Question

After pounding my head all day long, I am down to StackOverflow to pull me through.

I am making a NSURLRequest in my iPhone App …

NSURL* url = [[self serviceUrl] URLByAppendingPathComponent:[NSString stringWithFormat:@"Json"]];

NSString* json = [NSString stringWithFormat:@"{\"id\":\"%@\"}", id];

NSMutableURLRequest* urlRequest = [NSMutableURLRequest requestWithURL:url];
[urlRequest setHTTPMethod:@"POST"];
[urlRequest setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
[urlRequest setHTTPBody:[json dataUsingEncoding:NSUTF8StringEncoding]];

this is returning to me a JSON string, which comes back to me but it is broken in the since that the string will not parse correctly.

However if I make a normal request to the same url in the Safari browser then JSON is returned correctly. I am validating this JSON here.

So whats the deal? Is there a limit to the length of data in a NSString* that a 32Kb json file would not be stored in memory correctly? Sometimes the JSON can be parsed, which leads me to believe that I am not clearing my JSON string correctly after each request.

_json = [[NSString alloc] initWithData:_dataResponse encoding:NSUTF8StringEncoding];

NSArray* retrievedData = (NSArray*)[_json JSONValue];

// removed for brevity

_json = @"";

Other information, I am using ASP.NET MVC 3 to provide the web services for this app.

EDIT

- (NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)redirectResponse 
{   
    _loader.hidden = NO;

    [_loadingIndicator startAnimating];

    return request;
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response 
{
    _dataResponse = [[NSMutableData alloc] init];

    [_dataResponse setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data 
{
    [_dataResponse appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error 
{
    NSLog(@"Error receiving response: %@", error);

    _loader.hidden = YES;

    [_loadingIndicator stopAnimating];
}

- (void)connectionDidFinishLoading:(NSURLConnection*)connection 
{
    _json = [[NSString alloc] initWithData:_dataResponse encoding:NSUTF8StringEncoding];

    // Removed for brevity

    _json = @"";

    _loader.hidden = YES;

    [_dataResponse release];
    _dataResponse = nil;

    [_loadingIndicator stopAnimating];
}

FINAL SOLUTION

I was making multiple calls to have data already stored for views in order to switch views in a tab bar controller. I wasn’t checking the connection during the appending of the data, I was checking the connection when it was finished in order to store the data correctly. My final solution was to make each call sychronously after the previous one during the finished method call.

Answer 1

Unfortunately, nothing blatant is jumping out at me.

Some things to try that will hopefully help:

• double check your NSUrlConnection pattern against this doc. The only diff I see is they’re doing [[NSMutableData data] retain] instead of alloc, init. They also create NSMutableData with the connection request (not in response) and only length=0 in response. Not sure why it would matter though …

http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLConnection.html

• try something like Charles Proxy. It allows you to sniff the wire. You can see what’s different between browser and simulator/phone access. At a minimum, you’ll see what’s coming over the wire in the bad cases.

• add lots of logging. everytime you append data, log some details. After you convert to string and before the json call, log. Log sizes, etc… Something may offer you a hint.

• the use of _json string seems a bit off. You’re reallocating and then setting to empty string. You should either have an iVar that you alloc and release (not set to “”) or create a @property with retain, copy.