From c56e309956da3d41420db1c5d41ccf245c594e45 Mon Sep 17 00:00:00 2001
From: Håkon Nessjøen <haakon.nessjoen@gmail.com>
Date: Thu, 30 Sep 2010 11:42:19 +0200
Subject: Add a lot of comments to the code

---
 mactelnet.c | 45 ++++++++++++++++++++++++++++++++++++---------
 1 file changed, 36 insertions(+), 9 deletions(-)

(limited to 'mactelnet.c')

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;
 	}
 }
-- 
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