/*
   Unix SMB/CIFS implementation.

   DNS server handler for queries

   Copyright (C) 2010 Kai Blin  <kai@samba.org>

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "smbd/service_task.h"
#include "libcli/util/werror.h"
#include "librpc/ndr/libndr.h"
#include "librpc/gen_ndr/ndr_dns.h"
#include "librpc/gen_ndr/ndr_dnsp.h"
#include <ldb.h>
#include "param/param.h"
#include "dsdb/samdb/samdb.h"
#include "dsdb/common/util.h"
#include "dns_server/dns_server.h"
#include "libcli/dns/libdns.h"
#include "lib/util/util_net.h"
#include "lib/util/tevent_werror.h"

static WERROR create_response_rr(const struct dns_name_question *question,
				 const struct dnsp_DnssrvRpcRecord *rec,
				 struct dns_res_rec **answers, uint16_t *ancount)
{
	struct dns_res_rec *ans = *answers;
	uint16_t ai = *ancount;
	char *tmp;
	uint32_t i;

	ZERO_STRUCT(ans[ai]);

	switch (rec->wType) {
	case DNS_QTYPE_CNAME:
		ans[ai].rdata.cname_record = talloc_strdup(ans, rec->data.cname);
		W_ERROR_HAVE_NO_MEMORY(ans[ai].rdata.cname_record);
		break;
	case DNS_QTYPE_A:
		ans[ai].rdata.ipv4_record = talloc_strdup(ans, rec->data.ipv4);
		W_ERROR_HAVE_NO_MEMORY(ans[ai].rdata.ipv4_record);
		break;
	case DNS_QTYPE_AAAA:
		ans[ai].rdata.ipv6_record = talloc_strdup(ans, rec->data.ipv6);
		W_ERROR_HAVE_NO_MEMORY(ans[ai].rdata.ipv6_record);
		break;
	case DNS_TYPE_NS:
		ans[ai].rdata.ns_record = talloc_strdup(ans, rec->data.ns);
		W_ERROR_HAVE_NO_MEMORY(ans[ai].rdata.ns_record);
		break;
	case DNS_QTYPE_SRV:
		ans[ai].rdata.srv_record.priority = rec->data.srv.wPriority;
		ans[ai].rdata.srv_record.weight   = rec->data.srv.wWeight;
		ans[ai].rdata.srv_record.port     = rec->data.srv.wPort;
		ans[ai].rdata.srv_record.target   = talloc_strdup(
			ans, rec->data.srv.nameTarget);
		W_ERROR_HAVE_NO_MEMORY(ans[ai].rdata.srv_record.target);
		break;
	case DNS_QTYPE_SOA:
		ans[ai].rdata.soa_record.mname	 = talloc_strdup(
			ans, rec->data.soa.mname);
		W_ERROR_HAVE_NO_MEMORY(ans[ai].rdata.soa_record.mname);
		ans[ai].rdata.soa_record.rname	 = talloc_strdup(
			ans, rec->data.soa.rname);
		W_ERROR_HAVE_NO_MEMORY(ans[ai].rdata.soa_record.rname);
		ans[ai].rdata.soa_record.serial	 = rec->data.soa.serial;
		ans[ai].rdata.soa_record.refresh = rec->data.soa.refresh;
		ans[ai].rdata.soa_record.retry	 = rec->data.soa.retry;
		ans[ai].rdata.soa_record.expire	 = rec->data.soa.expire;
		ans[ai].rdata.soa_record.minimum = rec->data.soa.minimum;
		break;
	case DNS_QTYPE_PTR:
		ans[ai].rdata.ptr_record = talloc_strdup(ans, rec->data.ptr);
		break;
	case DNS_QTYPE_TXT:
		tmp = talloc_asprintf(ans, "\"%s\"", rec->data.txt.str[0]);
		W_ERROR_HAVE_NO_MEMORY(tmp);
		for (i=1; i<rec->data.txt.count; i++) {
			tmp = talloc_asprintf_append_buffer(
				tmp, " \"%s\"", rec->data.txt.str[i]);
			W_ERROR_HAVE_NO_MEMORY(tmp);
		}
		ans[ai].rdata.txt_record.txt = tmp;
		break;
	default:
		DEBUG(0, ("Got unhandled type %u query.\n", rec->wType));
		return DNS_ERR(NOT_IMPLEMENTED);
	}

