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

Functions
static void	dns_recv (void arg, struct udp_pcb pcb, struct pbuf p, const 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.
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.
void	dns_init (void)
	Initialize the resolver: set up the UDP pcb and configure the default server (if DNS_SERVER_ADDRESS is set).
void	dns_setserver (u8_t numdns, const ip_addr_t dnsserver, struct netif netif)
	Initialize one of the DNS servers.
const ip_addr_t *	dns_getserver (u8_t numdns, const char *interface_name)
	Obtain one of the currently configured DNS server.
void	dns_add_interface_server (u8_t numdns, const char interface_name, const ip_addr_t dnsserver)
	Initialize one of the DNS servers.
const ip_addr_t *	dns_get_interface_server (u8_t numdns, const char *interface_name)
	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).
size_t	dns_local_iterate (dns_found_callback iterator_fn, void *iterator_arg)
	Iterate the local host-list for a hostname.
err_t	dns_local_lookup (const char hostname, ip_addr_t addr, u8_t dns_addrtype)
	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 address.
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 err_t	dns_lookup (const char name, ip_addr_t addr LWIP_DNS_ADDRTYPE_ARG(u8_t dns_addrtype))
	Look up a hostname in the array of known hostnames.
static u16_t	dns_compare_name (const 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).
static u16_t	dns_skip_name (struct pbuf *p, u16_t query_idx)
	Walk through a compact encoded DNS name and return the end of the name.
static err_t	dns_send (u8_t idx)
	Send a DNS query packet.
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
static u8_t	dns_backupserver_available (struct dns_table_entry *pentry)
	Check whether there are other backup DNS servers available to try.
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.
static void	dns_correct_response (u8_t idx, u32_t ttl)
	Save TTL and call dns_call_found for correct response.
static err_t	dns_enqueue (const char name, size_t hostnamelen, dns_found_callback found, void callback_arg LWIP_DNS_ADDRTYPE_ARG(u8_t dns_addrtype) LWIP_DNS_ISMDNS_ARG(u8_t is_mdns))
	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.
err_t	dns_gethostbyname_addrtype (const char hostname, ip_addr_t addr, dns_found_callback found, void *callback_arg, u8_t dns_addrtype)
	Like dns_gethostbyname, but returned address type can be controlled:
Variables
static struct local_hostlist_entry *	local_hostlist_dynamic
	Local host-list.

Detailed Description

DNS - host name to IP address resolver.

Definition in file lwip_dns.c.

Function Documentation

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

Definition at line 1017 of file lwip_dns.c.

static u8_t dns_backupserver_available ( struct dns_table_entry * pentry ) [static]

Check whether there are other backup DNS servers available to try.

Definition at line 1141 of file lwip_dns.c.

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)

Definition at line 1059 of file lwip_dns.c.

static void dns_check_entries ( void ) [static]

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

Definition at line 1241 of file lwip_dns.c.

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

Definition at line 1164 of file lwip_dns.c.

static u16_t dns_compare_name	(	const 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).

For now, this function compares case-insensitive to cope with all kinds of servers. This also means that "dns 0x20 bit encoding" must be checked externally, if we want to implement it. Currently, the request is sent exactly as passed in by he user request.

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

Definition at line 768 of file lwip_dns.c.

static void dns_correct_response	(	u8_t	idx,
		u32_t	ttl
	)		`[static]`

Save TTL and call dns_call_found for correct response.

Definition at line 1254 of file lwip_dns.c.

static err_t dns_enqueue	(	const char *	name,
		size_t	hostnamelen,
		dns_found_callback	found,
		void *callback_arg	LWIP_DNS_ADDRTYPE_ARGu8_t dns_addrtype) LWIP_DNS_ISMDNS_ARG(u8_t is_mdns
	)		`[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:: err_t return code.

Definition at line 1492 of file lwip_dns.c.

void dns_init ( void )

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

Definition at line 319 of file lwip_dns.c.

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

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

Definition at line 1287 of file lwip_dns.c.

static err_t dns_send ( u8_t idx ) [static]

Send a DNS query packet.

Parameters:

idx	the DNS table entry index for which to send a request

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

Definition at line 865 of file lwip_dns.c.

static u16_t dns_skip_name	(	struct pbuf *	p,
		u16_t	query_idx
	)		`[static]`

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

Parameters:

p	pbuf containing the name
query_idx	start index into p pointing to encoded DNS name in the DNS server response

Returns:: index to end of the name

See also:: RFC 1035 - 4.1.4. Message compression

Definition at line 825 of file lwip_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 508 of file lwip_dns.c.

Variable Documentation

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 261 of file lwip_dns.c.

Type:	Library
Created:	17 Dec 2019
Imports:	79
Forks:	0
Commits:	2
Dependents:	2
Dependencies:	0
Followers:	1

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