From ea00f37d541ba2c75a4a33c5d37c9ae15dac5ab7 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Thu, 7 Jan 2016 16:05:12 +0200
Subject: [PATCH 1/1] Current version

---
 main.c | 258 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 258 insertions(+)
 create mode 100644 main.c

diff --git a/main.c b/main.c
new file mode 100644
index 0000000..fd2e878
--- /dev/null
+++ b/main.c
@@ -0,0 +1,258 @@
+/*
+netmon - a simple network connectivity monitor
+Copyright © 2008 Mikko Rasa, Mikkosoft Productions
+Distributed under the GPL
+*/
+
+#include <stdint.h>
+#include <stdio.h>
+#include <getopt.h>
+#include <errno.h>
+#include <syslog.h>
+#include <sys/poll.h>
+#include <netinet/ip_icmp.h>
+#include <netdb.h>
+#include <sys/wait.h>
+#include <stdlib.h>
+
+unsigned checksum(const char *, unsigned);
+void send_ping(in_addr_t, uint16_t);
+pid_t run_command(const char *);
+
+int sock;
+int pid;
+
+int main(int argc, char **argv)
+{
+	const char *target_name = "google.com";
+	struct hostent *target_host;
+	in_addr_t target;
+	struct pollfd pfd;
+	uint16_t seq = 1;
+	uint16_t pending = 0;
+	unsigned lost = 0;
+	unsigned streak = 0;
+	unsigned max_streak = 0;
+	unsigned next_stats = 0;
+	int o;
+	int no_daemon = 0;
+	int verbose = 0;
+	unsigned stats_interval = 1800;
+	unsigned trigger_count = 900;
+	const char *trigger_cmd = NULL;
+	unsigned next_trigger;
+	pid_t child_pid = 0;
+
+	/* Parse options */
+	while((o = getopt(argc, argv, "fvi:t:c:"))!=-1)
+		switch(o)
+		{
+		case 'f':
+			no_daemon = 1;
+			break;
+		case 'v':
+			verbose = 1;
+			break;
+		case 'i':
+			stats_interval = strtoul(optarg, NULL, 10);
+			break;
+		case 't':
+			trigger_count = strtoul(optarg, NULL, 10);
+			break;
+		case 'c':
+			trigger_cmd = optarg;
+			break;
+		}
+
+	/* Take target hostname from commandline if specified */
+	if(optind<argc)
+		target_name = argv[optind];
+
+	target_host = gethostbyname(target_name);
+	if(!target_host)
+	{
+		herror("gethostbyname");
+		return 1;
+	}
+
+	if(target_host->h_addrtype!=AF_INET)
+	{
+		fprintf(stderr, "Got a hostent, but it doesn't have an IPv4 address");
+		return 1;
+	}
+	target = ntohl(*(in_addr_t *)*target_host->h_addr_list);
+
+	if(verbose)
+		printf("Target is %s\n", inet_ntoa(htonl(target)));
+
+	/* Miscellaneous initialization */
+	pid = getpid();
+	sock = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP);
+	if(sock==-1)
+	{
+		perror("socket");
+		return 1;
+	}
+
+	pfd.fd = sock;
+	pfd.events = POLLIN;
+
+	if(!no_daemon && daemon(1, 0)==-1)
+		perror("daemon");
+
+	openlog("netmon", 0, LOG_LOCAL7);
+
+	next_trigger = trigger_count;
+	while(1)
+	{
+		struct timeval tv;
+		int res;
+
+		gettimeofday(&tv, NULL);
+
+		/* Send stats to syslog every stats_interval seconds */
+		if(tv.tv_sec>next_stats)
+		{
+			if(next_stats)
+			{
+				if(no_daemon)
+					printf("Lost %d, max streak %d\n", lost, max_streak);
+				else
+					syslog(LOG_INFO, "Lost %d, max streak %d", lost, max_streak);
