Updated function that parses config file.

[icmpmonitor] / icmpmonitor.c

diff --git a/icmpmonitor.c b/icmpmonitor.c
index 284da67..462c920 100644 (file)
--- a/icmpmonitor.c
+++ b/icmpmonitor.c
@@ -11,6 +11,12 @@
  * See LICENSE file for copyright and license details.
  */
 
  * See LICENSE file for copyright and license details.
  */
 

+/* Wishlist */
+/* TODO: Add IPv6 support. */
+/* TODO: Turn the global '-r' functionality into per-host config file option. */
+/* TODO: Add 'auto' keyword to 'start_condition', testing host on startup. */
+/* TODO: Double-check the network code when interrupted while receiving a packet. */
+

 #include <stdio.h>
 #include <stdlib.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdbool.h>


@@ -27,6 +33,7 @@
 #include <netinet/ip.h>
 #include <netinet/ip_icmp.h>
 #include <errno.h>
 #include <netinet/ip.h>
 #include <netinet/ip_icmp.h>
 #include <errno.h>

+#include <assert.h>

 
 #include "iniparser/iniparser.h"
 
 
 #include "iniparser/iniparser.h"
 


@@ -35,11 +42,20 @@
 #define MAXPACKETSIZE  (65536 - 60 - 8) /* TODO: What are the magic numbers? */
 #define DEFAULTDATALEN (64 - 8)         /* TODO: What are the magic numbers? */
 
 #define MAXPACKETSIZE  (65536 - 60 - 8) /* TODO: What are the magic numbers? */
 #define DEFAULTDATALEN (64 - 8)         /* TODO: What are the magic numbers? */
 

+/* ICMP header contains: type, code, checksum, identifier and sequence number. */
+#define ICMP_ECHO_HEADER_BYTES  8
+#define ICMP_ECHO_DATA_BYTES    sizeof(struct timeval)
+#define ICMP_ECHO_PACKET_BYTES  ICMP_ECHO_HEADER_BYTES + ICMP_ECHO_DATA_BYTES
+
+/* Minimum time in seconds between pings. If this value is increased above the */
+/* `ping_interval` for a given host, some pings to that host may not be sent.  */
+#define TIMER_RESOLUTION        1
+

 /* Must be larger than the length of the longest configuration key (currently 'start_condition'). */
 #define MAXCONFKEYLEN 20
 
 /* One struct per host as listed in the config file. */
 /* Must be larger than the length of the longest configuration key (currently 'start_condition'). */
 #define MAXCONFKEYLEN 20
 
 /* One struct per host as listed in the config file. */

-struct monitor_host {
+struct host_entry {

     /* From the config file */
     char * name;
     int    ping_interval;
     /* From the config file */
     char * name;
     int    ping_interval;


@@ -55,226 +71,187 @@ struct monitor_host {
     struct sockaddr_in dest;
 
     /* Linked list */
     struct sockaddr_in dest;
 
     /* Linked list */

-    struct monitor_host * next;
+    struct host_entry * next;

 };
 
 /* Globals */
     /* Since the program is based around signals, a linked list of hosts is maintained here. */
 };
 
 /* Globals */
     /* Since the program is based around signals, a linked list of hosts is maintained here. */

-    static struct monitor_host * hosts          = NULL;
+    static struct host_entry * first_host_in_list = NULL;

     /* Set by command line flags. */
     static bool                  verbose        = false;
     static bool                  retry_down_cmd = false;
     /* Set by command line flags. */
     static bool                  verbose        = false;
     static bool                  retry_down_cmd = false;

-    /* TODO: Get rid of this global. */
-    static int                   send_delay     = 1;

 
 /*
 
 /*

- * Checksum routine for Internet Protocol family headers
+ * Generate an Internet Checksum per RFC 1071.
+ *
+ * This is not a general purpose implementation of RFC 1071.  Since we only
+ * send ICMP echo packets, we assume 'data' will contain a specific number of
+ * bytes.

