I have a bluetooth device which I can control using gatttool on linux. I want to develop my own c program that can send commands to it.
I have done bluetooth programming in the past and it is relatively straightforward, similar to network programming but this time, it is a bluetooth low energy device and following the principles here results in a host is down message when I can clearly connect/disconnect from it using gatttool.
How do I create this program? I know I should be using the bluez library but I am not sure where to start with Low energy devices.
int main(int argc, char **argv)
{
struct sockaddr_rc addr = { 0 };
int s, status;
char dest[18] = "B4:99:4C:5C:EE:49";
char buf[2048];
pthread_t rthread;
setbuf(stdout, NULL);
// allocate a socket
s = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
// set the connection parameters (who to connect to)
addr.rc_family = AF_BLUETOOTH;
addr.rc_channel = (uint8_t) 1;
str2ba( dest, &addr.rc_bdaddr );
// connect to server
status = connect(s, (struct sockaddr *)&addr, sizeof(addr));
if( status < 0 ){
perror("Error connecting to host\n");
exit(1);
}
while(fgets(buf, sizeof(buf), stdin) != NULL){
status = send(s, buf, sizeof(buf), 0);
if(status < 0){
printf("Error sending.\n");
exit(1);
}
}
close(s);
return;
I've been trying to figure out how to do this too: you may want to take a look at the source code in sandeepmistry/noble:src/l2cap-ble.c on Github. (The C component was factored out in this commit, so you need to look at older versions of the source.)
After building it (requires libbluetooth-dev) and running it, the l2cap-ble example essentially creates a simple TTY-like connection to the BLE device:
$ gcc -o l2cap-ble l2cap-ble.c utility.c -lbluetooth
$ ./l2cap-ble 12:34:56:78:9A:BC [public|random]
The source code illustrates a few BLE-specific functions (hci_*) that need to be interspersed with the standard socket I/O code.
UPDATE: I wrote a much more substantial and fully-functional program starting from this code: https://github.com/dlenski/ttblue. You can use this source code as an example of how to talk to a BLE gadget using Bluez.
your program is for classic bluetooth,to support my statement i would say ON any classic bluetooth device your code work would work fine
To get lescan i suggest to go though this link.sudo ./st would scan for nearby ble divices
https://github.com/carsonmcdonald/bluez-experiments
Another project on github.com looks clean: https://github.com/edrosten/libblepp
It's been mentioned in a discussion here: https://mbientlab.com/community/discussion/2492/bluetooth-le-library-linux
It's C++ not C though.
Related
Don't get confused by me talking about L2TP. Although my problem is related to L2TP it is not an L2TP problem per se. It's more of an networking problem.
Background
I'm writing an application working with L2TP. This is my first time working with L2TP and the linux L2TP subysytem, so I hope I got all this right.
When creating an L2TP Ethernet session the subsystem automatically creates a virtual network interface.
After bringing the interface up I can check with Wireshark and indeed the desired data is sent to the interface. This is without any packaging tho. It's not inside an ethernet frame or anything, but just the data bytes which were included in the L2TP packet.
I have no control over actually creating the device, but I can query its name and therefore its index etc., so so far so good.
The actual problem
My question is actually pretty simple: How do I get the data which is sent to a virtual interface into my userspace application?
I don't have a lot of experience with networking on unix but my expectation would be that this is a fairly simple problem, solvable by either obtaining an file descriptor with which I can use read / recv or somehow binding a socket to just that network interface.
I couldn't find any (gen-)netlink / ioctl API (or anything else) to do this or something comparable.
Although my application is written in GO not in C, a solution in C would be completely sufficient. Tbh at this point I would be happy about any approach to solve this issue programmatically. :)
Thanks a lot in advance
I just found a tutorial which answers my own question. It was actually really easy using AF_PACKET sockets.
There is a lovely tutorial on microhowto.info, which explains how AF_PACKET sockets work, better than I ever could. It even includes a section "Capture only from a particular network interface".
