(Objective-C) Download File (Stream to Local Filesystem)

This example demonstrates how to download the content of a file from Google Drive. The file is streamed to the local filesystem.

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#import <CkoAuthGoogle.h>
#import <CkoRest.h>
#import <CkoCache.h>
#import <NSString.h>
#import <CkoStringBuilder.h>
#import <CkoStream.h>

BOOL success = YES;

// It 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 
// Google Drive scope.

CkoAuthGoogle *gAuth = [[CkoAuthGoogle alloc] init];
gAuth.AccessToken = @"GOOGLE_DRIVE_ACCESS_TOKEN";

CkoRest *rest = [[CkoRest alloc] init];

// Connect using TLS.
// A single REST object, once connected, can be used for many Google Drive REST API calls.
// The auto-reconnect indicates that if the already-established HTTPS connection is closed,
// then it will be automatically re-established as needed.
BOOL bAutoReconnect = YES;
success = [rest Connect: @"www.googleapis.com" port: [NSNumber numberWithInt: 443] tls: YES autoReconnect: bAutoReconnect];

// Provide the authentication credentials (i.e. the access token)
[rest SetAuthGoogle: gAuth];

// ------------------------------------------------------------------------------
// To download a file, we must know the file ID.
// In a previous example (see Build Local Metadata Cache
// we built a local cache to make it easy to lookup file IDs given a file path.
// Let's say we want to download "testFolder/abc/123/penguins.jpg".
// First we lookup the fileId in the cache.  With the fileId, we can download the file.
CkoCache *gdCache = [[CkoCache alloc] init];
gdCache.Level = [NSNumber numberWithInt:0];
[gdCache AddRoot: @"C:/ckCache/googleDrive"];

NSString *fileId = [gdCache FetchText: @"testFolder/abc/123/penguins.jpg"];
if (gdCache.LastMethodSuccess != YES) {
    NSLog(@"%@",@"Filepath not found in cache.");
    return;
}

// We need to send a GET request like this:
// GET https://www.googleapis.com/drive/v3/files/fileId?alt=media
// The fileId is part of the path.
CkoStringBuilder *sbPath = [[CkoStringBuilder alloc] init];
[sbPath Append: @"/drive/v3/files/"];
[sbPath Append: fileId];
[rest AddQueryParam: @"alt" value: @"media"];

// Create a stream object with a SinkFile set to the path where the downloaded file will go.
CkoStream *fileStream = [[CkoStream alloc] init];
fileStream.SinkFile = @"qa_output/penguins.jpg";
// Indicate that the response body should stream directly to fileStream,
// but only if the response status is 200.  
[rest SetResponseBodyStream: [NSNumber numberWithInt: 200] autoSetStreamCharset: YES responseStream: fileStream];

// Download the file, streaming the content to the SinkFile.
NSString *jsonResponse = [rest FullRequestNoBody: @"GET" uriPath: [sbPath GetAsString]];
if (rest.LastMethodSuccess != YES) {
    NSLog(@"%@",rest.LastErrorText);
    return;
}

// A successful response will have a status code equal to 200.
if ([rest.ResponseStatusCode intValue] != 200) {
    NSLog(@"%@%d",@"response status code = ",[rest.ResponseStatusCode intValue]);
    NSLog(@"%@%@",@"response status text = ",rest.ResponseStatusText);
    NSLog(@"%@%@",@"response header: ",rest.ResponseHeader);
    return;
}

NSLog(@"%@",@"File downloaded.");