Add a lot of comments to the code

5 files changed, 67 insertions, 13 deletions

diff --git a/devices.c b/devices.c
index b7c1254..1c69710 100644
--- a/devices.c
+++ b/devices.c
@@ -30,6 +30,7 @@
 int getDeviceIndex(int sockfd, unsigned char *deviceName) {
 	struct ifreq ifr;
 
+	/* Find interface index from deviceName */
 	strncpy(ifr.ifr_name, deviceName, 16);
 	if (ioctl(sockfd, SIOCGIFINDEX, &ifr) != 0) {
 		return -1;
@@ -42,6 +43,7 @@ int getDeviceIndex(int sockfd, unsigned char *deviceName) {
 int getDeviceMAC(const int sockfd, const unsigned char *deviceName, unsigned char *mac) {
 	struct ifreq ifr;
 
+	/* Find interface hardware address from deviceName */
 	strncpy(ifr.ifr_name, deviceName, 16);
 	if (ioctl(sockfd, SIOCGIFHWADDR, &ifr) != 0) {
 		return -1;
@@ -75,6 +77,7 @@ int getDeviceIp(const int sockfd, const unsigned char *deviceName, struct sockad
 		exit(1);
 	}
 
+	/* Do the actual query for info about all interfaces */
 	ifc.ifc_req = ifr;
 	if (ioctl(sockfd, SIOCGIFCONF, &ifc) != 0) {
 		free(ifr);
diff --git a/mactelnet.c b/mactelnet.c
index fd814a6..0d8de3d 100644
--- a/mactelnet.c
+++ b/mactelnet.c
@@ -22,12 +22,14 @@
 #include "mactelnet.h"
 #include "config.h"
 
+unsigned char mt_mactelnet_cpmagic[4] = { 0x56, 0x34, 0x12, 0xff };
+
 int initPacket(unsigned char *data, unsigned char ptype, unsigned char *srcmac, unsigned char *dstmac, unsigned short sessionkey, unsigned short counter) {
 
-	/* PACKET VERSION */
+	/* Packet version */
 	data[0] = 1;
 
-	/* PACKET TYPE */
+	/* Packet type */
 	data[1] = ptype;
 
 	/* src ethernet address */
@@ -36,25 +38,27 @@ int initPacket(unsigned char *data, unsigned char ptype, unsigned char *srcmac,
 	/* dst ethernet address */
 	memcpy(data + 8, dstmac, ETH_ALEN);
 
+	/* Session key */
 	data[14] = sessionkey >> 8;
 	data[15] = sessionkey & 0xff;
 
+	/* Magic number */
 	data[16] = 0x00;
 	data[17] = 0x15;
 
+	/* Received/sent data counter */
 	data[18] = (counter >> 24) & 0xff;
 	data[19] = (counter >> 16) & 0xff;
 	data[20] = (counter >> 8) & 0xff;
 	data[21] = counter & 0xff;
 
+	/* 22 bytes header */
 	return 22;
 }
 
 int addControlPacket(unsigned char *data, unsigned char cptype, void *cpdata, int data_len) {
-	data[0] = 0x56;
-	data[1] = 0x34;
-	data[2] = 0x12;
-	data[3] = 0xff;
+	/* Control Packet Magic id */
+	memcpy(data,  mt_mactelnet_cpmagic, sizeof(mt_mactelnet_cpmagic));
 
 	/* Control packet type */
 	data[4] = cptype;
@@ -70,40 +74,63 @@ int addControlPacket(unsigned char *data, unsigned char cptype, void *cpdata, in
 		memcpy(data+9, cpdata, data_len);
 	}
 
