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rfcomm - RFCOMM protocol
Contents
Copyright
Free use of this software is granted under the terms of the GNU Lesser General Public Licenses (LGPL).
BlueZ May 2024 RFCOMM(7)
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.
Name
rfcomm - RFCOMM protocol
Reporting Bugs
Resources
See Also
socket(7), rctest(1)
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(sinceLinux2.6.30)
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 │ 4 (Secure Only) │ Authenticated (P-256 │ Required │
│ (since Linux 3.15) │ │ based Secure Simple │ │
│ │ │ Pairing and Secure │ │
│ │ │ Authentication) │ │
└────────────────────┴──────────────────────┴────────────────────────┴──────────────┘
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(sinceLinux2.6.30)
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(sinceLinux2.6.39)
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(sinceLinux3.10)
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(sinceLinux5.10)
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 │
└────────────────────┴───────┴─────────────────┘
Synopsis
#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>
rfcomm_socket = socket(PF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
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