(Objective-C) Download Object from Google Cloud Storage

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

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#import <CkoStringBuilder.h>
#import <CkoHttp.h>
#import <NSString.h>
#import <CkoBinData.h>

// 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..
CkoStringBuilder *sbToken = [[CkoStringBuilder alloc] init];
[sbToken LoadFile: @"qa_data/tokens/googleCloudStorageAccessToken.txt" charset: @"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"

CkoHttp *http = [[CkoHttp alloc] init];

http.AuthToken = [sbToken GetAsString];

// Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
[http SetUrlVar: @"bucket_name" value: @"chilkat-ocean"];
[http SetUrlVar: @"object_name" value: @"starfish.jpg"];
NSString *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..
CkoBinData *fileData = [[CkoBinData alloc] init];
BOOL success = [http DownloadBd: url binData: fileData];
if (success == NO) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

CkoStringBuilder *sbErrorResponse = [[CkoStringBuilder alloc] init];
int responseCode = [http.LastStatus intValue];
if (responseCode == 401) {
    NSLog(@"%@",@"If invalid credentials, then it is likely the access token expired.");
    NSLog(@"%@",@"Your app should automatically fetch a new access token and re-try.");
}

if (responseCode != 200) {
    // Get the error response
    [sbErrorResponse AppendBd: fileData charset: @"utf-8" offset: [NSNumber numberWithInt: 0] numBytes: [NSNumber numberWithInt: 0]];
    NSLog(@"%@%d",@"Error response code = ",responseCode);
    NSLog(@"%@",@"Error:");
    NSLog(@"%@",[sbErrorResponse GetAsString]);
    return;
}

NSLog(@"%@",@"Success.");

// Save the downloaded data to a file.
success = [fileData WriteFile: @"qa_output/starfish.jpg"];