实战Linux Bluetooth编程(六) L2CAP编程实例

作者：Sam （甄峰） sam_code@hotmail.com

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SignalingCommand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SignalingCommand.需要建立SOCK_RAW类型的L2CAP连接Socket。这样才有机会自己填充CommandCode，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, (structsockaddr*)&remote_l2_addr, sizeof(structsockaddr_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CommandIdentifier

send_cmd->len = htobs(size);

send_cmd->code =L2CAP_ECHO_REQ; //如上图所示，此项为Commandcode.这项定为：

//EchoRequest。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("\nReceiveResponse Packet.\n");

printf("%dbytes 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

#defineL2CAP_CONN_REQ 0x02

#defineL2CAP_CONN_RSP 0x03

#defineL2CAP_CONF_REQ 0x04

#defineL2CAP_CONF_RSP 0x05

#define L2CAP_DISCONN_REQ 0x06

#define L2CAP_DISCONN_RSP 0x07

#defineL2CAP_ECHO_REQ 0x08

#defineL2CAP_ECHO_RSP 0x09

#defineL2CAP_INFO_REQ 0x0a

#defineL2CAP_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 outmtu.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, (structsockaddr*)(&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)

{

//hangup

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);

//readdata

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, (structsockaddr*)&remote_addr, sizeof(structsockaddr_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。