Losing responseData in NSURLConnection wrapper - objective-c

Question

I'm having some trouble implementing a NSURLConnection wrapper. I'm creating an NSURLConnection with POST data, and the connection appears to receive a response as well as data. The didReceiveData callback logs the responseData length, which is 2000 something bytes. However, by the time didFinishLoading fires, responseData contains 0 bytes. Any tips on where to look for what could be modifying the contents of responseData? It gets reset in didReceiveResponse, but didReceiveResponse does not appear to be called in between didReceiveData and didFinishLoading.
Here is some output from the log:
Current language: auto; currently objective-c 2012-01-24 13:35:40.020
PSIdea[24007:11903] didReceiveResponse: responseData length:(0)
warning: Attempting to create USE_BLOCK_IN_FRAME variable with block
that isn't in the frame. 2012-01-24 13:35:40.604 PSIdea[24007:11903]
didReceiveData. responseData length:(2233) 2012-01-24 13:35:40.604
PSIdea[24007:11903] didFinishLoading: responseData length:(0)
2012-01-24 13:35:41.881 PSIdea[24007:11903] responseData as string:
2012-01-24 13:35:41.882 PSIdea[24007:11903] responseData as
dictionary:
Here is the relevant code:
NetworkController.m
-(void)postRequestToURL:(NSURL*)url withData:(NSData*)data withContentType:(NSString*)contentType
{
NSMutableURLRequest* request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:#"POST"];
if (!contentType)
{
contentType = #"application/x-www-form-urlencoded";
}
[request setValue:contentType forHTTPHeaderField:#"Content-Type"];
[request setHTTPBody:data];
[[NSURLConnection alloc] initWithRequest:request delegate:self];
}
-(void)connection:(NSConnection*)conn didReceiveData:(NSData*)data
{
[_responseData appendData:data];
NSLog(#"didReceiveData. responseData length:(%d)", _responseData.length);
}
-(void)connection:(NSConnection*)conn didReceiveResponse:(NSURLResponse *)response
{
if (_responseData == NULL) {
_responseData = [[NSMutableData alloc] init];
}
[_responseData setLength:0];
NSLog(#"didReceiveResponse: responseData length:(%d)", _responseData.length);
}
-(void)connection:(NSConnection*)conn didFailWithError:(NSError *)error
{
NSLog([NSString stringWithFormat:#"Connection failed: %#", error.description]);
}
PSINetworkController.m (subclass)
-(void)connectionDidFinishLoading:(NSURLConnection*)connection
{
NSLog(#"didFinishLoading: responseData length:(%d)", _responseData.length);
NSString *responseString = [[NSString alloc] initWithData:_responseData encoding:NSUTF8StringEncoding];
NSLog(#"responseData as string: %#", responseString);
SBJsonParser* parser = [[SBJsonParser alloc] init];
NSDictionary* dict = [parser objectWithData:_responseData];
NSLog(#"responseData as dictionary:");
for (id key in dict) {
NSLog(#"%#=%#", key, [dict objectForKey:key]);
}
[_delegate connection:connection receivedResponse:dict];
}
Thanks.
EDIT:
Also, I seem to have stumbled across a solution. The problem does have something to do with the way _responseData is declared.
Declaring response data as an atomic property leads to the response data being reset just as before.
#property (retain) NSMutableData* responseData;
However, simply declaring the variable in the interface seems to eliminate the problem - the data persists from didReceiveData to didFinishLoading.
#interface NetworkController : NSObject
{
NSMutableData* _responseData;
}
It is my understanding that declaring properties simply generates setters and getters, but I'm failing to see how this relates in this situation. Can anyone explain?
EDIT: I neglected to mention that this project is using ARC.

Answer 1

if you have declared responseData as retain if your .h file, you should change the code to:
-(void)connection:(NSConnection*)conn didReceiveResponse:(NSURLResponse *)response
{
if (self._responseData) {
self._responseData = [[NSMutableData alloc] init] autorelease];
}
//further code
}
this should resolve your issue