实战Linux Bluetooth编程(六) L2CAP编程实例

例一：发送Signaling Packet：

Signaling Command是2个Bluetooth实体之间的L2CAP层命令传输。所以得Signaling Command使用CID 0x0001.

多个Command可以在一个C-frame（control frame）中发送。



如果要直接发送Signaling Command.需要建立SOCK_RAW类型的L2CAP连接Socket。这样才有机会自己填充Command Code，Identifier等。

以下是一个发送signaling Command以及接收Response的简单例子：

int main(int argc, char** argv)
{
int l2_sck = 0;
int iRel = 0;
struct sockaddr_l2 local_l2_addr;
struct sockaddr_l2 remote_l2_addr;
char str[24] ={0};
int len = 0;
int size = 50;
char* send_buf;
char* recv_buf;
int i = 0;
int id = 1; //不要为0

send_buf = malloc(L2CAP_CMD_HDR_SIZE + size);
recv_buf = malloc(L2CAP_CMD_HDR_SIZE + size);

if(argc < 2)
{
printf("/n%s <bdaddr>/n", argv[0]);
exit(0);
}

// create l2cap raw socket
l2_sck = socket(PF_BLUETOOTH, SOCK_RAW, BTPROTO_L2CAP); //创建L2CAP protocol的RAW Packet
if(l2_sck < 0)
{
perror("/nsocket:");
return -1;
}

//bind
memset(&local_l2_addr, 0, sizeof(struct sockaddr_l2));
local_l2_addr.l2_family = PF_BLUETOOTH;
bacpy(&local_l2_addr.l2_bdaddr , BDADDR_ANY);

iRel = bind(l2_sck, (struct sockaddr*) &local_l2_addr, sizeof(struct sockaddr_l2));
if(iRel < 0)
{
perror("/nbind()");
exit(0);
}

//connect
memset(&remote_l2_addr, 0 , sizeof(struct sockaddr_l2));
remote_l2_addr.l2_family = PF_BLUETOOTH;
//printf("/nConnect to %s/n", argv[1]);
str2ba(argv[1], &remote_l2_addr.l2_bdaddr);

iRel = connect(l2_sck, (struct sockaddr*)&remote_l2_addr, sizeof(struct sockaddr_l2));
if(iRel < 0)
{
perror("/nconnect()");
exit(0);
}

//get local bdaddr
len = sizeof(struct sockaddr_l2);
memset(&local_l2_addr, 0, sizeof(struct sockaddr_l2));

//注意，getsockname（）参数三是一个输入输出参数。输入时，为参数二的总体长度。输出时，

//为实际长度。
iRel = getsockname(l2_sck, (struct sockaddr*) &local_l2_addr, &len);
if(iRel < 0)
{
perror("/ngetsockname()");
exit(0);
}
ba2str(&(local_l2_addr.l2_bdaddr), str);
//printf("/nLocal Socket bdaddr:[%s]/n", str);
printf("l2ping: [%s] from [%s](data size %d) .../n", argv[1], str, size);

for (i = 0; i < size; i++)
send_buf[L2CAP_CMD_HDR_SIZE + i] = 'A';

l2cap_cmd_hdr *send_cmd = (l2cap_cmd_hdr *) send_buf;
l2cap_cmd_hdr *recv_cmd = (l2cap_cmd_hdr *) recv_buf;

send_cmd->ident = id; //如上图所示，这一项为此Command Identifier
send_cmd->len = htobs(size);
send_cmd->code = L2CAP_ECHO_REQ; //如上图所示，此项为Command code.这项定为：

//Echo Request。对端会发送Response回来。code=L2CAP_ECHO_RSP

while(1)
{
send_cmd->ident = id;
if(send(l2_sck, send_buf, size + L2CAP_CMD_HDR_SIZE, 0) <= 0)
{
perror("/nsend():");
}

while(1)
{
if(recv(l2_sck, recv_buf, size + L2CAP_CMD_HDR_SIZE, 0) <= 0)
{
perror("/nrecv()");
}

if (recv_cmd->ident != id)
continue;

if( recv_cmd->code == L2CAP_ECHO_RSP)
{
//printf("/nReceive Response Packet./n");
printf("%d bytes from [%s] id %d/n", recv_cmd->len, argv[1], recv_cmd->ident);
break;
}

}
sleep(1);
id ++;

}

close(l2_sck);

return 0;
}

所以说，如果想要发送接收signaling Command。只需要建立l2cap RAW socket. 并按规则填充command id, command code等。就可以接收发送了。

Command Code: 这个值放在l2cap.h中。

#define L2CAP_COMMAND_REJ 0x01
#define L2CAP_CONN_REQ 0x02
#define L2CAP_CONN_RSP 0x03
#define L2CAP_CONF_REQ 0x04
#define L2CAP_CONF_RSP 0x05
#define L2CAP_DISCONN_REQ 0x06
#define L2CAP_DISCONN_RSP 0x07
#define L2CAP_ECHO_REQ 0x08
#define L2CAP_ECHO_RSP 0x09
#define L2CAP_INFO_REQ 0x0a
#define L2CAP_INFO_RSP 0x0b

