Merge branch 'master' of https://github.com/maalvikabhat/ExercisesInC

exercises/ex04/trout/.#util.c

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+downey@rocky.colby.edu.25374:1 

exercises/ex04/trout/COPYRIGHT

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+TROUT is a simple version of traceroute.
+
+It is based on code written by W. Richard Stevens and published in
+"UNIX Network Programming Volume 1, Second Edition Networking APIs:
+Sockets and XTI," Prentice Hall PTR, Upper Saddle River, NJ 07458.
+
+It has been modified a fair amount by Allen Downey
+([email protected]).  Among other things, I did the following
+
+1) I collected all the procedures from Stevens's extensive library
+   and put them in util.c, and put their prototypes in trout.h
+
+2) I killed all the IPv6 support, because I didn't need it and
+   because I hate ifdefs and pointers to functions.
+
+3) For the same reason, I took out some of the configuration
+   ifdefs.  As a result, I don't know if this will still run
+   on anything other than Linux.
+
+4) I fixed a race condition that may or may not have been the
+   cause of some early problems I had.  Anyway, the fix also
+   came from Stevens, in Section 18.5 of Unix Network Programming. 
+
+5) I split things up into more procedures.
+
+The copyright for the original code is held by Prentice Hall,
+but they make it available under a license that is more or
+less identical to the GNU GPL.
+
+This version is Copyright (C) 1999 Allen B. Downey.
+
+I am making it available under the GNU General Public License
+(which does not, I think, violate the original copyright).
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

exercises/ex04/trout/Makefile

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+trout: trout.h trout.c util.h util.c main.c
+	gcc -Wall -g -o trout trout.c main.c util.c

exercises/ex04/trout/main.c

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+#include "trout.h"
+
+int main (int argc, char **argv)
+{
+  int c;
+  struct addrinfo *ai;
+  char *host;
+
+  opterr = 0;
+  while ( (c = getopt (argc, argv, "m:")) != -1) {
+    switch (c) {
+    case 'm':
+      if ( (max_ttl = atoi(optarg)) <= 1) {
+	      err_quit ("invalid -m value");
+      }
+      break;
+    default:
+      err_quit ("unrecognizd option: %c", c);
+    }
+  }
+
+  if (optind != argc - 1) {
+    err_quit ("usage: trout [ -m <maxttl>] <hostname>");
+  }
+  host = argv[optind];
+  ai = Host_serv (host, NULL, 0, 0);
+
+  printf ("trout to %s (%s): %d hops max, %d data bytes\n",
+	  ai->ai_canonname,
+	  Sock_ntop_host (ai->ai_addr, ai->ai_addrlen),
+	  max_ttl, datalen);
+
+  if (ai->ai_family != AF_INET) {
+    err_quit ("unknown address family %d", ai->ai_family);
+  }
+
+  sasend = ai->ai_addr;
+  salen = ai->ai_addrlen;
+  sarecv = Calloc (1, salen);
+  salast = Calloc (1, salen);
+  sabind = Calloc (1, salen);
+
+  loop_ttl ();
+  exit (0);
+}

