[SR-2679] corelibs-foundation URLSession delivers redirection delegate methods in the wrong order

[swift-ci]

Previous ID	SR-2679
Radar	None
Original Reporter	klassobanieras (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Environment

swift-3.0-GM-CANDIDATE
Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-34-generic x86_64)

Additional Detail from JIRA

Votes	1
Component/s	Foundation
Labels	Bug
Assignee	@spevans
Priority	Medium

md5: f06e5e5a7ff65a4cd57f89c8de0d496b

Issue Description:

When a corelibs-foundation URLSession data task encounters a redirection response, it first calls the didReceiveResponse delegate method and then calls willPerformHTTPRedirection.

Instead a single response should be delivered only after any redirections have occurred, or if the delegate indicates not to follow a redirection by passing 'nil' to the willPerformHTTPRedirection completion callback.

[swift-ci]

Comment by Nethra Ravindran (JIRA)

This issue can be recreated with the following test case.

import Foundation
import Dispatch

class DataTask : NSObject {
    var session: URLSession! = nil
    var task: URLSessionDataTask! = nil
    
    public var error = false
    
    override init() {
    }
    
    func run(with url: URL) {
        let config = URLSessionConfiguration.default
        config.timeoutIntervalForRequest = 8
        session = URLSession(configuration: config, delegate: self, delegateQueue: nil)
        task = session.dataTask(with: url)
        task.resume()
        dispatchMain()
    }
}

extension DataTask : URLSessionDataDelegate {
    public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        print("Delegate - didReceive data: \(data)")
    }
    
    public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
        print("Delegate - didReceive response: \(response)")
        completionHandler(URLSession.ResponseDisposition.allow)
    }
}

extension DataTask : URLSessionTaskDelegate {
    
    public func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        guard let e = error as? URLError else { return }
        self.error = true
    }
    
    public func urlSession(_ session: URLSession, task: URLSessionTask, willPerformHTTPRedirection response: HTTPURLResponse, newRequest request: URLRequest, completionHandler: @escaping (URLRequest?) -> Void) {
        print("Delegate - willPerformHTTPRedirection")
        print("Response : \(response)")
        completionHandler(request)
    }
}


let urlString = "http://www.google.com"
let url = URL(string: urlString)!
let d = DataTask()
d.run(with: url)

On Darwin, the order of delegate calls are
-> willPerformHTTPRedirection
-> didReceiveResponse

Whereas, on Linux the order of delegate calls are
-> didReceiveResponse
-> willPerformHTTPRedirection

Its is also observed that wrong URL is being passed to the delegate methods.

[spevans]

#2744

[spevans]

Fixed in swift-DEVELOPMENT-SNAPSHOT-2020-03-26