Store torrent 'announce' field correctly as BString instead of BList

Fixes #30

Author: ilyabreev

BencodeNET.Tests/Torrents/TorrentTests.cs

@@ -276,6 +276,46 @@ public void ToBDictionary_Announce_SingleTracker_AddsAnnounceButNotAddAnnounceLi
             result.Should().NotContainKey(TorrentFields.AnnounceList);
         }
 
+        [Fact]
+        public void ToBDictionary_Announce_SingleTracker_AnnounceMustBeAString()
+        {
+            var torrent = new Torrent
+            {
+                Trackers = new List<IList<string>>
+                {
+                    new List<string>
+                    {
+                        "http://sometracker.com"
+                    }
+                }
+            };
+
+            var result = torrent.ToBDictionary();
+            result[TorrentFields.Announce].Should().BeAssignableTo<BString>();
+        }
+
+        [Fact]
+        public void ToBDictionary_Announce_MultipleTrackers_AddAnnounceAndAnnounceList()
+        {
+            const string firstTracker = "http://sometracker.com";
+            var torrent = new Torrent
+            {
+                Trackers = new List<IList<string>>
+                {
+                    new List<string>
+                    {
+                        firstTracker,
+                        "http://someothertracker.com"
+                    }
+                }
+            };
+
+            var result = torrent.ToBDictionary();
+            result.Should().ContainKey(TorrentFields.Announce);
+            result.Should().ContainKey(TorrentFields.AnnounceList);
+            result[TorrentFields.Announce].ToString().Should().Be(firstTracker);
+        }
+
         [Theory]
         [AutoMockedData]
         public void ToBDictionary_Comment_AddsToCorrectField(string comment)

BencodeNET/Torrents/Torrent.cs

@@ -228,7 +228,7 @@ public virtual BDictionary ToBDictionary()
             var trackerCount = Trackers.Flatten().Count();
 
             if (trackerCount > 0)
-                torrent[TorrentFields.Announce] = new BList(Trackers.First().Select(x => new BString(x, Encoding)));
+                torrent[TorrentFields.Announce] = new BString(Trackers.Flatten().First(), Encoding);
 
             if (trackerCount > 1)
                 torrent[TorrentFields.AnnounceList] = new BList(Trackers.Select(x => new BList(x, Encoding)));