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BIO_s_accept(3) OpenSSL BIO_s_accept(3)
BIO_s_accept, BIO_set_accept_port, BIO_get_accept_port,
BIO_set_bind_mode, BIO_get_bind_mode, BIO_do_accept -
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);
BIO_s_accept() returns the accept BIO method. This is a
wrapper round the platform's TCP/IP socket accept rou-
Using accept BIOs, TCP/IP connections can be accepted and
data transferred using only BIO routines. In this way any
platform specific operations are hidden by the BIO
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 connection.
Accept BIOs support BIO_puts() but not BIO_gets().
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 BIO_reset() on a accept BIO will close any active
connection and reset the BIO into a state where it awaits
another incoming connection.
BIO_get_fd() and BIO_set_fd() can be called to retrieve or
set the accept socket. See BIO_s_fd(3)
BIO_set_accept_port() uses the string name 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. Either or both values can be "*"
which is interpreted as meaning any interface or port
respectively. "port" has the same syntax as the port spec-
ified in BIO_set_conn_port() for connect BIOs, that is it
can be a numerical port string or a string to lookup using
getservbyname() and a string table.
BIO_new_accept() combines BIO_new() and
BIO_set_accept_port() into a single call: that is it cre-
ates a new accept BIO with port host_port.
BIO_set_nbio_accept() sets the accept socket to blocking
mode (the default) if n is 0 or non blocking mode if n is
BIO_set_accept_bios() 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 con-
nection. The chain of BIOs must not be freed after this
call, they will be automatically freed when the accept BIO
BIO_set_bind_mode() and BIO_get_bind_mode() set and
retrieve the current 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_REUSEADDR_IF_UNUSED
is set then and attempt is first made to use BIO_BIN_NOR-
MAL, if this fails and the port is not in use then a sec-
ond attempt is made using BIO_BIND_REUSEADDR.
BIO_do_accept() 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 BIO_do_accept() will
await an incoming connection, or request a retry in non
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 cre-
ated 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 initial accept socket will await
an incoming connection then perform I/O on it.
If any additional BIOs have been set using
BIO_set_accept_bios() then they are placed between the
socket and the accept BIO, that is the chain will be
If a server wishes to process multiple connections (as is
normally the case) then the accept BIO must be made avail-
able for further incoming connections. This can be done by
waiting for a connection and then calling:
connection = BIO_pop(accept);
After this call connection will contain a BIO for the
recently established connection and accept will now be a
single BIO again which can be used to await further incom-
ing connections. If no further connections will be
accepted the accept can be freed using BIO_free().
If only a single connection will be processed it is possi-
ble to perform I/O using the accept BIO itself. This is
often undesirable however because the accept BIO will
still accept additional incoming connections. This can be
resolved by using BIO_pop() (see above) and freeing up the
accept BIO after the initial connection.
If the underlying accept socket is non-blocking and
BIO_do_accept() is called to await an incoming connection
it is possible for BIO_should_io_special() with the reason
BIO_RR_ACCEPT. If this happens then it is an indication
that an accept attempt would block: the application should
take appropriate action to wait until the underlying
socket has accepted a connection and retry the call.
BIO_set_bind_mode(), BIO_get_bind_mode() and
BIO_do_accept() are macros.
This example accepts two connections on port 4444, sends
messages down each and finally closes both down.
BIO *abio, *cbio, *cbio2;
abio = BIO_new_accept("4444");
/* First call to BIO_accept() sets up accept BIO */
if(BIO_do_accept(abio) SEE ALSO
0.9.7c 2002-12-12 BIO_s_accept(3)
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