Fix for handling of post with empty post body

Foundation/URLSession/http/HTTPURLProtocol.swift

@@ -133,7 +133,8 @@ internal class _HTTPURLProtocol: _NativeProtocol {
         }
         let customHeaders: [String]
         let headersForRequest = curlHeaders(for: httpHeaders)
-        if ((request.httpMethod == "POST") && (request.value(forHTTPHeaderField: "Content-Type") == nil)) {
+        if ((request.httpMethod == "POST") && (request.httpBody?.count ?? 0 > 0)
+            && (request.value(forHTTPHeaderField: "Content-Type") == nil)) {
             customHeaders = headersForRequest + ["Content-Type:application/x-www-form-urlencoded"]
         } else {
             customHeaders = headersForRequest

TestFoundation/HTTPServer.swift

@@ -426,6 +426,13 @@ public class TestURLSessionServer {
             return _HTTPResponse(response: .OK, headers: "Content-Length: \(text.data(using: .utf8)!.count)", body: text)
         }
 
+        if uri == "/emptyPost" {
+            if request.body.count == 0 && request.getHeader(for: "Content-Type") == nil {
+                return _HTTPResponse(response: .OK, body: "")
+            }
+            return _HTTPResponse(response: .NOTFOUND, body: "")
+        }
+
         if uri == "/requestCookies" {
             let text = request.getCommaSeparatedHeaders()
             return _HTTPResponse(response: .OK, headers: "Content-Length: \(text.data(using: .utf8)!.count)\r\nSet-Cookie: fr=anjd&232; Max-Age=7776000; path=/\r\nSet-Cookie: nm=sddf&232; Max-Age=7776000; path=/; domain=.swift.org; secure; httponly\r\n", body: text)

TestFoundation/TestURLSession.swift

@@ -43,6 +43,7 @@ class TestURLSession : LoopbackServerTest {
             ("test_setCookies", test_setCookies),
             ("test_dontSetCookies", test_dontSetCookies),
             ("test_redirectionWithSetCookies", test_redirectionWithSetCookies),
+            ("test_postWithEmptyBody", test_postWithEmptyBody),
         ]
     }
 
@@ -675,6 +676,25 @@ class TestURLSession : LoopbackServerTest {
         XCTAssertEqual(config.urlCache, nil)
         XCTAssertEqual(config.shouldUseExtendedBackgroundIdleMode, true)
     }
+
+    /* Test for SR-8970 to verify that content-type header is not added to post with empty body */
+    func test_postWithEmptyBody() {
+        let config = URLSessionConfiguration.default
+        config.timeoutIntervalForRequest = 5
+        let urlString = "http://127.0.0.1:\(TestURLSession.serverPort)/emptyPost"
+        let session = URLSession(configuration: config, delegate: nil, delegateQueue: nil)
+        var expect = expectation(description: "POST \(urlString): post with empty body")
+        var req = URLRequest(url: URL(string: urlString)!)
+        req.httpMethod = "POST"
+        var task = session.dataTask(with: req) { (_, response, error) -> Void in
+            defer { expect.fulfill() }
+            XCTAssertNil(error as? URLError, "error = \(error as! URLError)")
+            guard let httpresponse = response as? HTTPURLResponse else { fatalError() }
+            XCTAssertEqual(200, httpresponse.statusCode, "HTTP response code is not 200")
+        }
+        task.resume()
+        waitForExpectations(timeout: 30)
+    }
 }
 
 class SharedDelegate: NSObject {