Objective-C

Resume an Interrupted FTP Transfer

Demonstrates the RestartNext and PartialTransfer properties, which request that the next transfer resume from existing content and report whether a download was incomplete.

Note: The local paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: For a large transfer over a flaky link, restarting from zero after a drop is wasteful. Setting RestartNext makes the next download continue from the current local file size (and the next upload from the remote size); the flag is consumed by that one transfer and then reset. Afterward PartialTransfer tells you whether the download got only part of the file — the signal to set RestartNext again and resume once more.

Chilkat Objective-C Downloads

Download Chilkat for Objective-C

Objective-C

#import <CkoFtp2.h>

BOOL success = NO;

CkoFtp2 *ftp = [[CkoFtp2 alloc] init];

ftp.Hostname = @"ftp.example.com";
ftp.Username = @"myFtpLogin";

//  Normally you would not hard-code the password in source.  You should instead obtain it
//  from an interactive prompt, environment variable, or a secrets vault.
ftp.Password = @"myPassword";

success = [ftp Connect];
if (success == NO) {
    NSLog(@"%@",ftp.LastErrorText);
    return;
}

//  RestartNext requests that the NEXT transfer resume from existing content rather than starting
//  over.  It is consumed by that transfer and then automatically reset.
ftp.RestartNext = YES;

//  Resume a partially-downloaded file.  Because RestartNext is set, the download continues from
//  the current local file size.
success = [ftp GetFile: @"public_html/bigfile.zip" localPath: @"qa_output/bigfile.zip"];
if (success == NO) {
    NSLog(@"%@",ftp.LastErrorText);
    return;
}

//  PartialTransfer indicates whether the most recent download received some, but not all, of the
//  remote file -- distinguishing a mid-transfer failure from other outcomes.
if (ftp.PartialTransfer) {
    NSLog(@"%@",@"Only part of the file was received; another resume may be needed.");
}
else {
    NSLog(@"%@",@"The file was fully received.");
}

success = [ftp Disconnect];
if (success == NO) {
    NSLog(@"%@",ftp.LastErrorText);
    return;
}