Cannot download image using AFHTTPRequestOperationManager - ios

Question

I'm trying to download an image (jpeg) from a given URL using this code:
let manager = AFHTTPRequestOperationManager()
manager.responseSerializer = AFImageResponseSerializer()
manager.responseSerializer.acceptableContentTypes = NSSet(array: ["application/octet-stream"]) as Set<NSObject>
manager.GET(imageURL, parameters: nil,
success: { (operation: AFHTTPRequestOperation!, responseObject: AnyObject!) -> Void in
println("IMAGE SUCCESS")
}, failure: { (operation: AFHTTPRequestOperation!, error: NSError!) in
println("IMAGE FAIL")
})
With my internet at the moment, the success block is being called when testing on the simulator. However, the failure block is being called when testing on an iPhone. On another network, the success block is always called on both iPhone and simulator.
I can't figure out what's causing the issue. I have tried setting the Content-Type to "image/jpeg" but still got the same results. Did I miss something?
The error is:
Error Domain=NSURLErrorDomain Code=-1001 "The request timed out." UserInfo=0x1675f381 {NSErrorFailingURLStringKey=<...>, NSErrorFailingURLKey=<...>, NSLocalizedDescription=The request timed out., NSUnderlyingError=0x166c7891 "The request timed out."}

Answer 1

Are you requesting many images (or doing many network requests)? If so, you might want to constrain the AFHTTPRequestOperationManager:
manager.operationQueue.maxConcurrentOperationCount = 5
If you don't do this and then proceed to initiate many requests, the "timeout" starts when the network requests are enqueued even though NSURLConnection (which AFHTTPRequestOperationManager uses behind the scenes) can only run 4 or 5 at a time and the latter requests may not even start until earlier ones finish. You want to start the timeout logic for network requests on the basis of when the request starts, not when the request was enqueued. By constraining the maxConcurrentOperationCount, you're ensuring that network requests aren't initiated before they can reasonably be performed.
Note, that presumes that you use the same AFHTTPRequestOperationManager for all of your requests, not instantiating new operation managers for new requests. But this will ensure that requests aren't started until the backlog of other requests has been reduced to an acceptable level.
--
As an aside, rather than replacing acceptableContentTypes, I'd merely suggest augmenting it:
var acceptableContentTypes = manager.responseSerializer.acceptableContentTypes ?? Set<NSObject>()
acceptableContentTypes.insert("application/octet-stream")
manager.responseSerializer.acceptableContentTypes = acceptableContentTypes
Frankly, I'd rather see you fix the Content-Type of the images you're retrieving from the server so that it didn't send application/octet-stream responses, but if you can't do that, the above is probably a more prudent way to adjust the content types. This ensures that you accept both your custom application/octet-stream type, as well as the standard image types.