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
becff4310645f3734344897ffdcabb1853d4b7d93b59a6ea187c5ae40543b36b
CertUtil: -hashfile command executed.
becff4310645f3734344897ffdcabb1853d4b7d93b59a6ea187c5ae40543b36b

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.

Language	SHA-256 Value of the SDK Package
Java	becff4310645f3734344897ffdcabb1853d4b7d93b59a6ea187c5ae40543b36b
Go	bcf8cf19a21226e247195f2e584c8414da39b8d05840fb02948e1375d9bbb7e6
Python	c3da3b5814f828d6217963e856563d558d938b3da28993a8a13c8a7ebff5b95d
C#	a880b47e63ab35bfe216592e340a8135b866aef8f756ef7738fff3287885f33a
JavaScript	53261387f5fcf46e61d0bef5e890bea97952717f327c356412c3128389e848d6
PHP	29bf711144e77a4adaea1257cd6dedd2220e57b729a8fd000c51e68ccb42ad4b
C++	f604c6386c62cccb7c358007778037d5b15480987dc2860eef1b7bad37cb21d7
C	7086012c2d0569d5938830926b19fbea0d46682a983e04e52924978e8720c2f8
Android	89962b186707828b06b0c9f50c010b2f4cefd6a8e7ca9bdefb616bbbf6e739c8

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;
}