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BIO_S_CONNECT(3) Library Functions Manual BIO_S_CONNECT(3)

BIO_s_connect, BIO_new_connect, BIO_set_conn_hostname, BIO_set_conn_port, BIO_set_conn_ip, BIO_set_conn_int_port, BIO_get_conn_hostname, BIO_get_conn_port, BIO_get_conn_ip, BIO_get_conn_int_port, BIO_set_nbio, BIO_do_connectconnect BIO

#include <openssl/bio.h>

const BIO_METHOD *

BIO_new_connect(const char *name);

BIO_set_conn_hostname(BIO *b, char *name);

BIO_set_conn_port(BIO *b, char *port);

BIO_set_conn_ip(BIO *b, char *ip);

BIO_set_conn_int_port(BIO *b, char *port);

char *
BIO_get_conn_hostname(BIO *b);

char *
BIO_get_conn_port(BIO *b);

char *
BIO_get_conn_ip(BIO *b);

BIO_get_conn_int_port(BIO *b);

BIO_set_nbio(BIO *b, long n);

BIO_do_connect(BIO *b);

() returns the connect BIO method. This is a wrapper around the platform's TCP/IP socket connection routines.

Using connect BIOs, TCP/IP connections can be made and data transferred using only BIO routines. In this way any platform specific operations are hidden by the BIO abstraction.

Read and write operations on a connect BIO will perform I/O on the underlying connection. If no connection is established and the port and hostname (see below) is set up properly, then a connection is established first.

Connect BIOs support BIO_puts(3) but not BIO_gets(3).

If the close flag is set on a connect BIO, then any active connection is shutdown and the socket closed when the BIO is freed.

Calling BIO_reset(3) on a connect BIO will close any active connection and reset the BIO into a state where it can connect to the same host again.

BIO_get_fd(3) places the underlying socket in c if it is not NULL and also returns the socket. If c is not NULL, it should be of type int *.

BIO_set_info_callback(3) and BIO_callback_ctrl(3) with a cmd of BIO_CTRL_SET_CALLBACK save the pointer to the cb function internally in b and BIO_get_info_callback(3) retrieves this function pointer. If such an info callback is installed, it is invoked whenever a state change or error occurs in the connect BIO state machine. The arguments of the callback include the new state in case of a state change or the old state in case of an error and the value res that the state machine would return to whatever operation invoked it if no info callback had been installed. If an info callback is installed, the state machine returns the return value of the info callback instead. Consequently, the info callback is supposed to usually return res. The precise effect of the return value depends on which operation the state machine was invoked from. Usually, -1 is used to indicate failure and return values less than or equal to zero abort the operation in question, whereas positive values indicate success and allow the operation to proceed.

The state constants passed to the callback are named according to which operation needs to be performed next. They are listed here in the order the states are passed through:

The BIO is idle and no connection has been initiated yet.
The hostname to connect to needs to be converted to an IP address.
The service name to connect to needs to be converted to a TCP port number.
The TCP socket needs to be created with the socket(2) system call.
Socket options may need to be set using fcntl(2) and setsockopt(2).
The connection needs to be initiated with the connect(2) system call.
The connect(2) system call would have blocked and needs to be tried again.
The connection has been established and can now be used to transfer data.

() uses the string name to set the hostname. The hostname can be an IP address. The hostname can also include the port in the form hostname:port. It is also acceptable to use the forms hostname/any/other/path or hostname:port/any/other/path.

() sets the port to port. port is looked up as a service using getaddrinfo(3).

() sets the IP address to ip using binary form i.e. four bytes specifying the IP address in big-endian form.

() sets the port using port. port should be of type int *.

() returns the hostname of the connect BIO or NULL if the BIO is initialized but no hostname is set. This return value is an internal pointer which should not be modified.

() returns the port as a string. This return value is an internal pointer which should not be modified.

() returns the IP address in binary form.

() returns the port as an int.

() sets the non-blocking I/O flag to n. If n is zero then blocking I/O is set. If n is 1 then non-blocking I/O is set. Blocking I/O is the default. The call to BIO_set_nbio() should be made before the connection is established because non-blocking I/O is set during the connect process.

() combines BIO_new(3) and BIO_set_conn_hostname() into a single call. It creates a new connect BIO with name.

