Objective-C NSURLConnection didReceiveData creating bad JSON in NSData - ios

Question

I'm currently attempting to stream data from Twitter using their streaming API's. I've attached the code below for creating my NSData and appending to it on didReceiveData. For some reason, every time didReceiveData gets a response from Twitter, it's appended on as a new JSON root into the NSData, so when I attempt to parse the NSData into a JSON structure, it blows up.
I couldn't figure out what was going on and posted the JSON into a validator and it noted that there were multiple roots in the JSON. How can I modify the code to continue to append to the existing JSON root? Or is there an easier way to go about deserializing into JSON when there's multiple JSON entries in the NSData?
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
// A response has been received, this is where we initialize the instance var you created
// so that we can append data to it in the didReceiveData method
// Furthermore, this method is called each time there is a redirect so reinitializing it
// also serves to clear it
NSLog(#"Did receive response");
_responseData = [[NSMutableData alloc] init];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
// Append the new data to the instance variable you declared
NSLog(#"Did Receive data");
[_responseData appendData:data];
}

Answer 1

I think what you need is just some extra logic to handle the real-time nature of this. Use your NSMutableData as a container to continue receiving data, but at the end of each batch you should scan the data object for all valid objects, build them, and store them into a different object that holds all the built json objects. In this example lets assume you have this ivar: NSMutableArray *_wholeObjects
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
// Append the new data to the instance variable you declared
NSLog(#"Did Receive data");
[_responseData appendData:data];
[self buildWholeObjects]
}
- (void) buildWholeObjects {
NSArray *rootObjects = <#business logic to return one whole JSON object per array element, or return nil if none found#>
if (rootObjects != nil) {
NSUInteger bytesExtracted = 0;
for (rootObject in rootObjects) {
[_wholeObjects addElement:rootObject];
bytesExtracted += rootObject.length;
}
NSData *remainingData = [_responseData subdataWithRange:NSMakeRange(bytesExtracted, _responseData.length - bytesExtracted];
[_responseData setData:remainingData];
}
}
After doing this only access the objects in _wholeObjects, where each element represents a fully valid JSON object that you can deserialize or read in any way you need.
Just for the sake of clarity, lets say the first NSData represents:
{"a":"2"}{"c":"5
When you process it _wholeObjects will have one element representing {"a":"2"}, and _responseData will now be {"c":"5
Then the next stream of data should continue on the object. Lets say the second NSData is:
"}
Now _responseData is {"c":"5"} because we appended the new message onto the remaining old message. We build this one out, and get a second element in _wholeObjects, and _responseData will be empty and ready to receive the next set of data.
Hope that helps some. I think the hard part for you is going to be determining how much of the _responseData is considered a valid JSON object. If they are simple enough you can just count the number of opening {/[ to closing }/] and pull that substring out.

Answer 2

Just to follow up on this topic for anyone dealing with the same thing: I ended up using SBJson which has support for streaming. http://superloopy.io/json-framework/