Adds possibility to specify DNS in network request (#1423)

In some cases on Android C-Ares can't determine DNS
and the only way to make it work is to specify DNS
mannually.

Relates-To: IOTSDK-18883

Signed-off-by: Yauheni Khnykin <[email protected]>

Author: Hsilgos

olp-cpp-sdk-core/include/olp/core/http/NetworkSettings.h

@@ -22,6 +22,7 @@
 #include <chrono>
 #include <cstdint>
 #include <string>
+#include <vector>
 
 #include <olp/core/CoreApi.h>
 #include <olp/core/http/NetworkProxySettings.h>
@@ -160,6 +161,26 @@ class CORE_API NetworkSettings final {
    */
   NetworkSettings& WithProxySettings(NetworkProxySettings settings);
 
+  /**
+   * @brief Gets the DNS list.
+   *
+   * @return The DNS list.
+   */
+  const std::vector<std::string>& GetDNSServers() const;
+
+  /**
+   * @brief Sets the DNS servers to use. Works only with CURL implementation.
+   * The order is important.To reduce response time make sure that most probably
+   * servers are at the beginning.
+   *
+   * Note: This list replaces any other mechanism to retrieve DNS list.
+   *
+   * @param[in] dns_servers The DNS list.
+   *
+   * @return A reference to *this.
+   */
+  NetworkSettings& WithDNSServers(std::vector<std::string> dns_servers);
+
  private:
   /// The maximum number of retries for the HTTP request.
   std::size_t retries_{3};
@@ -171,6 +192,8 @@ class CORE_API NetworkSettings final {
   std::chrono::seconds connection_lifetime_{0};
   /// The network proxy settings.
   NetworkProxySettings proxy_settings_;
+  /// The additional DNS servers
+  std::vector<std::string> dns_servers_;
 };
 
 }  // namespace http

olp-cpp-sdk-core/src/http/NetworkSettings.cpp

@@ -53,6 +53,10 @@ const NetworkProxySettings& NetworkSettings::GetProxySettings() const {
   return proxy_settings_;
 }
 
+const std::vector<std::string>& NetworkSettings::GetDNSServers() const {
+  return dns_servers_;
+}
+
 NetworkSettings& NetworkSettings::WithRetries(std::size_t retries) {
   retries_ = retries;
   return *this;
@@ -90,5 +94,11 @@ NetworkSettings& NetworkSettings::WithProxySettings(
   return *this;
 }
 
+NetworkSettings& NetworkSettings::WithDNSServers(
+    std::vector<std::string> dns_servers) {
+  dns_servers_ = std::move(dns_servers);
+  return *this;
+}
+
 }  // namespace http
 }  // namespace olp

olp-cpp-sdk-core/src/http/curl/NetworkCurl.cpp

@@ -256,6 +256,19 @@ int64_t GetElapsedTime(std::chrono::steady_clock::time_point start) {
              std::chrono::steady_clock::now() - start)
       .count();
 }
+
+std::string ConcatenateDnsAddresses(
+    const std::vector<std::string>& dns_servers) {
+  std::string result;
+
+  const char* delimiter = "";
+  for (const auto& dns_server : dns_servers) {
+    result.append(delimiter).append(dns_server);
+    delimiter = ",";
+  }
+
+  return result;
+}
 }  // anonymous namespace
 
 NetworkCurl::NetworkCurl(NetworkInitializationSettings settings)
@@ -599,6 +612,16 @@ ErrorCode NetworkCurl::SendImplementation(
     }
   }
 
+#if CURL_AT_LEAST_VERSION(7, 24, 0)
+  const auto& dns_servers = config.GetDNSServers();
+  if (!dns_servers.empty()) {
+    const std::string& dns_list = dns_servers.size() == 1
+                                      ? dns_servers.front()
+                                      : ConcatenateDnsAddresses(dns_servers);
+    curl_easy_setopt(handle->handle, CURLOPT_DNS_SERVERS, dns_list.c_str());
+  }
+#endif
+
   if (handle->chunk) {
     curl_easy_setopt(handle->handle, CURLOPT_HTTPHEADER, handle->chunk);
   }

olp-cpp-sdk-core/tests/http/NetworkSettingsTest.cpp

@@ -77,6 +77,12 @@ TEST(NetworkSettingsTest, WithMaxConnectionLifetime) {
   EXPECT_EQ(settings.GetMaxConnectionLifetime(), std::chrono::seconds(15));
 }
 
+TEST(NetworkSettingsTest, WithDNSServers) {
+  const std::vector<std::string> expected = {"1.1.1.1", "1.1.1.2"};
+  const auto settings = olp::http::NetworkSettings().WithDNSServers(expected);
+  EXPECT_EQ(settings.GetDNSServers(), expected);
+}
+
 }  // namespace
 
 PORTING_POP_WARNINGS()