Here is a minimal example, which worked for my use case:
#include <stdlib.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <net/ethernet.h>
#include <linux/if_packet.h>
#include <sys/socket.h>
// [...]
// Create socket
int fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
if (fd == -1) {
perror("ERROR socket");
exit(1);
}
// Interface index (i.e. obtainable via ioctl SIOCGIFINDEX)
int ifindex = 1337;
// create link layer socket address
struct sockaddr_ll addr = {0};
addr.sll_family = AF_PACKET;
addr.sll_ifindex = ifindex;
addr.sll_protocol = htons(ETH_P_ALL)
if (bind(fd, (struct sockaddr*)&addr, sizeof(addr)) == -1) {
perror("ERROR bind");
exit(1);
}
char buffer[65535];
ssize_t len;
do {
len = recv(fd, buffer, sizeof(buffer) -1, 0);
if (len < 0) {
perror("ERROR recvfrom");
exit(1);
}
printf("recived data (length: %i)\n", (int) len);
} while (len > 0);
Before I get started. Yes, I could use leJOS, ev3dev, or some others, but I'd like to do it this way because that is how I learn.
I am using the CodeSourcery arm-2009q1 arm toolchain. I fetched the required libraries (bluetooth) from here: https://github.com/mindboards/ev3sources.
I am uploading the programs to the brick by using this tool: https://github.com/c4ev3/ev3duder
I have also fetched the brick's shared libraries, but I can not get them to work properly and there is 0 documentation on how to write a c program for the ev3 using the shared libraries. If I could get that working I might be able to use the c_com module to handle bluetooth, but right now bluez and rfcomm in conjunction with: https://github.com/c4ev3/EV3-API for motor and sensor control seems to be my best bet.
Now, with that out of the way:
I'd like to run the EV3 as a bluetooth "server" meaning that I start a program on it and the program opens a socket, binds it, listens for a connection, and then accepts a single connection.
I am able to do open a socket, bind it to anything but channel 1 (I believe this might be the crux of my issue), I am able to listen. These all return 0 (OK) and everything is fine.
Then I try to accept a connection. That instantly returns -1 and sets the remote to address 00:00:00:00:00:00.
My code is pretty much the same as can be found here: https://people.csail.mit.edu/albert/bluez-intro/x502.html
Here it is:
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>
#include <ev3.h>
int main(int argc, char **argv)
{
InitEV3();
struct sockaddr_rc loc_addr = { 0 }, rem_addr = { 0 };
char buf[1024] = { 0 };
int sock, client, bytes_read;
socklen_t opt = sizeof(rem_addr);
sock = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
loc_addr.rc_family = AF_BLUETOOTH;
loc_addr.rc_bdaddr = *BDADDR_ANY;
loc_addr.rc_channel = 2; // <-- Anything but 1. 1 seems to be taken
bind(sock, (struct sockaddr *)&loc_addr, sizeof(loc_addr));
listen(sock, 1);
// accept one connection <-- PROGRAM FAILS HERE AS accept() returns -1
client = accept(sock, (struct sockaddr *)&rem_addr, &opt);
// ---- All following code is irrelevant because accept fails ----
ba2str( &rem_addr.rc_bdaddr, buf );
fprintf(stderr, "accepted connection from %s\n", buf);
memset(buf, 0, sizeof(buf));
bytes_read = read(client, buf, sizeof(buf));
if( bytes_read > 0 )
printf("received [%s]\n", buf);
close(client);
close(sock);
FreeEV3();
return 0;
}
I am able to get the same code working on my pi. Even communication back and forth when the ev3api-specific functions are commented out. I just can't fathom why it won't work on the EV3.
I figured it out.
On my raspberry PI, the accept call worked as expected with no quirks. On the EV3 however, the accept call is non-blocking even if it has not been told to act like so.
