Make DownloadNuspec work

src/NuGet.CatalogReader/FeedReader/PackageEntry.cs

@@ -159,14 +159,18 @@ public Task<FileInfo> DownloadNuspecAsync(string outputDirectory, DownloadMode m
         /// </summary>
         protected async Task<FileInfo> DownloadNuspecAsync(string outputDirectory, DownloadMode mode, DateTimeOffset date, CancellationToken token)
         {
-            using (var stream = await GetNupkgAsync(token))
+            var reader = await GetNuspecAsync(token);
+
+            if (reader == null)
             {
-                var path = new FileInfo(Path.Combine(outputDirectory, $"{FileBaseName}.nuspec".ToLowerInvariant()));
+                throw new InvalidOperationException($"Nuspec not found: {NuspecUri}");
+            }
 
-                await CatalogReaderUtility.DownloadFileAsync(stream, path, date, mode, token);
+            var path = new FileInfo(Path.Combine(outputDirectory, $"{FileBaseName}.nuspec".ToLowerInvariant()));
 
-                return path;
-            }
+            File.WriteAllText(path.FullName, reader.Xml.ToString());
+
+            return path;
         }
 
         /// <summary>

test/NuGet.CatalogReader.Tests/CatalogReaderTests.cs

@@ -97,6 +97,25 @@ public async Task VerifySingleEntriesWhenReadingACatalogAsync()
             }
         }
 
+        [Fact]
+        public async Task VerifyDownloadNuspec()
+        {
+            // Arrange
+            await VerifyDownloadMode(
+                async (downloadFolder, entry) =>
+                {
+                    // Act
+                    var fileInfo = await entry.DownloadNuspecAsync(
+                        downloadFolder,
+                        DownloadMode.Force,
+                        CancellationToken.None);
+
+                    // Assert
+                    var reader = new NuspecReader(fileInfo.FullName);
+                    Assert.Equal("a", reader.GetId());
+                });
+        }
+
         [Fact]
         public async Task VerifyDownloadModeSkipIfExists_DoesNotExist()
         {