This code from Stevens et al., Advanced Programming in the Unix Environment, Figure 16.17 is a server program to provide system uptime:
#include "apue.h"
#include <netdb.h>
#include <errno.h>
#include <syslog.h>
#include <sys/socket.h>
#define BUFLEN 128
#define QLEN 10
#ifndef HOST_NAME_MAX
#define HOST_NAME_MAX 256
#endif
extern int initserver(int, const struct sockaddr *, socklen_t, int);
void
serve(int socked);
int
main(int argc, char *argv[])
{
struct addrinfo *ailist, *aip;
struct addrinfo hint;
int sockfd, err, n;
char *host;
if (argc != 1)
err_quit("usage: ruptimed");
if ((n = sysconf(_SC_HOST_NAME_MAX)) < 0)
n = HOST_NAME_MAX; /* best guess */
if ((host = malloc(n)) == NULL)
err_sys("malloc error");
if (gethostname(host, n) < 0)
err_sys("gethostname error");
daemonize("ruptimed");
memset(&hint, 0, sizeof(hint));
hint.ai_flags = AI_CANONNAME;
hint.ai_socktype = SOCK_STREAM;
hint.ai_canonname = NULL;
hint.ai_addr = NULL;
hint.ai_next = NULL;
if ((err = getaddrinfo(host, "ruptime", &hint, &ailist)) != 0) {
syslog(LOG_ERR, "ruptimed: getaddrinfo error: %s",
gai_strerror(err));
exit(1);
}
for (aip = ailist; aip != NULL; aip = aip->ai_next) {
if ((sockfd = initserver(SOCK_STREAM, aip->ai_addr,
aip->ai_addrlen, QLEN)) >= 0) {
serve(sockfd);
exit(0);
}
}
exit(1);
}
What confused me is the function call getaddrinfo, it just tells me the service name is ruptime, and I have no idea where this name comes from. Did the service-name get named after the name of this program? How can I determine the service name? Can I designate the service name by myself?
I didn't duplicate the code of initserver and serve, because I think it doesn't concern the question.
The service name is simply a key to look up in /etc/services; i.e. it's a symbolic reference to a port number.
Related
I coded a program in C of a tcp socket but once executed, the server returns an error from the accept function but i can't find out why..
If you guys can help me, that would be appreciated. Also, if you have any advice on the way i programmed this, please feel free to tell me.
Here is my code :
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
int main(int argc, char *argv[])
{
int listenSocket, status, socketClient;
unsigned short int msgLength;
struct addrinfo hints, *servinfo;
struct sockaddr_in clientAddress;
socklen_t clientAddressLength = sizeof clientAddress;
char msg[101];
//Test port number
if (argc != 2) {
fprintf(stderr,"Usage : %s [NUMERO_PORT]\n",argv[0]);
return 2;
}
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET; // IPv4
hints.ai_socktype = SOCK_DGRAM; // UDP
hints.ai_flags = 0; //Car on fait le test sur la meme machine
if ((status = getaddrinfo(NULL, argv[1], &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
return 3;
}
if ((listenSocket = socket(servinfo->ai_family, servinfo-
>ai_socktype, servinfo->ai_protocol)) == -1) {
perror("socket:");
return 4;
}
if (bind(listenSocket, servinfo->ai_addr, servinfo->ai_addrlen) ==
-1) {
close(listenSocket);
perror("bind:");
return 5;
}
listen(listenSocket,5);
int sizeOfSockAddr = sizeof(clientAddress);
socketClient= accept(listenSocket, NULL, NULL);
if (socketClient < 0) {
fprintf(stderr,"Erreur accept\n");
return 6;
}
freeaddrinfo(servinfo);
printf("Waiting for a client's request %s\n", argv[1]);
while (1) {
//some things
}
}`
I don't understand why the scanf call causes segmentation error. Tried making a separate file with only int number and scanf and it worked no problem. Really confused here need help. I use pointer in the scanf parameter so I'm suspecting the error might come from the interaction between scanf and shared memory somehow?
