.\" $OpenBSD: BIO_s_connect.3,v 1.19 2023/04/30 13:53:54 schwarze Exp $
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.Dd $Mdocdate: April 30 2023 $
.Dt BIO_S_CONNECT 3
.Os
.Sh NAME
.Nm BIO_s_connect ,
.Nm BIO_new_connect ,
.Nm BIO_set_conn_hostname ,
.Nm BIO_set_conn_port ,
.Nm BIO_set_conn_ip ,
.Nm BIO_set_conn_int_port ,
.Nm BIO_get_conn_hostname ,
.Nm BIO_get_conn_port ,
.Nm BIO_get_conn_ip ,
.Nm BIO_get_conn_int_port ,
.Nm BIO_set_nbio ,
.Nm BIO_do_connect
.Nd connect BIO
.Sh SYNOPSIS
.In openssl/bio.h
.Ft const BIO_METHOD *
.Fo BIO_s_connect
.Fa void
.Fc
.Ft BIO *
.Fo BIO_new_connect
.Fa "const char *name"
.Fc
.Ft long
.Fo BIO_set_conn_hostname
.Fa "BIO *b"
.Fa "char *name"
.Fc
.Ft long
.Fo BIO_set_conn_port
.Fa "BIO *b"
.Fa "char *port"
.Fc
.Ft long
.Fo BIO_set_conn_ip
.Fa "BIO *b"
.Fa "char *ip"
.Fc
.Ft long
.Fo BIO_set_conn_int_port
.Fa "BIO *b"
.Fa "char *port"
.Fc
.Ft char *
.Fo BIO_get_conn_hostname
.Fa "BIO *b"
.Fc
.Ft char *
.Fo BIO_get_conn_port
.Fa "BIO *b"
.Fc
.Ft char *
.Fo BIO_get_conn_ip
.Fa "BIO *b"
.Fc
.Ft long
.Fo BIO_get_conn_int_port
.Fa "BIO *b"
.Fc
.Ft long
.Fo BIO_set_nbio
.Fa "BIO *b"
.Fa "long n"
.Fc
.Ft long
.Fo BIO_do_connect
.Fa "BIO *b"
.Fc
.Sh DESCRIPTION
.Fn BIO_s_connect
returns the connect BIO method.
This is a wrapper around the platform's TCP/IP socket connection routines.
.Pp
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.
.Pp
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.
.Pp
Connect BIOs support
.Xr BIO_puts 3
but not
.Xr BIO_gets 3 .
.Pp
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.
.Pp
Calling
.Xr 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.
.Pp
.Xr BIO_get_fd 3
places the underlying socket in
.Fa c
if it is not
.Dv NULL
and also returns the socket.
If
.Fa c
is not
.Dv NULL ,
it should be of type
.Vt "int *" .
.Pp
.Xr BIO_set_info_callback 3
and
.Xr BIO_callback_ctrl 3
with a
.Fa cmd
of
.Dv BIO_CTRL_SET_CALLBACK
save the pointer to the
.Fa cb
function internally in
.Fa b
and
.Xr 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
.Fa state
in case of a state change or the old
.Fa state
in case of an error and the value
.Fa 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
.Fa 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.
.Pp
The
.Fa 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:
.Pp
.Bl -tag -width BIO_CONN_S_BLOCKED_CONNECT -offset 3n -compact
.It Dv BIO_CONN_S_BEFORE
The BIO is idle and no connection has been initiated yet.
.It Dv BIO_CONN_S_GET_IP
The hostname to connect to needs to be converted to an IP address.
.It Dv BIO_CONN_S_GET_PORT
The service name to connect to needs to be converted to a TCP port number.
.It Dv BIO_CONN_S_CREATE_SOCKET
The TCP socket needs to be created with the
.Xr socket 2
system call.
.It Dv BIO_CONN_S_NBIO
Socket options may need to be set using
.Xr fcntl 2
and
.Xr setsockopt 2 .
