Thread: Simple ping routine, not receiving anything.

Hi,

I'm trying to create a simple ping routine, that can be used in other programs to test internet connectivity. I'm stuck, as the following code seems to send the request, but `recvfrom` blocks forever.

Since I don't normally deal with sockets like this, I'm completely lost as to what is wrong. And I don't think I can look at more code that doesn't satisfy my need.

Here's what I have:

Code:

// Declare includes.
#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <netinet/in.h>
#include <netinet/ip_icmp.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

// Declare defines.
#define BUFFER_SIZE      1024
#define PING_ADDRESS        "8.8.8.8"
#define RETURN_FAILURE      0
#define RETURN_SUCCESS      1

// Declare function prototypes.
int pinger (char *address);

int main (int argc, __attribute__ ((unused)) char *argv[])
{
// Check number of arguments.
    if(argc != 1)
    {
        fprintf(stderr, "Usage: %s", program_invocation_short_name);
        exit(EXIT_FAILURE);
    }

// Check that user is root or that sudo is used.
    if(geteuid() != 0)
    {
        fprintf(stderr, "%s: must be run as root or with 'sudo'", program_invocation_short_name);
        exit(EXIT_FAILURE);
    }

// Run process.
    printf("Pinging %s was %s\n", PING_ADDRESS, pinger(PING_ADDRESS) == RETURN_SUCCESS ? "successful." : "unsuccessful.");

// Exit cleanly.
    exit(EXIT_SUCCESS);
}

int pinger (char *address)
{
// Declare variables.
    char buffer[BUFFER_SIZE] = {0};
    struct icmp icmp_hdr = {0};
    struct sockaddr_in dest_addr = {0};
    struct sockaddr_in from_addr = {0};
    socklen_t fromlen = {0};
    int sockfd = {0};

// Populate the icmp structure.
    icmp_hdr.icmp_type = ICMP_ECHO;
    icmp_hdr.icmp_code = 0;
    icmp_hdr.icmp_cksum = 0;
    icmp_hdr.icmp_id = getpid();
    icmp_hdr.icmp_seq = 1;

// Populate the socket address structure.
    dest_addr.sin_family = AF_INET;
    dest_addr.sin_addr.s_addr = inet_addr(address);
    memset(&dest_addr.sin_zero, 0, sizeof(dest_addr.sin_zero));

// Create a raw socket.
    if((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1)
    {
        fprintf(stderr, "%s: %s error: socket failed (%s)", program_invocation_short_name, __func__, strerror(errno));
        return(RETURN_FAILURE);
    }

// Send icmp request.
    if(sendto(sockfd, &icmp_hdr, sizeof(struct icmp), 0, (struct sockaddr *) &dest_addr, sizeof(struct sockaddr_in)) == -1)
    {
        fprintf(stderr, "%s: %s error: sendto failed (%s)", program_invocation_short_name, __func__, strerror(errno));
        return(RETURN_FAILURE);
    }

// Receive icmp response.
    if(recvfrom(sockfd, buffer, BUFFER_SIZE, 0, (struct sockaddr *) &from_addr, &fromlen) == -1)
    {
        fprintf(stderr, "%s: %s error: recvfrom failed (%s)", program_invocation_short_name, __func__, strerror(errno));
        return(RETURN_FAILURE);
    }

// Return success.
    return(RETURN_SUCCESS);
}

Any help or insight is greatly appreciated. Ty.

When compiling with gcc on Linux, I get the following errors:

Code:

com bar.c
bar.c: In function ‘main’:
bar.c:28:38: error: ‘program_invocation_short_name’ undeclared (first use in this function)
   28 |         fprintf(stderr, "Usage: %s", program_invocation_short_name);
      |                                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bar.c:28:38: note: each undeclared identifier is reported only once for each function it appears in
bar.c: In function ‘pinger’:
bar.c:50:12: error: variable ‘icmp_hdr’ has initializer but incomplete type
   50 |     struct icmp icmp_hdr = {0};
      |            ^~~~
bar.c:50:29: warning: excess elements in struct initializer
   50 |     struct icmp icmp_hdr = {0};
      |                             ^
bar.c:50:29: note: (near initialization for ‘icmp_hdr’)
bar.c:50:17: error: storage size of ‘icmp_hdr’ isn’t known
   50 |     struct icmp icmp_hdr = {0};
      |                 ^~~~~~~~
bar.c:71:61: error: ‘program_invocation_short_name’ undeclared (first use in this function)
   71 |         fprintf(stderr, "%s: %s error: socket failed (%s)", program_invocation_short_name, __func__, strerror(errno));
      |                                                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bar.c:76:41: error: invalid application of ‘sizeof’ to incomplete type ‘struct icmp’
   76 |     if(sendto(sockfd, &icmp_hdr, sizeof(struct icmp), 0, (struct sockaddr *) &dest_addr, sizeof(struct sockaddr_in)) == -1)
      |                                         ^~~~~~
bar.c:50:17: warning: unused variable ‘icmp_hdr’ [-Wunused-variable]
   50 |     struct icmp icmp_hdr = {0};
      |                 ^~~~~~~~

Clear these warnings/errors first. Turn on warnings options and turn up to the highest level in whatever O/S & Compiler you are using.