#include <unistd.h>
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <semaphore.h>
int main() {
const char *name = "message";
const char *names = "sem";
const int SIZE = 4096;
const int size = 1;
int number;
int shm_fd1;
int shm_fd2;
char *ptr; // Pointer to shared memory
sem_t *sem;
/* create the shared memory segment */
shm_fd1 = shm_open(name, O_CREAT | O_RDWR, 0666);
shm_fd2 = shm_open(names, O_CREAT | O_RDWR, 0666);
/* configure the size of the shared memory segment */
ftruncate(shm_fd1, SIZE);
ftruncate(shm_fd2, size);
/* initialize semaphore */
if (sem_init(sem, 1, 1) < 0) { // 1 = multiprocess
fprintf(stderr, "ERROR: could not initialize semaphore.\n");
exit(0);
}
/* now map the shared memory segment in the address space of the process */
ptr = mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd1, 0);
sem = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd2, 0);
if (ptr == MAP_FAILED) {
printf("Map failed\n");
return -1;
}
if (sem == MAP_FAILED) {
printf("Map failed\n");
return -1;
}
strcpy(ptr, "Hello from the server\n");
/* store and read from the shared memory region */
printf("Message: %s\n", ptr);
printf("0. Quit\n 1. Change message\n 2. Check message\n");
printf("Type an integer: ");
scanf("%d", &number); //confirmed this causes the error
if I remove the line above the program runs no problem. the part alone also works fine apart from this file.
if (number == 1) {
sem_wait(sem);
printf("Enter your message: ");
scanf("%s", ptr);
sem_post(sem);
}
else if (number == 2) {
printf("Message: %s\n", ptr);
}
else {
/*break;*/
}
/* remove the shared memory segment */
if (shm_unlink(name) == -1) {
printf("Error removing %s\n",name);
exit(-1);
}
return 0;
}
I am trying to implement TCP client, server program in C on Linux system. Here are my codes.
Client Source Code :
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int main(int argc, char *argv[])
{
char *address;
// Create socket
int client_socket;
client_socket = socket(AF_INET, SOCK_STREAM, 0);
// Set - Up Server Address
struct sockaddr_in server_address;
server_address.sin_family = AF_INET;
server_address.sin_port = htons(8001);
inet_aton(address, &server_address.sin_addr.s_addr);
// Connect to the server
int connect_stat;
connect_stat = connect(client_socket, (struct sockaddr *) &server_address, sizeof(server_address));
if(connect_stat == -1)
printf("Not Connected\n");
else
printf(" Connected \n");
// Recieve from server
char response[256];
recv(client_socket, &server_address, sizeof(server_address), 0);
// Printing the Response data
printf("Data Recieved : %s\n",response);
// Destroy the socket
close(client_socket);
return 0;
}
Server Source Code :
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int main(int argc, char *argv[])
{
// Address
char *address;
address = argv[1];
// Create message to send
char message[256] = "Connection Established";
// Create server socket
int server_socket;
server_socket = socket(AF_INET, SOCK_STREAM, 0);
// Set - Up Server Address
struct sockaddr_in server_address;
server_address.sin_family = AF_INET;
server_address.sin_port = htons(8001);
inet_aton(address, &server_address.sin_addr.s_addr);
// Bind it to an IP and PORT
bind(server_socket, (struct sockaddr *) &server_address, sizeof(server_address));
// Start listenting on address
listen(server_socket, 5);
// Start accepting the clients;
int client_socket;
client_socket = accept(server_socket, NULL, NULL);
// Send some data back to client
send(client_socket, message, sizeof(message), 0);
// Close the socket
close(server_socket);
close(client_socket);
return 0;
}
On passing an IP like 192.168.1.xxx to both client and server, server starts waiting for the clients but client always show not connected and thus no data received.
Client output :
root#kali:/home/mayank/Desktop/tcp_chat# ./tcp_client 192.168.1.111
Not Connected
Data Recieved :
But if i use INADDR_ANY instead of specific IP, it works. I know INADDR_ANY basically means it binds to all IP address, but why it is not binding to specific IP address which i want. Any suggestions, where i am wrong.
Instead of inet_aton(), you can also use
server_address.sin_addr.s_addr = inet_addr("IP address");
And use perror() after every function, like
client_socket = socket(...);
if (client_socket == -1)
perror("socket");
You are not doing any error checking, except on the connect() call. For example, you are getting an ENOTSOCK error because you are not checking whether socket() succeeds or fails.
