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
a7c0195ebf297f29ab0065da16d7e84f14911de177e6e0c8dbadf3464d12b75f
CertUtil: -hashfile command executed.

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	a7c0195ebf297f29ab0065da16d7e84f14911de177e6e0c8dbadf3464d12b75f
Go	caf22350181a4ecd49dc0d3f56097b10c1794792adae407140950be4ed9b6771
Python	c80b9ef282fc88d3fb16db4cb9d7525d3db71f7989782ed0b636920ea2fadb93
C#	b0e69ef60a561c54c1b86c3447ca855088a1fa2a672fbfba618aaf56b2841e8a
JavaScript	c64e595651de079766e446ce2c3262013256f81683bb9434bee27bed3a4caf01
PHP	e2eba2cae72aea794edb4057ed8eb7cb82f0dbaccabf9c5539694a7a7a9f3c89
C++	c173f59d816aba53f47750cf5ffdc65cc345b1613974b3d2a545ace48787f577
C	e4f22beb7b132fe6e57c9de79f596c3ff830228cd7221b02ca96198e501c642c
Android	d6c3032801ac88cf8cbc51f64d42457174447c8d159f34a187c036913b31ea2b

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);
sig_str_t app_key = sig_str("4f5f626b-073f-402f-a1e0-e52171c6100c");
sig_str_t app_secret = sig_str("******");
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;
}