dns_cache.h

/*
 * $Id: dns_cache.h 2 2006-11-14 22:37:20Z vingarzan $
 *
 * resolver/dns related functions, dns cache and failover
 *
 * Copyright (C) 2006 iptelorg GmbH
 *
 * This file is part of ser, a free SIP server.
 *
 * ser 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 2 of the License, or
 * (at your option) any later version
 *
 * For a license to use the ser software under conditions
 * other than those described here, or to purchase support for this
 * software, please contact iptel.org by e-mail at the following addresses:
 *    info@iptel.org
 *
 * ser 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, write to the Free Software 
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
/* History:
 * --------
 *  2006-07-13  created by andrei
 */


#ifndef __dns_cache_h
#define __dns_cache_h

#include "str.h"
#include "timer.h"
#include "ip_addr.h"
#include "atomic_ops.h"
#include "resolve.h"


#if defined(USE_DNS_FAILOVER) && !defined(USE_DNS_CACHE)
#error "DNS FAILOVER requires DNS CACHE support (define USE_DNS_CACHE)"
#endif

#define DNS_LU_LST

/* dns functions return them as negative values (e.g. return -E_DNS_NO_IP)
 * listed in the order of importance ( if more errors, only the most important
 * is returned)
 */
enum dns_errors{
					E_DNS_OK=0,
					E_DNS_EOR, /* no more records (not an error)
					              -- returned only by the dns_resolve* 
								  functions when called iteratively,; it
								  signals the end of the ip/records list */
					E_DNS_UNKNOWN /* unkown error */,
					E_DNS_INTERNAL_ERR /* internal error */,
					E_DNS_BAD_SRV_ENTRY,
					E_DNS_NO_SRV /* unresolvable srv record */,
					E_DNS_BAD_IP_ENTRY,
					E_DNS_NO_IP /* unresolvable a or aaaa records*/,
					E_DNS_BAD_IP /* the ip is invalid */, 
					E_DNS_BLACKLIST_IP /* the ip is blacklisted */, 
					E_DNS_NAME_TOO_LONG /* try again with a shorter name */,
					E_DNS_AF_MISMATCH /* ipv4 or ipv6 only requested, but 
										 name contains an ip addr. of the
										 opossite type */ ,
					E_DNS_CRITICAL /* critical error, marks the end
									  of the error table (always last) */
};


extern int dns_flags; /* default flags used for dns lookup */

/* return a short string, printable error description (err <=0) */
const char* dns_strerror(int err);

/* dns entry error flags */
#define DNS_BAD_NAME     1 /* unresolvable */

/* dns requests flags */
#define DNS_NO_FLAGS	0
#define DNS_IPV4_ONLY	1
#define DNS_IPV6_ONLY	2
#define DNS_IPV6_FIRST	4


/* ip blacklist error flags */
#define IP_ERR_BAD_DST      2 /* destination is marked as bad (e.g. bad ip) */
#define IP_ERR_SND          3 /* send error while using this as destination */
#define IP_ERR_TIMEOUT      4 /* timeout waiting for a response */
#define IP_ERR_TCP_CON      5 /* could not establish tcp connection */


/* stripped down dns rr */
struct dns_rr{
	struct dns_rr* next;
	void* rdata; /* depends on the type */
	/* name, type and class are not needed, contained in struct dns_query */
	ticks_t expire; /* = ttl + crt_time */
	unsigned char err_flags; /* if 0 everything is ok */

};



#ifdef DNS_LU_LST
struct dns_lu_lst{  /* last used ordered list */
	struct dns_lu_lst* next;
	struct dns_lu_lst* prev;
};
#endif

struct dns_hash_entry{
	/* hash table links */
	struct dns_hash_entry* next;
	struct dns_hash_entry* prev;
#ifdef DNS_LU_LST
	struct dns_lu_lst last_used_lst;
#endif
	struct dns_rr* rr_lst;
	atomic_t refcnt;
	ticks_t last_used;
	ticks_t expire; /* when the whole entry will expire */
	int total_size;
	unsigned short type;
	unsigned char err_flags;
	unsigned char name_len; /* can be maximum 255 bytes */
	char name[1]; /* variable length, name, null terminated 
	                 (actual lenght = name_len +1)*/
};



