C

Scenarios

To use C to call an API through App authentication, obtain the C SDK, and then call the API by referring to the API calling example.

Preparing the Environment

You have obtained the domain name, request URL, and request method of the API to be called, and the AppKey and AppSecret of the App for calling the API. For more information, see Preparation.
Install the OpenSSL library.
```
apt-get install libssl-dev
```
Install the curl library.
```
apt-get install libcurl4-openssl-dev
```

Obtaining the SDK

Log in to the DataArts Studio console.
Click DataArts DataService.
In the navigation pane, choose DataArts DataService Exclusive > SDKs.
On the SDKs page, download the SDK package.

Verify integrity of the SDK package. In Windows, open the CLI and run the following command to generate the SHA-256 value of the downloaded SDK package. In the command, D:\java-sdk.zip is an example local path and name of the SDK package. Replace it with the actual value.

certutil -hashfile D:\java-sdk.zip SHA256

The following is an example command output:

SHA-256 hash value of D:\java-sdk.zip
3a86f1ba249a00727db506e4075ec9630e6cf74f312bddf6c3901c9d0786f53e
CertUtil: -hashfile command executed.
3a86f1ba249a00727db506e4075ec9630e6cf74f312bddf6c3901c9d0786f53e

Compare the SHA-256 value of the downloaded SDK package with that provided in the following table. If they are the same, no tampering or packet loss occurred during the package download.

**Table 1** SDK packages and the corresponding SHA-256 values
Language	SHA-256 Value of the SDK Package
Java	3a86f1ba249a00727db506e4075ec9630e6cf74f312bddf6c3901c9d0786f53e
Go	23734867eae2e7ef61427c64aa33aa89512571946f2f43a1a5fef5e801e3129f
Python	57636d8bacc459cab9dc08c70d01ccc42391ace60e6960c4e947566da1dc5d26
C#	e5a3b677f75c28ba3f1e16645d8171f7b6f34a42143f8a32a68bb18719b5e65d
JavaScript	442ac2fcb41d84525dc0139ec3f05d190e4e337cdbcdfdfc82a09d79d2ecd25e
PHP	2cc76bd2ecd48f00899d18b0f76d05ce2623065180f111c3f70ac14ddf0506f3
C++	2a54c3f2486d562ea6af1384eca40b301918bdc02f98bbf2c114f282dc059c00
C	4957556c108e0174d55b4b8d720f296967a9367ca54010792b1b3de039b87363
Android	0fdcc6fd93a68dce5c3e1b8e6370cc9340429cabfb0f268c3f9e5ea05238ae96

Obtain the ApiGateway-c-sdk.zip package. The following table shows the files decompressed from the package.

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

API Calling Example

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 AppKey and AppSecret.

sig_params_t params;
sig_params_init(&params);

// Coded or plaintext AK and SK pose significant security risks. To ensure security, encrypt your AK and SK, store them in configuration files or environment variables, and decrypt them when needed.
// In this example, the AK and SK stored in the environment variables are used for identity authentication. Before running this example, configure environment variables SDK_AK and SDK_SK in the local environment.
char* ak = getenv("SDK_AK");
char* sk = getenv("SDK_SK");

sig_str_t app_key = sig_str(ak);
sig_str_t app_secret = sig_str(sk);
params.key = app_key;
params.secret = app_secret;

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

sig_str_t host = sig_str("{apig-endpoint}");
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;

Add a header to the request. The header contains specific parameters. Add other headers to be signed as necessary.
```
sig_headers_add(&params.headers, "x-stage", "RELEASE");
sig_headers_add(&params.headers, "name","value");
```
Execute the following function to add the generated headers to the request variable. Then, add the x-Authorization header to the request. The value of the x-Authorization header is the same as that of the Authorization header.
```
sig_sign(&params);
char* authorization = sig_headers_get(&params.headers, "Authorization")->value.data;
sig_headers_add(&params.headers, "x-Authorization", authorization);
```

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;
}