Originally Posted by rstanley

When compiling with gcc on Linux, I get the following errors:
Clear these warnings/errors first. Turn on warnings options and turn up to the highest level in whatever O/S & Compiler you are using.

Sorry, I don't get those errors, but it's because of my gcc compile options. I'm compiling with:

Code:

gcc -Wall -Werror -Wextra -Wfatal-errors -D_GNU_SOURCE -O3 -o ./pinger pinger.c

I just noticed something strange. I ran the program, and while it was hanging and not responding, I opened a terminal and ran `ping 8.8.8.8`. While ping ran, my program actually returned 'successful.'

So I'm thinking that my code might be correct, it's just missing something. But what?

Back to view more code...

Originally Posted by john.c

I think you need to set icmp_cksum properly.
Ping in C - GeeksforGeeks

I did come across that link, but the site clearly doesn't check it's work once posted. I found a bunch of problems with this code. For example, the following function:

Code:

// Calculating the Check Sum
 unsigned short checksum(void* b, int len)
 {
     unsigned short* buf = b;
     unsigned int sum = 0;

     unsigned short result;

  

     for (sum = 0; len & gt; 1; len -= 2)

         sum += *buf++;

     if (len == 1)

         sum += *(unsigned char*)buf;

     sum = (sum & gt; > 16) + (sum & amp; 0xFFFF);

     sum += (sum & gt; > 16);

     result = ~sum;

     return result;

 }

I'm not great with `ones' compliments`, so when I come across `sum += (sum & gt; > 16);` or this `sum = (sum & gt; > 16) + (sum & amp; 0xFFFF);`, it kills my spirit and I must stop looking at it.

I'll try to decipher this, but I'm not holding hope. Thanks for your reply.

I have seen the following in some code, but it doesn't seem to change/fix anything.

Code:

icmp_hdr.icmp_cksum = htons(~(ICMP_ECHO << 8));

I'll give the RFC a look.

Originally Posted by Yonut

I just noticed something strange. I ran the program, and while it was hanging and not responding, I opened a terminal and ran `ping 8.8.8.8`. While ping ran, my program actually returned 'successful.'

Why would the program only work once a proper ping is issued? Why would the second ping correct the checksum of the original ping? I'm thinking this might have something to do with bind.

The first function you posted didn't seem to help. So I threw in the towel.

During my searches the following became clear, regarding what I was trying to do...
1) ICMP request are the lowest priority, has to wait for everything else.
2) ICMP requires root access.
3) Just too many variables as to what I m supposed to do.

So I copped out and just wrote a simple http tester that checks for access to my service providers DNS server. Super quick, and it solves the 3 problems listed above.

Code:

int test_internet_conectivity (void)
{
// Declare variables.
    struct addrinfo hints = {0};
    struct addrinfo *res = NULL;
    int ret = {0};
    int sockfd = {0};

// Populate the structure.
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;

// Get network address translation.
    if((ret = getaddrinfo(IP_ADDRESS, "http", &hints, &res)) != 0)
    {
        fprintf(stderr, "%s: %s error: getaddrinfo failed (%s) (%s)", program_invocation_short_name, __func__, gai_strerror(ret), IP_ADDRESS);
        return(RETURN_FAILURE);
    }

// Open the socket.
    if((sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol)) == -1)
    {
        fprintf(stderr, "%s: %s error: socket failed (%s)", program_invocation_short_name, __func__, strerror(errno));
// Free allocated memory.
        freeaddrinfo(res);
        return(RETURN_FAILURE);
    }

// Connect to web server.
    if(connect(sockfd, res->ai_addr, res->ai_addrlen) == -1)
    {
        fprintf(stderr, "%s: %s error: connect failed (%s) (%s)", program_invocation_short_name, __func__, strerror(errno), IP_ADDRESS);
// Free allocated memory and close the socket.
        freeaddrinfo(res);
        close(sockfd);
        return(RETURN_FAILURE);
    }

// Free allocated memory and close the socket.
    freeaddrinfo(res);
    close(sockfd);
// Alert of success.
    return(RETURN_SUCCESS);
}

John, I will try your new function a little later, but I need let my brain decompress from today's events.