How to use PromiseKit to handle header-only response? - ios

Question

I'm using PromiseKit in an IOS app to communicate with a Rails RESTful backend,
and there're some calls that return only header, say by executing head 200 on the backend.
What I've tried is:
I used [NSURLConnection POST:url formURLEncodedParameters:parameters] to post data to backend, the backend did receive the data and responded with a head 200 message, but PromiseKit is reporting the following exception:
2014-07-31 11:19:39.501 HelloPOS[13223:60b] Error
Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be
completed. (Cocoa error 3840.)" (No value.) UserInfo=0xa4c5a90
{NSDebugDescription=No value., PMKURLErrorFailingDataKey={length = 1, capacity = 16, bytes = 0x20},
PMKURLErrorFailingURLResponseKey= { URL:
http://SOME_APP.SOME_HOST.com/api/v1/sales.json } { status code: 200,
headers {
"Cache-Control" = "max-age=0, private, must-revalidate";
Connection = "keep-alive";
"Content-Length" = 1;
"Content-Type" = "application/json";
Date = "Thu, 31 Jul 2014 03:19:25 GMT";
Etag = "\"7215ee9c7d9dc229d2921a40e899ec5f\"";
Server = "WEBrick/1.3.1 (Ruby/2.0.0/2014-05-08)";
Via = "1.1 vegur";
"X-Content-Type-Options" = nosniff;
"X-Frame-Options" = SAMEORIGIN;
"X-Request-Id" = "5a1c1aa1-4b42-41ea-8397-a5df8fa956bc";
"X-Runtime" = "0.013359";
"X-Xss-Protection" = "1; mode=block"; } }}
It's probably because header-only response has no body, and the error is caused
PS: I've changed the URL in the exception message

Answer 1

The problem is the server claims that the response has a JSON content of length 1 byte. But the response does not parse into JSON, so PromiseKit errors that promise.
PromiseKit doesn't provide a mechanism to ignore the response, but you could easily make your own promise here if you cannot fix the server to provide correct responses.
#import <OMGHTTPURLRQ.h>
- (PMKPromise *)myPromise:(id)args {
id rq = [OMGHTTPURLRQ POST:url:args];
id q = ;
return [PMKPromise new:^(PMKPromiseFulfiller fulfill, PMKPromiseRejecter reject){
[NSURLConnection sendAsynchronousRequest:rq queue:q completionHandler:^(id rsp, id data, NSError *urlError) {
if (urlError) {
reject(urlError)
} else {
fulfill(nil);
}
}];
}];
}
EDIT: PromiseKit now works around this specific situation, so you should no longer get this specific error.