linuxc 实现ping命令

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

#define PACKET_SIZE 4096
#define ERROR(...) fprintf(stderr, __VA_ARGS__), exit(EXIT_FAILURE)

unsigned short checksum(void *b, int len) {
    unsigned short *buf = b;
    unsigned int sum = 0;
    unsigned short result;

    for (sum = 0; len > 1; len -= 2) {
        sum += *buf++;
    }
    if (len == 1) {
        sum += *(unsigned char *)buf;
        sum = (sum >> 8) + (sum & 0xff);
    }
    sum += (sum >> 16);
    result = ~sum;
    return result;
}

int send_packet(int sockfd, struct sockaddr_in *addr) {
    char packet[PACKET_SIZE];
    struct icmp *icmp_header = (struct icmp *)packet;
    memset(packet, 0, PACKET_SIZE);
    icmp_header->icmp_type = ICMP_ECHO;
    icmp_header->icmp_code = 0;
    icmp_header->icmp_id = getpid();
    icmp_header->icmp_seq = 1;
    icmp_header->icmp_cksum = checksum(packet, PACKET_SIZE);

    if (sendto(sockfd, packet, PACKET_SIZE, 0, (struct sockaddr *)addr, sizeof(*addr)) < 0) {
        ERROR("sendto failed: %s\n", strerror(errno));
    }
    return 0;
}

int recv_packet(int sockfd, struct sockaddr_in *addr) {
    char packet[PACKET_SIZE];
    struct sockaddr_in from;
    socklen_t fromlen = sizeof(from);
    int n = recvfrom(sockfd, packet, PACKET_SIZE, 0, (struct sockaddr *)&from, &fromlen);
    if (n < 0) {
        ERROR("recvfrom failed: %s\n", strerror(errno));
    }

    struct ip *ip_header = (struct ip *)packet;
    struct icmp *icmp_header = (struct icmp *)(packet + (ip_header->ip_hl << 2));
    if (icmp_header->icmp_type == ICMP_ECHOREPLY) {
        if (icmp_header->icmp_id == getpid()) {
            printf("Received ping from %s\n", inet_ntoa(from.sin_addr));
            return 0;
        }
    }
    return -1;
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        ERROR("Usage: %s <IP address>\n", argv[0]);
    }

    int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sockfd < 0) {
        ERROR("socket failed: %s\n", strerror(errno));
    }

    struct sockaddr_in addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = 0;
    inet_pton(AF_INET, argv[1], &addr.sin_addr);

    send_packet(sockfd, &addr);
    recv_packet(sockfd, &addr);

    close(sockfd);
    return 0;
}