/*
 * Copyright (c) 2016 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include "dns_pack.h"
#include <string.h>

/* This is the label's length octet, see 4.1.2. Question section format */
#define DNS_LABEL_LEN_SIZE	1
#define DNS_LABEL_MAX_SIZE	63
#define DNS_ANSWER_MIN_SIZE	12
#define DNS_COMMON_UINT_SIZE	2

#define DNS_HEADER_ID_LEN	2
#define DNS_HEADER_FLAGS_LEN	2
#define DNS_QTYPE_LEN		2
#define DNS_QCLASS_LEN		2
#define DNS_QDCOUNT_LEN		2
#define DNS_ANCOUNT_LEN		2
#define DNS_NSCOUNT_LEN		2
#define DNS_ARCOUNT_LEN		2

/* RFC 1035 '4.1.1. Header section format' defines the following flags:
 * QR, Opcode, AA, TC, RD, RA, Z and RCODE.
 * This implementation only uses RD (Recursion Desired).
 */
#define DNS_RECURSION		1

/* These two defines represent the 3rd and 4th bytes of the DNS msg header.
 * See RFC 1035, 4.1.1. Header section format.
 */
#define DNS_FLAGS1		DNS_RECURSION	/* QR, Opcode, AA, and TC = 0 */
#define DNS_FLAGS2		0		/* RA, Z and RCODE = 0 */

static inline u16_t dns_strlen(const char *str)
{
	if (str == NULL) {
		return 0;
	}
	return (u16_t)strlen(str);
}

int dns_msg_pack_qname(u16_t *len, u8_t *buf, u16_t size,
		       const char *domain_name)
{
	u16_t dn_size;
	u16_t lb_start;
	u16_t lb_index;
	u16_t lb_size;
	u16_t i;

	lb_start = 0;
	lb_index = 1;
	lb_size = 0;

	dn_size = dns_strlen(domain_name);
	if (dn_size == 0) {
		return -EINVAL;
	}

	/* traverse the domain name str, including the null-terminator :) */
	for (i = 0; i < dn_size + 1; i++) {
		if (lb_index >= size) {
			return -ENOMEM;
		}

		switch (domain_name[i]) {
		default:
			buf[lb_index] = domain_name[i];
			lb_size += 1;
			break;
		case '.':
			buf[lb_start] = lb_size;
			lb_size = 0;
			lb_start = lb_index;
			break;
		case '\0':
			buf[lb_start] = lb_size;
			buf[lb_index] = 0;
			break;
		}
		lb_index += 1;
	}

	*len = lb_index;

	return 0;
}

static inline void set_dns_msg_response(struct dns_msg_t *dns_msg, int type,
					u16_t pos, u16_t len)
{
	dns_msg->response_type = type;
	dns_msg->response_position = pos;
	dns_msg->response_length = len;
}

int dns_unpack_answer(struct dns_msg_t *dns_msg, int dname_ptr, u32_t *ttl)
{
	u16_t buf_size;
	u16_t pos;
	u16_t len;
	u8_t *answer;
	int ptr;

	answer = dns_msg->msg + dns_msg->answer_offset;

	if (answer[0] < DNS_LABEL_MAX_SIZE) {
		return -ENOMEM;
	}

	/* Recovery of the pointer value */
	ptr = (((answer[0] & DNS_LABEL_MAX_SIZE) << 8) + answer[1]);
	if (ptr != dname_ptr) {
		return -ENOMEM;
	}

	/*
	 * We need to be sure this buffer has enough space
	 * to contain the answer.
	 *
	 * size: dname_size + type + class + ttl + rdlength + rdata
	 *            2     +   2  +   2   +  4  +     2    +  ?
	 *
	 * So, answer size >= 12
	 *
	 * See RFC-1035 4.1.3. Resource record format
	 */
	buf_size = dns_msg->msg_size - dns_msg->answer_offset;
	if (buf_size < DNS_ANSWER_MIN_SIZE) {
		return -ENOMEM;
	}

	/* Only DNS_CLASS_IN answers
	 * Here we use 2 as an offset because a ptr uses only 2 bytes.
	 */
	if (dns_answer_class(DNS_COMMON_UINT_SIZE, answer) != DNS_CLASS_IN) {
		return -EINVAL;
	}

