HTTPDNS:Integrate HTTPDNS SDK for C

Step 1: Prepare the environment

The integration of the SDK depends on necessary build tools and third-party libraries. Before you integrate the SDK, install the dependencies on your build machine.

1. Install a build tool

During the build process, you must clone code from GitHub, use CMake to build projects, and use GCC or G++ to compile code. Make sure that the following CLIs are installed on your computer. If not, run the provided commands to install them:

• Ubuntu or Debian

  sudo  apt update
  sudo  apt install -y git cmake gcc g++

• Alibaba Cloud, CentOS Stream, or Fedora

  sudo yum check-update
  sudo yum install -y git cmake  gcc  gcc-c++

• OpenSUSE

  sudo zypper refresh
  sudo zypper install -y git cmake  gcc  gcc-c++

• macOS

  export HOMEBREW_NO_AUTO_UPDATE=1
  brew install git gcc cmake

  Note

  brew is a package manager. It is not built in macOS. You must install brew before you install a package.

  /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

• Windows

  • Download and install Git

  • Download and install Visual Studio. For the workload, select Desktop development with C++.

2. Install a dependency library

The SDK uses libcurl 7.33.0 and later for network operations, apr or apr-util 1.5.2 and later to resolve memory management and cross-platform issues, and cJSON to parse server-side response messages. The SDK does not include these external libraries. Make sure that the libraries are installed, and add their header and library file directories to your project. In this example, the project supports VCPKG-based installation and manual installation of the C or C++ libraries.

2.1 Installation using VCPKG

• Install VCPKG.

• Install the dependency libraries of the SDK.

  • macOS or Linux

     ./vcpkg install apr apr-util curl[openssl,http2] cjson

  • Windows

    .\vcpkg.exe install apr apr-util curl[openssl,http2] cjson

    Note

    By default, VCPKG installs libraries that correspond to the current platform. To perform cross-platform compilation, such as compiling an x86 library in a Windows x64 environment, you must specify a triplet. The following command is an example:

    ./vcpkg.exe install apr:x86-windows apr-util:x86-windows curl[openssl,http2]:x86-windows cjson:x86-windows

2.2 Manual installation

• Ubuntu or Debian

  sudo  apt update
  sudo apt install -y libcurl4-openssl-dev libapr1-dev libaprutil1-dev libcjson-dev

• Alibaba Cloud, CentOS Stream, or Fedora

  sudo yum check-update
  sudo yum install -y libcurl-devel apr-devel apr-util-devel cjson-devel

• OpenSUSE

  sudo zypper refresh
  sudo zypper install -y libcurl-devel libapr1-devel libapr-util1-devel cJSON-devel

• macOS

  brew install curl apr apr-util cjson

• Windows

  • Download and install cJSON

  • download and install OpenSSL

  • Download curl

  • install curl

  • download and install apr or apr-util

git clone https://github.com/DaveGamble/cJSON.git && cd cJSON && mkdir build && cd build && cmake  ../ && sudo make install && cd ../../ && rm -rf cJSON

Step 2: Install the SDK

• Linux or macOS

  git clone https://github.com/aliyun/alibabacloud-httpdns-c-sdk.git
  cd alibabacloud-httpdns-c-sdk
  mkdir build
  cd build
  # If the dependency library is installed using VCPKG, add the Cmake parameter: -DVCPKG_ROOT=${Installation directory of VCPKG}
  cmake -DCMAKE_BUILD_TYPE=Release ../ 
  make hdns_unite_test
  sudo make install
  sudo ldconfig

• Windows

  • Download the CMake project.

  • Open the CMake project in Visual Studio.

  • Add the Cmake parameter in the management configuration: -DVCPKG_ROOT=${Installation directory of VCPKG}

Step 3: Integrate the SDK

For more information about how to integrate the SDK, see Integration example. The following sections describe how to integrate the SDK.

3.1. Import the SDK

To integrate the SDK, you must import the locally installed libraries and header files. For example, add the following commands to the CMakeLists.txt file of a CMake project:

find_library(HTTPDNS_LIBRARY httpdns_c_sdk_static)
include_directories(${CMAKE_INSTALL_PREFIX}/include/httpdns)

3.2 Initialize the SDK

Initialize the SDK runtime environment.

 if (hdns_sdk_init() != HDNS_OK) {
        hdns_sdk_cleanup();
  }
   
  // Use the API of the SDK.
  
  

3.3 Create a client

 hdns_client_t *client = hdns_client_create(HTTPDNS_ACCOUNT, HTTPDNS_SECRET);
 if (client == NULL) {
    hdns_sdk_cleanup();
  }
 // Use HTTPDNS Client.

