async_callback(3)



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

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #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);

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 nonblocking 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.

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.

SEE ALSO
       ssl(7)

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.

COPYRIGHT
       Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (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
       <https://www.openssl.org/source/license.html>.



3.0.12                            2023-05-07         SSL_set_async_callback(3)