Beyond that, on the client side, this statement:
inet_aton(address, &server_address.sin_addr.s_addr);
Should be this instead:
inet_aton(address, &server_address.sin_addr);
inet_aton() expects a pointer to a struct in_addr, but you are passing it a pointer to a uint32_t instead. In fact, the original code should not have even compiled because of that.
But, more importantly, your address variable is uninitialized, so you are passing a bad memory pointer to inet_aton(), and not checking its return value for failure.
Even if you could connect to the server, you are also passing the wrong output buffer to recv(), so you would end up writing garbage to the console.
Try this instead:
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int main(int argc, char *argv[])
{
if (argc != 2)
{
printf("usage: %s <IPv4 address>\n", argv[0]);
return 0;
}
// Set - Up Server Address
struct sockaddr_in server_address = {0};
server_address.sin_family = AF_INET;
server_address.sin_port = htons(8001);
if (inet_aton(argv[1], &server_address.sin_addr) != 0)
{
printf("invalid IPv4 address specified\n");
return 0;
}
// Create socket
int client_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (client_socket == -1)
{
perror("socket() failed");
return 0;
}
// Connect to the server
if (connect(client_socket, (struct sockaddr *) &server_address, sizeof(server_address)) == -1)
{
perror("Not Connected");
}
else
{
printf("Connected\n");
// Receive from server
char response[256];
int numRecvd = recv(client_socket, response, sizeof(response), 0);
// Printing the Response data
if (numRecvd == -1)
perror("recv() failed");
else if (numRecvd == 0)
printf("Disconnected by server\n");
else
printf("Data Received: [%d] %.*s\n", numRecvd, numRecvd, response);
}
// Destroy the socket
close(client_socket);
return 0;
}
#include <netinet/in.h>
#include <arpa/inet.h>
int main(int argc, char *argv[])
{
// Set - Up Server Address
struct sockaddr_in server_address = {0};
server_address.sin_family = AF_INET;
server_address.sin_port = htons(8001);
if (argc >= 2)
{
if (inet_aton(argv[1], &server_address.sin_addr) != 0)
{
printf("invalid IPv4 address specified\n");
return 0;
}
}
else
server_address.sin_addr.s_addr = INADDR_ANY;
// Create message to send
char message[256] = "Connection Established";
// Create server socket
int server_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (server_socket == -1)
{
perror("socket() failed");
return 0;
}
// Bind it to an IP and PORT
if (bind(server_socket, (struct sockaddr *) &server_address, sizeof(server_address)) == -1)
{
perror("bind() failed");
}
// Start listenting on address
else if (listen(server_socket, 5) == -1)
{
perror("listen() failed");
}
// Start accepting the clients
else
{
int client_socket = accept(server_socket, NULL, 0);
if (client_socket == -1)
{
perror("accept() failed");
}
else
{
// Send some data back to client
int numSent = send(client_socket, message, sizeof(message), 0);
if (numSent == -1)
perror("send() failed");
else
printf("Data Sent: [%d] %.*s\n", numSent, numSent, message);
// Close the socket
close(client_socket);
}
}
// Destroy the socket
close(server_socket);
return 0;
}
I referenced C code on this website: https://gist.github.com/austinmarton/2862515
Here is a image to explain:
I edit it at two parts, one pat is for ethertype（change 0x0800 to a custom-protocol 0x1234）
and another part is deleting code for IP header processing (because original code is based on IP, but I need a raw ethernet frame).
I used wireshark to detect packets, and I can receive the packets I sent（in left of image）,and I can see send.out exactly sending packets(bottom right of image). But recv.out cannot receive packet !?(upper right of image).
However, if I use 0x0800 for protocol, recv.out can receive packets from outside, but still cannot receive the packets I sent.
