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.

Prerequisites

You have obtained API calling information. For details, 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 APIG console, and download the SDK on the SDKs page by referring to section "SDKs" in the API Gateway User Guide.

Then obtain the ApiGateway-cpp-sdk.zip package. The following table shows the files decompressed from the package.

Name	Description
hasher.cpp	SDK code
hasher.h
header.h
RequestParams.cpp
RequestParams.h
signer.cpp
signer.h
Makefile	Makefile file
main.cpp	Sample code

API Calling Example

Add the following references to main.cpp:

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

Generate a new signer and enter the AppKey and AppSecret.
```
Signer signer("4f5f****100c", "******");
```

Generate a new RequestParams request, and specify the method, domain name, request URI, query strings, and request body.

 RequestParams* request = new RequestParams("POST", "c967a237-cd6c-470e-906f-a8655461897e.apigw.exampleRegion.com", "/app1",
        "Action=ListUsers&Version=2010-05-08", "demo");

Add the x-stage header to the request to specify an environment name. Add other headers to be signed as necessary.
```
request->addHeader("x-stage", "RELEASE");
```
Execute the following function to add the generated headers to the request variable.
```
signer.createSignature(request);
```

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 = (char*)malloc(1);
    resp_header.size = 0;
    struct MemoryStruct resp_body;
    resp_body.memory = (char*)malloc(1);
    resp_body.size = 0;

    curl_global_init(CURL_GLOBAL_ALL);
    curl = curl_easy_init();

    curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, request->getMethod().c_str());
    std::string url = "http://" + request->getHost() + request->getUri() + "?" + request->getQueryParams();
    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    struct curl_slist *chunk = NULL;
    std::set<Header>::iterator it;
    for (auto header : *request->getHeaders()) {
        std::string headerEntry = header.getKey() + ": " + header.getValue();
        printf("%s\n", headerEntry.c_str());
        chunk = curl_slist_append(chunk, headerEntry.c_str());
    }
    printf("-------------\n");
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);
    curl_easy_setopt(curl, CURLOPT_COPYPOSTFIELDS, request->getPayload().c_str());
    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();

    return 0;
}