SSL_ACCEPT(3) Library Functions Manual SSL_ACCEPT(3)

SSL_accept — wait for a TLS/SSL client to initiate a TLS/SSL handshake

/* -lssl -lcrypto */
#include <openssl/ssl.h>

int
SSL_accept(SSL *ssl);

() 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 object by setting an underlying BIO.

The behaviour of () depends on the underlying BIO.

If the underlying BIO is , () will only return once the handshake has been finished or an error occurred.

If the underlying BIO is , () 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(3) 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(2) 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:

0
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(3) with the return value ret to find out the reason.
1
The TLS/SSL handshake was successfully completed, and a TLS/SSL connection has been established.
<0
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(3) with the return value ret to find out the reason.

BIO_new(3), ssl(3), SSL_connect(3), SSL_CTX_new(3), SSL_do_handshake(3), SSL_get_error(3), SSL_set_connect_state(3), SSL_shutdown(3)

SSL_accept() appeared in SSLeay 0.4 or earlier and has been available since OpenBSD 2.4.

OpenBSD 7.8 June 8, 2025 SSL_ACCEPT(3)