Is there any mistake for setting socket
Here is my code:
send.c
#include <arpa/inet.h>
#include <linux/if_packet.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <net/if.h>
#include <netinet/ether.h>
#define MY_DEST_MAC0 0xbc
#define MY_DEST_MAC1 0xee
#define MY_DEST_MAC2 0x7b
#define MY_DEST_MAC3 0x75
#define MY_DEST_MAC4 0x56
#define MY_DEST_MAC5 0x2a
#define DEFAULT_IF "eth0"
#define BUF_SIZ 1024
int main(int argc, char *argv[])
{
int sockfd;
struct ifreq if_idx;
struct ifreq if_mac;
int tx_len = 0;
char sendbuf[BUF_SIZ];
struct ether_header *eh = (struct ether_header *) sendbuf; /*structure*/
struct iphdr *iph = (struct iphdr *) (sendbuf + sizeof(struct ether_header));
struct sockaddr_ll socket_address;
char ifName[IFNAMSIZ];
unsigned short proto = 0x1234;
/* Get interface name *//*eth0*/
if (argc > 1)
strcpy(ifName, argv[1]);
else
strcpy(ifName, DEFAULT_IF);
/* Open RAW socket to send on *//*IPv4*/
if ((sockfd = socket(AF_PACKET, SOCK_RAW, htons(proto))) == -1) {
perror("socket");
}
/* Get the index of the interface to send on *//*0*/
memset(&if_idx, 0, sizeof(struct ifreq));
strncpy(if_idx.ifr_name, ifName, IFNAMSIZ-1);
if (ioctl(sockfd, SIOCGIFINDEX, &if_idx) < 0)/*save INDEX info into if_idx*/
perror("SIOCGIFINDEX");
/* Get the MAC address of the interface to send on *//*local*//*save MAC info into if_mac*/
memset(&if_mac, 0, sizeof(struct ifreq));
strncpy(if_mac.ifr_name, ifName, IFNAMSIZ-1);
if (ioctl(sockfd, SIOCGIFHWADDR, &if_mac) < 0)
perror("SIOCGIFHWADDR");
/* Construct the Ethernet header */
memset(sendbuf, 0, BUF_SIZ);
/* Ethernet header */
eh->ether_shost[0] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[0];
eh->ether_shost[1] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[1];
eh->ether_shost[2] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[2];
eh->ether_shost[3] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[3];
eh->ether_shost[4] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[4];
eh->ether_shost[5] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[5];
eh->ether_dhost[0] = MY_DEST_MAC0;
eh->ether_dhost[1] = MY_DEST_MAC1;
eh->ether_dhost[2] = MY_DEST_MAC2;
eh->ether_dhost[3] = MY_DEST_MAC3;
eh->ether_dhost[4] = MY_DEST_MAC4;
eh->ether_dhost[5] = MY_DEST_MAC5;
/* Ethertype field */
eh->ether_type = htons(proto);
tx_len += sizeof(struct ether_header);
/* Packet data */
sendbuf[tx_len++] = "h";
sendbuf[tx_len++] = "e";
sendbuf[tx_len++] = "l";
sendbuf[tx_len++] = "l";
sendbuf[tx_len++] = "o";
/* Index of the network device */
socket_address.sll_ifindex = if_idx.ifr_ifindex;
/* Address length*/
socket_address.sll_halen = ETH_ALEN;
/* Destination MAC */
socket_address.sll_addr[0] = MY_DEST_MAC0;
socket_address.sll_addr[1] = MY_DEST_MAC1;
socket_address.sll_addr[2] = MY_DEST_MAC2;
socket_address.sll_addr[3] = MY_DEST_MAC3;
socket_address.sll_addr[4] = MY_DEST_MAC4;
socket_address.sll_addr[5] = MY_DEST_MAC5;
/* Send packet */
int cnt=0;
while(cnt<5){
if (sendto(sockfd, sendbuf, tx_len, 0, (struct sockaddr*)&socket_address, sizeof(struct sockaddr_ll)) < 0)
printf("Send failed\n");
else
printf("success!\n");
cnt++;
}
return 0;
}
recv.c
#include <arpa/inet.h>
#include <linux/if_packet.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <net/if.h>
#include <netinet/ether.h>
#define DEST_MAC0 0xbc
#define DEST_MAC1 0xee
#define DEST_MAC2 0x7b
#define DEST_MAC3 0x75
#define DEST_MAC4 0x56
#define DEST_MAC5 0x2a
#define ETHER_TYPE 0x1234
#define DEFAULT_IF "eth0"
#define BUF_SIZ 1024
int main(int argc, char *argv[])
{
char sender[INET6_ADDRSTRLEN];
int sockfd, ret, i;
int sockopt;
ssize_t numbytes;
struct ifreq ifopts; /* set promiscuous mode */
struct sockaddr_storage their_addr;
uint8_t buf[BUF_SIZ];
char ifName[IFNAMSIZ];
/* Get interface name *//*eth0*/
if (argc > 1)
strcpy(ifName, argv[1]);
else
strcpy(ifName, DEFAULT_IF);
/* Header structures */
struct ether_header *eh = (struct ether_header *) buf;
/* Open PF_PACKET socket, listening for EtherType ETHER_TYPE *//*0x1234*/
if ((sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETHER_TYPE))) == -1) {
perror("listener: socket");
return -1;
}
/* Set interface to promiscuous mode - do we need to do this every time? *//*cpy ifname into ifr_name*/