  */
  */

-static int
-in_cksum(unsigned short * addr, int len)
+uint16_t
+checksum(const uint16_t * data)

 {
 {

-    int nleft = len;
-    unsigned short * w = addr;
-    int sum = 0;
-    unsigned short answer = 0;
-
-    /*
-     * Our algorithm is simple, using a 32 bit accumulator (sum), we add
-     * sequential 16 bit words to it, and at the end, fold back all the
-     * carry bits from the top 16 bits into the lower 16 bits.
-     */
-    while (nleft > 1) {
-        sum += *w++;
-        nleft -= 2;
+    uint32_t accumulator = 0;
+    for (size_t i = 0; i < ICMP_ECHO_PACKET_BYTES / 2; i++) {
+        accumulator += ntohs(data[i]);
+        if (accumulator > 0xffff) accumulator -= 0xffff;

     }
     }

-
-    /* mop up an odd byte, if necessary */
-    if (nleft == 1) {
-        *(u_char *)(&answer) = *(u_char *)w;
-        sum += answer;
-    }
-
-    /* add back carry outs from top 16 bits to low 16 bits */
-    sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
-    sum += (sum >> 16);                 /* add carry */
-    answer = ~sum;                      /* truncate to 16 bits */
-    return(answer);
+    return htons(~accumulator);

 }
 
 /*
 }
 
 /*

- * Subtracts two timeval structs.
- * Ensure out >= in.
- * Modifies out = out - in.
+ * Calculate difference (a-b) between two timeval structs.

  */
  */

-static void
-tv_sub(register struct timeval * out, register struct timeval * in)
+void
+timeval_diff(struct timeval * a, const struct timeval * b)

 {
 {

-    if ((out->tv_usec -= in->tv_usec) < 0) {
-        --out->tv_sec;
-        out->tv_usec += 1000000;
+    if (a->tv_usec < b->tv_usec) {
+        a->tv_sec--;
+        a->tv_usec += 1000000;

     }
     }

-    out->tv_sec -= in->tv_sec;
+    a->tv_usec -= b->tv_usec;
+    a->tv_sec -= b->tv_sec;

 }
 
 /*
 }
 
 /*

- * Compose and transmit an ICMP ECHO REQUEST packet. The IP packet
- * will be added on by the kernel. The ID field is our UNIX process ID,
- * and the sequence number is an ascending integer. The first 8 bytes
- * of the data portion are used to hold a UNIX "timeval" struct in VAX
- * byte-order, to compute the round-trip time.
+ * This function iterates over the list of hosts, pinging any which are due.

  */
  */

-static void
-pinger(int ignore)
+void
+pinger(int ignore) /* Dummy parameter since this function registers as a signal handler. */

 {
 {

-    int i;
-    struct icmp * icp;
-    struct monitor_host * p = hosts;
-    u_char outpack[MAXPACKETSIZE];
-
-    while (p) {
-        if (p->socket != -1) {
-            struct timeval now;
-
-            gettimeofday(&now, (struct timezone *) NULL);
-            tv_sub(&now, &p->last_ping_received);
-
-            if (now.tv_sec > (p->max_delay + p->ping_interval)) {
-                if ((p->host_up) || retry_down_cmd) {
-                    if (verbose) printf("INFO: Host %s stopped responding. Executing DOWN command.\n", p->name);
-                    p->host_up = false;
-                    if (!fork()) {
-                        system(p->down_cmd);
-                        exit(EXIT_SUCCESS);
-                    } else {
-                        wait(NULL);
-                    }
-                }
-            }
+    assert(first_host_in_list);

 
 

-            gettimeofday(&now, (struct timezone *) NULL);
-            tv_sub(&now, &p->last_ping_sent);
+    struct icmp * icmp_packet;
+    struct host_entry * host = first_host_in_list;
+    unsigned char packet[IP_PACKET_MAX_BYTES]; /* Use char so this can be aliased later. */

 
 

