NSURLConnection expectedContentLength returns -1 - ios

Question

I'm trying to view the progress bar while downloading a file. The file is generated through PHP, I'm sending the "Content-length" header, which actually works.
The file is downloaded OK so that's not the problem. Unfortunately I just can't get the file size in order to properly display the progress bar.
Here is my code:
write_to_filename = [issue objectForKeyedSubscript:filename];
NSString *post =[[NSString alloc] initWithFormat:#"user_id=%#&email=%#&password=%#",[userData stringForKey:#"userId"],[userData stringForKey:#"email"],[userData stringForKey:#"password"]];
NSData *postData = [post dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:#"http://MY_API_REQUEST"]];
NSString *postLength = [NSString stringWithFormat:#"%d", [postData length]];
[request setValue:#"application/pdf" forHTTPHeaderField:#"Accept"];
[request setValue:postLength forHTTPHeaderField:#"Content-Length"];
[request setValue:#"application/x-www-form-urlencoded" forHTTPHeaderField:#"Content-Type"];
[request setHTTPMethod:#"POST"];
[request setHTTPBody:postData];
[NSURLConnection connectionWithRequest:request delegate:self];
[issueArray writeToFile:[self saveFilePath] atomically:YES];
The NSURLConnection
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse
*)response {
NSLog(#"%lld",[response expectedContentLength]);
_responseData = [[NSMutableData alloc] init];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[_responseData appendData:data];
}
- (NSCachedURLResponse *)connection:(NSURLConnection *)connection
willCacheResponse:(NSCachedURLResponse*)cachedResponse {
return nil;
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *fileName = [[paths objectAtIndex:0] stringByAppendingPathComponent:write_to_filename];
[_responseData writeToFile:fileName atomically:YES];
write_to_filename = nil;
_responseData = nil;
[[self IssuesOverviewCollection] reloadData];
}
I've tried many different things, unfortunately it's not working and keeps return -1.

Answer 1

This can happen if your server is employing compression (which it can do transparently). You can turn off compression on the server by changing your request Accept-Encoding parameter:
[request setValue:#"identity" forHTTPHeaderField:#"Accept-Encoding"];