strncpy(ifopts.ifr_name, ifName, IFNAMSIZ-1);
ioctl(sockfd, SIOCGIFFLAGS, &ifopts); /*set promisc mode*/
ifopts.ifr_flags |= IFF_PROMISC;
ioctl(sockfd, SIOCSIFFLAGS, &ifopts);
/* Allow the socket to be reused - incase connection is closed prematurely */
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &sockopt, sizeof sockopt) == -1) {
perror("setsockopt");
close(sockfd);
exit(EXIT_FAILURE);
}
/* Bind to device */
if (setsockopt(sockfd, SOL_SOCKET, SO_BINDTODEVICE, ifName, IFNAMSIZ-1) == -1) {
perror("SO_BINDTODEVICE");
close(sockfd);
exit(EXIT_FAILURE);
}
repeat: printf("listener: Waiting to recvfrom...\n");
numbytes = recvfrom(sockfd, buf, BUF_SIZ, 0, NULL, NULL);
printf("listener: got packet %lu bytes\n", numbytes);
/* Check the packet is for me */
if (eh->ether_dhost[0] == DEST_MAC0 &&
eh->ether_dhost[1] == DEST_MAC1 &&
eh->ether_dhost[2] == DEST_MAC2 &&
eh->ether_dhost[3] == DEST_MAC3 &&
eh->ether_dhost[4] == DEST_MAC4 &&
eh->ether_dhost[5] == DEST_MAC5) {
printf("Correct destination MAC address\n");
} else {
printf("Wrong destination MAC: %x:%x:%x:%x:%x:%x\n",
eh->ether_dhost[0],
eh->ether_dhost[1],
eh->ether_dhost[2],
eh->ether_dhost[3],
eh->ether_dhost[4],
eh->ether_dhost[5]);
ret = -1;
goto done;
}
/* Print packet */
printf("\tData:");
for (i=0; i<numbytes; i++) printf("%02x:", buf[i]);
printf("\n");
done: goto repeat;
close(sockfd);
return ret;
}
you can get All frames from your target with below changes in your receive code :
please replace line :
if ((sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETHER_TYPE))) == -1) {
with this line :
if ((sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) == -1) {
Because in your original code you changed normal ethernet header type then OS can not detect its process listener(your program) and get it to you but when you set this line, OS can get you all results so you can get your special answers.
I'm starting to do socket programming so someone should confirm this.
I'm pretty sure the interface will drop the packet because the source and destination mac are the same... try using another PC and change the destination mac on each side to confirm this (virtual machines work as well)
I have also used a similar code to transfer Ethernet frames. This type of socket does not work locally. As #Goncalo suggested use a different PC or if you have two NICs on your PC you should use them. Here is the Code I used to receive Frames.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <linux/if.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <sys/ioctl.h>
union ethframe
{
struct
{
struct ethhdr header;
unsigned char data[ETH_DATA_LEN];
} field;
unsigned char buffer[ETH_FRAME_LEN];
};
int main(int argc, char **argv) {
char *iface = "eth1";
unsigned char dest[ETH_ALEN]
= { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
unsigned short proto = 0x1234;
int recv_result,i;
char buff[ETH_FRAME_LEN];
unsigned short data_len;
int s;
if ((s = socket(AF_PACKET, SOCK_RAW, htons(proto))) < 0) {
printf("Error: could not open socket\n");
return -1;
}
struct ifreq buffer;
int ifindex;
memset(&buffer, 0x00, sizeof(buffer));
strncpy(buffer.ifr_name, iface, IFNAMSIZ);
if (ioctl(s, SIOCGIFINDEX, &buffer) < 0) {
printf("Error: could not get interface index\n");
close(s);
return -1;
}
ifindex = buffer.ifr_ifindex;
unsigned char source[ETH_ALEN];
if (ioctl(s, SIOCGIFHWADDR, &buffer) < 0) {
printf("Error: could not get interface address\n");
close(s);
return -1;
}
memcpy((void*)source, (void*)(buffer.ifr_hwaddr.sa_data),
ETH_ALEN);
struct sockaddr_ll saddrll;
memset((void*)&saddrll, 0, sizeof(saddrll));
saddrll.sll_family = PF_PACKET;
saddrll.sll_ifindex = ifindex;
saddrll.sll_halen = ETH_ALEN;
memcpy((void*)(saddrll.sll_addr), (void*)dest, ETH_ALEN);
socklen_t sll_len = (socklen_t)sizeof(saddrll);
if (recv_result = recvfrom(s, buff, ETH_FRAME_LEN, 0,
(struct sockaddr *)&saddrll, &sll_len) > 0)
printf("Success!\n");
else
printf("Error, could not send\n");
data_len=sizeof(buff);
printf("\tData:");
for (i=0; i<data_len; i++) printf("%c", buff[i]);
printf("\tDone: \n");
close(s);
return 0;
}
This question already has answers here:
How can I determine the default gateway on iPhone?