-            if (now.tv_sec > p->ping_interval) { /* Time to send ping */
-                icp = (struct icmp *) outpack;
-                icp->icmp_type  = ICMP_ECHO;
-                icp->icmp_code  = 0;
-                icp->icmp_cksum = 0;
-                icp->icmp_seq   = p->socket;
-                icp->icmp_id    = getpid() & 0xFFFF;
+    while (host) {
+        struct timeval elapsed_time;
+        gettimeofday(&elapsed_time, NULL);
+        timeval_diff(&elapsed_time, &host->last_ping_received);

 
 

-                if (verbose) printf("INFO: Sending ICMP packet to %s.\n", p->name);
+        if ((elapsed_time.tv_sec > host->max_delay) && (host->host_up || retry_down_cmd)) {
+            if (verbose) printf("INFO: Host %s stopped responding. Executing DOWN command.\n", host->name);
+            host->host_up = false;
+            if (!fork()) {
+                system(host->down_cmd);
+                exit(EXIT_SUCCESS);
+            }
+        }

 
 

-                gettimeofday((struct timeval *) &outpack[8], (struct timezone *) NULL);
+        if (elapsed_time.tv_sec > host->ping_interval) {
+            if (verbose) printf("INFO: Sending ICMP packet to %s.\n", host->name);

 
 

-                int cc = DEFAULTDATALEN + 8;  /* skips ICMP portion */
+            icmp_packet = (struct icmp *) packet;
+            icmp_packet->icmp_type  = ICMP_ECHO;
+            icmp_packet->icmp_code  = 0;
+            icmp_packet->icmp_cksum = 0;
+            icmp_packet->icmp_seq   = host->socket;
+            icmp_packet->icmp_id    = getpid() & 0xFFFF;

 
 

-                /* compute ICMP checksum */
-                icp->icmp_cksum = in_cksum((unsigned short *) icp, cc);
+            /* Write a timestamp struct in the packet's data segment for use in calculating travel times. */
+            gettimeofday((struct timeval *) &packet[ICMP_ECHO_HEADER_BYTES], NULL);

 
 

-                i = sendto(p->socket, (char *) outpack, cc, 0, (const struct sockaddr *) (&p->dest), sizeof(struct sockaddr));
+            icmp_packet->icmp_cksum = checksum((uint16_t *) packet);

 
 

-                gettimeofday(&p->last_ping_sent, (struct timezone *) NULL);
+            size_t bytes_sent = sendto(host->socket, packet, ICMP_ECHO_PACKET_BYTES, 0,
+                                       (const struct sockaddr *) &host->dest,
+                                       sizeof(struct sockaddr));

 
 

-                if (i < 0 || i != cc) {
-                    if (i<0) fprintf(stderr, "WARN: Failed sending ICMP packet to %s.\n", p->name);
-                }
+            if (bytes_sent == ICMP_ECHO_PACKET_BYTES) {
+                gettimeofday(&host->last_ping_sent, NULL);
+            } else {
+                fprintf(stderr, "WARN: Failed sending ICMP packet to %s.\n", host->name);

             }
         }
             }
         }

-        p = p->next;
+        host = host->next;

     }
 
     }
 

-    signal(SIGALRM, pinger); /* restore handler */
-    alarm(send_delay);
+    signal(SIGALRM, pinger);
+    alarm(TIMER_RESOLUTION);

 }
 
 }
 

-static void
-read_icmp_data(struct monitor_host * p)
+void
+read_icmp_data(struct host_entry * host)

 {
 {

-    int cc, iphdrlen, delay;
-    socklen_t fromlen;
-    struct sockaddr_in from;
-    struct ip * ip;
-    struct icmp * icmp;
-    struct timeval tv;
-    unsigned char buf[MAXPACKETSIZE];
+    struct timeval now;
+    gettimeofday(&now, NULL);

 
 