.It Dv BIO_CONN_S_CONNECT
The connection needs to be initiated with the
.Xr connect 2
system call.
.It Dv BIO_CONN_S_BLOCKED_CONNECT
The
.Xr connect 2
system call would have blocked and needs to be tried again.
.It Dv BIO_CONN_S_OK
The connection has been established and can now be used to transfer data.
.El
.Pp
.Fn BIO_set_conn_hostname
uses the string
.Fa name
to set the hostname.
The hostname can be an IP address.
The hostname can also include the port in the form
.Ar hostname : Ns Ar port .
It is also acceptable to use the forms
.Ar hostname Ns / Ns Pa any/other/path
or
.Ar hostname : Ns Ar port Ns / Ns Pa any/other/path .
.Pp
.Fn BIO_set_conn_port
sets the port to
.Fa port .
.Fa port
is looked up as a service using
.Xr getaddrinfo 3 .
.Pp
.Fn BIO_set_conn_ip
sets the IP address to
.Fa ip
using binary form i.e. four bytes specifying the IP address
in big-endian form.
.Pp
.Fn BIO_set_conn_int_port
sets the port using
.Fa port .
.Fa port
should
be of type
.Vt "int *" .
.Pp
.Fn BIO_get_conn_hostname
returns the hostname of the connect BIO or
.Dv NULL
if the BIO is initialized but no hostname is set.
This return value is an internal pointer which should not be modified.
.Pp
.Fn BIO_get_conn_port
returns the port as a string.
This return value is an internal pointer which should not be modified.
.Pp
.Fn BIO_get_conn_ip
returns the IP address in binary form.
.Pp
.Fn BIO_get_conn_int_port
returns the port as an
.Vt int .
.Pp
.Fn BIO_set_nbio
sets the non-blocking I/O flag to
.Fa n .
If
.Fa n
is zero then blocking I/O is set.
If
.Fa n
is 1 then non-blocking I/O is set.
Blocking I/O is the default.
The call to
.Fn BIO_set_nbio
should be made before the connection is established
because non-blocking I/O is set during the connect process.
.Pp
.Fn BIO_new_connect
combines
.Xr BIO_new 3
and
.Fn BIO_set_conn_hostname
into a single call.
It creates a new connect BIO with
.Fa name .
.Pp
.Fn BIO_do_connect
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
.Xr BIO_should_retry 3
should be used for non-blocking connect BIOs
to determine if the call should be retried.
.Pp
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.
.Pp
If the port name is supplied as part of the host name then this will
override any value set with
.Fn BIO_set_conn_port .
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
.Sq \&:
character in the passed hostname and either indicating an error
or truncating the string at that point.
.Pp
The values returned by
.Fn BIO_get_conn_hostname ,
.Fn BIO_get_conn_port ,
.Fn BIO_get_conn_ip ,
and
.Fn 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.
.Pp
Applications do not have to call
.Fn BIO_do_connect
but may wish to do so to separate the connection process
from other I/O processing.
.Pp
If non-blocking I/O is set,
then retries will be requested as appropriate.
.Pp
In addition to
.Xr BIO_should_read 3
and
.Xr BIO_should_write 3
it is also possible for
.Xr BIO_should_io_special 3
to be true during the initial connection process with the reason
.Dv 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.
.Pp
When a chain containing a connect BIO is copied with
.Xr BIO_dup_chain 3 ,
.Fn BIO_set_conn_hostname ,
.Fn BIO_set_conn_port ,
.Fn BIO_set_nbio ,
and
.Xr 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.
