/*
 * include/types/dns.h
 * This file provides structures and types for DNS.
 *
 * Copyright (C) 2014 Baptiste Assmann <bedis9@gmail.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation, version 2.1
 * exclusively.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

#ifndef _TYPES_DNS_H
#define _TYPES_DNS_H

/*DNS maximum values */
/*
 * Maximum issued from RFC:
 *  RFC 1035: https://www.ietf.org/rfc/rfc1035.txt chapter 2.3.4
 *  RFC 2671: http://tools.ietf.org/html/rfc2671
 */
#define DNS_MAX_LABEL_SIZE	63
#define DNS_MAX_NAME_SIZE	255
#define DNS_MAX_UDP_MESSAGE	4096

/* DNS error messages */
#define DNS_TOO_LONG_FQDN	"hostname too long"
#define DNS_LABEL_TOO_LONG	"one label too long"
#define DNS_INVALID_CHARACTER	"found an invalid character"

/* dns query class */
#define DNS_RCLASS_IN		1	/* internet class */

/* dns record types (non exhaustive list) */
#define DNS_RTYPE_A		1	/* IPv4 address */
#define DNS_RTYPE_CNAME		5	/* canonical name */
#define DNS_RTYPE_AAAA		28	/* IPv6 address */
#define DNS_RTYPE_ANY		255	/* all records */

/* dns rcode values */
#define DNS_RCODE_NO_ERROR	0	/* no error */
#define DNS_RCODE_NX_DOMAIN	3	/* non existent domain */
#define DNS_RCODE_REFUSED	5	/* query refused */

/* DNS request or response header structure */
struct dns_header {
	unsigned short	id:16;		/* identifier */
	unsigned char	rd :1;		/* recursion desired 0: no, 1: yes */
	unsigned char	tc :1;		/* truncation 0:no, 1: yes */
	unsigned char	aa :1;		/* authoritative answer 0: no, 1: yes */
	unsigned char	opcode :4;	/* operation code */
	unsigned char	qr :1;		/* query/response 0: query, 1: response */
	unsigned char	rcode :4;	/* response code */
	unsigned char	z :1;		/* no used */
	unsigned char	ad :1;		/* authentic data */
	unsigned char	cd :1;		/* checking disabled */
	unsigned char	ra :1;		/* recursion available 0: no, 1: yes */
	unsigned short	qdcount :16;	/* question count */
	unsigned short	ancount :16;	/* answer count */
	unsigned short	nscount :16;	/* authority count */
	unsigned short	arcount :16;	/* additional count */
};

/* short structure to describe a DNS question */
struct dns_question {
	unsigned short	qtype;		/* question type */
	unsigned short	qclass;		/* query class */
};

/*
 * resolvers section and parameters. It is linked to the name servers
 * servers points to it.
 * current resolution are stored in a FIFO list.
 */
struct dns_resolvers {
	struct list list;		/* resolvers list */
	char *id;			/* resolvers unique identifier */
	struct {
		const char *file;	/* file where the section appears */
		int line;		/* line where the section appears */
	} conf;				/* config information */
	struct list nameserver_list;	/* dns server list */
	int count_nameservers;			/* total number of nameservers in a resolvers section */
	int resolve_retries;		/* number of retries before giving up */
	struct {			/* time to: */
		int retry;		/*   wait for a response before retrying */
	} timeout;
	struct {			/* time to hold current data when */
		int valid;		/*   a response is valid */
	} hold;
	struct task *t;			/* timeout management */
	struct list curr_resolution;	/* current running resolutions */
	struct eb_root query_ids;	/* tree to quickly lookup/retrieve query ids currently in use */
					/* used by each nameserver, but stored in resolvers since there must */
					/* be a unique relation between an eb_root and an eb_node (resolution) */
};