(5 answers)
Closed 5 years ago.
I need to get the gateway address of the wifi network I connect with the iPhone. Anyone knows how to get that ?
Just to clarify, I am looking for the information of this screen :
Thanks.
Add to your project route.h file from http://opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/net/route.h
Create getgateway.h
int getdefaultgateway(in_addr_t * addr);
Create getgateway.c
#include <stdio.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <sys/sysctl.h>
#include "getgateway.h"
#include "TargetConditionals.h"
#if TARGET_IPHONE_SIMULATOR
#include <net/route.h>
#define TypeEN "en1"
#else
#include "route.h"
#define TypeEN "en0"
#endif
#include <net/if.h>
#include <string.h>
#define CTL_NET 4 /* network, see socket.h */
#if defined(BSD) || defined(__APPLE__)
#define ROUNDUP(a) \
((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long))
int getdefaultgateway(in_addr_t * addr)
{
int mib[] = {CTL_NET, PF_ROUTE, 0, AF_INET,
NET_RT_FLAGS, RTF_GATEWAY};
size_t l;
char * buf, * p;
struct rt_msghdr * rt;
struct sockaddr * sa;
struct sockaddr * sa_tab[RTAX_MAX];
int i;
int r = -1;
if(sysctl(mib, sizeof(mib)/sizeof(int), 0, &l, 0, 0) < 0) {
return -1;
}
if(l>0) {
buf = malloc(l);
if(sysctl(mib, sizeof(mib)/sizeof(int), buf, &l, 0, 0) < 0) {
return -1;
}
for(p=buf; p<buf+l; p+=rt->rtm_msglen) {
rt = (struct rt_msghdr *)p;
sa = (struct sockaddr *)(rt + 1);
for(i=0; i<RTAX_MAX; i++) {
if(rt->rtm_addrs & (1 << i)) {
sa_tab[i] = sa;
sa = (struct sockaddr *)((char *)sa + ROUNDUP(sa->sa_len));
} else {
sa_tab[i] = NULL;
}
}
if( ((rt->rtm_addrs & (RTA_DST|RTA_GATEWAY)) == (RTA_DST|RTA_GATEWAY))
&& sa_tab[RTAX_DST]->sa_family == AF_INET
&& sa_tab[RTAX_GATEWAY]->sa_family == AF_INET) {
if(((struct sockaddr_in *)sa_tab[RTAX_DST])->sin_addr.s_addr == 0) {
char ifName[128];
if_indextoname(rt->rtm_index,ifName);
if(strcmp(TypeEN,ifName)==0){
*addr = ((struct sockaddr_in *)(sa_tab[RTAX_GATEWAY]))->sin_addr.s_addr;
r = 0;
}
}
}
}
free(buf);
}
return r;
}
#endif
Through the following snippet, this example will be good work on the simulator and the devise.
