receive.c

#include "receive.h"


bool receive_all (int socket, int ttl, pid_t pid, struct in_addr addr[3], float* time, int* packets_received) {
    bool last_packet_received = false;
    struct timeval time1, time2;
    gettimeofday(&time1, NULL);

    int received_status;
    float response_time = 0.0;

    while ((*packets_received < 3) && (response_time < TIMEOUT_MS)) {
        received_status = receive(socket, ttl, pid, TIMEOUT_MS - response_time, &addr[*packets_received]);
        gettimeofday(&time2, NULL);
        response_time = (time2.tv_sec - time1.tv_sec) * 1000.0 + (time2.tv_usec - time1.tv_usec) / 1000.0;

        if (received_status != DISCARD_PACKET) {
            (*packets_received)++;
            *time += response_time;

            if (received_status == LAST_PACKET)
                last_packet_received = true;
        }
    }

    if (last_packet_received)
        return true;
    else
        return false;
}


int receive (int socket, int ttl, pid_t pid, float wait, struct in_addr* addr) {
    fd_set descriptors;
    FD_ZERO(&descriptors);
    FD_SET(socket, &descriptors);

    struct timeval time;
    time.tv_sec = 0;
    time.tv_usec = wait;

    int ready = select(socket + 1, &descriptors, NULL, NULL, &time);

    if (ready < 0) {
        fprintf(stderr, "Select error: %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
    else if (ready == 0)
        return DISCARD_PACKET;

    uint8_t buffer[IP_MAXPACKET];
    if (recv(socket, buffer, IP_MAXPACKET, 0) < 0) {
        fprintf(stderr, "Error while receiving a packet: %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }

    struct ip* ip_packet = (struct ip *) buffer;
    struct icmp* icmp_packet = (struct icmp *) ((uint8_t *)ip_packet + (*ip_packet).ip_hl * 4);

    if (icmp_packet->icmp_type == ICMP_TIME_EXCEEDED) {
        struct ip* temp_ip = (struct ip *) ((uint8_t *)icmp_packet + 8);
        struct icmp* temp_icmp = (struct icmp *) ((uint8_t *)temp_ip + (*temp_ip).ip_hl * 4);

        if ((temp_icmp->icmp_id == pid) && (temp_icmp->icmp_seq == ttl)) {
            *addr = ip_packet->ip_src;
            return NODE_PACKET;
        }
    }

    else if ((icmp_packet->icmp_id == pid) && (icmp_packet->icmp_seq == ttl) && (icmp_packet->icmp_type == ICMP_ECHOREPLY)) {
        *addr = ip_packet->ip_src;
        return LAST_PACKET;
    }

    return DISCARD_PACKET;
}