DNS - host name to IP address resolver.

#include "lwip/opt.h"
#include "lwip/udp.h"
#include "lwip/mem.h"
#include "lwip/memp.h"
#include "lwip/dns.h"
#include <string.h>

Data Structures
struct	dns_answer
	DNS answer message structure. More...

struct	dns_hdr
	DNS message header. More...

struct	dns_query
	DNS query message structure. More...

struct	dns_req_entry
	DNS request table entry: used when dns_gehostbyname cannot answer the request from the DNS table. More...

struct	dns_table_entry
	DNS table entry. More...

Macros
#define	DNS_FLAG1_AUTHORATIVE 0x04

#define	DNS_FLAG1_OPCODE_INVERSE 0x08

#define	DNS_FLAG1_OPCODE_STANDARD 0x00

#define	DNS_FLAG1_OPCODE_STATUS 0x10

#define	DNS_FLAG1_RD 0x01

#define	DNS_FLAG1_RESPONSE 0x80

#define	DNS_FLAG1_TRUNC 0x02

#define	DNS_FLAG2_ERR_MASK 0x0f

#define	DNS_FLAG2_ERR_NAME 0x03

#define	DNS_FLAG2_ERR_NONE 0x00

#define	DNS_FLAG2_RA 0x80

#define	DNS_MAX_REQUESTS DNS_TABLE_SIZE

#define	DNS_MAX_RETRIES 4
	DNS maximum number of retries when asking for a name, before "timeout". More...

#define	DNS_MAX_SOURCE_PORTS DNS_MAX_REQUESTS

#define	DNS_MAX_TTL 604800
	DNS resource record max. More...

#define	DNS_PORT_ALLOWED(port) ((port) >= 1024)
	Limits the source port to be >= 1024 by default. More...

#define	DNS_RAND_TXID LWIP_RAND
	Random generator function to create random TXIDs and source ports for queries. More...

#define	DNS_SERVER_ADDRESS(ipaddr) (ip4_addr_set_u32(ipaddr, ipaddr_addr("208.67.222.222"))) /* resolver1.opendns.com */
	DNS server IP address. More...

#define	DNS_SERVER_PORT 53
	DNS server port address. More...

#define	DNS_STATE_ASKING 2

#define	DNS_STATE_DONE 3

#define	DNS_STATE_NEW 1

#define	DNS_STATE_UNUSED 0

#define	LWIP_DNS_SECURE (LWIP_DNS_SECURE_RAND_XID \| LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING \| LWIP_DNS_SECURE_RAND_SRC_PORT)
	Use all DNS security features by default. More...

#define	LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING 2

#define	LWIP_DNS_SECURE_RAND_SRC_PORT 4

#define	LWIP_DNS_SECURE_RAND_XID 1
	This file implements a DNS host name to IP address resolver. More...

#define	LWIP_DNS_STRICMP(str1, str2) dns_stricmp(str1, str2)

#define	SIZEOF_DNS_ANSWER 10

#define	SIZEOF_DNS_ANSWER_ASSERT 12

#define	SIZEOF_DNS_HDR 12

#define	SIZEOF_DNS_QUERY 4

Functions
static u8_t	dns_alloc_pcb (void)
	dns_alloc_pcb() - allocates a new pcb (or reuses an existing one) to be used for sending a request More...

static struct udp_pcb *	dns_alloc_random_port (void)

static void	dns_call_found (u8_t idx, ip_addr_t *addr)
	dns_call_found() - call the found callback and check if there are duplicate entries for the given hostname. More...

static void	dns_check_entries (void)
	Call dns_check_entry for each entry in dns_table - check all entries. More...

static void	dns_check_entry (u8_t i)
	dns_check_entry() - see if entry has not yet been queried and, if so, sends out a query. More...

static u16_t	dns_compare_name (char query, struct pbuf p, u16_t start_offset)
	Compare the "dotted" name "query" with the encoded name "response" to make sure an answer from the DNS server matches the current dns_table entry (otherwise, answers might arrive late for hostname not on the list any more). More...

static u16_t	dns_create_txid (void)

static err_t	dns_enqueue (const char name, size_t hostnamelen, dns_found_callback found, void callback_arg)
	Queues a new hostname to resolve and sends out a DNS query for that hostname. More...

err_t	dns_gethostbyname (const char hostname, ip_addr_t addr, dns_found_callback found, void *callback_arg)
	Resolve a hostname (string) into an IP address. More...

ip_addr_t *	dns_getserver (u8_t numdns)
	Obtain one of the currently configured DNS server. More...

