[tracker] Generate useful and random tracker IDs

They indicate that monotorrent is used, the version which is running
and then end in a random unique(ish) positive integer.

src/MonoTorrent/MonoTorrent.Client.Tracker/HTTPTracker.cs

@@ -66,7 +66,7 @@ public HTTPTracker(Uri announceUrl)
 
             // Use a random integer prefixed by our identifier.
             lock (random)
-                Key = VersionInfo.ClientIdentifier + random.Next (1, int.MaxValue).ToString ();
+                Key = $"{VersionInfo.ClientVersion}-{random.Next (1, int.MaxValue)}";
         }
 
         protected override async Task<List<Peer>> DoAnnounceAsync(AnnounceParameters parameters)

src/MonoTorrent/MonoTorrent.Client/ClientEngine.cs

@@ -460,7 +460,9 @@ internal void Stop()
         static string GeneratePeerId()
         {
             StringBuilder sb = new StringBuilder(20);
+            sb.Append ("-");
             sb.Append(VersionInfo.ClientVersion);
+            sb.Append ("-");
 
             var random = new Random(count++);
             while (sb.Length < 20)

src/MonoTorrent/MonoTorrent.Tracker/Tracker.cs

@@ -41,6 +41,8 @@ public class Tracker : IEnumerable<SimpleTorrentManager>, IDisposable
     {
         #region Static BEncodedStrings
 
+        static readonly Random Random = new Random ();
+
         internal static readonly BEncodedString PeersKey = "peers";
         internal static readonly BEncodedString IntervalKey = "interval";
         internal static readonly BEncodedString MinIntervalKey = "min interval";
@@ -149,7 +151,7 @@ public BEncodedString TrackerId
         /// Creates a new tracker
         /// </summary>
         public Tracker()
-            : this(new BEncodedString("monotorrent-tracker"))
+            : this (null)
         {
 
         }
@@ -160,6 +162,12 @@ public Tracker(BEncodedString trackerId)
             allowScrape = true;
             monitor = new RequestMonitor();
             torrents = new Dictionary<InfoHash, SimpleTorrentManager>();
+
+            // Generate an ID which shows that this is monotorrent, and the version, and then a unique(ish) integer.
+            if (trackerId == null) {
+                lock (Random)
+                    trackerId = $"{VersionInfo.ClientVersion}-{Random.Next (1, int.MaxValue)}";
+            }
             this.trackerId = trackerId;
 
             announceInterval = TimeSpan.FromMinutes(45);

src/MonoTorrent/MonoTorrent/VersionInfo.cs

@@ -39,15 +39,18 @@ public static class VersionInfo
         /// </summary>
         internal static readonly string ProtocolStringV100 = "BitTorrent protocol";
 
-        public static readonly string ClientIdentifier = "MO";
+        static readonly string ClientIdentifier = "MO";
 
         /// <summary>
-        /// The current version of the client
+        /// The current version of the client in the form "MO1234", which represents 'MonoTorrent version 1.2.3.4'.
         /// </summary>
         internal static readonly string ClientVersion;
 
         internal static readonly string DhtClientVersion = $"{ClientIdentifier}06";
 
+        /// <summary>
+        /// The full version of this library.
+        /// </summary>
         public static readonly Version Version;
 
         static VersionInfo ()
@@ -63,7 +66,7 @@ static VersionInfo ()
                 version = version.Substring (0, 4);
             else
                 version = version.PadRight (4, '0');
-            ClientVersion = $"-{ClientIdentifier}{version}-";
+            ClientVersion = $"{ClientIdentifier}{version}";
         }
     }
 }