BIO_s_accept(3) OpenSSL BIO_s_accept(3) NNAAMMEE BIO_s_accept, BIO_set_accept_port, BIO_get_accept_port, BIO_set_nbio_accept, BIO_set_accept_bios, BIO_set_bind_mode, BIO_get_bind_mode, BIO_do_accept - accept BIO SSYYNNOOPPSSIISS #include BIO_METHOD *BIO_s_accept(void); long BIO_set_accept_port(BIO *b, char *name); char *BIO_get_accept_port(BIO *b); BIO *BIO_new_accept(char *host_port); long BIO_set_nbio_accept(BIO *b, int n); long BIO_set_accept_bios(BIO *b, char *bio); long BIO_set_bind_mode(BIO *b, long mode); long BIO_get_bind_mode(BIO *b, long dummy); #define BIO_BIND_NORMAL 0 #define BIO_BIND_REUSEADDR_IF_UNUSED 1 #define BIO_BIND_REUSEADDR 2 int BIO_do_accept(BIO *b); DDEESSCCRRIIPPTTIIOONN _B_I_O___s___a_c_c_e_p_t_(_) returns the accept BIO method. This is a wrapper round the platform's TCP/IP socket accept routines. Using accept BIOs, TCP/IP connections can be accepted and data trans- ferred using only BIO routines. In this way any platform specific oper- ations are hidden by the BIO abstraction. Read and write operations on an accept BIO will perform I/O on the underlying connection. If no connection is established and the port (see below) is set up properly then the BIO waits for an incoming con- nection. Accept BIOs support _B_I_O___p_u_t_s_(_) but not _B_I_O___g_e_t_s_(_). If the close flag is set on an accept BIO then any active connection on that chain is shutdown and the socket closed when the BIO is freed. Calling _B_I_O___r_e_s_e_t_(_) on a accept BIO will close any active connection and reset the BIO into a state where it awaits another incoming connec- tion. _B_I_O___g_e_t___f_d_(_) and _B_I_O___s_e_t___f_d_(_) can be called to retrieve or set the accept socket. See _B_I_O___s___f_d(3) _B_I_O___s_e_t___a_c_c_e_p_t___p_o_r_t_(_) uses the string nnaammee to set the accept port. The port is represented as a string of the form "host:port", where "host" is the interface to use and "port" is the port. The host can be can be "*" which is interpreted as meaning any interface; "port" has the same syntax as the port specified in _B_I_O___s_e_t___c_o_n_n___p_o_r_t_(_) for connect BIOs, that is it can be a numerical port string or a string to lookup using _g_e_t_s_e_r_v_b_y_n_a_m_e_(_) and a string table. _B_I_O___n_e_w___a_c_c_e_p_t_(_) combines _B_I_O___n_e_w_(_) and _B_I_O___s_e_t___a_c_c_e_p_t___p_o_r_t_(_) into a single call: that is it creates a new accept BIO with port hhoosstt__ppoorrtt. _B_I_O___s_e_t___n_b_i_o___a_c_c_e_p_t_(_) sets the accept socket to blocking mode (the default) if nn is 0 or non blocking mode if nn is 1. _B_I_O___s_e_t___a_c_c_e_p_t___b_i_o_s_(_) can be used to set a chain of BIOs which will be duplicated and prepended to the chain when an incoming connection is received. This is useful if, for example, a buffering or SSL BIO is required for each connection. The chain of BIOs must not be freed after this call, they will be automatically freed when the accept BIO is freed. _B_I_O___s_e_t___b_i_n_d___m_o_d_e_(_) and _B_I_O___g_e_t___b_i_n_d___m_o_d_e_(_) set and retrieve the cur- rent bind mode. If BIO_BIND_NORMAL (the default) is set then another socket cannot be bound to the same port. If BIO_BIND_REUSEADDR is set then other sockets can bind to the same port. If BIO_BIND_REUSE- ADDR_IF_UNUSED is set then and attempt is first made to use BIO_BIN_NORMAL, if this fails and the port is not in use then a second attempt is made using BIO_BIND_REUSEADDR. _B_I_O___d_o___a_c_c_e_p_t_(_) serves two functions. When it is first called, after the accept BIO has been setup, it will attempt to create the accept socket and bind an address to it. Second and subsequent calls to _B_I_O___d_o___a_c_c_e_p_t_(_) will await an incoming connection, or request