DNS - host name to IP address resolver. More...

Functions
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.
static void	dns_check_entries (void)
	Call dns_check_entry for each entry in dns_table - check all entries.
void	dns_init ()
	Initialize the resolver: set up the UDP pcb and configure the default server (DNS_SERVER_ADDRESS).
void	dns_setserver (u8_t numdns, ip_addr_t *dnsserver)
	Initialize one of the DNS servers.
ip_addr_t	dns_getserver (u8_t numdns)
	Obtain one of the currently configured DNS server.
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).
static u32_t	dns_lookup_local (const char *hostname)
	Scans the local host-list for a hostname.
int	dns_local_removehost (const char hostname, const ip_addr_t addr)
	Remove all entries from the local host-list for a specific hostname and/or IP addess.
err_t	dns_local_addhost (const char hostname, const ip_addr_t addr)
	Add a hostname/IP address pair to the local host-list.
static u32_t	dns_lookup (const char *name)
	Look up a hostname in the array of known hostnames.
static u8_t	dns_compare_name (unsigned char query, unsigned char response)
	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).
static unsigned char *	dns_parse_name (unsigned char *query)
	Walk through a compact encoded DNS name and return the end of the name.
static err_t	dns_send (u8_t numdns, const char *name, u8_t id)
	Send a DNS query packet.
static void	dns_check_entry (u8_t i)
	dns_check_entry() - see if pEntry has not yet been queried and, if so, sends out a query.
static err_t	dns_enqueue (const char name, dns_found_callback found, void callback_arg)
	Queues a new hostname to resolve and sends out a DNS query for that hostname.
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.
Variables
static struct local_hostlist_entry *	local_hostlist_dynamic
	Local host-list.
static u8_t	dns_payload_buffer [LWIP_MEM_ALIGN_BUFFER(DNS_MSG_SIZE)]
	Contiguous buffer for processing responses.

Detailed Description

DNS - host name to IP address resolver.

Definition in file dns.c.

Function Documentation

static void dns_check_entries ( void ) [static]

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

Definition at line 718 of file dns.c.

static void dns_check_entry ( u8_t i ) [static]

dns_check_entry() - see if pEntry 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

Definition at line 636 of file dns.c.

static u8_t dns_compare_name	(	unsigned char *	query,
		unsigned char *	response
	)		`[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
response	encoded hostname in the DNS response

Returns:: 0: names equal; 1: names differ

See also:: RFC 1035 - 4.1.4. Message compression

Definition at line 493 of file dns.c.

static err_t dns_enqueue	(	const char *	name,
		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
found	a callback founction to be called on success, failure or timeout
callback_arg	argument to pass to the callback function

Returns:: a err_t return code.

Definition at line 860 of file dns.c.

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.

Definition at line 936 of file dns.c.

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.

Definition at line 289 of file dns.c.

void dns_init ( void )

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

Definition at line 232 of file dns.c.

err_t dns_local_addhost	(	const char *	hostname,
		const ip_addr_t *	addr
	)

Add a hostname/IP address pair to the local host-list.

Duplicates are not checked.

Parameters:

hostname	hostname of the new entry
addr	IP address of the new entry

Returns:: ERR_OK if succeeded or ERR_MEM on memory error

Definition at line 414 of file dns.c.

int dns_local_removehost	(	const char *	hostname,
		const ip_addr_t *	addr
	)

Remove all entries from the local host-list for a specific hostname and/or IP addess.

Parameters:

hostname	hostname for which entries shall be removed from the local host-list
addr	address for which entries shall be removed from the local host-list

Returns:: the number of removed entries

Definition at line 379 of file dns.c.

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.

Definition at line 450 of file dns.c.

static u32_t dns_lookup_local ( const char * hostname ) [static]

Scans the local host-list for a hostname.

Parameters:

hostname Hostname to look for in the local host-list

Returns:: The first IP address for the hostname in the local host-list or IPADDR_NONE if not found.

Definition at line 348 of file dns.c.

static unsigned char* dns_parse_name ( unsigned char * query ) [static]

Walk through a compact encoded DNS name and return the end of the name.

Parameters:

query encoded DNS name in the DNS server response

Returns:: end of the name

See also:: RFC 1035 - 4.1.4. Message compression

Definition at line 528 of file dns.c.

static void dns_recv	(	void *	arg,
		struct udp_pcb *	pcb,
		struct pbuf *	p,
		ip_addr_t *	addr,
		u16_t	port
	)		`[static]`

Receive input function for DNS response packets arriving for the dns UDP pcb.

see udp.h

Definition at line 733 of file dns.c.

static err_t dns_send	(	u8_t	numdns,
		const char *	name,
		u8_t	id
	)		`[static]`

Send a DNS query packet.

Parameters:

numdns	index of the DNS server in the dns_servers table
name	hostname to query
id	index of the hostname in dns_table, used as transaction ID in the DNS query packet

Returns:: ERR_OK if packet is sent; an err_t indicating the problem otherwise

Definition at line 560 of file dns.c.

void dns_setserver	(	u8_t	numdns,
		ip_addr_t *	dnsserver
	)

Initialize one of the DNS servers.

Parameters:

numdns	the index of the DNS server to set must be < DNS_MAX_SERVERS
dnsserver	IP address of the DNS server to set

Definition at line 273 of file dns.c.

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).

Definition at line 303 of file dns.c.

Variable Documentation

u8_t dns_payload_buffer[LWIP_MEM_ALIGN_BUFFER(DNS_MSG_SIZE)] [static]

Contiguous buffer for processing responses.

Definition at line 224 of file dns.c.

struct local_hostlist_entry* local_hostlist_dynamic [static]

Local host-list.

For hostnames in this list, no external name resolution is performed

Definition at line 188 of file dns.c.

Type:	Library
Created:	15 Sep 2014
Imports:	0
Forks:	1
Commits:	30
Dependents:	1
Dependencies:	0
Followers:	6

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