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sys: net: introduce simple sock DNS client

pr/rotary
Kaspar Schleiser 6 years ago
parent
commit
7af03ab624
  1. 4
      Makefile.dep
  2. 3
      sys/Makefile
  3. 98
      sys/include/net/sock/dns.h
  4. 2
      sys/net/application_layer/dns/Makefile
  5. 192
      sys/net/application_layer/dns/dns.c

4
Makefile.dep

@ -611,6 +611,10 @@ ifneq (,$(filter vfs,$(USEMODULE)))
endif
endif
ifneq (,$(filter sock_dns,$(USEMODULE)))
USEMODULE += sock_util
endif
# include package dependencies
-include $(USEPKG:%=$(RIOTPKG)/%/Makefile.dep)

3
sys/Makefile

@ -114,6 +114,9 @@ endif
ifneq (,$(filter sock_util,$(USEMODULE)))
DIRS += net/sock
endif
ifneq (,$(filter sock_dns,$(USEMODULE)))
DIRS += net/application_layer/dns
endif
ifneq (,$(filter constfs,$(USEMODULE)))
DIRS += fs/constfs

98
sys/include/net/sock/dns.h

@ -0,0 +1,98 @@
/*
* Copyright (C) 2017 Kaspar Schleiser <kaspar@schleiser.de>
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @defgroup net_sock_dns DNS sock API
* @ingroup net_sock
*
* @brief Sock DNS client
*
* @{
*
* @file
* @brief DNS sock definitions
*
* @author Kaspar Schleiser <kaspar@schleiser.de>
*/
#ifndef SOCK_DNS_H
#define SOCK_DNS_H
#include <errno.h>
#include <stdint.h>
#include <unistd.h>
#include "net/sock/udp.h"
#ifdef __cplusplus
extern "C" {
#endif
/**
* @brief DNS internal structure
*/
typedef struct {
uint16_t id; /**< read */
uint16_t flags; /**< DNS */
uint16_t qdcount; /**< RFC */
uint16_t ancount; /**< for */
uint16_t nscount; /**< detailed */
uint16_t arcount; /**< explanations */
uint8_t payload[]; /**< !! */
} sock_dns_hdr_t;
/**
* @name DNS defines
* @{
*/
#define DNS_TYPE_A (1)
#define DNS_TYPE_AAAA (28)
#define DNS_CLASS_IN (1)
#define SOCK_DNS_PORT (53)
#define SOCK_DNS_RETRIES (2)
#define SOCK_DNS_MAX_NAME_LEN (64U) /* we're in embedded context. */
#define SOCK_DNS_QUERYBUF_LEN (sizeof(sock_dns_hdr_t) + 4 + SOCK_DNS_MAX_NAME_LEN)
/** @} */
/**
* @brief Get IP address for DNS name
*
* This function will synchronously try to resolve a DNS A or AAAA record by contacting
* the DNS server specified in the global variable @ref sock_dns_server.
*
* By supplying AF_INET, AF_INET6 or AF_UNSPEC in @p family requesting of A
* records (IPv4), AAAA records (IPv6) or both can be selected.
*
* This fuction will return the first DNS record it receives. IF both A and
* AAAA are requested, AAAA will be preferred.
*
* @note @p addr_out needs to provide space for any possible result!
* (4byte when family==AF_INET, 16byte otherwise)
*
* @param[in] domain_name DNS name to resolve into address
* @param[out] addr_out buffer to write result into
* @param[in] family Either AF_INET, AF_INET6 or AF_UNSPEC
*
* @return 0 on success
* @return !=0 otherwise
*/
int sock_dns_query(const char *domain_name, void *addr_out, int family);
/**
* @brief global DNS server endpoint
*/
extern sock_udp_ep_t sock_dns_server;
#ifdef __cplusplus
}
#endif
#endif /* SOCK_DNS_H */
/** @} */

