URLSession Error -1009 when offline with local server

Using XCode 10.1, Swift 4.2, iOS 11.0 Base SDK, with a simple project to invoke URLSession to hit an endpoint configured on a local, vanilla Apache server;

http://localhost/test.php

With the following App Transport Security correctly configured in my app's .plist;

<key>NSAppTransportSecurity</key>

<dict>

<key>NSAllowsArbitraryLoads</key>

<true/>

<key>NSAllowsLocalNetworking</key>

<true/>

</dict>

Using the following URLSession code;

let requestURL = URL(string: "http://localhost/test.php")

var getRequest = URLRequest(url: requestURL, cachePolicy: URLRequest.CachePolicy.reloadIgnoringLocalAndRemoteCacheData, timeoutInterval: 60)

getRequest.httpMethod = "GET"

getRequest.setValue("application/json", forHTTPHeaderField: "Content-Type")

getRequest.setValue("application/json", forHTTPHeaderField: "Accept")

URLSession.shared.dataTask(with: getRequest, completionHandler: { (data, response, error) -> Void in

if error != nil

{

Logging.error("GET Request: Communication error: \(error!)") // <- -1009 here

}

}

When 'online' on WiFi, with a working internet connection, all is well, and my app can access the endpoint and obtain my JSON data.

As soon as my WiFi loses internet connectivity (which happens a lot on my train commute), URLSession starts returning -1009 instantly (full error below), even though I can hit this endpoint through a local browser and view the JSON.

Error Domain=NSURLErrorDomain Code=-1009 "The Internet connection appears to be offline." UserInfo={NSUnderlyingError=0x7b0c0005f6d0 {Error Domain=kCFErrorDomainCFNetwork Code=-1009 "(null)" UserInfo={_kCFStreamErrorCodeKey=50, _kCFStreamErrorDomainKey=1}}, NSErrorFailingURLStringKey=http://localhost/test.php, _kCFStreamErrorDomainKey=1, _kCFStreamErrorCodeKey=50, NSLocalizedDescription=The Internet connection appears to be offline.

This also happens if I turn off WiFi. While this isn't a 'production' oriented issue AFAIK, it's sure painful and prevents software development on a commute!

At this time, I can find no way to 'tune' URLSession to work in this scenario, although I am really happy to told I am missing something...

I suspect URLSession is (internally) performing some Reachability check against a remote endpoint, and thus failing with the -1009 without honouring the actual request.

Has anyone encountered this issue / resolved it? If not, I'll raise a 'bug' report accordingly (though it's not really a bug in 'iOS platform terms').

Thanks in advance!