	ans[ai].name = talloc_strdup(ans, question->name);
	W_ERROR_HAVE_NO_MEMORY(ans[ai].name);
	ans[ai].rr_type = rec->wType;
	ans[ai].rr_class = DNS_QCLASS_IN;
	ans[ai].ttl = rec->dwTtlSeconds;
	ans[ai].length = UINT16_MAX;
	ai++;

	*answers = ans;
	*ancount = ai;

	return WERR_OK;
}

struct ask_forwarder_state {
	struct tevent_context *ev;
	uint16_t id;
	struct dns_name_packet in_packet;
};

static void ask_forwarder_done(struct tevent_req *subreq);

static struct tevent_req *ask_forwarder_send(
	TALLOC_CTX *mem_ctx, struct tevent_context *ev,
	const char *forwarder, struct dns_name_question *question)
{
	struct tevent_req *req, *subreq;
	struct ask_forwarder_state *state;
	struct dns_name_packet out_packet = { 0, };
	DATA_BLOB out_blob;
	enum ndr_err_code ndr_err;

	req = tevent_req_create(mem_ctx, &state, struct ask_forwarder_state);
	if (req == NULL) {
		return NULL;
	}
	state->ev = ev;
	generate_random_buffer((uint8_t *)&state->id, sizeof(state->id));

	if (!is_ipaddress(forwarder)) {
		DEBUG(0, ("Invalid 'dns forwarder' setting '%s', needs to be "
			  "an IP address\n", forwarder));
		tevent_req_werror(req, DNS_ERR(NAME_ERROR));
		return tevent_req_post(req, ev);
	}

	out_packet.id = state->id;
	out_packet.operation |= DNS_OPCODE_QUERY | DNS_FLAG_RECURSION_DESIRED;
	out_packet.qdcount = 1;
	out_packet.questions = question;

	ndr_err = ndr_push_struct_blob(
		&out_blob, state, &out_packet,
		(ndr_push_flags_fn_t)ndr_push_dns_name_packet);
	if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
		tevent_req_werror(req, DNS_ERR(SERVER_FAILURE));
		return tevent_req_post(req, ev);
	}
	subreq = dns_udp_request_send(state, ev, forwarder, out_blob.data,
				      out_blob.length);
	if (tevent_req_nomem(subreq, req)) {
		return tevent_req_post(req, ev);
	}
	tevent_req_set_callback(subreq, ask_forwarder_done, req);
	return req;
}

static void ask_forwarder_done(struct tevent_req *subreq)
{
	struct tevent_req *req = tevent_req_callback_data(
		subreq, struct tevent_req);
	struct ask_forwarder_state *state = tevent_req_data(
		req, struct ask_forwarder_state);
	DATA_BLOB in_blob;
	enum ndr_err_code ndr_err;
	WERROR ret;

	ret = dns_udp_request_recv(subreq, state,
				   &in_blob.data, &in_blob.length);
	TALLOC_FREE(subreq);
	if (tevent_req_werror(req, ret)) {
		return;
	}

	ndr_err = ndr_pull_struct_blob(
		&in_blob, state, &state->in_packet,
		(ndr_pull_flags_fn_t)ndr_pull_dns_name_packet);
	if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
		tevent_req_werror(req, DNS_ERR(SERVER_FAILURE));
		return;
	}
	if (state->in_packet.id != state->id) {
		tevent_req_werror(req, DNS_ERR(NAME_ERROR));
		return;
	}
	tevent_req_done(req);
}