-    gettimeofday(&tv, (struct timezone *) NULL);
-
-    fromlen = sizeof(from);
-    if ((cc = recvfrom(p->socket, buf, sizeof(buf), 0, (struct sockaddr *)&from, &fromlen)) < 0) {
-        if (errno != EINTR) fprintf(stderr, "WARN: Error reading ICMP data from %s.\n", p->name);
+    struct sockaddr_in from;
+    socklen_t fromlen = sizeof(from);
+    int bytes;
+    unsigned char packet[IP_PACKET_MAX_BYTES]; /* Use char so this can be aliased later. */
+    if ((bytes = recvfrom(host->socket, packet, sizeof(packet), 0, (struct sockaddr *) &from, &fromlen)) < 0) {
+        if (errno != EINTR) fprintf(stderr, "WARN: Error reading ICMP data from %s.\n", host->name);

         return;
     }
 
         return;
     }
 

-    /* check IP header actual len */
-    ip       = (struct ip *) buf;
-    iphdrlen = ip->ip_hl << 2;
-    icmp     = (struct icmp *) (buf + iphdrlen);
+    struct ip * ip     = (struct ip *) packet;
+    int iphdrlen       = ip->ip_hl << 2;
+    struct icmp * icmp = (struct icmp *) (packet + iphdrlen);

 
 

-    if (cc < iphdrlen + ICMP_MINLEN) {
-        fprintf(stderr, "WARN: Received short packet from %s.\n", p->name);
+    if (bytes < iphdrlen + ICMP_MINLEN) {
+        fprintf(stderr, "WARN: Received short packet from %s.\n", host->name);

         return;
     }
 
         return;
     }
 

-    if (icmp->icmp_type == ICMP_ECHOREPLY && icmp->icmp_id == (getpid() & 0xFFFF) && icmp->icmp_seq == p->socket) {
-
-        memcpy(&p->last_ping_received, &tv, sizeof(tv));
-
-        tv_sub(&tv, (struct timeval *) &icmp->icmp_data[0]);
-        delay = tv.tv_sec * 1000 + (tv.tv_usec / 1000);
-
-        if (verbose) printf("INFO: Got ICMP reply from %s in %d ms.\n", p->name, delay);
-        if (!p->host_up) {
-            if (verbose) printf("INFO: Host %s started responding. Executing UP command.\n", p->name);
-            p->host_up = true;
+    if (icmp->icmp_type == ICMP_ECHOREPLY && icmp->icmp_id == (getpid() & 0xFFFF) && icmp->icmp_seq == host->socket) {
+        memcpy(&host->last_ping_received, &now, sizeof(now));
+        if (verbose) printf("INFO: Got ICMP reply from %s.\n", host->name);
+        if (!host->host_up) {
+            if (verbose) printf("INFO: Host %s started responding. Executing UP command.\n", host->name);
+            host->host_up = true;

             if (!fork()) {
             if (!fork()) {

-                system(p->up_cmd);
+                system(host->up_cmd);

                 exit(EXIT_SUCCESS);
                 exit(EXIT_SUCCESS);

-            } else {
-                wait(NULL);

             }
         }
     } else {
             }
         }
     } else {

-        /* TODO: Do anything here? */
+        /* The packet isn't what we expected. Ignore it and move on. */

     }
 }
 
     }
 }
 

-static void
+/*
+ * This function contains the main program loop, listening for replies to pings
+ * sent from the signal-driven pinger().
+ */
+void

 get_response(void)
 {
 get_response(void)
 {

-    fd_set rfds;
-    int retval, maxd = -1;
-    struct monitor_host * p;
-
-    while (1) {
-        p = hosts;
+    while (true) {
+        fd_set rfds;

         FD_ZERO(&rfds);
         FD_ZERO(&rfds);

-        while (p) {
-            if (p->socket != -1) {
-                if (p->socket > maxd) maxd = p->socket;
-                FD_SET(p->socket, &rfds);
-            }
-            p = p->next;
+
+        assert(first_host_in_list);
+        struct host_entry * host = first_host_in_list;
+
+        int max_fd = -1;
+        while (host) {
+            if (host->socket > max_fd) max_fd = host->socket;
+            FD_SET(host->socket, &rfds);
+            host = host->next;