exercises/ex04/trout/trout.c

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+#include "trout.h"
+
+/* variables we might want to configure */
+Rec *rec = (Rec *) sendbuf;
+
+void sig_alrm (int signo)
+{
+  Write (pipefd[1], "", 1);  /* write 1 null byte to pipe */
+  return;
+}
+
+int process_ip (struct ip *ip, int len)
+{
+  int hlen1, hlen2, icmplen;
+  struct icmp *icmp;
+  struct ip *hip;
+  struct udphdr *udp;
+  seq = 0;
+  u_short dport = 32768 + 668;        /* destination port -- hopefully unused */
+
+  hlen1 = ip->ip_hl << 2;                        /* length of IP header */
+  icmp = (struct icmp *) (recvbuf + hlen1);
+  icmplen = len - hlen1;
+
+  if (icmplen < 8 + 20 + 8) return 0;
+
+  if (icmp->icmp_type != ICMP_TIME_EXCEEDED &&
+      icmp->icmp_type != ICMP_DEST_UNREACH)
+    return 0;
+
+  /* hip is the header of the enclosed IP packets, supposedly
+     the header of the packet that caused the error */
+
+  hip = (struct ip *) (recvbuf + hlen1 + 8);
+  if (hip->ip_p != IPPROTO_UDP) return 0;
+
+  hlen2 = hip->ip_hl << 2;
+  udp = (struct udphdr *) (recvbuf + hlen1 + 8 + hlen2);
+
+  if (udp->source != htons (sport)) return 0;
+  if (udp->dest != htons (dport + seq)) return 0;
+
+  if (icmp->icmp_type == ICMP_TIME_EXCEEDED) {
+    if (icmp->icmp_code == ICMP_EXC_TTL) {
+      return -2;
+    } else {
+      return 0;
+    }
+  }
+
+  if (icmp->icmp_type == ICMP_DEST_UNREACH) {
+    if (icmp->icmp_code == ICMP_PORT_UNREACH) {
+      return -1;
+    } else {
+      return 0;
+    }
+  }
+  return 0;
+}
+
+
+
+int recv_dgram ()
+{
+  int err;
+  socklen_t len;
+  ssize_t n;
+  struct ip *ip;
+  int maxfdp1 = max (recvfd, pipefd[0]) + 1;
+  fd_set rset[1];  
+  FD_ZERO (rset);
+
+  alarm(3);       /* set the timeout alarm to handle dropped packets */
+
+  while (1) {
+    FD_SET (recvfd, rset);
+    FD_SET (pipefd[0], rset);
+
+    n = select (maxfdp1, rset, NULL, NULL, NULL);
+    if (n < 0 && errno != EINTR) {
+      err_sys ("select error");
+    }
+
+    if (FD_ISSET (recvfd, rset)) {
+      len = salen;
+      n = recvfrom (recvfd, recvbuf, sizeof(recvbuf), 0, sarecv, &len);
+      err = errno;
+      Gettimeofday (recvtv, NULL);   /* get time of packet arrival */
+      if (n < 0 && err != EAGAIN) {
+	err_sys ("recvfrom error");
+      }
+    }
+
+    if (FD_ISSET (pipefd[0], rset)) {
+      Read (pipefd[0], &n, 1);
+      return -3;                 /* timeout */
+    }
+
+    ip = (struct ip *) recvbuf;
+    return process_ip (ip, n);
+  }
+}
+
+/* sub_tv: subtract minus from plus and put the result in res */
+
+void sub_tv (Timeval *plus, Timeval *minus, Timeval *res)
+{
+  res->tv_sec = plus->tv_sec - minus->tv_sec;
+  res->tv_usec = plus->tv_usec - minus->tv_usec;
+
+  if (res->tv_usec < 0) {
+    res->tv_sec--;
+    res->tv_usec += 1000000;
+  }
+}
+
+/* time_to_double: convert a Timeval to a double.  This only
+   works with Timevals that are small (like the difference between
+   two real Timevals) */
+
+double time_to_double (Timeval *time)
+{
+  return time->tv_sec * 1000.0 + time->tv_usec / 1000.0;
+}
+
+/* print_report: prints all the information about a successful round trip */
+
+void print_report ()
+{
+  int stat;
+  char str[NI_MAXHOST];
+
+  stat = sock_cmp_addr (sarecv, salast, salen);
+
+  /* if this reply comes from source different from the previous
+     one, print the full host information */