The solution was to place the accept call in a loop until an incoming connection was in the queue.
while (errno == EAGAIN && ButtonIsUp(BTNEXIT) && client < 0)
client = accept(sock, (struct sockaddr*)&rem_addr, sizeof(rem_addr));
I'll upload the code to github. Contact me if you'd like to do something similar with the EV3.
I'm creating a C library that manage a lot of pheripherical of my embedded device. The S.O. used, is a linux dristro compiled with yocto. I'm trying to make some functions to connect my device to a wifi (well-know) router, with netlink (using the libnl commands). With the help of this community i've developed a function able to scan the routers in the area link here . Some of you know how to use the libnl command for connect my device to a router wifi?
I've developed the following code, that try to connect to an AP called "Validator_Test" (that have no password for authentication). The software return no error, but my device still remain disconneted from the ap.
static int iw_conn() {
struct nl_msg *msg = nlmsg_alloc();
int if_index = if_nametoindex("wlan0"); // Use this wireless interface for scanning.
// Open socket to kernel.
struct nl_sock *socket = nl_socket_alloc(); // Allocate new netlink socket in memory.
genl_connect(socket); // Create file descriptor and bind socket.
int driver_id = genl_ctrl_resolve(socket, "nl80211"); // Find the nl80211 driver ID.
genlmsg_put(msg, 0, 0, driver_id, 0, (NLM_F_REQUEST | NLM_F_ACK), NL80211_CMD_CONNECT, 0);
nla_put_u32(msg, NL80211_ATTR_IFINDEX, if_index); // Add message attribute, which interface to use.
nla_put(msg, NL80211_ATTR_SSID, strlen("Validator_Test"), "Validator_Test");
nla_put(msg, NL80211_ATTR_MAC, strlen("00:1e:42:21:e4:e9"), "00:1e:42:21:e4:e9");
int ret = nl_send_auto_complete(socket, msg); // Send the message.
printf("NL80211_CMD_CONNECT sent %d bytes to the kernel.\n", ret);
ret = nl_recvmsgs_default(socket); // Retrieve the kernel's answer. callback_dump() prints SSIDs to stdout.
nlmsg_free(msg);
if (ret < 0) {
printf("ERROR: nl_recvmsgs_default() returned %d (%s).\n", ret, nl_geterror(-ret));
return ret;
}
nla_put_failure:
return -ENOSPC;
}
It seems similar to this one:
How to use libnl and netlink socket for connect devices to AP programatically?
--
Thanks for the code.
Based on your code, I modified and did the test here; it works. The source code is at: https://github.com/neojou/nl80211/blob/master/test_connect/src/test_connect_nl80211.c
Some suggestions for this:
Make sure the test environment is correct
Before test the code, maybe you can try to use iw to do the test. iw is the open source tool, which uses netlink also. you can type "sudo iw wlan0 connect Validator_Test" and then use iwconfig to see if it is connected or not first. ( Suppose there is no security setting at the AP as you said )
there are two differences between your source code and mine
(1) don't need to set NL80211_ATTR_MAC
(2) ret = nl_recvmsgs_default(socket);
not sure if there is any judgement of the return value of your ap_conn(), but it seems better to return 0 in ap_conn(), when nl_recvmsgs_default() returns 0.
I'm creating a C library that manages a lot of peripherical of my embedded device. The S.O. used, is a Linux distro compiled with yocto. I'm trying to make some functions to connect my device to wifi (well-know) router, with netlink (using the libnl commands). With the help of this community, I've developed a function able to scan the routers in the area. Some of you know how to use the libnl command to connecting my device to router wifi?
I've developed the following code, that tries to connect to an AP called "Validator_Test" (that have no authentication password). The software return no error, but my device still remain disconnected from the AP. Some of you know what is wrong in my code? Unfortunately, i've not found any example or documentation for this operation.
static int ap_conn() {
struct nl_msg *msg = nlmsg_alloc();
int if_index = if_nametoindex("wlan0"); // Use this wireless interface for scanning.
