Question

Functionality in an iPhone app that searches twitter for some text. The code is very straightforward, I pass the url string to the twitter api, and then parse the result. Although half the time JSON parser fails with errors for Unescaped control character ‘0x0’. Code and full error message below.

    - (void)grabData:(NSString *)searchTerm {
     NSString *urlString = [NSString stringWithFormat:@"http://search.twitter.com/search.json?q=%@&rpp=25",searchTerm];

     NSURL *url = [NSURL URLWithString:urlString];

     NSLog(@"Created url:%@",url);

     //Setup and start async download
     NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];
     NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
     [connection release];
     [request release];
    }

    - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

     // Store incoming data into a string
     NSString *jsonString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

     //NSLog(@"Did receive some data %@",jsonString);

     //Create a dictionary from the JSON string
     NSDictionary *results = [jsonString JSONValue];

     // Build an Array from the dictionary for easy access to each entry
     NSDictionary *tweets = [results objectForKey:@"results"];

            // Loop through each entry in the dictionary
    for(NSDictionary *tweet in tweets) {
     // Get the user string for the tweet
     NSString *tUser = [tweet objectForKey:@"from_user"];
           NSLog(@"Tweet from %@",tUser);
          }

    }

Error Message from console, 50% of the time, other 50% it works as expected.

2010-12-20 21:22:02.022 TwitterSearch[47362:207] Created url:http://search.twitter.com/search.json?q=red&rpp=25
2010-12-20 21:22:02.361 TwitterSearch[47362:207] -JSONValue failed. Error trace is: (
    "Error Domain=org.brautaset.JSON.ErrorDomain Code=5 \"Unescaped control character '0x0'\" UserInfo=0x4d6a130 {NSLocalizedDescription=Unescaped control character '0x0'}",
    "Error Domain=org.brautaset.JSON.ErrorDomain Code=3 \"Object value expected for key: profile_image_url\" UserInfo=0x4d6a200 {NSUnderlyingError=0x4d6a170 \"Unescaped control character '0x0'\", NSLocalizedDescription=Object value expected for key: profile_image_url}",
    "Error Domain=org.brautaset.JSON.ErrorDomain Code=3 \"Expected value while parsing array\" UserInfo=0x4d6a240 {NSUnderlyingError=0x4d6a1e0 \"Object value expected for key: profile_image_url\", NSLocalizedDescription=Expected value while parsing array}",
    "Error Domain=org.brautaset.JSON.ErrorDomain Code=3 \"Object value expected for key: results\" UserInfo=0x4d6a310 {NSUnderlyingError=0x4d6a2d0 \"Expected value while parsing array\", NSLocalizedDescription=Object value expected for key: results}"
)

Answer 1

The didReceiveData method can be called multiple times as the data is delivered. So in that method, you should simply append each incoming chunk to an NSMutableData class variable (not process it).

The processing of the complete data should be done in the connectionDidFinishLoading method.

The error is probably happening because it is trying to parse a partial block of data.