static WERROR ask_forwarder_recv(
	struct tevent_req *req, TALLOC_CTX *mem_ctx,
	struct dns_res_rec **answers, uint16_t *ancount,
	struct dns_res_rec **nsrecs, uint16_t *nscount,
	struct dns_res_rec **additional, uint16_t *arcount)
{
	struct ask_forwarder_state *state = tevent_req_data(
		req, struct ask_forwarder_state);
	struct dns_name_packet *in_packet = &state->in_packet;
	WERROR err;

	if (tevent_req_is_werror(req, &err)) {
		return err;
	}

	*ancount = in_packet->ancount;
	*answers = talloc_move(mem_ctx, &in_packet->answers);

	*nscount = in_packet->nscount;
	*nsrecs = talloc_move(mem_ctx, &in_packet->nsrecs);

	*arcount = in_packet->arcount;
	*additional = talloc_move(mem_ctx, &in_packet->additional);

	return WERR_OK;
}

static WERROR handle_question(struct dns_server *dns,
			      TALLOC_CTX *mem_ctx,
			      const struct dns_name_question *question,
			      struct dns_res_rec **answers, uint16_t *ancount)
{
	struct dns_res_rec *ans = *answers;
	WERROR werror;
	unsigned int ri;
	struct dnsp_DnssrvRpcRecord *recs;
	uint16_t rec_count, ai = *ancount;
	struct ldb_dn *dn = NULL;

	werror = dns_name2dn(dns, mem_ctx, question->name, &dn);
	W_ERROR_NOT_OK_RETURN(werror);

	werror = dns_lookup_records(dns, mem_ctx, dn, &recs, &rec_count);
	W_ERROR_NOT_OK_RETURN(werror);

	ans = talloc_realloc(mem_ctx, ans, struct dns_res_rec, rec_count + ai);
	if (ans == NULL) {
		return WERR_NOMEM;
	}

	for (ri = 0; ri < rec_count; ri++) {
		if ((recs[ri].wType == DNS_TYPE_CNAME) &&
		    ((question->question_type == DNS_QTYPE_A) ||
		     (question->question_type == DNS_QTYPE_AAAA))) {
			struct dns_name_question *new_q =
				talloc(mem_ctx, struct dns_name_question);

			if (new_q == NULL) {
				return WERR_NOMEM;
			}

			/* We reply with one more record, so grow the array */
			ans = talloc_realloc(mem_ctx, ans, struct dns_res_rec,
					     rec_count + 1);
			if (ans == NULL) {
				TALLOC_FREE(new_q);
				return WERR_NOMEM;
			}

			/* First put in the CNAME record */
			werror = create_response_rr(question, &recs[ri], &ans, &ai);
			if (!W_ERROR_IS_OK(werror)) {
				return werror;
			}

			/* And then look up the name it points at.. */

			/* First build up the new question */
			new_q->question_type = question->question_type;
			new_q->question_class = question->question_class;
			if (new_q->question_type == DNS_QTYPE_A) {
				new_q->name = talloc_strdup(new_q, recs[ri].data.ipv4);
			} else if (new_q->question_type == DNS_QTYPE_AAAA) {
				new_q->name = talloc_strdup(new_q, recs[ri].data.ipv6);
			}
			if (new_q->name == NULL) {
				TALLOC_FREE(new_q);
				return WERR_NOMEM;
			}
			/* and then call the lookup again */
			werror = handle_question(dns, mem_ctx, new_q, &ans, &ai);
			if (!W_ERROR_IS_OK(werror)) {
				return werror;
			}


			continue;
		}
		if ((question->question_type != DNS_QTYPE_ALL) &&
		    (recs[ri].wType != question->question_type)) {
			continue;
		}
		werror = create_response_rr(question, &recs[ri], &ans, &ai);
		if (!W_ERROR_IS_OK(werror)) {
			return werror;
		}
	}

	if (ai == 0) {
		return DNS_ERR(NAME_ERROR);
	}

	*ancount = ai;
	*answers = ans;

	return WERR_OK;