() attempts to connect the supplied BIO. It returns 1 if the connection was established successfully. A zero or negative value is returned if the connection could not be established. The call BIO_should_retry(3) should be used for non-blocking connect BIOs to determine if the call should be retried.

If blocking I/O is set then a non-positive return value from any I/O call is caused by an error condition, although a zero return will normally mean that the connection was closed.

If the port name is supplied as part of the host name then this will override any value set with (). This may be undesirable if the application does not wish to allow connection to arbitrary ports. This can be avoided by checking for the presence of the ‘:’ character in the passed hostname and either indicating an error or truncating the string at that point.

The values returned by (), BIO_get_conn_port(), BIO_get_conn_ip(), and BIO_get_conn_int_port() are updated when a connection attempt is made. Before any connection attempt the values returned are those set by the application itself.

Applications do not have to call () but may wish to do so to separate the connection process from other I/O processing.

If non-blocking I/O is set, then retries will be requested as appropriate.

In addition to BIO_should_read(3) and BIO_should_write(3) it is also possible for BIO_should_io_special(3) to be true during the initial connection process with the reason BIO_RR_CONNECT. If this is returned, it is an indication that a connection attempt would block. The application should then take appropriate action to wait until the underlying socket has connected and retry the call.

When a chain containing a connect BIO is copied with BIO_dup_chain(3), (), BIO_set_conn_port(), BIO_set_nbio(), and BIO_set_info_callback(3) are called internally to automatically copy the hostname, port, non-blocking I/O flag, and info callback from the original BIO object to the new one.

BIO_ctrl(3) cmd and larg arguments correspond to macros as follows:

cmd constant larg corresponding macro
0 ()
0 BIO_get_conn_hostname()
1 BIO_get_conn_port()
2 BIO_get_conn_ip()
3 BIO_get_conn_int_port()
0 BIO_get_fd(3)
0 BIO_set_conn_hostname()
1 BIO_set_conn_port()
2 BIO_set_conn_ip()
3 BIO_set_conn_int_port()
n BIO_set_nbio()
0 BIO_get_close(3)
0 BIO_reset(3)
flag BIO_set_close(3)

BIO_s_connect() returns the connect BIO method.

When called on a connect BIO object, BIO_method_type(3) returns the constant BIO_TYPE_CONNECT and BIO_method_name(3) returns a pointer to the static string "socket connect".

BIO_get_fd(3) returns the socket or -1 if the BIO has not been initialized.

BIO_set_conn_hostname(), BIO_set_conn_port(), BIO_set_conn_ip(), and BIO_set_conn_int_port() always return 1.

BIO_get_conn_hostname() returns the connected hostname or NULL if none is set.

BIO_get_conn_port() returns a string representing the connected port or NULL if not set.

BIO_get_conn_ip() returns a pointer to the connected IP address in binary form or all zeros if not set.

BIO_get_conn_int_port() returns the connected port or 0 if none was set.

BIO_set_nbio() always returns 1.

BIO_do_connect() returns 1 if the connection was successfully established and 0 or -1 if the connection failed.

This example connects to a webserver on the local host and attempts to retrieve a page and copy the result to standard output.

BIO *cbio, *out;
int len;
char tmpbuf[1024];

cbio = BIO_new_connect("localhost:http");
out = BIO_new_fp(stdout, BIO_NOCLOSE);
if (BIO_do_connect(cbio) <= 0) {
	fprintf(stderr, "Error connecting to server\n");
	/* whatever ... */
BIO_puts(cbio, "GET / HTTP/1.0\n\n");
for(;;) {
	len = BIO_read(cbio, tmpbuf, 1024);
	if (len <= 0)
	BIO_write(out, tmpbuf, len);


BIO_s_connect(), BIO_new_connect(), BIO_set_nbio(), and BIO_do_connect() first appeared in SSLeay 0.8.0. BIO_set_conn_hostname(), BIO_set_conn_port(), BIO_set_conn_ip(), BIO_set_conn_int_port(), BIO_get_conn_hostname(), BIO_get_conn_port(), BIO_get_conn_ip(), and BIO_get_conn_int_port() first appeared in SSLeay 0.9.0. All these functions have been available since OpenBSD 2.4.

April 30, 2023 OpenBSD-current