#include "TargetConditionals.h"
#if TARGET_IPHONE_SIMULATOR
#include <net/route.h>
#define TypeEN "en1"
#else
#include "route.h"
#define TypeEN "en0"
#endif
Use this code in your Objective C project
#import "getgateway.h"
#import <arpa/inet.h>
- (NSString *)getGatewayIP {
NSString *ipString = nil;
struct in_addr gatewayaddr;
int r = getdefaultgateway(&(gatewayaddr.s_addr));
if(r >= 0) {
ipString = [NSString stringWithFormat: #"%s",inet_ntoa(gatewayaddr)];
NSLog(#"default gateway : %#", ipString );
} else {
NSLog(#"getdefaultgateway() failed");
}
return ipString;
}
The following works for me, but a copy of route.h is required.
My general understanding is that this code queries and retrieves the systems routing table.
It uses its entries to determine the default route aka gateway ip
/* $Id: getgateway.c,v 1.6 2007/12/13 14:46:06 nanard Exp $ */
/* libnatpmp
* Copyright (c) 2007, Thomas BERNARD <miniupnp#free.fr>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
#include <stdio.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <sys/sysctl.h>
#include "getgateway.h"
#include "route.h"
#include <net/if.h>
#include <string.h>
#define CTL_NET 4 /* network, see socket.h */
#if defined(BSD) || defined(__APPLE__)
#define ROUNDUP(a) \
((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long))
int getdefaultgateway(in_addr_t * addr)
{
int mib[] = {CTL_NET, PF_ROUTE, 0, AF_INET,
NET_RT_FLAGS, RTF_GATEWAY};
size_t l;
char * buf, * p;
struct rt_msghdr * rt;
struct sockaddr * sa;
struct sockaddr * sa_tab[RTAX_MAX];
int i;
int r = -1;
if(sysctl(mib, sizeof(mib)/sizeof(int), 0, &l, 0, 0) < 0) {
return -1;
}
if(l>0) {
buf = malloc(l);
if(sysctl(mib, sizeof(mib)/sizeof(int), buf, &l, 0, 0) < 0) {
return -1;
}
for(p=buf; p<buf+l; p+=rt->rtm_msglen) {
rt = (struct rt_msghdr *)p;
sa = (struct sockaddr *)(rt + 1);
for(i=0; i<RTAX_MAX; i++) {
if(rt->rtm_addrs & (1 << i)) {
sa_tab[i] = sa;
sa = (struct sockaddr *)((char *)sa + ROUNDUP(sa->sa_len));
} else {
sa_tab[i] = NULL;
}
}
if( ((rt->rtm_addrs & (RTA_DST|RTA_GATEWAY)) == (RTA_DST|RTA_GATEWAY))
&& sa_tab[RTAX_DST]->sa_family == AF_INET
&& sa_tab[RTAX_GATEWAY]->sa_family == AF_INET) {
if(((struct sockaddr_in *)sa_tab[RTAX_DST])->sin_addr.s_addr == 0) {
char ifName[128];
if_indextoname(rt->rtm_index,ifName);
if(strcmp("en0",ifName)==0){
*addr = ((struct sockaddr_in *)(sa_tab[RTAX_GATEWAY]))->sin_addr.s_addr;
r = 0;
}
}
}
}
free(buf);
}
return r;
}
#endif
After checking back with Apple, the SDK does not offer an easy way to do that. The hard way, if any, is to dig deep into the system or use a traceroute.
I filed a bug report, maybe they will add it in the future.
Take a look at the answers to Objective-C : How to fetch the router address?
Perhaps only tangentially related, but see the technique outlined in this blog post: http://blog.zachwaugh.com/post/309927273/programmatically-retrieving-ip-address-of-iphone
It obtains the IP address of the Wi-Fi interface, and might be a another jumping off point to finding another solution....
- (NSString *)getIPAddress
{
NSString *address = #"error";
struct ifaddrs *interfaces = NULL;
struct ifaddrs *temp_addr = NULL;
int success = 0;
// retrieve the current interfaces - returns 0 on success
success = getifaddrs(&interfaces);
if (success == 0)
{
// Loop through linked list of interfaces
temp_addr = interfaces;
while(temp_addr != NULL)
{
if(temp_addr->ifa_addr->sa_family == AF_INET)
{
// Check if interface is en0 which is the wifi connection on the iPhone
if([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:#"en0"])
{
// Get NSString from C String
address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_addr)->sin_addr)];
}
}
temp_addr = temp_addr->ifa_next;
}
}
// Free memory
freeifaddrs(interfaces);
return address;
}