+				lost = 0;
+				max_streak = 0;
+			}
+			next_stats = tv.tv_sec+stats_interval;
+		}
+
+		if(child_pid)
+		{
+			if(waitpid(child_pid, NULL, WNOHANG)==child_pid)
+				child_pid = 0;
+		}
+
+		res = poll(&pfd, 1, 1000);
+		if(res>0)
+		{
+			struct sockaddr_in addr;
+			socklen_t alen = sizeof(addr);
+			char data[1500];
+			int len;
+			struct iphdr *ip;
+			struct icmphdr *icmp;
+
+			/* Receive a packet */
+			len = recvfrom(sock, data, sizeof(data), 0, (struct sockaddr *)&addr, &alen);
+			if(len==-1)
+				fprintf(stderr, "recvfrom error: %s\n", strerror(errno));
+			else
+			{
+				ip = (struct iphdr *)data;
+				if(ip->protocol==IPPROTO_ICMP)
+				{
+					icmp = (struct icmphdr *)(ip+1);
+					if(icmp->type==ICMP_ECHOREPLY && icmp->un.echo.id==pid)
+					{
+						/* It's an ICMP echo reply and ours, process it */
+						if(verbose)
+							printf("Ping reply from %s\n", inet_ntoa(addr.sin_addr.s_addr));
+						if(icmp->un.echo.sequence==pending)
+						{
+							pending = 0;
+							streak = 0;
+							next_trigger = trigger_count;
+						}
+						else if(verbose)
+							printf("Sequence %d, expected %d\n", icmp->un.echo.sequence, pending);
+					}
+				}
+			}
+		}
+		else
+		{
+			/* Poll timed out, check for lost ping and send more */
+			if(pending)
+			{
+				if(verbose)
+					printf("Lost ping\n");
+				++lost;
+				++streak;
+				if(streak>max_streak)
+					max_streak = streak;
+				if(streak>=next_trigger && trigger_cmd && !child_pid)
+				{
+					if(no_daemon)
+						printf("Running %s\n", trigger_cmd);
+					else
+						syslog(LOG_INFO, "Running %s\n", trigger_cmd);
+					child_pid = run_command(trigger_cmd);
+					next_trigger += trigger_count;
+				}
+			}
+			send_ping(target, seq);
+			pending = seq;
+			if(!++seq)
+				++seq;
+		}
+	}
+
+	closelog();
+
+	return 0;
+}
+
+unsigned checksum(const char *data, unsigned len)
+{
+	unsigned	sum = 0;
+	unsigned i;
+
+	for(i=0; i<len; i+=2)
+		sum += *(const unsigned short *)(data+i);
+	while(sum>0xFFFF)
+		sum = (sum>>16)+(sum&0xFFFF);
+
+	return ~sum;
+}
+
+void send_ping(in_addr_t target, uint16_t seq)
+{
+	char data[64];
+	unsigned i;
+	struct icmphdr *hdr;
+	struct sockaddr_in addr;
+
+	for(i=0; i<sizeof(data); ++i)
+		data[i] = i;
+
+	hdr = (struct icmphdr *)data;
+	hdr->type = ICMP_ECHO;
+	hdr->code = 0;
+	hdr->checksum = 0;
+	hdr->un.echo.id = pid;
+	hdr->un.echo.sequence = seq;
+	hdr->checksum = checksum(data, sizeof(data));
+
+	addr.sin_family = AF_INET;
+	addr.sin_addr.s_addr = htonl(target);
+	addr.sin_port = 0;
+
+	if(sendto(sock, data, sizeof(data), 0, (struct sockaddr *)&addr, sizeof(addr))==-1)
+		fprintf(stderr, "sendto error: %s\n", strerror(errno));
+}
+
+pid_t run_command(const char *cmd)
+{
+	pid_t pid;
+
+	pid = fork();
+	if(pid==0)
+	{
+		const char *argv[2];
+		argv[0] = cmd;
+		argv[1] = 0;
+		execv(cmd, argv);
+		exit(127);
+	}
+	else
+		return pid;
+}
-- 
2.45.2