[vs17.10] DownloadFile should not rely on the response headers

DownloadFile should not rely on the remote server response headers. Unless the DestinationFileName task parameter is specified - let's just fallback to the request URI - which is as well the publicly documented behavior.

Author: Mariana Dematte

eng/Versions.props

@@ -2,7 +2,7 @@
 <!-- Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the MIT license. See License.txt in the project root for full license information. -->
 <Project>
   <PropertyGroup>
-    <VersionPrefix>17.10.27</VersionPrefix>
+    <VersionPrefix>17.10.28</VersionPrefix>
     <DotNetFinalVersionKind>release</DotNetFinalVersionKind>
     <PackageValidationBaselineVersion>17.8.3</PackageValidationBaselineVersion>
     <AssemblyVersion>15.1.0.0</AssemblyVersion>

src/Tasks/DownloadFile.cs

@@ -168,7 +168,7 @@ private async Task DownloadAsync(Uri uri, CancellationToken cancellationToken)
 #endif
                     }
 
-                    if (!TryGetFileName(response, out string filename))
+                    if (!TryGetFileName(uri, out string filename))
                     {
                         Log.LogErrorWithCodeFromResources("DownloadFile.ErrorUnknownFileName", SourceUrl, nameof(DestinationFileName));
                         return;
@@ -306,25 +306,24 @@ private static bool IsRetriable(Exception exception, out Exception actualExcepti
         /// <summary>
         /// Attempts to get the file name to use when downloading the file.
         /// </summary>
-        /// <param name="response">The <see cref="HttpResponseMessage"/> with information about the response.</param>
+        /// <param name="requestUri">The uri we sent request to.</param>
         /// <param name="filename">Receives the name of the file.</param>
         /// <returns><code>true</code> if a file name could be determined, otherwise <code>false</code>.</returns>
-        private bool TryGetFileName(HttpResponseMessage response, out string filename)
+        private bool TryGetFileName(Uri requestUri, out string filename)
         {
-            if (response == null)
+            if (requestUri == null)
             {
-                throw new ArgumentNullException(nameof(response));
+                throw new ArgumentNullException(nameof(requestUri));
             }
 
             // Not all URIs contain a file name so users will have to specify one
             // Example: http://www.download.com/file/1/
 
-            filename = !String.IsNullOrWhiteSpace(DestinationFileName?.ItemSpec)
+            filename = !string.IsNullOrWhiteSpace(DestinationFileName?.ItemSpec)
                 ? DestinationFileName.ItemSpec // Get the file name from what the user specified
-                : response.Content?.Headers?.ContentDisposition?.FileName // Attempt to get the file name from the content-disposition header value
-                  ?? Path.GetFileName(response.RequestMessage.RequestUri.LocalPath); // Otherwise attempt to get a file name from the URI
+                : Path.GetFileName(requestUri.LocalPath); // Otherwise attempt to get a file name from the URI
 
-            return !String.IsNullOrWhiteSpace(filename);
+            return !string.IsNullOrWhiteSpace(filename);
         }
 
 #if !NET6_0_OR_GREATER