         }
 
         }
 

-        retval = select(maxd+1, &rfds, NULL, NULL, NULL);
-        if (retval < 0) {
-            /* Intentionally empty. We arrive here when interrupted by a signal. No action should be taken. */
-        } else {
-            if (retval > 0) {
-                p = hosts;
-                while (p) {
-                    if (p->socket!=-1 && FD_ISSET(p->socket, &rfds)) read_icmp_data(p);
-                    p = p->next;
-                }
-            } else {
-                /* TODO: How to handle this error? */
+        int retval;
+        if ((retval = select(max_fd+1, &rfds, NULL, NULL, NULL)) > 0) {
+            assert(first_host_in_list);
+            host = first_host_in_list;
+            while (host) {
+                if (FD_ISSET(host->socket, &rfds)) read_icmp_data(host);
+                host = host->next;

             }
             }

+        } else {
+            /* An error or interruption occurred.                    */
+            /* We can't do anything about it, so loop and try again. */

         }
     }
 }
 
         }
     }
 }
 

-static void
+/*
+ * Parse a configuration file using the `iniparser` library.
+ * See `icmpmonitor.ini` and `README.md` for examples and reference.
+ */
+void

 parse_config(const char * conf_file)
 {
     dictionary * conf = iniparser_load(conf_file);
 parse_config(const char * conf_file)
 {
     dictionary * conf = iniparser_load(conf_file);


@@ -289,42 +266,41 @@ parse_config(const char * conf_file)
         exit(EXIT_FAILURE);
     }
 
         exit(EXIT_FAILURE);
     }
 

-    struct monitor_host * host_list_end = NULL;
+    struct host_entry * host_list_end = NULL;

     for (int i=0; i < host_count; i++) {
         /* Allocate a reusable buffer large enough to hold the full 'section:key' string. */
         int section_len = strlen(iniparser_getsecname(conf, i));
     for (int i=0; i < host_count; i++) {
         /* Allocate a reusable buffer large enough to hold the full 'section:key' string. */
         int section_len = strlen(iniparser_getsecname(conf, i));

-        char * key_buf = malloc(section_len + 1 + MAXCONFKEYLEN + 1);
+        char * key_buf = malloc(section_len + 1 + MAX_CONF_KEY_LEN + 1); /* +1 for ':' and '\0' */

         strcpy(key_buf, iniparser_getsecname(conf, i));
         key_buf[section_len++] = ':';
 
         strcpy(key_buf, iniparser_getsecname(conf, i));
         key_buf[section_len++] = ':';
 

-        struct monitor_host * cur_host = malloc(sizeof(struct monitor_host));
+        struct host_entry * cur_host = malloc(sizeof(struct host_entry));

 
         key_buf[section_len] = '\0';
 
         key_buf[section_len] = '\0';

-        strncat(key_buf, "host", MAXCONFKEYLEN);
+        strncat(key_buf, "host", MAX_CONF_KEY_LEN);

         cur_host->name = strdup(iniparser_getstring(conf, key_buf, NULL));
 
         key_buf[section_len] = '\0';
         cur_host->name = strdup(iniparser_getstring(conf, key_buf, NULL));
 
         key_buf[section_len] = '\0';

-        strncat(key_buf, "interval", MAXCONFKEYLEN);
+        strncat(key_buf, "interval", MAX_CONF_KEY_LEN);

         cur_host->ping_interval = iniparser_getint(conf, key_buf, -1);
 
         key_buf[section_len] = '\0';
         cur_host->ping_interval = iniparser_getint(conf, key_buf, -1);
 
         key_buf[section_len] = '\0';

-        strncat(key_buf, "max_delay", MAXCONFKEYLEN);
+        strncat(key_buf, "max_delay", MAX_CONF_KEY_LEN);

         cur_host->max_delay = iniparser_getint(conf, key_buf, -1);
 
         key_buf[section_len] = '\0';
         cur_host->max_delay = iniparser_getint(conf, key_buf, -1);
 
         key_buf[section_len] = '\0';