	/* TTL value */
	*ttl = dns_answer_ttl(DNS_COMMON_UINT_SIZE, answer);
	pos = dns_msg->answer_offset + DNS_ANSWER_MIN_SIZE;
	len = dns_answer_rdlength(DNS_COMMON_UINT_SIZE, answer);

	switch (dns_answer_type(DNS_COMMON_UINT_SIZE, answer)) {
	case DNS_RR_TYPE_A:
	case DNS_RR_TYPE_AAAA:
		set_dns_msg_response(dns_msg, DNS_RESPONSE_IP, pos, len);
		return 0;

	case DNS_RR_TYPE_CNAME:
		set_dns_msg_response(dns_msg, DNS_RESPONSE_CNAME_NO_IP,
				     pos, len);
		return 0;

	default:
		/* malformed dns answer */
		return -EINVAL;
	}

	return 0;
}

int dns_unpack_response_header(struct dns_msg_t *msg, int src_id)
{
	u8_t *dns_header;
	u16_t size;
	int qdcount;
	int ancount;
	int rc;

	dns_header = msg->msg;
	size = msg->msg_size;

	if (size < DNS_MSG_HEADER_SIZE) {
		return -ENOMEM;
	}

	if (dns_unpack_header_id(dns_header) != src_id) {
		return -EINVAL;
	}

	if (dns_header_qr(dns_header) != DNS_RESPONSE) {
		return -EINVAL;
	}

	if (dns_header_opcode(dns_header) != DNS_QUERY) {
		return -EINVAL;
	}

	if (dns_header_z(dns_header) != 0) {
		return -EINVAL;
	}

	rc = dns_header_rcode(dns_header);
	switch (rc) {
	case DNS_HEADER_NOERROR:
		break;
	default:
		return rc;

	}

	qdcount = dns_unpack_header_qdcount(dns_header);
	ancount = dns_unpack_header_ancount(dns_header);
	if (qdcount < 1 || ancount < 1) {
		return -EINVAL;
	}

	return 0;
}

static int dns_msg_pack_query_header(u8_t *buf, u16_t size, u16_t id)
{
	u16_t offset;

	if (size < DNS_MSG_HEADER_SIZE) {
		return -ENOMEM;
	}

	UNALIGNED_PUT(htons(id), (u16_t *)(buf));

	/* RD = 1, TC = 0, AA = 0, Opcode = 0, QR = 0 <-> 0x01 (1B)
	 * RCode = 0, Z = 0, RA = 0		      <-> 0x00 (1B)
	 *
	 * QDCOUNT = 1				      <-> 0x0001 (2B)
	 */

	offset = DNS_HEADER_ID_LEN;
	/* Split the following assignements just in case we need to alter
	 * the flags in future releases
	 */
	*(buf + offset) = DNS_FLAGS1;		/* QR, Opcode, AA, TC and RD */
	*(buf + offset + 1) = DNS_FLAGS2;	/* RA, Z and RCODE */

	offset += DNS_HEADER_FLAGS_LEN;
	/* set question counter */
	UNALIGNED_PUT(htons(1), (u16_t *)(buf + offset));

	offset += DNS_QDCOUNT_LEN;
	/* set answer and ns rr */
	UNALIGNED_PUT(0, (u32_t *)(buf + offset));

	offset += DNS_ANCOUNT_LEN + DNS_NSCOUNT_LEN;
	/* set the additional records */
	UNALIGNED_PUT(0, (u16_t *)(buf + offset));

	return 0;
}

int dns_msg_pack_query(u8_t *buf, u16_t *len, u16_t size,
		       u8_t *qname, u16_t qname_len, u16_t id,
		       enum dns_rr_type qtype)
{
	u16_t msg_size;
	u16_t offset;
	int rc;

	msg_size = DNS_MSG_HEADER_SIZE + DNS_QTYPE_LEN + DNS_QCLASS_LEN;
	if (msg_size + qname_len > size) {
		return -ENOMEM;
	}

	rc = dns_msg_pack_query_header(buf, size, id);
	if (rc != 0) {
		return rc;
	}

	offset = DNS_MSG_HEADER_SIZE;
	memcpy(buf + offset, qname, qname_len);

	offset += qname_len;