void	dns_init ()
	Initialize the resolver: set up the UDP pcb and configure the default server (DNS_SERVER_ADDRESS). More...

static u32_t	dns_lookup (const char *name)
	Look up a hostname in the array of known hostnames. More...

static u16_t	dns_parse_name (struct pbuf *p, u16_t query_idx)
	Walk through a compact encoded DNS name and return the end of the name. More...

static void	dns_recv (void arg, struct udp_pcb pcb, struct pbuf p, ip_addr_t addr, u16_t port)
	Receive input function for DNS response packets arriving for the dns UDP pcb. More...

static err_t	dns_send (struct dns_table_entry *entry)
	Send a DNS query packet. More...

void	dns_setserver (u8_t numdns, ip_addr_t *dnsserver)
	Initialize one of the DNS servers. More...

static int	dns_stricmp (const char str1, const char str2)
	A small but sufficient implementation for case insensitive strcmp. More...

void	dns_tmr (void)
	The DNS resolver client timer - handle retries and timeouts and should be called every DNS_TMR_INTERVAL milliseconds (every second by default). More...

Variables
static u8_t	dns_last_pcb_idx

static struct udp_pcb *	dns_pcbs [DNS_MAX_SOURCE_PORTS]

static struct dns_req_entry	dns_requests [DNS_MAX_REQUESTS]

static u8_t	dns_seqno

static ip_addr_t	dns_servers [DNS_MAX_SERVERS]

static struct dns_table_entry	dns_table [DNS_TABLE_SIZE]

PACK_STRUCT_BEGIN struct dns_hdr	PACK_STRUCT_STRUCT

#define DNS_FLAG1_AUTHORATIVE 0x04

#define DNS_FLAG1_OPCODE_INVERSE 0x08

#define DNS_FLAG1_OPCODE_STANDARD 0x00

#define DNS_FLAG1_OPCODE_STATUS 0x10

#define DNS_FLAG1_RD 0x01

Referenced by dns_send().

#define DNS_FLAG1_RESPONSE 0x80

Referenced by dns_recv().

#define DNS_FLAG1_TRUNC 0x02

#define DNS_FLAG2_ERR_MASK 0x0f

Referenced by dns_recv().

#define DNS_FLAG2_ERR_NAME 0x03

#define DNS_FLAG2_ERR_NONE 0x00

#define DNS_FLAG2_RA 0x80

#define DNS_MAX_REQUESTS DNS_TABLE_SIZE

Referenced by dns_call_found(), and dns_enqueue().

#define DNS_MAX_RETRIES 4

DNS maximum number of retries when asking for a name, before "timeout".

Referenced by dns_check_entry().

#define DNS_MAX_SOURCE_PORTS DNS_MAX_REQUESTS

Referenced by dns_alloc_pcb(), dns_call_found(), and dns_enqueue().

#define DNS_MAX_TTL 604800

DNS resource record max.

TTL (one week as default)

Referenced by dns_recv().

#define DNS_PORT_ALLOWED ( port ) ((port) >= 1024)

Limits the source port to be >= 1024 by default.

Referenced by dns_alloc_random_port().

#define DNS_RAND_TXID LWIP_RAND

Random generator function to create random TXIDs and source ports for queries.

Referenced by dns_alloc_random_port(), and dns_create_txid().

#define DNS_SERVER_ADDRESS ( ipaddr ) (ip4_addr_set_u32(ipaddr, ipaddr_addr("208.67.222.222"))) /* resolver1.opendns.com */

DNS server IP address.

Referenced by dns_init().

#define DNS_SERVER_PORT 53

DNS server port address.

Referenced by dns_send().

#define DNS_STATE_ASKING 2

Referenced by dns_call_found(), dns_check_entry(), dns_create_txid(), dns_enqueue(), and dns_recv().

#define DNS_STATE_DONE 3

Referenced by dns_check_entry(), dns_enqueue(), dns_lookup(), and dns_recv().

#define DNS_STATE_NEW 1

Referenced by dns_check_entry(), and dns_enqueue().

#define DNS_STATE_UNUSED 0

Referenced by dns_check_entry(), dns_enqueue(), dns_init(), and dns_recv().

#define LWIP_DNS_SECURE (LWIP_DNS_SECURE_RAND_XID | LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING | LWIP_DNS_SECURE_RAND_SRC_PORT)

Use all DNS security features by default.

This is overridable but should only be needed by very small targets or when using against non standard DNS servers.