-        strncat(key_buf, "up_cmd", MAXCONFKEYLEN);
+        strncat(key_buf, "up_cmd", MAX_CONF_KEY_LEN);

         cur_host->up_cmd = strdup(iniparser_getstring(conf, key_buf, NULL));
 
         key_buf[section_len] = '\0';
         cur_host->up_cmd = strdup(iniparser_getstring(conf, key_buf, NULL));
 
         key_buf[section_len] = '\0';

-        strncat(key_buf, "down_cmd", MAXCONFKEYLEN);
+        strncat(key_buf, "down_cmd", MAX_CONF_KEY_LEN);

         cur_host->down_cmd = strdup(iniparser_getstring(conf, key_buf, NULL));
 
         key_buf[section_len] = '\0';
         cur_host->down_cmd = strdup(iniparser_getstring(conf, key_buf, NULL));
 
         key_buf[section_len] = '\0';

-        /* TODO: Parse for up/down/auto in start_condition. */
-        /* TODO: Do a host up/down check if necessary. */
-        cur_host->host_up = true;
+        strncat(key_buf, "start_condition", MAX_CONF_KEY_LEN);
+        const char * value = iniparser_getstring(conf, key_buf, NULL);
+        if (value) cur_host->host_up = *value == 'u' ? true : false;

 
 

-        /* TODO: Do I want to make any checks for start_condition? */

         if (cur_host->name == NULL || cur_host->ping_interval == -1 || cur_host->max_delay == -1) {
             fprintf(stderr, "ERROR: Problems parsing section %s.\n", iniparser_getsecname(conf, i));
             exit(EXIT_FAILURE);
         if (cur_host->name == NULL || cur_host->ping_interval == -1 || cur_host->max_delay == -1) {
             fprintf(stderr, "ERROR: Problems parsing section %s.\n", iniparser_getsecname(conf, i));
             exit(EXIT_FAILURE);


@@ -334,8 +310,8 @@ parse_config(const char * conf_file)
         cur_host->next = NULL;
         gettimeofday(&(cur_host->last_ping_received), (struct timezone *) NULL);
 
         cur_host->next = NULL;
         gettimeofday(&(cur_host->last_ping_received), (struct timezone *) NULL);
 

-        if (hosts == NULL) {
-            hosts = cur_host;
+        if (first_host_in_list == NULL) {
+            first_host_in_list = cur_host;

             host_list_end = cur_host;
         } else {
             host_list_end->next = cur_host;
             host_list_end = cur_host;
         } else {
             host_list_end->next = cur_host;


@@ -347,62 +323,84 @@ parse_config(const char * conf_file)
     iniparser_freedict(conf);
 }
 
     iniparser_freedict(conf);
 }
 

-static int
+/*
+ * Parse string (IP or hostname) to Internet address.
+ *
+ * Returns 0 if host can't be resolved, otherwise returns an Internet address.
+ */
+uint32_t

 get_host_addr(const char * name)
 {
 get_host_addr(const char * name)
 {

-    static int res;
-    struct hostent * host_ent;
-
-    if ((res = inet_addr(name)) < 0) {
-        host_ent = gethostbyname(name);
-        if (!host_ent) return -1;
-        memcpy(&res, host_ent->h_addr, host_ent->h_length);
-    }
-    return(res);
+    struct addrinfo hints;
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_family = AF_INET;
+
+    int rv;
+    struct addrinfo * address;
+    if ((rv = getaddrinfo(name, NULL, &hints, &address)) != 0) return 0;
+    uint32_t result = ((struct sockaddr_in *)(address->ai_addr))->sin_addr.s_addr;
+    freeaddrinfo(address);
+    return result;

 }
 
 }
 

-static int
-gcd(int x, int y)
+size_t
+gcd(const size_t x, const size_t y)

