(Objective-C) Get Object MetaData from Google Cloud Storage

Demonstrates how to download a Google Cloud Storage object's metadata.

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#import <CkoStringBuilder.h>
#import <CkoHttp.h>
#import <NSString.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]?projection=full"

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

http.AuthToken = [sbToken GetAsString];

// Construct a URL to download the metadata for the object named "starfish.jpg" located in 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}?projection=full";

// If there is an error response, then we didn't actually download the metadata,
// but instead we downloaded an error response..
CkoStringBuilder *sbMetaData = [[CkoStringBuilder alloc] init];
BOOL success = [http DownloadSb: url charset: @"utf-8" sb: sbMetaData];
if (success == NO) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

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) {
    NSLog(@"%@%d",@"Error response code = ",responseCode);
    NSLog(@"%@",@"Error:");
    NSLog(@"%@",[sbMetaData GetAsString]);
    return;
}

NSLog(@"%@",[sbMetaData GetAsString]);
NSLog(@"%@",@"Success.");

// Sample output:

// {
//  "kind": "storage#object",
//  "id": "chilkat-ocean/starfish.jpg/1502670320090292",
//  "selfLink": "https://www.googleapis.com/storage/v1/b/chilkat-ocean/o/starfish.jpg",
//  "name": "starfish.jpg",
//  "bucket": "chilkat-ocean",
//  "generation": "1502670320090292",
//  "metageneration": "1",
//  "contentType": "image/jpeg",
//  "timeCreated": "2017-08-14T00:25:20.040Z",
//  "updated": "2017-08-14T00:25:20.040Z",
//  "storageClass": "MULTI_REGIONAL",
//  "timeStorageClassUpdated": "2017-08-14T00:25:20.040Z",
//  "size": "6229",
//  "md5Hash": "LpxZ2/JmI2fcl9/dqF2gSA==",
//  "mediaLink": "https://www.googleapis.com/download/storage/v1/b/chilkat-ocean/o/starfish.jpg?generation=1502670320090292&alt=media",
//  "acl": [
//   {
//    "kind": "storage#objectAccessControl",
//    "id": "chilkat-ocean/starfish.jpg/1502670320090292/project-owners-933037264567",
//    "selfLink": "https://www.googleapis.com/storage/v1/b/chilkat-ocean/o/starfish.jpg/acl/project-owners-933037264567",
//    "bucket": "chilkat-ocean",
//    "object": "starfish.jpg",
//    "generation": "1502670320090292",
//    "entity": "project-owners-933037264567",
//    "role": "OWNER",
//    "projectTeam": {
//     "projectNumber": "933037264567",
//     "team": "owners"
//    },
//    "etag": "CLT5kpW71dUCEAE="
//   },
//   {
//    "kind": "storage#objectAccessControl",
//    "id": "chilkat-ocean/starfish.jpg/1502670320090292/project-editors-933037264567",
//    "selfLink": "https://www.googleapis.com/storage/v1/b/chilkat-ocean/o/starfish.jpg/acl/project-editors-933037264567",
//    "bucket": "chilkat-ocean",
//    "object": "starfish.jpg",
//    "generation": "1502670320090292",
//    "entity": "project-editors-933037264567",
//    "role": "OWNER",
//    "projectTeam": {
//     "projectNumber": "933037264567",
//     "team": "editors"
//    },
//    "etag": "CLT5kpW71dUCEAE="
//   },
//   {
//    "kind": "storage#objectAccessControl",
//    "id": "chilkat-ocean/starfish.jpg/1502670320090292/project-viewers-933037264567",
//    "selfLink": "https://www.googleapis.com/storage/v1/b/chilkat-ocean/o/starfish.jpg/acl/project-viewers-933037264567",
//    "bucket": "chilkat-ocean",
//    "object": "starfish.jpg",
//    "generation": "1502670320090292",
//    "entity": "project-viewers-933037264567",
//    "role": "READER",
//    "projectTeam": {
//     "projectNumber": "933037264567",
//     "team": "viewers"
//    },
//    "etag": "CLT5kpW71dUCEAE="
//   },
//   {
//    "kind": "storage#objectAccessControl",
//    "id": "chilkat-ocean/starfish.jpg/1502670320090292/user-starfish@chilkat-176611.iam.gserviceaccount.com",
//    "selfLink": "https://www.googleapis.com/storage/v1/b/chilkat-ocean/o/starfish.jpg/acl/user-starfish@chilkat-176611.iam.gserviceaccount.com",
//    "bucket": "chilkat-ocean",
//    "object": "starfish.jpg",
//    "generation": "1502670320090292",
//    "entity": "user-starfish@chilkat-176611.iam.gserviceaccount.com",
//    "role": "OWNER",
//    "email": "starfish@chilkat-176611.iam.gserviceaccount.com",
//    "etag": "CLT5kpW71dUCEAE="
//   }
//  ],
//  "owner": {
//   "entity": "user-starfish@chilkat-176611.iam.gserviceaccount.com"
//  },
//  "crc32c": "9RjgwQ==",
//  "etag": "CLT5kpW71dUCEAE="
// }
//