3.4 Configure the client

After a client is created, you can configure the following settings to customize the HTTPDNS client:

// The request timeout period. Unit: milliseconds.
hdns_client_set_timeout(client, 2000);
// Specify whether to enable local caching.
hdns_client_set_using_cache(client, true);
// Specify whether to use HTTPS to access the HTTPDNS server.
hdns_client_set_using_https(client, true);
// Specify whether to sign a request.
hdns_client_set_using_sign(client,  true);
// The number of request retries.
hdns_client_set_retry_times(client, 1);
// The HTTPDNS service cluster.
hdns_client_set_region(client, "global");
// The HTTPDNS scheduling cluster.
hdns_client_set_schedule_center_region(client, "cn");
// Specify whether to update the local cache after a network change.
hdns_client_enable_update_cache_after_net_change(client, true);
// Specify whether to allow HTTPDNS to obtain the expired data from the cache.
hdns_client_enable_expired_ip(client, true);
// Specify whether to automatically use local Domain Name System (DNS) servers.
hdns_client_enable_failover_localdns(client, true);
// The domain name that you want to pre-resolve.
hdns_client_add_pre_resolve_host(client, "www.aliyun.com");
// Add IP sniffing.
hdns_client_add_ip_probe_item(client, "www.aliyun.com", 443);
// The custom time to live (TTL).
hdns_client_add_custom_ttl_item(client, "www.aliyun.com", 120);

3.5 Start the client

   hdns_client_start(client);

3.6 Resolve a domain name

After you start the client, you can call the API operations provided by the SDK to resolve domain names. The SDK provides multiple operations for different scenarios. The following code provides an example on resolving a single domain name by calling a synchronous operation.

    hdns_list_head_t *results = NULL;
    hdns_status_t status = hdns_get_result_for_host_sync_with_cache(client,
                                                                    MOCK_BUSINESS_HOST,
                                                                    HDNS_QUERY_AUTO,
                                                                    NULL, &results);

3.7 Select an IP address

After you obtain the resolution result of the domain name, you can access the workloads of your customer using the IP address to which the domain name is resolved.

 if (hdns_status_is_ok(&status)) {
        char ip[HDNS_IP_ADDRESS_STRING_LENGTH];
        if (hdns_select_ip_randomly(results, HDNS_QUERY_AUTO, ip) == HDNS_OK) {
            mock_access_business_web_server(ip);
        }
  }
  if (hdns_status_is_ok(&status)) {
        char ip[HDNS_IP_ADDRESS_STRING_LENGTH];
        if (hdns_select_ip_randomly(results, HDNS_QUERY_AUTO, ip) == HDNS_OK) {
            mock_access_business_web_server(ip);
        }
  }
  hdns_list_free(results);

3.8 Access the workloads

static void mock_access_business_web_server(const char *dst_ip) {
    CURL *curl;
    CURLcode res;
    curl = curl_easy_init();
    if (curl) {
        // Concatenate the request URL.
        char url[256];
        strcpy(url, "https://");
        strcat(url, MOCK_BUSINESS_HOST);
        curl_easy_setopt(curl, CURLOPT_URL, url);
        curl_easy_setopt(curl, CURLOPT_TIMEOUT, 30);

        // Specify the pre-resolved host and IP address for HTTPS requests.
        struct curl_slist *dns;
        char sni[256];
        strcpy(sni, MOCK_BUSINESS_HOST);
        strcat(sni, ":443:");
        strcat(sni, dst_ip);
        dns = curl_slist_append(NULL, sni);
        curl_easy_setopt(curl, CURLOPT_RESOLVE, dns);
        // The callback.
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data_callback);
#if defined(_WIN32)
        curl_easy_setopt(curl, CURLOPT_SSL_OPTIONS, CURLSSLOPT_NATIVE_CA);
#endif
        // Initiate an HTTP request.
        res = curl_easy_perform(curl);
        if (res != CURLE_OK) {
            fprintf(stderr, "curl_easy_perform() failed, url=%s, ip=%s, error=%s\n",
                    url,
                    dst_ip,
                    curl_easy_strerror(res));
        }
        // Release the resources related to workload access.
        curl_slist_free_all(dns);
        /* always cleanup */
        curl_easy_cleanup(curl);
    }
}

3.9 Client Cleanup

If the client is no longer required, you must release it.

hdns_client_cleanup(client);

3.10 Release SDK resources

If the SDK resources are no longer required, you must release them.

hdns_sdk_cleanup();