 {
 {

-    int remainder = x % y;
+    size_t remainder = x % y;

     if (remainder == 0) return y;
     return gcd(y, remainder);
 }
 
     if (remainder == 0) return y;
     return gcd(y, remainder);
 }
 

-static void
+void
+remove_host_from_list(struct host_entry * host)
+{
+    assert(first_host_in_list);
+    assert(host);
+
+    if (host == first_host_in_list) {
+        first_host_in_list = host->next;
+    } else {
+        struct host_entry * temp = first_host_in_list;
+        while (temp->next != host && temp->next != NULL) temp = temp->next;
+        if (temp->next == NULL) return;
+        temp->next = temp->next->next;
+    }
+    free(host);
+}
+
+void

 init_hosts(void)
 {
 init_hosts(void)
 {

-    struct monitor_host * p = hosts;
+    struct host_entry * host;

     struct protoent * proto;
     struct protoent * proto;

-    int ok = 0;

 
     if ((proto = getprotobyname("icmp")) == NULL) {
         fprintf(stderr, "ERROR: Unknown protocol: icmp.\n");
         exit(EXIT_FAILURE);
     }
 
 
     if ((proto = getprotobyname("icmp")) == NULL) {
         fprintf(stderr, "ERROR: Unknown protocol: icmp.\n");
         exit(EXIT_FAILURE);
     }
 

-    while (p) {
-        bzero(&p->dest, sizeof(p->dest));
-        p->dest.sin_family = AF_INET;
-        if ((p->dest.sin_addr.s_addr = get_host_addr(p->name)) <= 0) {
-            fprintf(stderr, "WARN: Can't resolve host. Skipping client %s.\n", p->name);
-            p->socket=-1;
-        } else {
-            if ((p->socket = socket(AF_INET,SOCK_RAW,proto->p_proto)) < 0) {
-                fprintf(stderr, "WARN: Can't create socket. Skipping client %s.\n", p->name);
-                p->socket=-1;
-            } else {
-                if (ok == 0) send_delay = p->ping_interval;
-                else send_delay = gcd(send_delay, p->ping_interval);
-                ok++;
-            }
+    assert(first_host_in_list);
+    host = first_host_in_list;
+    while (host) {
+        struct host_entry * next_host = host->next;
+        bzero(&host->dest, sizeof(host->dest));
+        host->dest.sin_family = AF_INET;
+        if (!(host->dest.sin_addr.s_addr = get_host_addr(host->name))) {
+            fprintf(stderr, "WARN: Removing unresolvable host %s from list.\n", host->name);
+            remove_host_from_list(host);

         }
         }

-        p = p->next;
+        host = next_host;

     }
 
     }
 

-    if (!ok) {
-        fprintf(stderr, "ERROR: No hosts left to process.\n");
-        exit(EXIT_FAILURE);
+    assert(first_host_in_list);
+    host = first_host_in_list;
+    while (host) {
+        struct host_entry * next_host = host->next;
+        if ((host->socket = socket(AF_INET, SOCK_RAW, proto->p_proto)) < 0) {
+            fprintf(stderr, "WARN: Failed creating socket. Removing host %s from list.\n", host->name);
+            remove_host_from_list(host);
+        }
+        host = next_host;

     }
 }
 
     }
 }
 


@@ -441,7 +439,7 @@ parse_params(int argc, char ** argv)
                 break;
         }
     }
                 break;
         }
     }

-    if (hosts == NULL) {
+    if (first_host_in_list == NULL) {

         fprintf(stderr, "ERROR: Unable to parse a config file.\n");
         exit(EXIT_FAILURE);
     }
         fprintf(stderr, "ERROR: Unable to parse a config file.\n");
         exit(EXIT_FAILURE);
     }


@@ -455,7 +453,7 @@ main(int argc, char ** argv)
     init_hosts();
 
     signal(SIGALRM, pinger);
     init_hosts();
 
     signal(SIGALRM, pinger);

-    alarm(send_delay);
+    alarm(TIMER_RESOLUTION);

 
     get_response();
 
 
     get_response();