Resume download functionality in NSURLConnection - iphone

Question

I am downloading some very large data from a server with the NSURLConnection class.
How can I implement a pause facility so that I can resume downloading?

Answer 1

You can't pause, per-se, but you can cancel a connection, and then create a new one to resume where the old left off. However, the server you're connecting to must support the Range header. Set this to "bytes=size_already_downloaded-", and it should pick up right where you cancelled it.

Answer 2

To resume downloading and get the rest of the file you can set the Range value in HTTP request header by doing something like this:
- (void)downloadFromUrl:(NSURL*)url toFilePath:(NSString *)filePath {
NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:10];
if (!request) {
NSLog(#"Error creating request");
// Do something
}
[request setHTTPMethod:#"GET"];
// Add header to existing file
NSFileManager *fm = [NSFileManager defaultManager];
if([fm fileExistsAtPath:filePath]) {
NSError *error = nil;
NSDictionary * fileProp = [fm attributesOfItemAtPath:filePath error:&error];
if (error) {
NSLog(#"Error: %#", [error localizedDescription]);
// Do something
} else {
// Set header to resume
long long fileSize = [[fileProp objectForKey:#"NSFileSize"]longLongValue];
NSString *range = #"bytes=";
range = [[range stringByAppendingString:[[NSNumber numberWithLongLong:fileSize] stringValue]] stringByAppendingString:#"-"];
[request setValue:range forHTTPHeaderField:#"Range"];
}
}
NSURLConnection * connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
if (!connection) {
NSLog(#"Connection failed.");
// Do something
}
}
Also you can use
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response to check if the existing file is fully downloaded by checking the expected size: [response expectedContentLength];. If sizes match you probably want to cancel the connection.