sys: net: introduce simple sock DNS client

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)
 

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

sys/include/net/sock/dns.h

+/*
+ * 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 */
+/** @} */

sys/net/application_layer/dns/Makefile

+MODULE=sock_dns
+include $(RIOTBASE)/Makefile.base

sys/net/application_layer/dns/dns.c

+/*
+ * 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;
+}