+
+  if (stat != 0) {
+    stat = getnameinfo (sarecv, salen, str, sizeof(str), NULL, 0, 0);
+    if (stat == 0) {
+      printf (" %s (%s)", str, Sock_ntop_host (sarecv, salen));
+    } else {
+      printf (" %s", Sock_ntop_host (sarecv, salen));
+    }
+    memcpy (salast, sarecv, salen);
+  }
+
+  /* calculate and print the round trip time using user-level timestamps */
+
+  sub_tv (recvtv, sendtv, difftv);
+
+  printf ("  %.3f", time_to_double (difftv));
+}
+
+/* send_dgram: generate an outgoing UDP packet */
+
+    /* the second effort send is a kludge to handle a funny
+       thing, which is that the last host seems to refuse the
+       second or third connection consistently, which might
+       might mean that something breaks when we get the
+       ICMP_DEST_UNREACH error.  The second attempt seems
+       to succeed consistently. */
+
+void send_dgram (int ttl)
+{
+  int n;
+  datalen = sizeof (Rec);         /* length of the data in a datagram */
+  seq = 0;
+  u_short dport = 32768 + 668;        /* destination port -- hopefully unused */
+
+  rec->seq = seq++;
+  sock_set_port (sasend, salen, htons(dport+seq));
+
+  Gettimeofday (sendtv, NULL);
+  n = sendto(sendfd, sendbuf, datalen, 0, sasend, salen);
+
+  if (n==-1 && errno == ECONNREFUSED) {
+    Gettimeofday (sendtv, NULL);
+    n = sendto(sendfd, sendbuf, datalen, 0, sasend, salen);
+  }
+
+  if (n != datalen) {
+    err_sys("sendto error");
+  }
+}
+
+/* send_probes: sends a set of probes with the given ttl and
+   then waits for the replies.  The weird TOS options are there
+   as a signal to the kernel to identify clink packets so it can
+   fill in the timestamps.  I am assuming that they don't have
+   any actual effect. */
+
+int send_probes (int ttl) 
+{
+  int probe, code, done;
+
+  Setsockopt (sendfd, IPPROTO_IP, IP_TTL, &ttl, sizeof(int));
+  bzero (salast, salen);
+  int nprobes = 2;
+
+  printf ("%2d  ", ttl);
+  fflush (stdout);
+
+  done = 0; /* count the number of probes that generate an ICMP_DEST_UNREACH */
+
+  for (probe = 0; probe < nprobes; probe++) {
+    send_dgram (ttl);
+    code = recv_dgram ();
+
+    if (code == -3) {
+      printf (" *");
+    } else {
+      print_report ();
+    }
+
+    if (code == -1) done++;
+    fflush (stdout);
+  }
+  printf ("ms\n");
+  return done;
+}
+
+/* loop_ttl: starting with ttl=1, gradually increase ttl until
+   we start getting ICMP_DEST_UNREACH instead of ICMP_TIME_EXCEEDED */
+
+void loop_ttl ()
+{
+  int ttl, done;
+
+  Pipe (pipefd);     /* the pipe for the alarm handler */
+  max_ttl = 30;
+
+
+  recvfd = socket (sasend->sa_family, SOCK_RAW, IPPROTO_ICMP);
+  if (recvfd == -1) {
+    if (errno == EPERM) {
+      printf ("\nclink was unable to open a raw socket.  The most\n");
+      printf ("likely cause is that you are not running it as root.\n");
+      exit (1);
+    } else {
+      err_sys ("opening raw socket in clink");
+    }
+  }
+
+  fcntl (recvfd, F_SETFL, O_NONBLOCK);
+  setuid (getuid ());
+
+  sendfd = socket (sasend->sa_family, SOCK_DGRAM, 0);
+
+  sabind->sa_family = sasend->sa_family;
+  sport = (getpid() & 0xffff) | 0x8000;       /* source UDP port # */
+  sock_set_port (sabind, salen, htons(sport));
+  Bind (sendfd, sabind, salen);
+
+  Signal (SIGALRM, sig_alrm);
+
+  for (ttl = 1; ttl <= max_ttl; ttl++) {
+    done = send_probes (ttl);
+    if (done > 0) break;
+  }
+}