didReceiveData only getting called once on resuming download - download

Question

I have a problem which I could really do with some help with please
I am using NSURLconnection to download a large file (27MB). the code work fine when there is no network interruption. In order to allow for network issues and only partially downloaded file I have added code to check to see how much of the file is downloaded and then using a server request to download the missing portion.
The code works as it should IF I download part of file, stop the program running and then run again - the download then commences where it left off and i have complete file.
However if I hit the download button a second time without stopping the program then didReceiveData only gets called once and adds just 200KB to the file and it tells me file has been succesfully downloaded.
Help please - I have spent ages trying to figure out what I'm doing wrong.
Code below:
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
NSLog(#"Response code = %d",httpResponse.statusCode );
file = [NSFileHandle fileHandleForUpdatingAtPath:filename] ;// file is in .h
if (file) {
[file seekToEndOfFile];
}
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
if (file) {
[file seekToEndOfFile];
NSLog(#"file is %#",file);
}
[self.file writeData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
if([[NSFileManager defaultManager] fileExistsAtPath:filename])
{
[file closeFile];
file = nil;
theConnection = nil;
filename = nil;
theRequest = nil;
}
NSLog(#"Connection failed! Error - %# %#",
[error localizedDescription],
[[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
[file closeFile];
file = nil;
theConnection = nil;
filename = nil;
}
- (IBAction)downloadFile:(id)sender {
filename = [[NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:movie1]; // filename is in .h file
theRequest=[NSMutableURLRequest requestWithURL:[NSURL URLWithString:movieDownload1] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
NSUInteger downloadedBytes = 0;
NSFileManager *fm = [NSFileManager defaultManager];
if ([fm fileExistsAtPath:filename]) {
NSError *error = nil;
NSDictionary *fileDictionary = [fm attributesOfItemAtPath:filename error:&error];
if (!error && fileDictionary)
downloadedBytes = [fileDictionary fileSize];
} else {
[fm createFileAtPath:filename contents:nil attributes:nil];
}
if (downloadedBytes > 0) {
NSString *requestRange = [NSString stringWithFormat:#"bytes=%d-",downloadedBytes];
[theRequest setValue:requestRange forHTTPHeaderField:#"Range"];
}
theConnection = nil;
theConnection = [NSURLConnection connectionWithRequest:theRequest delegate:self];
}

Answer 1

Instead of using seekToEndOfFile in didReceiveResponse and didReceiveData, you can try the following code snippet. It worked well for me.
- (id)initWithURL:(NSString *)downloadString
{
if (![super init])
return nil;
// Construct the URL to be downloaded
self.downloadURL = [[NSURL alloc]initWithString:downloadString];
self.downloadData = [[NSMutableData alloc] init];
self.downloadedFilename = [[self.downloadURL path] lastPathComponent];
[self downloadFile];
return self;
}
-(void) downloadFile
{
// set the filePath
docFolderPath = [NSHomeDirectory() stringByAppendingPathComponent: [NSString stringWithFormat: #"Documents/%#", self.downloadedFilename]];
self.downloadStream = [NSOutputStream outputStreamToFileAtPath:docFolderPath append:NO];
if (!self.downloadStream)
{
self.error = [NSError errorWithDomain:[NSBundle mainBundle].bundleIdentifier
code:-1
userInfo:#{#"message": #"Unable to create NSOutputStream", #"function" : #(__FUNCTION__), #"path" : self.downloadedFilename}];
return;
}
[self.downloadStream open];
self.downloadConnection = [[NSURLConnection alloc] initWithRequest:downloadRequest delegate:self];
[self.downloadConnection start];
}
//code snippet for the Resume functionality after your downloading gets paused/cancel
-(void) resumeInterruptedDownload
{
NSFileManager *fm = [NSFileManager defaultManager];
if ([fm fileExistsAtPath:docFolderPath])
{
NSError *error = nil;
NSDictionary *fileDictionary = [fm attributesOfItemAtPath:docFolderPath
error:&error];
if (!error && fileDictionary)
self.downloadedBytes = [fileDictionary fileSize];
} else
{
[fm createFileAtPath:docFolderPath contents:nil attributes:nil];
}
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:self.downloadURL cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:30.0];
// Define the bytes we wish to download.
if(self.downloadedBytes != 0)
{
NSString *range = [NSString stringWithFormat:#"bytes=%i-", self.downloadedBytes];
[request setValue:range forHTTPHeaderField:#"Range"];
}
// Data should immediately start downloading after the connection is created.
self.downloadConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:TRUE];
}
It worked perfectly for me in case of the large files in Mbs but for the small files in Kbs it sometimes fails. You don't have to try much in all these delegate methods of NSURLConnection. One thing you can do is that set the macros for each state i.e, cancel, pause, downloading,downloaded so that you can come to know that when do you want to resume the downloading. Also you can try the following http://nachbaur.com/blog/resuming-large-downloads-with-nsurlconnection.
I know it is too late to reply, but I just got into IOS. If you try this, please let me know whether it worked or not. Thanks :) :)