Updated on 2026-02-09 GMT+08:00

C Signing Guide

Preparing the Environment

This section uses Linux Ubuntu as an example. Before calling APIs, install the required SSL tools.

Install the OpenSSL library.
1

apt-get install libssl-dev
Install the curl library.
1

apt-get install libcurl4-openssl-dev

Obtaining the SDK

Decompress the downloaded package to the current folder. The following table shows the directory structure.

Name	Description
signer_common.c	SDK code
signer_common.h
signer.c
signer.h
Makefile	Makefile file
main.c	Sample code

Request Signing and API Calling

After the calling information is modified, the sample code can be directly called. For details about the calling information, see Preparations.

Add the following references to main.c:

     #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <curl/curl.h>
#include "signer.h"
 
 
  

Generate a sig_params_t variable, and enter the AK and SK.

In this example, the AK and SK stored in the environment variables are used. Specify the environment variables CLOUD_SDK_AK and CLOUD_SDK_SK in the local environment first. The following uses Linux as an example to describe how to set the obtained AK/SK as environment variables.
1. Open the terminal and run the following command to open the environment variable configuration file:
  vi ~/.bashrc
2. Set environment variables, save the file, and exit the editor.
```
export CLOUD_SDK_AK="Obtained AK"
export CLOUD_SDK_SK="Obtained SK"
```
3. Run the following command to apply the modification:
  source ~/.bashrc

Generate a sig_params_t variable, and enter the configured environment variables.

     sig_params_t params;
sig_params_init(&params);
sig_str_t ak = sig_str(getenv("CLOUD_SDK_AK"));
sig_str_t sk = sig_str(getenv("CLOUD_SDK_SK"));
params.key = ak;
params.secret = sk;
 
 
  

Specify the method, domain name, request URI, query strings, and request body.

     sig_str_t host = sig_str("service.region.example.com");
sig_str_t method = sig_str("GET");
sig_str_t uri = sig_str("/v1/{project_id}/vpcs");
sig_str_t query_str = sig_str("limit=2");
sig_str_t payload = sig_str("");
params.host = host;
params.method = method;
params.uri = uri;
params.query_str = query_str;
params.payload = payload;
 
 
  

Add header parameters or other headers required for other purposes. For example, add the X-Project-Id header in multi-project scenarios or the X-Domain-Id header for a global service.

     //Add header parameters, for example, X-Domain-Id for invoking a global service and X-Project-Id for invoking a project-level service.
sig_headers_add(&params.headers, "X-Project-Id", "xxx");

Execute the following function to add the generated headers as request variables.
1

sig_sign(&params);

Use the curl library to access the API and view the access result.

     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;
}
 
 
  

Run the make command to obtain a main executable file, execute the file, and then view the execution result.

C Signing Guide

Preparing the Environment

Obtaining the SDK

Request Signing and API Calling

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