struct dns_srv_handle{
	struct dns_hash_entry* srv; /* srv entry */
	struct dns_hash_entry* a;   /* a or aaaa current entry */
	unsigned short port; /* current port */
	unsigned char srv_no; /* current record no. in the srv entry */
	unsigned char ip_no;   /* current record no. in the a/aaaa entry */
};



const char* dns_strerror(int err);

int init_dns_cache();
void destroy_dns_cache();


void dns_hash_put(struct dns_hash_entry* e);
void dns_hash_put_shm_unsafe(struct dns_hash_entry* e);

inline static void dns_srv_handle_put(struct dns_srv_handle* h)
{
	if (h){
		if (h->srv){
			dns_hash_put(h->srv);
			h->srv=0;
		}
		if (h->a){
			dns_hash_put(h->a);
			h->a=0;
		}
	}
}



/* use it when copying, it manually increases the ref cound */
inline static void dns_srv_handle_ref(struct dns_srv_handle *h)
{
	if (h){
		if (h->srv)
			atomic_inc(&h->srv->refcnt);
		if (h->a)
			atomic_inc(&h->a->refcnt);
	}
}



/* safe copy increases the refcnt, src must not change while in this function
 * WARNING: the copy must be dns_srv_handle_put ! */
inline static void dns_srv_handle_cpy(struct dns_srv_handle* dst,
										struct dns_srv_handle* src)
{
	dns_srv_handle_ref(src);
	*dst=*src;
}



/* same as above but assume shm_lock held (for internal tm use only) */
inline static void dns_srv_handle_put_shm_unsafe(struct dns_srv_handle* h)
{
	if (h){
		if (h->srv){
			dns_hash_put_shm_unsafe(h->srv);
			h->srv=0;
		}
		if (h->a){
			dns_hash_put_shm_unsafe(h->a);
			h->a=0;
		}
	}
}



/* get "next" ip next time a dns_srv_handle function is called
 * params: h   - struct dns_srv_handler
 *         err - return code of the last dns_*_resolve* call 
 * returns: 0 if it doesn't make sense to try another record,
 * 1 otherwise
 */
inline static int dns_srv_handle_next(struct dns_srv_handle* h, int err)
{
	if (err<0) return 0;
	h->ip_no++;
	return (h->srv || h->a);
}



inline static void dns_srv_handle_init(struct dns_srv_handle* h)
{
	h->srv=h->a=0;
	h->srv_no=h->ip_no=0;
}



/* performes a srv query on name
 * Params:  name  - srv query target (e.g. _sip._udp.foo.bar)
 *          ip    - result: first good ip found
 *          port  - result: corresponding port number
 *          flags - resolve options (like ipv4 only, ipv6 prefered a.s.o)
 * Returns: < 0 on error (can be passed to dns_strerror(), 0 on success
 */
int dns_srv_get_ip(str* name, struct ip_addr* ip, unsigned short* port,
					int flags);

/* performs an A, AAAA (or both) query/queries
 * Params:  name  - query target (e.g. foo.bar)
 *          ip    - result: first good ip found
 *          flags - resolve options (like ipv4 only, ipv6 prefered a.s.o)
 * Returns: < 0 on error (can be passed to dns_strerror(), 0 on success
 */
int dns_get_ip(str* name, struct ip_addr* ip, int flags);

struct hostent* dns_srv_get_he(str* name, unsigned short* port, int flags);
struct hostent* dns_get_he(str* name, int flags);


/* resolve name to an ip, using srv record. Can be called multiple times
 * to iterate on all the possible ips, e.g :
 * dns_srv_handle_init(h);
 * ret_code=dns_sip_resolve(h,...);
 *  while( dns_srv_handle_next(h, ret_code){ ret_code=dns_sip_resolve(h...); }
 * dns_srv_handle_put(h);
 * WARNING: dns_srv_handle_init() must be called to initialize h and
 *  dns_srv_handle_put(h) must be called when h is no longer needed
 */
int dns_sip_resolve(struct dns_srv_handle* h,  str* name, struct ip_addr* ip,
					unsigned short* port, int proto, int flags);

/* same as above, but fills su intead of changing port and filling an ip */ 
inline static int dns_sip_resolve2su(struct dns_srv_handle* h,
									 union sockaddr_union* su,
									 str* name, unsigned short port,
									 int proto, int flags)
{
	struct ip_addr ip;
	int ret;
	
	ret=dns_sip_resolve(h, name, &ip, &port, proto, flags);
	if (ret>=0)
		init_su(su, &ip, port);
	return ret;
}
#endif