#define LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING 2

#define LWIP_DNS_SECURE_RAND_SRC_PORT 4

#define LWIP_DNS_SECURE_RAND_XID 1

This file implements a DNS host name to IP address resolver.

Port to lwIP from uIP by Jim Pettinato April 2007

security fixes and more by Simon Goldschmidt

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
The name of the author may not be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

DNS.C

The lwIP DNS resolver functions are used to lookup a host name and map it to a numerical IP address. It maintains a list of resolved hostnames that can be queried with the dns_lookup() function. New hostnames can be resolved using the dns_query() function.

The lwIP version of the resolver also adds a non-blocking version of gethostbyname() that will work with a raw API application. This function checks for an IP address string first and converts it if it is valid. gethostbyname() then does a dns_lookup() to see if the name is already in the table. If so, the IP is returned. If not, a query is issued and the function returns with a ERR_INPROGRESS status. The app using the dns client must then go into a waiting state.

Once a hostname has been resolved (or found to be non-existent), the resolver code calls a specified callback function (which must be implemented by the module that uses the resolver).

Todo:: : define good default values (rfc compliance)

Todo:: : improve answer parsing, more checkings...

Todo:: : check RFC1035 - 7.3. Processing responses

#define LWIP_DNS_STRICMP	(	str1,
		str2
	)	dns_stricmp(str1, str2)

Referenced by dns_enqueue(), and dns_lookup().

#define SIZEOF_DNS_ANSWER 10

Referenced by dns_recv().

#define SIZEOF_DNS_ANSWER_ASSERT 12

Referenced by dns_init().

#define SIZEOF_DNS_HDR 12

Referenced by dns_recv(), and dns_send().

#define SIZEOF_DNS_QUERY 4

Referenced by dns_init(), dns_recv(), and dns_send().

static u8_t dns_alloc_pcb ( void )

static

dns_alloc_pcb() - allocates a new pcb (or reuses an existing one) to be used for sending a request

Returns: an index into dns_pcbs

References dns_alloc_random_port(), dns_last_pcb_idx, DNS_MAX_SOURCE_PORTS, and NULL.

Referenced by dns_enqueue().

static struct udp_pcb* dns_alloc_random_port ( void )

static

References DNS_PORT_ALLOWED, DNS_RAND_TXID, dns_recv(), ERR_OK, ERR_USE, IP_ADDR_ANY, NULL, udp_bind(), udp_new(), udp_recv(), and udp_remove().

Referenced by dns_alloc_pcb().

static void dns_call_found	(	u8_t	idx,
		ip_addr_t *	addr
	)

static

dns_call_found() - call the found callback and check if there are duplicate entries for the given hostname.

If there are any, their found callback will be called and they will be removed.

Parameters

idx	dns table index of the entry that is resolved or removed
addr	IP address for the hostname (or NULL on error or memory shortage)

References arg, DNS_MAX_REQUESTS, DNS_MAX_SOURCE_PORTS, dns_requests, DNS_STATE_ASKING, dns_table, dns_req_entry::found, NULL, dns_table_entry::pcb_idx, and udp_remove().

Referenced by dns_check_entry(), and dns_recv().

static void dns_check_entries ( void )

static

Call dns_check_entry for each entry in dns_table - check all entries.

References dns_check_entry().

Referenced by dns_tmr().

static void dns_check_entry ( u8_t i )

static

dns_check_entry() - see if entry has not yet been queried and, if so, sends out a query.

Check an entry in the dns_table:

send out query for new entries
retry old pending entries on timeout (also with different servers)
remove completed entries from the table if their TTL has expired

Parameters

i	index of the dns_table entry to check

References dns_call_found(), dns_create_txid(), DNS_DEBUG, DNS_MAX_RETRIES, dns_send(), dns_servers, DNS_STATE_ASKING, DNS_STATE_DONE, DNS_STATE_NEW, DNS_STATE_UNUSED, dns_table, ERR_OK, ip_addr_isany, LWIP_ASSERT, LWIP_DBG_LEVEL_WARNING, LWIP_DEBUGF, lwip_strerr, dns_table_entry::name, NULL, dns_table_entry::retries, dns_table_entry::server_idx, dns_table_entry::state, dns_table_entry::tmr, dns_table_entry::ttl, and dns_table_entry::txid.

Referenced by dns_check_entries(), and dns_enqueue().

static u16_t dns_compare_name	(	char *	query,
		struct pbuf *	p,
		u16_t	start_offset
	)

static

Compare the "dotted" name "query" with the encoded name "response" to make sure an answer from the DNS server matches the current dns_table entry (otherwise, answers might arrive late for hostname not on the list any more).

