(Objective-C) Refresh Access Token on 401 Unauthorized and Retry (Service Account)

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Demonstrates how to handle an expired access token error, refresh the token, and retry the request. (In this case, the request is to download an object from Google Cloud Storage.)

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#import <CkoStringBuilder.h>
#import <CkoHttp.h>
#import <NSString.h>
#import <CkoBinData.h>
#import <CkoFileAccess.h>
#import <CkoAuthGoogle.h>
#import <CkoSocket.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];
BOOL success = [sbToken LoadFile: @"qa_data/tokens/googleCloudStorageAccessToken.txt" charset: @"utf-8"];
if (success == NO) {
    NSLog(@"%@",@"Failed to load access token.");
    return;
}

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];
success = [http DownloadBd: url binData: fileData];
int responseCode = [http.LastStatus intValue];
if ((success == NO) && (responseCode != 401)) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

if (responseCode == 401) {
    NSLog(@"%@",@"Received 401 Unauthorized response. Attempting to refresh the access token...");

    // May be that the access token expired.
    // Load our JSON key and request a new access token, then retry the original request.
    CkoFileAccess *fac = [[CkoFileAccess alloc] init];
    NSString *jsonKey = [fac ReadEntireTextFile: @"qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json" charset: @"utf-8"];
    if (fac.LastMethodSuccess != YES) {
        NSLog(@"%@",fac.LastErrorText);
        return;
    }

    CkoAuthGoogle *gAuth = [[CkoAuthGoogle alloc] init];
    gAuth.JsonKey = jsonKey;
    gAuth.Scope = @"https://www.googleapis.com/auth/cloud-platform";
    gAuth.ExpireNumSeconds = [NSNumber numberWithInt:3600];
    gAuth.SubEmailAddress = @"";

    CkoSocket *tlsSock = [[CkoSocket alloc] init];
    success = [tlsSock Connect: @"www.googleapis.com" port: [NSNumber numberWithInt: 443] ssl: YES maxWaitMs: [NSNumber numberWithInt: 5000]];
    if (success != YES) {
        NSLog(@"%@",tlsSock.LastErrorText);
        return;
    }

    success = [gAuth ObtainAccessToken: tlsSock];
    if (success != YES) {
        NSLog(@"%@",gAuth.LastErrorText);
        return;
    }

    [fac WriteEntireTextFile: @"qa_data/tokens/googleCloudStorageAccessToken.txt" fileData: gAuth.AccessToken charset: @"utf-8" includePreamble: NO];

    // Retry the original request.
    http.AuthToken = gAuth.AccessToken;
    success = [http DownloadBd: url binData: fileData];
    if (success == NO) {
        NSLog(@"%@",http.LastErrorText);
        return;
    }

}

if (responseCode != 200) {
    // Get the error response
    CkoStringBuilder *sbErrorResponse = [[CkoStringBuilder alloc] init];
    [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"];