(C++) Download Object from Google Cloud Storage

Demonstrates how to download an object from Google Cloud Storage to a file.

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#include <CkStringBuilder.h>
#include <CkHttp.h>
#include <CkBinData.h>

void ChilkatSample(void)
    {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // This example uses a previously obtained access token having permission for the 
    // scope "https://www.googleapis.com/auth/cloud-platform"

    // In this example, Get Google Cloud Storage OAuth2 Access Token, 
    // the service account access token was saved to a text file.  This example fetches the access token from the file..
    CkStringBuilder sbToken;
    sbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8");

    // Send a GET equivalent to this curl command.

    // curl -X GET \
    //     -H "Authorization: Bearer [OAUTH2_TOKEN]" \
    //     -o "[SAVE_TO_LOCATION]" \
    //     "https://www.googleapis.com/storage/v1/b/[BUCKET_NAME]/o/[OBJECT_NAME]?alt=media"

    CkHttp http;

    http.put_AuthToken(sbToken.getAsString());

    // Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
    http.SetUrlVar("bucket_name","chilkat-ocean");
    http.SetUrlVar("object_name","starfish.jpg");
    const char *url = "https://www.googleapis.com/storage/v1/b/{$bucket_name}/o/{$object_name}?alt=media";

    // If there is an error response, then we didn't actually download the file data,
    // but instead we downloaded an error response..
    CkBinData fileData;
    bool success = http.DownloadBd(url,fileData);
    if (success == false) {
        std::cout << http.lastErrorText() << "\r\n";
        return;
    }

    CkStringBuilder sbErrorResponse;
    int responseCode = http.get_LastStatus();
    if (responseCode == 401) {
        std::cout << "If invalid credentials, then it is likely the access token expired." << "\r\n";
        std::cout << "Your app should automatically fetch a new access token and re-try." << "\r\n";
    }

    if (responseCode != 200) {
        // Get the error response
        sbErrorResponse.AppendBd(fileData,"utf-8",0,0);
        std::cout << "Error response code = " << responseCode << "\r\n";
        std::cout << "Error:" << "\r\n";
        std::cout << sbErrorResponse.getAsString() << "\r\n";
        return;
    }

    std::cout << "Success." << "\r\n";

    // Save the downloaded data to a file.
    success = fileData.WriteFile("qa_output/starfish.jpg");
    }