+	/* Control packet header length + data length */
 	return 9+data_len;
 }
 
 void parsePacket(unsigned char *data, struct mt_mactelnet_hdr *pkthdr) {
+	/* Packet version */
 	pkthdr->ver = data[0];
+
+	/* Packet type */
 	pkthdr->ptype = data[1];
+
+	/* src ethernet addr */
 	memcpy(pkthdr->srcaddr, data+2,6);
+
+	/* dst ethernet addr */
 	memcpy(pkthdr->dstaddr, data+8,6);
+
+	/* Session key */
 	pkthdr->seskey = data[16] << 8 | data[17];
+
+	/* Received/sent data counter */
 	pkthdr->counter = data[18] << 24 | data[19] << 16 | data[20] << 8 | data[21];
+
+	/* Set pointer to actual data */
 	pkthdr->data = data + 22;
 }
 
 
 int parseControlPacket(unsigned char *data, const int data_len, struct mt_mactelnet_control_hdr *cpkthdr) {
-	unsigned char magic[] = { 0x56, 0x34, 0x12, 0xff };
 
-	if (data_len <= 0)
+	if (data_len < 0)
 		return 0;
 
-	if (memcmp(data, &magic, 4) == 0) {
+	/* Check for valid minimum packet length & magic header */
+	if (data_len >= 9 && memcmp(data, &mt_mactelnet_cpmagic, 4) == 0) {
 		if (DEBUG)
 			printf("\t----Control packet:\n\t\tType: %d\n\t\tLength: %d\n", data[4], data[5]<<24|data[6]<<16|data[7]<<8|data[8]);
 
+		/* Control packet type */
 		cpkthdr->cptype = data[4];
+
+		/* Control packet data length */
 		cpkthdr->length = data[5]<<24|data[6]<<16|data[7]<<8|data[8];
+
+		/* Set pointer to actual data */
 		cpkthdr->data = data + 9;
 
+		/* Return number of bytes in packet */
 		return cpkthdr->length + 9;
 
 	} else {
+		/* Mark data as raw terminal data */
 		cpkthdr->cptype = MT_CPTYPE_PLAINDATA;
 		cpkthdr->length = data_len;
 		cpkthdr->data = data;
+
+		/* Consume the whole rest of the packet */
 		return data_len;
 	}
 }
diff --git a/mactelnet.h b/mactelnet.h
index d2af675..8275169 100644
--- a/mactelnet.h
+++ b/mactelnet.h
@@ -59,4 +59,7 @@ extern int addControlPacket(unsigned char *data, unsigned char cptype, void *cpd
 extern void parsePacket(unsigned char *data, struct mt_mactelnet_hdr *pkthdr);
 extern int parseControlPacket(unsigned char *data, const int data_len, struct mt_mactelnet_control_hdr *cpkthdr);
 
+/* Control packet magic header */
+extern unsigned char mt_mactelnet_cpmagic[4];
+
 #endif
diff --git a/mndp.c b/mndp.c
index 8bc3292..ec0a188 100644
--- a/mndp.c
+++ b/mndp.c
@@ -31,13 +31,16 @@ int main(int argc, char **argv)  {
 	unsigned char name[100];
 	unsigned char mac[ETH_ALEN];
 
+	/* Open a UDP socket handle */
 	sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
 
+	/* Set initialize address/port */
 	memset((char *) &si_me, 0, sizeof(si_me));
 	si_me.sin_family = AF_INET;
 	si_me.sin_port = htons(5678);
 	si_me.sin_addr.s_addr = htonl(INADDR_ANY);
 
+	/* Bind to specified address/port */
 	if (bind(sock, (struct sockaddr *)&si_me, sizeof(si_me))==-1) {
 		fprintf(stderr, "Error binding to %s:5678\n", inet_ntoa(si_me.sin_addr));
 		return 1;
@@ -47,25 +50,33 @@ int main(int argc, char **argv)  {
 	fprintf(stderr, "Searching for MikroTik routers... Abort with CTRL+C.\n");
 
 	while(1) {
+		/* Wait for a UDP packet */
 		result = recvfrom(sock, buff, 1500, 0, 0, 0);
 		if (result < 0) {
 			fprintf(stderr, "Error occured. aborting\n");
 			exit(1);
 		}
 
