NSURLConnection retrieving JSON - ios

I am using PromiseKit and I want to retrieve a JSON file.
[NSURLConnection GET:#"http://127.0.0.1/pack01.json"].then(^(NSDictionary *json) {
NSArray *questions = json[#"questions"];
Everything is fine on localhost but when I try it from another source (same file) it gives me an error:
[NSURLConnection GET:#"https://dl.dropboxusercontent.com/u/11377305/resources/pack01.json"].then(^(NSDictionary *json) {
NSArray *questions = json[#"questions"];
Error
[__NSCFData objectForKeyedSubscript:]: unrecognized selector sent to instance 0xb07c880
JSON file:
https://dl.dropboxusercontent.com/u/11377305/resources/pack01.json
Why is it working on localhost?
I would appreciate any suggestions or even any thoughts on what questions I should be asking.

The error indicates that you're being passed an NSData rather than an NSDictionary from the remote URL.
The PromiseKit documentation states:
PromiseKit reads the response headers and decodes the result you actually wanted (in a background thread):
Therefore it's a safe bet that your remote server (which is DropBox in this case) isn't indicating that the returned data is formatted as JSON. So PromiseKit isn't parsing it.
EDIT: confirmed. DropBox is returning:
Content-Type text/plain; charset=utf-8
So PromiseKit has no way of knowing that the included data is meant to be JSON. You need a server that will return an application/json Content-Type. Or else you can force the JSON parse yourself, but then you're missing out on a large part of the PromiseKit benefit as you end up writing the same boilerplate code as the rest of us.

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Is there any text length limit for the iOS JSON framework to parse it?
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I have an iOS app using Restkit. Most of the response bodies from the server are in XML format. However, there is a few API's that will only send a response like "Success" in text/plain format. When calling these API's I get a 200 response but restkit will throw a mapping error because it is expecting Content-Type = application/xml as is seen in the error below.
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After further research and help from Wain I discovered the error above was actually stating that the response-header for content-type had a value of application/xml. This keyed restkit to try and map the response.body as an application/xml formatted body. With a response.body containing only the word "success" the response was unprocessable. I ended up pointing this out to my server guy and he corrected the response to be formatted in the MIMEType declared by the Accept header sent with the request.
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This question "Send post request in XML format using RestKit " is what I was looking for but the answer from Imran Raheem is now (as far as I can tell) obsolete due to changes in RestKit.
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However if I set the MIMEType to XML the Trace shows the request.body=(null)
Here is the line I use to change the MIMEType
[RKObjectManager sharedManager].requestSerializationMIMEType = RKMIMETypeJSON;
I am pretty new to iOS and Objective-C so I may be setting up the NSDictionary that is used in the parameters of the `postObject' method wrong. Here it is just in case....
NSArray *objects =[NSArray arrayWithObjects:#"trending", nil];
NSArray *keys =[NSArray arrayWithObjects: #"Search",nil];
NSDictionary *params = [NSDictionary dictionaryWithObjects:objects forKeys:keys];
self.search=params;
Any help would be greatly appreciated! Given that I am new Snippets are especially helpful!
Oh and BTW if anyone can point me to REST method that accepts JSON input I would gladly pass it on to my server guy so I can just avoid XML all together.
As feared and suggested in other posts on this topic writing XML is not supported in version of RestKit 0.20.1. Here is a link to my conversation with Blake Watters on the subject.
https://github.com/RestKit/RestKit/issues/1430#issuecomment-19150316
I never did clear up why the request.body= (null) when the MIMEType is set to XML.
The manager of the server has agreed to set it up to receive JSON. That is how I plan to work around this.

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