SSL_accept.3ssl man page
SSL_accept — wait for a TLS/SSL client to initiate a TLS/SSL handshake
#include <openssl/ssl.h> int SSL_accept(SSL *ssl);
SSL_accept() waits for a TLS/SSL client to initiate the TLS/SSL handshake. The communication channel must already have been set and assigned to the ssl by setting an underlying BIO.
The behaviour of SSL_accept() depends on the underlying BIO.
If the underlying BIO is blocking, SSL_accept() will only return once the handshake has been finished or an error occurred.
If the underlying BIO is non-blocking, SSL_accept() will also return when the underlying BIO could not satisfy the needs of SSL_accept() to continue the handshake, indicating the problem by the return value -1. In this case a call to SSL_get_error() with the return value of SSL_accept() will yield SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE. The calling process then must repeat the call after taking appropriate action to satisfy the needs of SSL_accept(). The action depends on the underlying BIO. When using a non-blocking socket, nothing is to be done, but select() can be used to check for the required condition. When using a buffering BIO, like a BIO pair, data must be written into or retrieved out of the BIO before being able to continue.
The following return values can occur:
The TLS/SSL handshake was not successful but was shut down controlled and by the specifications of the TLS/SSL protocol. Call SSL_get_error() with the return value ret to find out the reason.
The TLS/SSL handshake was successfully completed, a TLS/SSL connection has been established.
The TLS/SSL handshake was not successful because a fatal error occurred either at the protocol level or a connection failure occurred. The shutdown was not clean. It can also occur of action is need to continue the operation for non-blocking BIOs. Call SSL_get_error() with the return value ret to find out the reason.
SSL_get_error(3), SSL_connect(3), SSL_shutdown(3), ssl(3), bio(3), SSL_set_connect_state(3), SSL_do_handshake(3), SSL_CTX_new(3)
DTLSv1_listen.3ssl(3), ssl.3ssl(3), SSL_connect.3ssl(3), SSL_CTX_new.3ssl(3), SSL_do_handshake.3ssl(3), SSL_read.3ssl(3), SSL_set_bio.3ssl(3), SSL_set_connect_state.3ssl(3), SSL_set_fd.3ssl(3), SSL_shutdown.3ssl(3), SSL_write.3ssl(3).