+		/* Fetch length of Identifier string */
 		memcpy(&nameLen, buff+16,2);
 		nameLen = (nameLen >> 8) | ((nameLen&0xff)<<8);
 
 		/* Max name length = 99 */
 		nameLen = nameLen < 100 ? nameLen : 99;
 
+		/* Read Identifier string */
 		memcpy(&name, buff+18, nameLen);
+
+		/* Append zero */
 		name[nameLen] = 0;
 
+		/* Read source MAC address */
 		memcpy(&mac, buff+8, ETH_ALEN);
 
+		/* Print it */
 		printf("%17s %s\n", ether_ntoa((struct ether_addr *)mac), name);
 	}
 
+	/* We'll never get here.. */
 	return 0;
 }
diff --git a/udp.c b/udp.c
index 10c8f7b..3b55d17 100644
--- a/udp.c
+++ b/udp.c
@@ -36,25 +36,32 @@ unsigned short in_cksum(unsigned short *addr, int len)
 
 int sendCustomUDP(const int socket, const int ifindex, const unsigned char *sourcemac, const unsigned char *destmac, const struct in_addr *sourceip, const int sourceport, const struct in_addr *destip, const int destport, const char *data, const int datalen) {
 	struct sockaddr_ll socket_address;
+
+	/*
+	 * Create a buffer for the full ethernet frame
+	 * and align header pointers to the correct positions.
+	*/
 	void* buffer = (void*)malloc(ETH_FRAME_LEN);
 	struct ethhdr *eh = (struct ethhdr *)buffer;
 	struct iphdr *ip = (struct iphdr *)(buffer+14);
 	struct udphdr *udp = (struct udphdr *)(buffer+14+20);
 	unsigned char *rest = (unsigned char *)(buffer+20+14+sizeof(struct udphdr));
+
 	static unsigned int id = 1;
 	int send_result = 0;
 
+	/* Abort if we couldn't allocate enough memory */
 	if (buffer == NULL) {
 		perror("malloc");
 		exit(1);
 	}
 
-	/* Ethernet header */
+	/* Init ethernet header */
 	memcpy(eh->h_source, sourcemac, ETH_ALEN);
 	memcpy(eh->h_dest, destmac, ETH_ALEN);
 	eh->h_proto = 8;
 
-	/* SendTo struct */
+	/* Init SendTo struct */
 	socket_address.sll_family   = PF_PACKET;	
 	socket_address.sll_protocol = htons(ETH_P_IP);	
 	socket_address.sll_ifindex  = ifindex;
@@ -66,7 +73,7 @@ int sendCustomUDP(const int socket, const int ifindex, const unsigned char *sour
 	socket_address.sll_addr[6]  = 0x00;/*not used*/
 	socket_address.sll_addr[7]  = 0x00;/*not used*/
 
-	/* IP Header */
+	/* Init IP Header */
 	ip->version = 4;
 	ip->ihl = 5;
 	ip->tos = 0x10;
@@ -78,19 +85,22 @@ int sendCustomUDP(const int socket, const int ifindex, const unsigned char *sour
 	ip->check = 0x0000;
 	ip->saddr = sourceip->s_addr;
 	ip->daddr = destip->s_addr;
+	/* Calculate checksum for IP header */
 	ip->check = in_cksum((unsigned short *)ip, sizeof(struct iphdr));
 
-	/* UDP Header */
+	/* Init UDP Header */
 	udp->source = htons(20561);
 	udp->dest = htons(20561);
 	udp->check = 0;
 	udp->len = htons(sizeof(struct udphdr) + datalen);
 
+	/* Insert actual data */
 	memcpy(rest, data, datalen);
 
 	/* Send the packet */
 	send_result = sendto(socket, buffer, datalen+8+14+20, 0, (struct sockaddr*)&socket_address, sizeof(socket_address));
 	free(buffer);
 
+	/* Return amount of _data_ bytes sent */
 	return send_result-8-14-20;
 }