Cryptography and SSL/TLS Toolkit



SSL_waiting_for_async, SSL_get_all_async_fds, SSL_get_changed_async_fds - manage asynchronous operations


#include <openssl/async.h>
#include <openssl/ssl.h>

int SSL_waiting_for_async(SSL *s);
int SSL_get_all_async_fds(SSL *s, OSSL_ASYNC_FD *fd, size_t *numfds);
int SSL_get_changed_async_fds(SSL *s, OSSL_ASYNC_FD *addfd, size_t *numaddfds,
                              OSSL_ASYNC_FD *delfd, size_t *numdelfds);


SSL_waiting_for_async() determines whether an SSL connection is currently waiting for asynchronous operations to complete (see the SSL_MODE_ASYNC mode in SSL_CTX_set_mode(3)).

SSL_get_all_async_fds() returns a list of file descriptor which can be used in a call to select() or poll() to determine whether the current asynchronous operation has completed or not. A completed operation will result in data appearing as "read ready" on the file descriptor (no actual data should be read from the file descriptor). This function should only be called if the SSL object is currently waiting for asynchronous work to complete (i.e. SSL_ERROR_WANT_ASYNC has been received - see SSL_get_error(3)). Typically the list will only contain one file descriptor. However, if multiple asynchronous capable engines are in use then more than one is possible. The number of file descriptors returned is stored in *numfds and the file descriptors themselves are in *fds. The fds parameter may be NULL in which case no file descriptors are returned but *numfds is still populated. It is the callers responsibility to ensure sufficient memory is allocated at *fds so typically this function is called twice (once with a NULL fds parameter and once without).

SSL_get_changed_async_fds() returns a list of the asynchronous file descriptors that have been added and a list that have been deleted since the last SSL_ERROR_WANT_ASYNC was received (or since the SSL object was created if no SSL_ERROR_WANT_ASYNC has been received). Similar to SSL_get_all_async_fds() it is the callers responsibility to ensure that *addfd and *delfd have sufficient memory allocated, although they may be NULL. The number of added fds and the number of deleted fds are stored in *numaddfds and *numdelfds respectively.


SSL_waiting_for_async() will return 1 if the current SSL operation is waiting for an async operation to complete and 0 otherwise.

SSL_get_all_async_fds() and SSL_get_changed_async_fds() return 1 on success or 0 on error.


On Windows platforms the <openssl/async.h> header is dependent on some of the types customarily made available by including <windows.h>. The application developer is likely to require control over when the latter is included, commonly as one of the first included headers. Therefore, it is defined as an application developer's responsibility to include <windows.h> prior to <openssl/async.h>.


ssl(7), SSL_get_error(3), SSL_CTX_set_mode(3)


The SSL_waiting_for_async(), SSL_get_all_async_fds() and SSL_get_changed_async_fds() functions were added in OpenSSL 1.1.0.

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