/*
 * structure describing a name server used during name resolution.
 * A name server belongs to a resolvers section.
 */
struct dns_nameserver {
	struct list list;		/* nameserver chained list */
	char *id;			/* nameserver unique identifier */
	struct {
		const char *file;	/* file where the section appears */
		int line;		/* line where the section appears */
	} conf;				/* config information */
	struct dns_resolvers *resolvers;
	struct dgram_conn *dgram;		/* transport layer */
	struct sockaddr_storage addr;	/* IP address */
	struct {			/* numbers relted to this name server: */
		long int sent;		/* - queries sent */
		long int valid;		/* - valid response */
		long int update;	/* - valid response used to update server's IP */
		long int cname;		/* - CNAME response requiring new resolution */
		long int cname_error;	/* - error when resolving CNAMEs */
		long int any_err;	/* - void response (usually because ANY qtype) */
		long int nx;		/* - NX response */
		long int timeout;	/* - queries which reached timeout */
		long int refused;	/* - queries refused */
		long int other;		/* - other type of response */
		long int invalid;	/* - malformed DNS response */
		long int too_big;	/* - too big response */
		long int outdated;	/* - outdated response (server slower than the other ones) */
	} counters;
};

/*
 * resolution structure associated to single server and used to manage name resolution for
 * this server.
 * The only link between the resolution and a nameserver is through the query_id.
 */
struct dns_resolution {
	struct list list;		/* resolution list */
	struct dns_resolvers *resolvers;	/* resolvers section associated to this resolution */
	void *requester;		/* owner of this name resolution */
	int (*requester_cb)(struct dns_resolution *, struct dns_nameserver *, unsigned char *, int);
					/* requester callback for valid response */
	int (*requester_error_cb)(struct dns_resolution *, int);
					/* requester callback, for error management */
	char *hostname_dn;		/* server hostname in domain name label format */
	int hostname_dn_len;		/* server domain name label len */
	int resolver_family_priority;	/* which IP family should the resolver use when both are returned */
	time_t last_resolution;		/* time of the lastest valid resolution */
	time_t last_sent_packet;	/* time of the latest DNS packet sent */
	time_t last_status_change;	/* time of the latest DNS resolution status change */
	int query_id;			/* DNS query ID dedicated for this resolution */
	struct eb32_node qid;		/* ebtree query id */
	int query_type;			/* query type to send. By default DNS_RTYPE_ANY */
	int status;			/* status of the resolution being processed RSLV_STATUS_* */
	int step;			/* */
	int try;			/* current resolution try */
	int try_cname;			/* number of CNAME requests sent */
	int nb_responses;		/* count number of responses received */
};

/* last resolution status code */
enum {
	RSLV_STATUS_NONE	= 0,	/* no resolution occured yet */
	RSLV_STATUS_VALID,		/* no error */
	RSLV_STATUS_INVALID,		/* invalid responses */
	RSLV_STATUS_ERROR,		/* error */
	RSLV_STATUS_NX,			/* NXDOMAIN */
	RSLV_STATUS_REFUSED,		/* server refused our query */
	RSLV_STATUS_TIMEOUT,		/* no response from DNS servers */
	RSLV_STATUS_OTHER,		/* other errors */
};

/* current resolution step */
enum {
	RSLV_STEP_NONE		= 0,	/* nothing happening currently */
	RSLV_STEP_RUNNING,		/* resolution is running */
};

/* return codes after analyzing a DNS response */
enum {
	DNS_RESP_VALID		= 0,	/* valid response */
	DNS_RESP_INVALID,		/* invalid response (various type of errors can trigger it) */
	DNS_RESP_ERROR,			/* DNS error code */
	DNS_RESP_NX_DOMAIN,		/* resolution unsuccessful */
	DNS_RESP_REFUSED,		/* DNS server refused to answer */
	DNS_RESP_ANCOUNT_ZERO,		/* no answers in the response */
	DNS_RESP_WRONG_NAME,		/* response does not match query name */
	DNS_RESP_CNAME_ERROR,		/* error when resolving a CNAME in an atomic response */
	DNS_RESP_TIMEOUT,		/* DNS server has not answered in time */
};

/* return codes after searching an IP in a DNS response buffer, using a family preference */
enum {
	DNS_UPD_NO 		= 1,	/* provided IP was found and preference is matched
					 * OR provided IP found and preference is not matched, but no IP
					 *    matching preference was found */
	DNS_UPD_SRVIP_NOT_FOUND,	/* provided IP not found
					 * OR provided IP found and preference is not match and an IP
					 *    matching preference was found */
	DNS_UPD_CNAME,			/* CNAME without any IP provided in the response */
	DNS_UPD_NAME_ERROR,		/* name in the response did not match the query */
};

#endif /* _TYPES_DNS_H */