例二：任意PSM的L2CAP连接间数据的传输：

此例子中：Server，client其实是使用网络的概念定义的。

server用来监听指定PSM的连接，并监听数据。同时，利用poll来查看peer是否断掉了。

Server：

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <poll.h>

#include <bluetooth/bluetooth.h>
#include <bluetooth/hci.h>
#include <bluetooth/hci_lib.h>
#include <bluetooth/l2cap.h>

void * Read_thread(void* pSK);

int main(int argc, char** argv)
{
int iRel = 0;
int sk = 0;
struct sockaddr_l2 local_addr;
struct sockaddr_l2 remote_addr;
int len;
int nsk = 0;
pthread_t nth = 0;
struct l2cap_options opts;
int optlen = 0;
int slen = 0;
char str[16] = {0};

if(argc < 2)
{
printf("/nUsage:%s psm/n", argv[0]);
exit(0);
}

// create l2cap socket
sk = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP); //发送数据，使用SOCK_SEQPACKET为好
if(sk < 0)
{
perror("/nsocket():");
exit(0);
}

//bind
local_addr.l2_family = PF_BLUETOOTH;
local_addr.l2_psm = htobs(atoi(argv[argc -1])); //last psm
bacpy(&local_addr.l2_bdaddr, BDADDR_ANY);
iRel = bind(sk, (struct sockaddr *)&local_addr, sizeof(struct sockaddr));
if(iRel < 0)
{
perror("/nbind()");
exit(0);
}

//get opts

// in mtu 和 out mtu.每个包的最大值
memset(&opts, 0, sizeof(opts));
optlen = sizeof(opts);
getsockopt(sk, SOL_L2CAP, L2CAP_OPTIONS, &opts, &optlen);
printf("/nomtu:[%d]. imtu:[%d]. flush_to:[%d]. mode:[%d]/n", opts.omtu, opts.imtu, opts.flush_to, opts.mode);

//set opts. default value
opts.omtu = 0;
opts.imtu = 672;
if (setsockopt(sk, SOL_L2CAP, L2CAP_OPTIONS, &opts, sizeof(opts)) < 0)
{
perror("/nsetsockopt():");
exit(0);
}

//listen
iRel = listen(sk, 10);
if(iRel < 0)
{
perror("/nlisten()");
exit(0);
}

len = sizeof(struct sockaddr_l2);
while(1)
{
memset(&remote_addr, 0, sizeof(struct sockaddr_l2));
nsk = accept(sk, (struct sockaddr*)(&remote_addr), &len);
if(nsk < 0)
{
perror("/naccept():");
continue;
}
ba2str(&(remote_addr.l2_bdaddr), str);
printf("/npeer bdaddr:[%s]./n", str); //得到peer的信息

iRel = pthread_create(&nth, NULL, Read_thread, &nsk);
if(iRel != 0)
{
perror("pthread_create():");
continue;
}
pthread_detach(nth); // 分离之

}

return 0;
}

void * Read_thread(void* pSK)
{
//struct pollfd fds[10];
struct pollfd fds[100];
char buf[1024] = {0};
int iRel = 0;
int exit_val = 0;

//fds[0].fd = *(int*)pSK;
//fds[0].events = POLLIN | POLLHUP;

fds[0].fd = (int)(*(int*)pSK);
fds[0].events = POLLIN | POLLHUP;

while(1)
{
if(poll(fds, 1, -1) < 0)
{
perror("/npoll():");
}
if(fds[0].revents & POLLHUP)
{
//hang up
printf("/n[%d] Hang up/n", *(int*)pSK);
close(*(int*)pSK);
pthread_exit(&exit_val);

break;
}

if(fds[0].revents & POLLIN)
{
memset(buf, 0 , 1024);
//read data
iRel = recv(*(int*)pSK, buf, 572, 0);
//printf("/nHandle[%d] Receive [%d] data:[%s]", *(int*)pSK, iRel, buf);
}

}

return 0;
}

client:

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>

#include <bluetooth/bluetooth.h>
#include <bluetooth/hci.h>
#include <bluetooth/hci_lib.h>
#include <bluetooth/l2cap.h>

int main(int argc, char** argv)
{
int sk;
int i = 0;
char buf[24] = "Sam is Good Guy!";
struct sockaddr_l2 local_addr;
struct sockaddr_l2 remote_addr;
int iRel = 0;

if(argc < 3)
{
printf("/nUsage:%s <bdaddr> <PSM>/n", argv[0]);
exit(0);
}

sk = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP);
if(sk < 0)
{
perror("/nsocket():");
exit(0);
}

//bind. bluetooth好像不许有无名Socket
local_addr.l2_family = PF_BLUETOOTH;
bacpy(&local_addr.l2_bdaddr, BDADDR_ANY);
iRel = bind(sk, (struct sockaddr *)&local_addr, sizeof(struct sockaddr));
if(iRel < 0)
{
perror("/nbind()");
exit(0);
}

memset(&remote_addr, 0, sizeof(struct sockaddr_l2));
remote_addr.l2_family = PF_BLUETOOTH;
str2ba(argv[1], &remote_addr.l2_bdaddr);
remote_addr.l2_psm = htobs(atoi(argv[argc -1]));

connect(sk, (struct sockaddr*)&remote_addr, sizeof(struct sockaddr_l2));

for(i = 0; i < 60; i++)
{
iRel = send(sk, buf, strlen(buf)+1, 0);
printf("Send [%d] data/n", strlen(buf)+1);
sleep(1);
}

close(sk);
return 0;
}

注意：

1. 在Linux 网络编程中,主动发起连接方，因为不关心地址具体是什么，所以可以作为无名socket,也就是说可以不bind. 但Bluetooth则不可以，一定需要bind.

2. poll可以查出连接断连，但需要注意：断开的revent值为：11001B。也就是说：POLLIN | POLLERR |POLLHUP。

3. 被连接一方，一定要指定PSM。