2
sys/net/application_layer/dns/Makefile

@ -0,0 +1,2 @@
MODULE=sock_dns
include $(RIOTBASE)/Makefile.base

192
sys/net/application_layer/dns/dns.c

@ -0,0 +1,192 @@
/*
* Copyright (C) 2017 Kaspar Schleiser <kaspar@schleiser.de>
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @ingroup net_sock_dns
* @{
* @file
* @brief sock DNS client implementation
* @author Kaspar Schleiser <kaspar@schleiser.de>
* @}
*/
#include <string.h>
#include <stdio.h>
#include "net/sock/udp.h"
#include "net/sock/dns.h"
#ifdef RIOT_VERSION
#include "byteorder.h"
#define ntohs NTOHS
#define htons HTONS
#endif
/* min domain name length is 1, so minimum record length is 7 */
#define DNS_MIN_REPLY_LEN (unsigned)(sizeof(sock_dns_hdr_t ) + 7)
static ssize_t _enc_domain_name(uint8_t *out, const char *domain_name)
{
/*
* DNS encodes domain names with "<len><part><len><part>", e.g.,
* "example.org" ends up as "\7example\3org" in the packet.
*/
uint8_t *part_start = out;
uint8_t *out_pos = ++out;
char c;
while ((c = *domain_name)) {
if (c == '.') {
/* replace dot with length of name part as byte */
*part_start = (out_pos - part_start - 1);
part_start = out_pos++;
}
else {
*out_pos++ = c;
}
domain_name++;
}
*part_start = (out_pos - part_start - 1);
*out_pos++ = 0;
return out_pos - out + 1;
}
static unsigned _put_short(uint8_t *out, uint16_t val)
{
memcpy(out, &val, 2);
return 2;
}
static unsigned _get_short(uint8_t *buf)
{
uint16_t _tmp;
memcpy(&_tmp, buf, 2);
return _tmp;
}
static size_t _skip_hostname(uint8_t *buf)
{
uint8_t *bufpos = buf;
/* handle DNS Message Compression */
if (*bufpos >= 192) {
return 2;
}
while(*bufpos) {
bufpos += *bufpos + 1;
}
return (bufpos - buf + 1);
}
static int _parse_dns_reply(uint8_t *buf, size_t len, void* addr_out, int family)
{
sock_dns_hdr_t *hdr = (sock_dns_hdr_t*) buf;
uint8_t *bufpos = buf + sizeof(*hdr);
/* skip all queries that are part of the reply */
for (unsigned n = 0; n < ntohs(hdr->qdcount); n++) {
bufpos += _skip_hostname(bufpos);
bufpos += 4; /* skip type and class of query */
}
for (unsigned n = 0; n < ntohs(hdr->ancount); n++) {
bufpos += _skip_hostname(bufpos);
uint16_t _type = ntohs(_get_short(bufpos));
bufpos += 2;
uint16_t class = ntohs(_get_short(bufpos));
bufpos += 2;
bufpos += 4; /* skip ttl */
unsigned addrlen = ntohs(_get_short(bufpos));
bufpos += 2;
if ((bufpos + addrlen) > (buf + len)) {
return -EBADMSG;
}
/* skip unwanted answers */
if ((class != DNS_CLASS_IN) ||
((_type == DNS_TYPE_A) && (family == AF_INET6)) ||
((_type == DNS_TYPE_AAAA) && (family == AF_INET)) ||
! ((_type == DNS_TYPE_A) || ((_type == DNS_TYPE_AAAA))
)) {
bufpos += addrlen;
continue;
}
memcpy(addr_out, bufpos, addrlen);
return addrlen;
}
return -1;
}
int sock_dns_query(const char *domain_name, void *addr_out, int family)
{
uint8_t buf[SOCK_DNS_QUERYBUF_LEN];
uint8_t reply_buf[512];
if (strlen(domain_name) > SOCK_DNS_MAX_NAME_LEN) {
return -ENOSPC;
}
sock_dns_hdr_t *hdr = (sock_dns_hdr_t*) buf;
memset(hdr, 0, sizeof(*hdr));
hdr->id = 0; /* random? */
hdr->flags = htons(0x0120);
hdr->qdcount = htons(1 + (family == AF_UNSPEC));
uint8_t *bufpos = buf + sizeof(*hdr);
unsigned _name_ptr;
if ((family == AF_INET6) || (family == AF_UNSPEC)) {
_name_ptr = (bufpos - buf);
bufpos += _enc_domain_name(bufpos, domain_name);
bufpos += _put_short(bufpos, htons(DNS_TYPE_AAAA));
bufpos += _put_short(bufpos, htons(DNS_CLASS_IN));
}
if ((family == AF_INET) || (family == AF_UNSPEC)) {
if (family == AF_UNSPEC) {
bufpos += _put_short(bufpos, htons((0xc000) | (_name_ptr)));
}
else {
bufpos += _enc_domain_name(bufpos, domain_name);
}
bufpos += _put_short(bufpos, htons(DNS_TYPE_A));
bufpos += _put_short(bufpos, htons(DNS_CLASS_IN));
}
sock_udp_t sock_dns;
ssize_t res = sock_udp_create(&sock_dns, NULL, &sock_dns_server, 0);
if (res) {
puts("a");
goto out;
}
for (int i = 0; i < SOCK_DNS_RETRIES; i++) {
res = sock_udp_send(&sock_dns, buf, (bufpos-buf), NULL);
if (res <= 0) {
continue;
}
res = sock_udp_recv(&sock_dns, reply_buf, sizeof(reply_buf), 1000000LU, NULL);
if ((res > 0) && (res > (int)DNS_MIN_REPLY_LEN)) {
if ((res = _parse_dns_reply(reply_buf, res, addr_out, family)) > 0) {
goto out;
}
}
}
out:
sock_udp_close(&sock_dns);
return res;
}
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