(Objective-C) S3 Resume Download

Suppose an S3 download of a very large file failed for some reason and you have a partial file on disk. Rather than restart the entire download, you wish to download the remaining portion. This example demonstrates how to finish a previously failed download.

Note: This example requires Chilkat v9.5.0.83 or above.

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#import <CkoRest.h>
#import <CkoAuthAws.h>
#import <CkoFileAccess.h>
#import <NSString.h>
#import <CkoStringBuilder.h>
#import <CkoStream.h>

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

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

// Connect to the Amazon AWS REST server.
BOOL bTls = YES;
int port = 443;
BOOL bAutoReconnect = YES;
BOOL success = [rest Connect: @"s3.amazonaws.com" port: [NSNumber numberWithInt: port] tls: bTls autoReconnect: bAutoReconnect];

// ---------------------------------------------------------------------------
// Important: For buckets created in regions outside us-east-1,
// there are three important changes that need to be made.
// See Working with S3 Buckets in Non-us-east-1 Regions for the details.
// ---------------------------------------------------------------------------

// Provide AWS credentials for the REST call.
CkoAuthAws *authAws = [[CkoAuthAws alloc] init];
authAws.AccessKey = @"AWS_ACCESS_KEY";
authAws.SecretKey = @"AWS_SECRET_KEY";
authAws.ServiceName = @"s3";
success = [rest SetAuthAws: authAws];

// Set the bucket name via the HOST header.
// In this case, the bucket name is "chilkat100".
rest.Host = @"chilkat100.s3.amazonaws.com";

// We want to continue downloading a file.
// The relative local filepath of our previously partially downoaded file is: qa_output/hamlet.xml
// Let's find out how many bytes are already downloaded.
CkoFileAccess *fac = [[CkoFileAccess alloc] init];
NSString *localFilepath = @"qa_output/hamlet.xml";
// Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
// the size of the file as a string, then convert to an integer value.
int sz = [[fac FileSize: localFilepath] intValue];
if (sz > 0) {
    NSLog(@"%@%d",@"sz = ",sz);

    // If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
    // Range: bytes=42375-
    CkoStringBuilder *sbRange = [[CkoStringBuilder alloc] init];
    [sbRange Append: @"bytes="];
    [sbRange AppendInt: [NSNumber numberWithInt: sz]];
    [sbRange Append: @"-"];
    [rest AddHeader: @"Range" value: [sbRange GetAsString]];
    NSLog(@"%@%@",@"Added Range: ",[sbRange GetAsString]);
}

// Send the request to download the remainder of the file.
success = [rest SendReqNoBody: @"GET" uriPath: @"/hamlet.xml"];
if (success != YES) {
    NSLog(@"%@",rest.LastErrorText);
    return;
}

// Read the response header.
int responseStatusCode = [[rest ReadResponseHeader] intValue];
if (responseStatusCode < 0) {
    NSLog(@"%@",rest.LastErrorText);
    return;
}

NSLog(@"%@%d",@"Response status code = ",responseStatusCode);

// We expect a 200 or 206 response status if the file data is coming.
// Otherwise, we'll get a string response body with an error message(or no response body).
if ((responseStatusCode == 200) || (responseStatusCode == 206)) {

    CkoStream *bodyStream = [[CkoStream alloc] init];

    // The stream's sink will be a file.
    // We will append to the file..
    bodyStream.SinkFile = localFilepath;

    // Indicate that we wish to append to the output file.
    // The SinkFileAppend property was added in Chilkat v9.50.83
    bodyStream.SinkFileAppend = YES;

    // Read the response body to the stream.  Given that we've
    // set the stream's sink to a file, it will stream directly
    // to the file.
    success = [rest ReadRespBodyStream: bodyStream autoSetStreamCharset: YES];
    if (success != YES) {
        NSLog(@"%@",rest.LastErrorText);
        return;
    }

    NSLog(@"%@",@"Successfully downloaded the file.");

}
else {
    NSString *errResponse = [rest ReadRespBodyString];
    if (rest.LastMethodSuccess != YES) {
        NSLog(@"%@",rest.LastErrorText);
    }
    else {
        NSLog(@"%@",errResponse);
    }

}