.Pp
.Xr BIO_ctrl 3
.Fa cmd
and
.Fa larg
arguments correspond to macros as follows:
.Bl -column BIO_C_DO_STATE_MACHINE larg BIO_get_conn_hostname(3) -offset 3n
.It Fa cmd No constant        Ta Fa larg Ta corresponding macro
.It Dv BIO_C_DO_STATE_MACHINE Ta 0       Ta Fn BIO_do_connect
.It Dv BIO_C_GET_CONNECT      Ta 0       Ta Fn BIO_get_conn_hostname
.It                           Ta 1       Ta Fn BIO_get_conn_port
.It                           Ta 2       Ta Fn BIO_get_conn_ip
.It                           Ta 3       Ta Fn BIO_get_conn_int_port
.It Dv BIO_C_GET_FD           Ta 0       Ta Xr BIO_get_fd 3
.It Dv BIO_C_SET_CONNECT      Ta 0       Ta Fn BIO_set_conn_hostname
.It                           Ta 1       Ta Fn BIO_set_conn_port
.It                           Ta 2       Ta Fn BIO_set_conn_ip
.It                           Ta 3       Ta Fn BIO_set_conn_int_port
.It Dv BIO_C_SET_NBIO         Ta Fa n    Ta Fn BIO_set_nbio
.It Dv BIO_CTRL_GET_CLOSE     Ta 0       Ta Xr BIO_get_close 3
.It Dv BIO_CTRL_RESET         Ta 0       Ta Xr BIO_reset 3
.It Dv BIO_CTRL_SET_CLOSE     Ta Fa flag Ta Xr BIO_set_close 3
.El
.Sh RETURN VALUES
.Fn BIO_s_connect
returns the connect BIO method.
.Pp
When called on a connect BIO object,
.Xr BIO_method_type 3
returns the constant
.Dv BIO_TYPE_CONNECT
and
.Xr BIO_method_name 3
returns a pointer to the static string
.Qq socket connect .
.Pp
.Xr BIO_get_fd 3
returns the socket or -1 if the BIO has not been initialized.
.Pp
.Fn BIO_set_conn_hostname ,
.Fn BIO_set_conn_port ,
.Fn BIO_set_conn_ip ,
and
.Fn BIO_set_conn_int_port
always return 1.
.Pp
.Fn BIO_get_conn_hostname
returns the connected hostname or
.Dv NULL
if none is set.
.Pp
.Fn BIO_get_conn_port
returns a string representing the connected port or
.Dv NULL
if not set.
.Pp
.Fn BIO_get_conn_ip
returns a pointer to the connected IP address in binary form
or all zeros if not set.
.Pp
.Fn BIO_get_conn_int_port
returns the connected port or 0 if none was set.
.Pp
.Fn BIO_set_nbio
always returns 1.
.Pp
.Fn BIO_do_connect
returns 1 if the connection was successfully
established and 0 or -1 if the connection failed.
.Sh EXAMPLES
This example connects to a webserver on the local host and attempts
to retrieve a page and copy the result to standard output.
.Bd -literal -offset 2n
BIO *cbio, *out;
int len;
char tmpbuf[1024];

ERR_load_crypto_strings();
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\en");
	ERR_print_errors_fp(stderr);
	/* whatever ... */
}
BIO_puts(cbio, "GET / HTTP/1.0\en\en");
for(;;) {
	len = BIO_read(cbio, tmpbuf, 1024);
	if (len <= 0)
		break;
	BIO_write(out, tmpbuf, len);
}
BIO_free(cbio);
BIO_free(out);
.Ed
.Sh SEE ALSO
.Xr BIO_new 3
.Sh HISTORY
.Fn BIO_s_connect ,
.Fn BIO_new_connect ,
.Fn BIO_set_nbio ,
and
.Fn BIO_do_connect
first appeared in SSLeay 0.8.0.
.Fn BIO_set_conn_hostname ,
.Fn BIO_set_conn_port ,
.Fn BIO_set_conn_ip ,
.Fn BIO_set_conn_int_port ,
.Fn BIO_get_conn_hostname ,
.Fn BIO_get_conn_port ,
.Fn BIO_get_conn_ip ,
and
.Fn BIO_get_conn_int_port
first appeared in SSLeay 0.9.0.
All these functions have been available since
.Ox 2.4 .