Add initial implementation of DNS Client (#1460)

* [DNS] Initial DNS Client implementation.

include/openthread/Makefile.am

@@ -55,6 +55,7 @@ openthread_headers                      = \
     diag.h                                \
     dhcp6_client.h                        \
     dhcp6_server.h                        \
+    dns.h                                 \
     icmp6.h                               \
     instance.h                            \
     ip6.h                                 \

include/openthread/dns.h

@@ -0,0 +1,114 @@
+/*
+ *  Copyright (c) 2017, The OpenThread Authors.
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions are met:
+ *  1. Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *  2. 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.
+ *  3. Neither the name of the copyright holder nor the
+ *     names of its contributors may be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT HOLDER OR CONTRIBUTORS 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.
+ */
+
+/**
+ * @file
+ * @brief
+ *  This file defines the top-level dns functions for the OpenThread library.
+ */
+
+#ifndef OPENTHREAD_DNS_H_
+#define OPENTHREAD_DNS_H_
+
+#include <openthread/types.h>
+#include <openthread/message.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @addtogroup dns  DNS
+ *
+ * @brief
+ *   This module includes functions that control DNS communication.
+ *
+ * @{
+ *
+ */
+
+#define OT_DNS_MAX_HOSTNAME_LENGTH 62  ///< Maximum allowed hostname length (maximum label size - 1 for compression).
+
+#define OT_DNS_DEFAULT_DNS_SERVER_IP  "2001:4860:4860::8888" ///< Defines default DNS Server address - Google DNS.
+#define OT_DNS_DEFAULT_DNS_SERVER_PORT 53                    ///< Defines default DNS Server port.
+
+/**
+ * This structure implements DNS Query parameters.
+ *
+ */
+typedef struct otDnsQuery
+{
+    const char          *mHostname;     ///< Identifies hostname to be found. It shall not change during resolving.
+    const otMessageInfo *mMessageInfo;  ///< A reference to the message info related with DNS Server.
+    bool                 mNoRecursion;  ///< If cleared, it directs name server to pursue the query recursively.
+} otDnsQuery;
+
+/**
+ * This function pointer is called when a DNS response is received.
+ *
+ * @param[in]  aContext   A pointer to application-specific context.
+ * @param[in]  aHostname  Identifies hostname related with DNS response.
+ * @param[in]  aAddress   A pointer to the IPv6 address received in DNS response. May be null.
+ * @param[in]  aTtl       Specifies the maximum time in seconds that the resource record may be cached.
+ * @param[in]  aResult    A result of the DNS transaction.
+ *
+ * @retval  kThreadError_None             A response was received successfully and IPv6 address is provided
+ *                                        in @p aAddress.
+ * @retval  kThreadError_Abort            A DNS transaction was aborted by stack.
+ * @retval  kThreadError_ResponseTimeout  No DNS response has been received within timeout.
+ * @retval  kThreadError_NotFound         A response was received but no IPv6 address has been found.
+ * @retval  kThreadError_Failed           A response was received but status code is different than success.
+ *
+ */
+typedef void (*otDnsResponseHandler)(void *aContext, const char *aHostname, otIp6Address *aAddress,
+                                     uint32_t aTtl, ThreadError aResult);
+
+#if OPENTHREAD_ENABLE_DNS_CLIENT
+/**
+ * This function sends a DNS query for AAAA (IPv6) record.
+ *
+ * @param[in]  aInstance   A pointer to an OpenThread instance.
+ * @param[in]  aQuery      A pointer to specify DNS query parameters.
+ * @param[in]  aHandler    A function pointer that shall be called on response reception or time-out.
+ * @param[in]  aContext    A pointer to arbitrary context information.
+ *
+ */
+ThreadError otDnsClientQuery(otInstance *aInstance, const otDnsQuery *aQuery, otDnsResponseHandler aHandler,
+                             void *aContext);
+#endif
+
+/**
+ * @}
+ *
+ */
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // OPENTHREAD_DNS_H_

include/openthread/types.h

@@ -185,7 +185,7 @@ typedef enum ThreadError
     kThreadError_NotCapable = 29,
 
     /**
-     * Coap response or acknowledgment not received.
+     * Coap response or acknowledgment or DNS response not received.
      */
     kThreadError_ResponseTimeout = 30,