// Open socket to kernel.
struct nl_sock *socket = nl_socket_alloc(); // Allocate new netlink socket in memory.
genl_connect(socket); // Create file descriptor and bind socket.
int driver_id = genl_ctrl_resolve(socket, "nl80211"); // Find the nl80211 driver ID.
genlmsg_put(msg, 0, 0, driver_id, 0, (NLM_F_REQUEST | NLM_F_ACK), NL80211_CMD_CONNECT, 0);
nla_put_u32(msg, NL80211_ATTR_IFINDEX, if_index); // Add message attribute, which interface to use.
nla_put(msg, NL80211_ATTR_SSID, strlen("Validator_Test"), "Validator_Test");
nla_put(msg, NL80211_ATTR_MAC, strlen("00:1e:42:21:e4:e9"), "00:1e:42:21:e4:e9");
int ret = nl_send_auto_complete(socket, msg); // Send the message.
printf("NL80211_CMD_CONNECT sent %d bytes to the kernel.\n", ret);
ret = nl_recvmsgs_default(socket); // Retrieve the kernel's answer. callback_dump() prints SSIDs to stdout.
nlmsg_free(msg);
if (ret < 0) {
printf("ERROR: nl_recvmsgs_default() returned %d (%s).\n", ret, nl_geterror(-ret));
return ret;
}
nla_put_failure:
return -ENOSPC;
}
Thanks to all of you!
Thanks for the code.
Based on your code, I modified and did the test here; it works.
The source code is at:
https://github.com/neojou/nl80211/blob/master/test_connect/src/test_connect_nl80211.c
Some suggestions for this:
Make sure the test environment is correct
Before test the code, maybe you can try to use iw to do the test.
iw is the open source tool, which uses netlink also.
you can type "sudo iw wlan0 connect Validator_Test"
and then use iwconfig to see if it is connected or not first.
( Suppose there is no security setting at the AP as you said )
there are two differences between your source code and mine
(1) don't need to set NL80211_ATTR_MAC
(2) ret = nl_recvmsgs_default(socket);
not sure if there is any judgement of the return value of your ap_conn(),
but it seems better to return 0 in ap_conn(), when nl_recvmsgs_default() returns 0.
I have a setup that looks like this:
Target ---- Switch ---- Switch ---- Windows computer
|
Linux computer
So I have a target connected to a switch it sends out UDP-packets for debug purpose. Normally these packets goes to a Windows computer for analysis, this works. I have now added a Linux computer as well, to get the same data to both Linux and Windows I have setup a managed switch to mirror the traffic, this works fine when I look in Wireshark. I have then written a simple C-application for analysing the data on the Linux computer, this software does only work if Wireshark is running at the same time. Otherwise it does not receive any data from the target. Why is this?
int main()
{
int saddr_size, data_size;
struct sockaddr saddr;
unsigned char *buffer = (unsigned char *) malloc(BUFFER_SIZE);
printf("Starting...\n");
int sock_raw = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
if (sock_raw < 0)
{
printf("Socket Error");
return 1;
}
while (1)
{
saddr_size = sizeof saddr;
data_size = recvfrom(sock_raw, buffer, BUFFER_SIZE, 0, &saddr, (socklen_t*) &saddr_size);
if (data_size < 0)
{
printf("Recvfrom error , failed to get packets\n");
return 1;
}
processPacket(buffer);
}
close(sock_raw);
printf("Finished");
return 0;
}
The data coming from the target are sent on a format similar to RTP and is addressed to the Windows computer.
So to sum up; Why do I not receive any data from the target in my C-application without Wireshark running?
Same as here, you need to put the interface (not socket as I originally posted) into promiscuous mode. Wireshark does that, which is why your code works when Wireshark is running.
Just a guess: promiscuous mode is not turned on and the ethernet controller is discarding frames not addressed to it.