# C SDK使用说明
#### 操作场景
使用C语言调用APP认证的API时，您需要先获取SDK，参考API调用示例调用API。
#### 前提条件
- 已获取API的调用信息，具体请参见[开发准备](https://support.huaweicloud.com/devg-roma/apic-dev-190216004.html)。
- 安装openssl库。
  ```
  apt-get install libssl-dev
  ```
  
- 安装curl库。
  ```
  apt-get install libcurl4-openssl-dev
  ```
  
 
#### 获取SDK
**旧版界面**：登录ROMA Connect实例控制台，在"服务集成 APIC \> API调用"的"SDK"页签中下载SDK。
**新版界面**：登录ROMA Connect实例控制台，在"服务集成 APIC \> 凭据管理"的"SDKs"页签中下载SDK。
解压后目录结构如下：
| 名称              | 说明         |
|:---|:---|
| signer_common.c | SDK代码      |
| signer_common.h | SDK代码      |
| signer.c        | SDK代码      |
| signer.h        | SDK代码      |
| Makefile        | Makefile文件 |
| main.c          | 示例代码       |
   
#### 调用API示例
1. 在main.c中加入以下引用。
   ```
   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>
   #include <curl/curl.h>
   #include "signer.h"
   ```
   
2. 生成一个sig_params_t类型的变量，输入API所授权凭据的Key和Secret，可参考[获取API的调用信息](https://support.huaweicloud.com/devg-roma/apic-dev-190216004.html#apic-dev-190216004__section17143919101020)获取。
   ```
   sig_params_t params;
   sig_params_init(&params);
   // Directly writing AK/SK in code is risky. For security, encrypt your AK/SK and store them in the configuration file or environment variables. 
   // In this example, the AK/SK are stored in environment variables for identity authentication. Before running this example, set environment variables HUAWEICLOUD_SDK_AK and HUAWEICLOUD_SDK_SK. 
   sig_str_t app_key = sig_str(getenv("HUAWEICLOUD_SDK_AK"));
   sig_str_t app_secret = sig_str(getenv("HUAWEICLOUD_SDK_SK"));
   params.key = app_key;
   params.secret = app_secret;
   ```
   
3. 指定方法名、域名、请求uri、查询字符串和body，可参考[获取API的调用信息](https://support.huaweicloud.com/devg-roma/apic-dev-190216004.html#apic-dev-190216004__section17143919101020)获取。
   ```
   sig_str_t host = sig_str("c967a237-cd6c-470e-906f-a8655461897e.apigw.exampleRegion.com");
   sig_str_t method = sig_str("GET");
   sig_str_t uri = sig_str("/app1");
   sig_str_t query_str = sig_str("a=1&b=2");
   sig_str_t payload = sig_str("");
   params.host = host;
   params.method = method;
   params.uri = uri;
   params.query_str = query_str;
   params.payload = payload;
   ```
   
4. 给请求添加x-stage头，内容为环境名。如果有需要，添加需要签名的其他头域。
   ```
   sig_headers_add(&params.headers, "x-stage", "RELEASE");
   ```
   
5. 进行签名，执行此函数会将生成的签名头加入request变量中。
   ```
   sig_sign(&params);
   ```
   
6. 使用curl库访问API，查看访问结果。
   ```
   static size_t
   WriteMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp)
   {
       size_t realsize = size * nmemb;
       struct MemoryStruct *mem = (struct MemoryStruct *)userp;
       mem->memory = (char*)realloc(mem->memory, mem->size + realsize + 1);
       if (mem->memory == NULL) {
           /* out of memory! */
           printf("not enough memory (realloc returned NULL)\n");
           return 0;
       }
       memcpy(&(mem->memory[mem->size]), contents, realsize);
       mem->size += realsize;
       mem->memory[mem->size] = 0;
       return realsize;
   }
   //send http request using curl library
   int perform_request(RequestParams* request)
   {
       CURL *curl;
       CURLcode res;
       struct MemoryStruct resp_header;
       resp_header.memory = malloc(1);
       resp_header.size = 0;
       struct MemoryStruct resp_body;
       resp_body.memory = malloc(1);
       resp_body.size = 0;
       curl_global_init(CURL_GLOBAL_ALL);
       curl = curl_easy_init();
       curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, params.method.data);
       char url[1024];
       sig_snprintf(url, 1024, "http://%V%V?%V", &params.host, &params.uri, &params.query_str);
       curl_easy_setopt(curl, CURLOPT_URL, url);
       struct curl_slist *chunk = NULL;
       for (int i = 0; i < params.headers.len; i++) {
           char header[1024];
           sig_snprintf(header, 1024, "%V: %V", &params.headers.data[i].name, &params.headers.data[i].value);
           printf("%s\n", header);
           chunk = curl_slist_append(chunk, header);
       }
       printf("-------------\n");
       curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);
       curl_easy_setopt(curl, CURLOPT_POSTFIELDS, params.payload.data);
       curl_easy_setopt(curl, CURLOPT_NOBODY, 0L);
       curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
       curl_easy_setopt(curl, CURLOPT_HEADERDATA, (void *)&resp_header);
       curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&resp_body);
       //curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
       res = curl_easy_perform(curl);
       if (res != CURLE_OK) {
           fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
       }
       else {
           long status;
           curl_easy_getinfo(curl, CURLINFO_HTTP_CODE, &status);
           printf("status %d\n", status);
           printf(resp_header.memory);
           printf(resp_body.memory);
       }
       free(resp_header.memory);
       free(resp_body.memory);
       curl_easy_cleanup(curl);
       curl_global_cleanup();
       //free signature params
       sig_params_free(&params);
       return 0;
   }
   ```
   
7. 运行make命令编译，得到可执行文件main，执行main文件，查看结果。