rfcomm

RFCOMM protocol

Version:

BlueZ

Copyright:

Free use of this software is granted under the terms of the GNU Lesser General Public Licenses (LGPL).

Date:

May 2024

Manual section:

7

Manual group:

Linux System Administration

SYNOPSIS

#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>

rfcomm_socket = socket(PF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);

DESCRIPTION

The RFCOMM protocol provides emulation of serial ports over the L2CAP(7) protocol. The protocol is based on the ETSI standard TS 07.10.

RFCOMM is a simple transport protocol, with additional provisions for emulating the 9 circuits of RS-232 (EIATIA-232-E) serial ports.

SOCKET ADDRESS

struct sockaddr_rc {
    sa_family_t rc_family;
    unsigned short rc_bdaddr;
    unsigned char rc_channel;
};

Example:

struct sockaddr_rc addr;

memset(&addr, 0, sizeof(addr));
addr.rc_family = AF_BLUETOOTH;
bacpy(&addr.rc_bdaddr, bdaddr);
addr.rc_channel = channel;

SOCKET OPTIONS

The socket options listed below can be set by using setsockopt(2) and read with getsockopt(2) with the socket level set to SOL_BLUETOOTH.

BT_SECURITY (since Linux 2.6.30)

Channel security level, possible values:

Value	Security Level	Link Key Type	Encryption
BT_SECURITY_SDP	0 (SDP Only)	None	Not required
BT_SECURITY_LOW	1 (Low)	Unauthenticated	Not required
BT_SECURITY_MEDIUM	2 (Medium - default)	Unauthenticated	Desired
BT_SECURITY_HIGH	3 (High)	Authenticated	Required
BT_SECURITY_FIPS (since Linux 3.15)	4 (Secure Only)	Authenticated (P-256 based Secure Simple Pairing and Secure Authentication)	Required

Example:

int level = BT_SECURITY_HIGH;
int err = setsockopt(rfcomm_socket, SOL_BLUETOOTH, BT_SECURITY, &level,
                     sizeof(level));
if (err == -1) {
    perror("setsockopt");
    return 1;
}

BT_DEFER_SETUP (since Linux 2.6.30)

Channel defer connection setup, this control if the connection procedure needs to be authorized by userspace before responding which allows authorization at profile level, possible values:

Value	Description	Authorization
0	Disable (default)	Not required
1	Enable	Required

Example:

int defer_setup = 1;
int err = setsockopt(rfcomm_socket, SOL_BLUETOOTH, BT_DEFER_SETUP,
                     &defer_setup, sizeof(defer_setup));
if (err == -1) {
    perror("setsockopt");
    return err;
}

err = listen(rfcomm_socket, 5);
if (err) {
    perror("listen");
    return err;
}

struct sockaddr_rc remote_addr = {0};
socklen_t addr_len = sizeof(remote_addr);
int new_socket = accept(rfcomm_socket, (struct sockaddr*)&remote_addr,
                        &addr_len);
if (new_socket < 0) {
    perror("accept");
    return new_socket;
}

/* To complete the connection setup of new_socket read 1 byte */
char c;
struct pollfd pfd;

memset(&pfd, 0, sizeof(pfd));
pfd.fd = new_socket;
pfd.events = POLLOUT;

err = poll(&pfd, 1, 0);
if (err) {
    perror("poll");
    return err;
}

if (!(pfd.revents & POLLOUT)) {
    err = read(sk, &c, 1);
    if (err < 0) {
        perror("read");
        return err;
    }
}

BT_FLUSHABLE (since Linux 2.6.39)

Channel flushable flag, this control if the channel data can be flushed or not, possible values:

Define	Value	Description
BT_FLUSHABLE_OFF	0x00 (default)	Do not flush data
BT_FLUSHABLE_ON	0x01	Flush data

BT_CHANNEL_POLICY (since Linux 3.10)

High-speed (AMP) channel policy, possible values:

Define	Value	Description
BT_CHANNEL_POLICY_BREDR_ONLY	0 (default)	BR/EDR only
BT_CHANNEL_POLICY_BREDR_PREFERRED	1	BR/EDR Preferred
BT_CHANNEL_POLICY_BREDR_PREFERRED	2	AMP Preferred

BT_PHY (since Linux 5.10)

Channel supported PHY(s), possible values:

Define	Value	Description
BT_PHY_BR_1M_1SLOT	BIT 0	BR 1Mbps 1SLOT
BT_PHY_BR_1M_3SLOT	BIT 1	BR 1Mbps 3SLOT
BT_PHY_BR_1M_5SLOT	BIT 2	BR 1Mbps 5SLOT
BT_PHY_BR_2M_1SLOT	BIT 3	EDR 2Mbps 1SLOT
BT_PHY_BR_2M_3SLOT	BIT 4	EDR 2Mbps 3SLOT
BT_PHY_BR_2M_5SLOT	BIT 5	EDR 2Mbps 5SLOT
BT_PHY_BR_3M_1SLOT	BIT 6	EDR 3Mbps 1SLOT
BT_PHY_BR_3M_3SLOT	BIT 7	EDR 3Mbps 3SLOT
BT_PHY_BR_3M_5SLOT	BIT 8	EDR 3Mbps 5SLOT

RESOURCES

http://www.bluez.org

REPORTING BUGS

linux-bluetooth@vger.kernel.org

SEE ALSO

socket(7), rctest(1)