gnunet/src/vpn/gnunet-dns-parser.c

#include "platform.h"
#include "gnunet-dns-parser.h"
#include "gnunet-vpn-packet.h"

/**
 * Parse a name from DNS to a normal .-delimited, 0-terminated string.
 *
 * @param d The destination of the name. Should have at least 255 bytes allocated.
 * @param src The DNS-Packet
 * @param idx The offset inside the Packet from which on the name should be read
 * @returns The offset of the first unparsed byte (the byte right behind the name)
 */
static unsigned int
parse_dns_name(char* d, const unsigned char* src, unsigned short idx) {/*{{{*/
    char* dest = d;

    int len = src[idx++];
    while (len != 0)
      {
	if (len & 0xC0)
	  { /* Compressed name, offset in this and the next octet */
	    unsigned short offset = ((len & 0x3F) << 8) | src[idx++];
	    parse_dns_name(dest, src, offset - 12); /* 12 for the Header of the DNS-Packet, idx starts at 0 which is 12 bytes from the start of the packet */
	    return idx;
	  }
	memcpy(dest, src+idx, len);
	idx += len;
	dest += len;
	*dest = '.';
	dest++;
	len = src[idx++];
      };
    *dest = 0;

    return idx;
}
/*}}}*/

/**
 * Parse a complete DNS-Record from raw DNS-data to a struct dns_record
 *
 * @param data The DNS-data
 * @param dst Pointer to count pointers; individual pointers will be allocated
 * @param count Number of records to parse
 * @param idx The offset inside the Packet from which on the name should be read
 * @returns The offset of the first unparsed byte (the byte right behind the last record)
 */
static unsigned short
parse_dns_record(unsigned char* data, /*{{{*/
		 struct dns_record** dst,
		 unsigned short count,
		 unsigned short idx) {
    int i;
    unsigned short _idx;
    for (i = 0; i < count; i++) {
	dst[i] = GNUNET_malloc(sizeof(struct dns_record));
	dst[i]->name = alloca(255); // see RFC1035, no name can be longer than this.
	char* name = dst[i]->name;

	_idx = parse_dns_name(name, data, idx);
	dst[i]->namelen = _idx - idx;

	dst[i]->name = GNUNET_malloc(dst[i]->namelen);
	memcpy(dst[i]->name, name, dst[i]->namelen);

	idx = _idx;

	dst[i]->type = *((unsigned short*)(data+idx));
	idx += 2;
	dst[i]->class = *((unsigned short*)(data+idx));
	idx += 2;
	dst[i]->ttl = *((unsigned int*)(data+idx));
	idx += 4;
	dst[i]->data_len = *((unsigned short*)(data+idx));
	idx += 2;
	dst[i]->data = GNUNET_malloc(ntohs(dst[i]->data_len));
	memcpy(dst[i]->data, data+idx, ntohs(dst[i]->data_len));
	idx += ntohs(dst[i]->data_len);
    }
    return idx;
}/*}}}*/

/**
 * Parse a raw DNS-Packet into an usable struct
 */
struct dns_pkt_parsed*
parse_dns_packet(struct dns_pkt* pkt) {/*{{{*/
    struct dns_pkt_parsed* ppkt = GNUNET_malloc(sizeof(struct dns_pkt_parsed));
    memcpy(&ppkt->s, &pkt->s, sizeof pkt->s);

    unsigned short qdcount = ntohs(ppkt->s.qdcount);
    unsigned short ancount = ntohs(ppkt->s.ancount);
    unsigned short nscount = ntohs(ppkt->s.nscount);
    unsigned short arcount = ntohs(ppkt->s.arcount);

    ppkt->queries = GNUNET_malloc(qdcount*sizeof(struct dns_query*));
    ppkt->answers = GNUNET_malloc(ancount*sizeof(struct dns_record*));
    ppkt->nameservers = GNUNET_malloc(nscount*sizeof(struct dns_record*));
    ppkt->additional = GNUNET_malloc(arcount*sizeof(struct dns_record*));

    unsigned short idx = 0, _idx; /* This keeps track how far we have parsed the data */

    /* Parse the Query */
    int i;
    for (i = 0; i < qdcount; i++)
      { /*{{{*/
	ppkt->queries[i] = GNUNET_malloc(sizeof(struct dns_query));
	char* name = alloca(255); /* see RFC1035, it can't be more than this. */

	_idx = parse_dns_name(name, pkt->data, idx);
	ppkt->queries[i]->namelen = _idx - idx;
	idx = _idx;

	ppkt->queries[i]->name = GNUNET_malloc(ppkt->queries[i]->namelen);
	memcpy(ppkt->queries[i]->name, name, ppkt->queries[i]->namelen);

	ppkt->queries[i]->qtype = *((unsigned short*)(pkt->data+idx));
	idx += 2;
	ppkt->queries[i]->qclass = *((unsigned short*)(pkt->data+idx));
	idx += 2;
    }
    /*}}}*/
    idx = parse_dns_record(pkt->data, ppkt->answers, ancount, idx);
    idx = parse_dns_record(pkt->data, ppkt->nameservers, nscount, idx);
    idx = parse_dns_record(pkt->data, ppkt->additional, arcount, idx);
    return ppkt;
}/*}}}*/

void
free_parsed_dns_packet(struct dns_pkt_parsed* ppkt) {
    unsigned short qdcount = ntohs(ppkt->s.qdcount);
    unsigned short ancount = ntohs(ppkt->s.ancount);
    unsigned short nscount = ntohs(ppkt->s.nscount);
    unsigned short arcount = ntohs(ppkt->s.arcount);

    int i;
    for (i = 0; i < qdcount; i++) {
	GNUNET_free(ppkt->queries[i]->name);
	GNUNET_free(ppkt->queries[i]);
    }
    GNUNET_free(ppkt->queries);
    for (i = 0; i < ancount; i++) {
	GNUNET_free(ppkt->answers[i]->name);
	GNUNET_free(ppkt->answers[i]->data);
	GNUNET_free(ppkt->answers[i]);
    }
    GNUNET_free(ppkt->answers);
    for (i = 0; i < nscount; i++) {
	GNUNET_free(ppkt->nameservers[i]->name);
	GNUNET_free(ppkt->nameservers[i]->data);
	GNUNET_free(ppkt->nameservers[i]);
    }
    GNUNET_free(ppkt->nameservers);
    for (i = 0; i < arcount; i++) {
	GNUNET_free(ppkt->additional[i]->name);
	GNUNET_free(ppkt->additional[i]->data);
	GNUNET_free(ppkt->additional[i]);
    }
    GNUNET_free(ppkt->additional);
    GNUNET_free(ppkt);
}