Here is my similar network kit library for uploading files as multipart form:
WebRequest *request = [[WebRequest alloc] initWithPath:@"...documents/create.json"];
// optional attributes
request.delegate = delegate;
request.notificationName = @"NotificationDocumentUploaded";
request.queue = myQueue;
NSMutableData *body = [NSMutableData data];
NSString *boundary = @"TeslaSchoolProjectFormBoundary";
[body appendPartName:@"document[name]" value:@"Test" boundary:boundary];
[body appendPartName:@"document[description]" value:@"This is a description" boundary:boundary];
[body appendPartName:@"document[category]" value:@"Drama" boundary:boundary];
...
[body appendPartName:@"commit" value:@"Save" boundary:boundary];
NSData *fileData = [[NSData alloc] initWithContentsOfURL:someFileURL];
[body appendPartFile:fileName name:@"document[file]" data:fileData mimeType:mimeType boundary:boundary];
[body appendData:[[NSString stringWithFormat:@"--%@--\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
[request setHTTPBody:body];
NSString *bodyLength = [NSString stringWithFormat:@"%lu",(unsigned long)[body length]];
[request addValue:bodyLength forHTTPHeaderField:@"Content-Length"];
[request setValue:[NSString stringWithFormat:@"multipart/form-data; charset=utf-8; boundary=%@", boundary] forHTTPHeaderField:@"Content-Type"];
// optional values
[request addValue:@"gzip,deflate,sdch" forHTTPHeaderField:@"Accept-Encoding"];
[request addValue:@"max-age=0" forHTTPHeaderField:@"Cache-Control"];
[request addValue:@"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8" forHTTPHeaderField:@"Accept"];
[request addValue:@"en-US,en;q=0.8,hr;q=0.6,it;q=0.4,sk;q=0.2,sl;q=0.2,sr;q=0.2" forHTTPHeaderField:@"Accept-Language"];
[request setHTTPMethod:@"POST"];
[WebRequestProcessor process:request];
Use the delegate for notifying about uploading progress.
Use the notificationName for notifying when request has finished.
Use the queue for adding this request into your operation queue so it will be processed in right time.