a retry in non blocking mode. NNOOTTEESS When an accept BIO is at the end of a chain it will await an incoming connection before processing I/O calls. When an accept BIO is not at then end of a chain it passes I/O calls to the next BIO in the chain. When a connection is established a new socket BIO is created for the connection and appended to the chain. That is the chain is now accept->socket. This effectively means that attempting I/O on an ini- tial accept socket will await an incoming connection then perform I/O on it. If any additional BIOs have been set using _B_I_O___s_e_t___a_c_c_e_p_t___b_i_o_s_(_) then they are placed between the socket and the accept BIO, that is the chain will be accept->otherbios->socket. If a server wishes to process multiple connections (as is normally the case) then the accept BIO must be made available for further incoming connections. This can be done by waiting for a connection and then calling: connection = BIO_pop(accept); After this call ccoonnnneeccttiioonn will contain a BIO for the recently estab- lished connection and aacccceepptt will now be a single BIO again which can be used to await further incoming connections. If no further connec- tions will be accepted the aacccceepptt can be freed using _B_I_O___f_r_e_e_(_). If only a single connection will be processed it is possible to perform I/O using the accept BIO itself. This is often undesirable however because the accept BIO will still accept additional incoming connec- tions. This can be resolved by using _B_I_O___p_o_p_(_) (see above) and freeing up the accept BIO after the initial connection. If the underlying accept socket is non-blocking and _B_I_O___d_o___a_c_c_e_p_t_(_) is called to await an incoming connection it is possible for _B_I_O___s_h_o_u_l_d___i_o___s_p_e_c_i_a_l_(_) with the reason BIO_RR_ACCEPT. If this happens then it is an indication that an accept attempt would block: the appli- cation should take appropriate action to wait until the underlying socket has accepted a connection and retry the call. _B_I_O___s_e_t___a_c_c_e_p_t___p_o_r_t_(_), _B_I_O___g_e_t___a_c_c_e_p_t___p_o_r_t_(_), _B_I_O___s_e_t___n_b_i_o___a_c_c_e_p_t_(_), _B_I_O___s_e_t___a_c_c_e_p_t___b_i_o_s_(_), _B_I_O___s_e_t___b_i_n_d___m_o_d_e_(_), _B_I_O___g_e_t___b_i_n_d___m_o_d_e_(_) and _B_I_O___d_o___a_c_c_e_p_t_(_) are macros. RREETTUURRNN VVAALLUUEESS TBA EEXXAAMMPPLLEE This example accepts two connections on port 4444, sends messages down each and finally closes both down. BIO *abio, *cbio, *cbio2; ERR_load_crypto_strings(); abio = BIO_new_accept("4444"); /* First call to BIO_accept() sets up accept BIO */ if(BIO_do_accept(abio) <= 0) { fprintf(stderr, "Error setting up accept\n"); ERR_print_errors_fp(stderr); exit(0); } /* Wait for incoming connection */ if(BIO_do_accept(abio) <= 0) { fprintf(stderr, "Error accepting connection\n"); ERR_print_errors_fp(stderr); exit(0); } fprintf(stderr, "Connection 1 established\n"); /* Retrieve BIO for connection */ cbio = BIO_pop(abio); BIO_puts(cbio, "Connection 1: Sending out Data on initial connection\n"); fprintf(stderr, "Sent out data on connection 1\n"); /* Wait for another connection */ if(BIO_do_accept(abio) <= 0) { fprintf(stderr, "Error accepting connection\n"); ERR_print_errors_fp(stderr); exit(0); } fprintf(stderr, "Connection 2 established\n"); /* Close accept BIO to refuse further connections */ cbio2 = BIO_pop(abio); BIO_free(abio); BIO_puts(cbio2, "Connection 2: Sending out Data on second\n"); fprintf(stderr, "Sent out data on connection 2\n"); BIO_puts(cbio, "Connection 1: Second connection established\n"); /* Close the two established connections */ BIO_free(cbio); BIO_free(cbio2); SSEEEE AALLSSOO TBA 1.0.1u 2016-09-22 BIO_s_accept(3)