Parameters

query	hostname (not encoded) from the dns_table
p	pbuf containing the encoded hostname in the DNS response
start_offset	offset into p where the name starts

Returns: 0xFFFF: names differ, other: names equal -> offset behind name

See Also: RFC 1035 - 4.1.4. Message compression

References pbuf_get_at().

Referenced by dns_recv().

static u16_t dns_create_txid ( void )

static

References DNS_RAND_TXID, DNS_STATE_ASKING, and dns_table.

Referenced by dns_check_entry().

static err_t dns_enqueue	(	const char *	name,
		size_t	hostnamelen,
		dns_found_callback	found,
		void *	callback_arg
	)

static

Queues a new hostname to resolve and sends out a DNS query for that hostname.

Parameters

name	the hostname that is to be queried
hostnamelen	length of the hostname
found	a callback function to be called on success, failure or timeout
callback_arg	argument to pass to the callback function

Returns: a err_t return code.

References dns_req_entry::arg, dns_alloc_pcb(), dns_check_entry(), DNS_DEBUG, DNS_MAX_REQUESTS, DNS_MAX_SOURCE_PORTS, dns_requests, dns_seqno, DNS_STATE_ASKING, DNS_STATE_DONE, DNS_STATE_NEW, DNS_STATE_UNUSED, dns_table, dns_req_entry::dns_table_idx, ERR_INPROGRESS, ERR_MEM, dns_req_entry::found, LWIP_DEBUGF, LWIP_DNS_STRICMP, LWIP_MIN, dns_table_entry::name, NULL, dns_table_entry::pcb_idx, dns_table_entry::seqno, dns_table_entry::state, and U16_F.

Referenced by dns_gethostbyname().

err_t dns_gethostbyname	(	const char *	hostname,
		ip_addr_t *	addr,
		dns_found_callback	found,
		void *	callback_arg
	)

Resolve a hostname (string) into an IP address.

NON-BLOCKING callback version for use with raw API!!!

Returns immediately with one of err_t return codes:

ERR_OK if hostname is a valid IP address string or the host name is already in the local names table.
ERR_INPROGRESS enqueue a request to be sent to the DNS server for resolution if no errors are present.
ERR_ARG: dns client not initialized or invalid hostname

Parameters

hostname	the hostname that is to be queried
addr	pointer to a ip_addr_t where to store the address if it is already cached in the dns_table (only valid if ERR_OK is returned!)
found	a callback function to be called on success, failure or timeout (only if ERR_INPROGRESS is returned!)
callback_arg	argument to pass to the callback function

Returns: a err_t return code.

References DNS_DEBUG, dns_enqueue(), dns_lookup(), ERR_ARG, ERR_OK, ip4_addr_set_u32, ip_addr_set_loopback, ipaddr_addr(), IPADDR_NONE, LWIP_DEBUGF, and NULL.

Referenced by lwip_netconn_do_gethostbyname(), and wifi_cb().

ip_addr_t* dns_getserver ( u8_t numdns )

Obtain one of the currently configured DNS server.

Parameters

numdns the index of the DNS server

Returns: IP address of the indexed DNS server or "ip_addr_any" if the DNS server has not been configured.

References dns_servers, and IP_ADDR_ANY.

void dns_init ( void )

Initialize the resolver: set up the UDP pcb and configure the default server (DNS_SERVER_ADDRESS).

References DNS_DEBUG, dns_recv(), DNS_SERVER_ADDRESS, dns_setserver(), DNS_STATE_UNUSED, IP_ADDR_ANY, LWIP_ASSERT, LWIP_DEBUGF, NULL, SIZEOF_DNS_ANSWER_ASSERT, SIZEOF_DNS_QUERY, udp_bind(), udp_new(), and udp_recv().

Referenced by lwip_init().

static u32_t dns_lookup ( const char * name )

static

Look up a hostname in the array of known hostnames.

Note: This function only looks in the internal array of known hostnames, it does not send out a query for the hostname if none was found. The function dns_enqueue() can be used to send a query for a hostname.

Parameters

name	the hostname to look up

Returns: the hostname's IP address, as u32_t (instead of ip_addr_t to better check for failure: != IPADDR_NONE) or IPADDR_NONE if the hostname was not found in the cached dns_table.

References DNS_DEBUG, DNS_STATE_DONE, dns_table, ip4_addr_get_u32, ip_addr_debug_print, IPADDR_NONE, LWIP_DEBUGF, and LWIP_DNS_STRICMP.

Referenced by dns_gethostbyname().