}

struct dns_server_process_query_state {
	struct dns_res_rec *answers;
	uint16_t ancount;
	struct dns_res_rec *nsrecs;
	uint16_t nscount;
	struct dns_res_rec *additional;
	uint16_t arcount;
};

static void dns_server_process_query_got_response(struct tevent_req *subreq);

struct tevent_req *dns_server_process_query_send(
	TALLOC_CTX *mem_ctx, struct tevent_context *ev,
	struct dns_server *dns,	struct dns_request_state *req_state,
	const struct dns_name_packet *in)
{
	struct tevent_req *req, *subreq;
	struct dns_server_process_query_state *state;

	req = tevent_req_create(mem_ctx, &state,
				struct dns_server_process_query_state);
	if (req == NULL) {
		return NULL;
	}
	if (in->qdcount != 1) {
		tevent_req_werror(req, DNS_ERR(FORMAT_ERROR));
		return tevent_req_post(req, ev);
	}

	/* Windows returns NOT_IMPLEMENTED on this as well */
	if (in->questions[0].question_class == DNS_QCLASS_NONE) {
		tevent_req_werror(req, DNS_ERR(NOT_IMPLEMENTED));
		return tevent_req_post(req, ev);
	}

	if (dns_authorative_for_zone(dns, in->questions[0].name)) {
		WERROR err;

		req_state->flags |= DNS_FLAG_AUTHORITATIVE;
		err = handle_question(dns, state, &in->questions[0],
				      &state->answers, &state->ancount);
		if (tevent_req_werror(req, err)) {
			return tevent_req_post(req, ev);
		}
		tevent_req_done(req);
		return tevent_req_post(req, ev);
	}

	if ((req_state->flags & DNS_FLAG_RECURSION_DESIRED) &&
	    (req_state->flags & DNS_FLAG_RECURSION_AVAIL)) {
		DEBUG(2, ("Not authoritative for '%s', forwarding\n",
			  in->questions[0].name));

		subreq = ask_forwarder_send(
			state, ev, lpcfg_dns_forwarder(dns->task->lp_ctx),
			&in->questions[0]);
		if (tevent_req_nomem(subreq, req)) {
			return tevent_req_post(req, ev);
		}
		tevent_req_set_callback(
			subreq, dns_server_process_query_got_response, req);
		return req;
	}

	tevent_req_werror(req, DNS_ERR(NAME_ERROR));
	return tevent_req_post(req, ev);
}

static void dns_server_process_query_got_response(struct tevent_req *subreq)
{
	struct tevent_req *req = tevent_req_callback_data(
		subreq, struct tevent_req);
	struct dns_server_process_query_state *state = tevent_req_data(
		req, struct dns_server_process_query_state);
	WERROR err;

	err = ask_forwarder_recv(subreq, state,
				 &state->answers, &state->ancount,
				 &state->nsrecs, &state->nscount,
				 &state->additional, &state->arcount);
	TALLOC_FREE(subreq);
	if (tevent_req_werror(req, err)) {
		return;
	}
	tevent_req_done(req);
}

WERROR dns_server_process_query_recv(
	struct tevent_req *req, TALLOC_CTX *mem_ctx,
	struct dns_res_rec **answers,    uint16_t *ancount,
	struct dns_res_rec **nsrecs,     uint16_t *nscount,
	struct dns_res_rec **additional, uint16_t *arcount)
{
	struct dns_server_process_query_state *state = tevent_req_data(
		req, struct dns_server_process_query_state);
	WERROR err;

	if (tevent_req_is_werror(req, &err)) {
		return err;
	}
	*answers = talloc_move(mem_ctx, &state->answers);
	*ancount = state->ancount;
	*nsrecs = talloc_move(mem_ctx, &state->nsrecs);
	*nscount = state->nscount;
	*additional = talloc_move(mem_ctx, &state->additional);
	*arcount = state->arcount;
	return WERR_OK;
}