	/* QType */
	UNALIGNED_PUT(htons(qtype), (u16_t *)(buf + offset + 0));
	offset += DNS_QTYPE_LEN;

	/* QClass */
	UNALIGNED_PUT(htons(DNS_CLASS_IN), (u16_t *)(buf + offset));

	*len = offset + DNS_QCLASS_LEN;

	return 0;
}

static int dns_find_null(int *qname_size, u8_t *buf, u16_t size)
{
	*qname_size = 0;
	while (*qname_size < size) {
		if (buf[(*qname_size)++] == 0x00) {
			return 0;
		}
	}

	return -ENOMEM;
}

int dns_unpack_response_query(struct dns_msg_t *dns_msg)
{
	u8_t *dns_query;
	u8_t *buf;
	int remaining_size;
	int qname_size;
	int offset;
	int rc;

	dns_msg->query_offset = DNS_MSG_HEADER_SIZE;
	dns_query = dns_msg->msg + dns_msg->query_offset;
	remaining_size = dns_msg->msg_size - dns_msg->query_offset;

	rc = dns_find_null(&qname_size, dns_query, remaining_size);
	if (rc != 0) {
		return rc;
	}

	/* header already parsed + qname size */
	offset = dns_msg->query_offset + qname_size;

	/* 4 bytes more due to qtype and qclass */
	offset += DNS_QTYPE_LEN + DNS_QCLASS_LEN;
	if (offset > dns_msg->msg_size) {
		return -ENOMEM;
	}

	buf = dns_query + qname_size;
	if (dns_unpack_query_qtype(buf) != DNS_RR_TYPE_A &&
	    dns_unpack_query_qtype(buf) != DNS_RR_TYPE_AAAA) {
		return -EINVAL;
	}

	if (dns_unpack_query_qclass(buf) != DNS_CLASS_IN) {
		return -EINVAL;
	}

	dns_msg->answer_offset = dns_msg->query_offset + qname_size +
				 DNS_QTYPE_LEN + DNS_QCLASS_LEN;

	return 0;
}

int dns_copy_qname(u8_t *buf, u16_t *len, u16_t size,
		   struct dns_msg_t *dns_msg, u16_t pos)
{
	u16_t msg_size = dns_msg->msg_size;
	u8_t *msg = dns_msg->msg;
	u16_t lb_size;
	int rc = -EINVAL;
	int i = 0;

	*len = 0;

	/* Iterate ANCOUNT + 1 to allow the Query's QNAME to be parsed.
	 * This is required to avoid 'alias loops'
	 */
	while (i++ < dns_header_ancount(dns_msg->msg) + 1) {
		if (pos >= msg_size) {
			rc = -ENOMEM;
			break;
		}

		lb_size = msg[pos];

		/* pointer */
		if (lb_size > DNS_LABEL_MAX_SIZE) {
			u8_t mask = DNS_LABEL_MAX_SIZE;

			if (pos + 1 >= msg_size) {
				rc = -ENOMEM;
				break;
			}

			/* See: RFC 1035, 4.1.4. Message compression */
			pos = ((msg[pos] & mask) << 8) + msg[pos + 1];

			continue;
		}

		/* validate that the label (i.e. size + elements),
		 * fits the current msg buffer
		 */
		if (DNS_LABEL_LEN_SIZE + lb_size > size - *len) {
			rc = -ENOMEM;
			break;
		}

		/* copy the lb_size value and label elements */
		memcpy(buf + *len, msg + pos, DNS_LABEL_LEN_SIZE + lb_size);
		/* update destination buffer len */
		*len += DNS_LABEL_LEN_SIZE + lb_size;
		/* update msg ptr position */
		pos += DNS_LABEL_LEN_SIZE + lb_size;

		/* The domain name terminates with the zero length octet
		 * for the null label of the root
		 */
		if (lb_size == 0) {
			rc = 0;
			break;
		}
	}

	return rc;
}