From 8e7ea6742a94ea62b421d7184e9eab17fb5da934 Mon Sep 17 00:00:00 2001
From: Joel Grunbaum <joelgrun@gmail.com>
Date: Wed, 21 Oct 2020 12:29:13 +0000
Subject: [PATCH] Added threading, progress and some comments, nearly done

---
 dns.c |   65 +++++++++++++++++++++-----------
 1 files changed, 42 insertions(+), 23 deletions(-)

diff --git a/dns.c b/dns.c
index 042902b..ad58873 100644
--- a/dns.c
+++ b/dns.c
@@ -6,9 +6,13 @@
 //#include <netint/in.h>
 //#include <netdb.h>
 //#include <sys/time.h>
+#include <time.h>
 #include <unistd.h>
 #include "dns.h"
 
+void change_to_DNS_name_format(unsigned char* dns, unsigned char* host);
+char* read_name(unsigned char* reader, unsigned char* buffer, int* count);
+
 // DNS code copied from
 // https://gist.github.com/fffaraz/9d9170b57791c28ccda9255b48315168
 
@@ -26,7 +30,7 @@
 	 unsigned char ad :1;		//authenticated data
 	 unsigned char z :1;		//reserved for future use
 	 unsigned char ra :1;		//recursion available
-	 unsigned short q_count;	//number of question entries
+	 unsigned short q_count;	//number of question entrise
 	 unsigned short ans_count;	//number of answer entries
 	 unsigned short auth_count; //number of authority entries
 	 unsigned short add_count;  //number of resource entries
@@ -60,26 +64,30 @@
 /* Pointers to record components */
 struct RES_RECORD
 {
-	 unsigned char* name;
+	 char* name;
 	 struct R_DATA resource;
-	 unsigned char* rdata;
+	 char* rdata;
 };
 
-void resolve(char* hostname, char* dns_ip, int query_type, int read)
+// Test server dns_ip as IPv4 string for hostname
+// Writes received packet to buf, which is supplied and returns time for request
+struct timespec resolve(unsigned char* buf, char* hostname, char* dns_ip, int query_type)
 {
-	 int s, i, j;
-	 struct sockaddr_in dest, a;
-	 unsigned char buf[65536], *qname, *reader;
-	 struct DNS_HEADER* dns = NULL;
-	 struct QUESTION* qinfo = NULL;
+	 int s, i;
+	 struct sockaddr_in dest;
+	 unsigned char *qname;
+	 struct DNS_HEADER* dns = (struct DNS_HEADER*)buf;
+	 struct QUESTION* qinfo;
+	 struct timespec start, end, total, timeout;
+	 timeout.tv_nsec=0; timeout.tv_sec=1;
 
 	 s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+	 setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(struct timespec)); //use a 1 second timeout for receiving, should be more than enough and anything more is really bad
 	 dest.sin_family = AF_INET;
 	 dest.sin_port = htons(53);
 	 dest.sin_addr.s_addr = inet_addr(dns_ip);
 
 	 //dns packet header
-	 dns = (struct DNS_HEADER*)&buf;
 	 dns->id = (unsigned short) htons(getpid());
 	 dns->qr = 0;				//make query
 	 dns->opcode = 0;			//standard query
@@ -105,26 +113,35 @@
 
 	 //send request
 	 // return less than 0 is a fail
+	 clock_gettime(CLOCK_MONOTONIC, &start);
 	 sendto(s,(char*)buf, sizeof(struct DNS_HEADER)+strlen((const char*)qname)+1+sizeof(struct QUESTION), 0, (struct sockaddr*)&dest, sizeof(dest));
 
 	 //receive response
 	 //negative return is a fail
 	 i = sizeof(dest);
-	 recvfrom(s, (char*)buf, 65536, 0, (struct sockaddr*)&dest, (socklen_t*)&i);
+	 i = recvfrom(s, (char*)buf, 65536, 0, (struct sockaddr*)&dest, (socklen_t*)&i);
+	 clock_gettime(CLOCK_MONOTONIC, &end);
 
-	 //read response
-	 if (read) {
-		  print_packet(buf);
-	 }
-	 return;
+	 // Make sure packet was returned
+	 if (i == -1)
+		  total.tv_nsec = -1;
+	 else
+		  total.tv_sec = end.tv_sec - start.tv_sec;
+	 if ((end.tv_nsec - start.tv_nsec) < 0)
+		  total.tv_nsec = start.tv_nsec - end.tv_nsec;
+	 else
+		  total.tv_nsec = end.tv_nsec - start.tv_nsec;
+	 close(s);
+	 return total;
 }
 
+// Print dns packet content, not terribly reliable but works for testing resolve with A requests
 void print_packet(unsigned char* buf)
 {
 	 struct RES_RECORD answers[20], auth[20], addit[20];
 	 struct DNS_HEADER *dns;
 	 struct sockaddr_in a;
-	 char* qname = buf+sizeof(struct DNS_HEADER), *reader;
+	 unsigned char* qname = buf+sizeof(struct DNS_HEADER), *reader;
 	 int stop, i, j;
 	 dns = (struct DNS_HEADER*)buf;
 	 reader = &buf[sizeof(struct DNS_HEADER)+strlen((const char*)qname)+1+sizeof(struct QUESTION)];
@@ -139,7 +156,7 @@
 		  reader = reader+sizeof(struct R_DATA);
 
 		  if (ntohs(answers[i].resource.type) == T_A) { //IPv4 address
-			   answers[i].rdata = (unsigned char*)malloc(ntohs(answers[i].resource.data_len));
+			   answers[i].rdata = (char*)malloc(ntohs(answers[i].resource.data_len));
 			   for (j = 0; j < ntohs(answers[i].resource.data_len); j++) {
 					answers[i].rdata[j] = reader[j];
 			   }
@@ -229,15 +246,16 @@
 	 }
 }
 
-
+// convert from dot format to dns format
+// eg google.com to 6google3com
 void change_to_DNS_name_format(unsigned char* dns, unsigned char* host)
 {
 	 int lock = 0;
 	 char h[300];
-	 strcpy(h, host);
+	 strcpy(h, (char*)host);
 	 strcat((char*)h,".");
 
-	 for (int i = 0; i < strlen((char*)h); i++) {
+	 for (int i = 0; i < strlen(h); i++) {
 		  if (h[i] == '.') {
 			   *dns++ = i-lock;
 			   for (;lock<i;lock++) {
@@ -249,13 +267,14 @@
 	 *dns++ = '\0';
 }
 
+// Convert from dns to dot format
 char* read_name(unsigned char* reader, unsigned char* buffer, int* count)
 {
-	 unsigned char* name;
+	 char* name;
 	 unsigned int p=0, jumped=0, offset;
 	 int i, j;
 	 *count = 1;
-	 name = (unsigned char*)malloc(256);
+	 name = (char*)malloc(256);
 	 name[0]='\0';
 
 	 while (*reader != 0) {

--
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