Added an IPv4/IPv6 toggle to TelegramClient constructor (#925)

Fixes https://github.com/sochix/TLSharp/issues/857

TLSharp.Core/DataCenterIPVersion.cs

@@ -0,0 +1,30 @@
+namespace TLSharp.Core
+{
+    /// <summary>
+    /// When the Telegram server responds with a set of addresses to connect to, DataCenterIPVersion indicates a preference 
+    /// for how to choose the IP address to connect to 
+    /// </summary>
+    public enum DataCenterIPVersion
+    {
+        /// <summary>
+        /// Picks the first available address passed by Telegram
+        /// </summary>
+        Default,
+        /// <summary>
+        /// Takes only IPv4 addresses
+        /// </summary>
+        OnlyIPv4,
+        /// <summary>
+        /// Takes only IPv6 addresses
+        /// </summary>
+        OnlyIPv6,
+        /// <summary>
+        /// Connection to IPv4 addresses is preferred to IPv6 addresses
+        /// </summary>
+        PreferIPv4,
+        /// <summary>
+        /// Connection to IPv6 addresses is preferred to IPv4 addresses 
+        /// </summary>
+        PreferIPv6,
+    }
+}

TLSharp.Core/Network/TcpTransport.cs

@@ -24,7 +24,13 @@ namespace TLSharp.Core.Network
                 var endpoint = new IPEndPoint(ipAddress, port);
 
                 tcpClient = new TcpClient(ipAddress.AddressFamily);
-                tcpClient.Connect(endpoint);
+
+                try {
+                    tcpClient.Connect (endpoint);
+                } catch (Exception ex) {
+                    throw new Exception ($"Problem when trying to connect to {endpoint}; either there's no internet connection or the IP address version is not compatible (if the latter, consider using DataCenterIPVersion enum)",
+                                         ex);
+                }
             }
             else
                 tcpClient = handler(address, port);

TLSharp.Core/TLSharp.Core.csproj

@@ -45,6 +45,7 @@
     <Compile Include="Auth\Step1_PQRequest.cs" />
     <Compile Include="Auth\Step2_DHExchange.cs" />
     <Compile Include="Auth\Step3_CompleteDHExchange.cs" />
+    <Compile Include="DataCenterIPVersion.cs" />
     <Compile Include="Exceptions\CloudPasswordNeededException.cs" />
     <Compile Include="Exceptions\InvalidPhoneCodeException.cs" />
     <Compile Include="Exceptions\MissingApiConfigurationException.cs" />

TLSharp.Core/TelegramClient.cs

@@ -31,14 +31,25 @@ namespace TLSharp.Core
         private Session session;
         private List<TLDcOption> dcOptions;
         private TcpClientConnectionHandler handler;
+        private DataCenterIPVersion dcIpVersion;
 
         public Session Session
         {
             get { return session; }
         }
 
+        /// <summary>
+        /// Creates a new TelegramClient
+        /// </summary>
+        /// <param name="apiId">The API ID provided by Telegram. Get one at https://my.telegram.org </param>
+        /// <param name="apiHash">The API Hash provided by Telegram. Get one at https://my.telegram.org </param>
+        /// <param name="store">An ISessionStore object that will handle the session</param>
+        /// <param name="sessionUserId">The name of the session that tracks login info about this TelegramClient connection</param>
+        /// <param name="handler">A delegate to invoke when a connection is needed and that will return a TcpClient that will be used to connect</param>
+        /// <param name="dcIpVersion">Indicates the preferred IpAddress version to use to connect to a Telegram server</param>
         public TelegramClient(int apiId, string apiHash,
-            ISessionStore store = null, string sessionUserId = "session", TcpClientConnectionHandler handler = null)
+            ISessionStore store = null, string sessionUserId = "session", TcpClientConnectionHandler handler = null,
+            DataCenterIPVersion dcIpVersion = DataCenterIPVersion.Default)
         {
             if (apiId == default(int))
                 throw new MissingApiConfigurationException("API_ID");
@@ -51,6 +62,7 @@ namespace TLSharp.Core
             this.apiHash = apiHash;
             this.apiId = apiId;
             this.handler = handler;
+            this.dcIpVersion = dcIpVersion;
 
             session = Session.TryLoadOrCreateNew(store, sessionUserId);
             transport = new TcpTransport (session.DataCenter.Address, session.DataCenter.Port, this.handler);
@@ -101,7 +113,25 @@ namespace TLSharp.Core
                 exported = await SendRequestAsync<TLExportedAuthorization>(exportAuthorization, token).ConfigureAwait(false);
             }
 
-            var dc = dcOptions.First(d => d.Id == dcId);
+            IEnumerable<TLDcOption> dcs;
+            if (dcIpVersion == DataCenterIPVersion.OnlyIPv6)
+                dcs = dcOptions.Where(d => d.Id == dcId && d.Ipv6); // selects only ipv6 addresses 	
+            else if (dcIpVersion == DataCenterIPVersion.OnlyIPv4)
+                dcs = dcOptions.Where(d => d.Id == dcId && !d.Ipv6); // selects only ipv4 addresses
+            else
+                dcs = dcOptions.Where(d => d.Id == dcId); // any
+
+            TLDcOption dc;
+            if (dcIpVersion != DataCenterIPVersion.Default)
+            {
+                if (!dcs.Any())
+                    throw new Exception($"Telegram server didn't provide us with any IPAddress that matches your preferences. If you chose OnlyIPvX, try switch to PreferIPvX instead.");
+                dcs = dcs.OrderBy(d => d.Ipv6);
+                dc = dcIpVersion == DataCenterIPVersion.PreferIPv4 ? dcs.First() : dcs.Last(); // ipv4 addresses are at the beginning of the list because it was ordered
+            }
+            else
+                dc = dcs.First();
+            
             var dataCenter = new DataCenter (dcId, dc.IpAddress, dc.Port);
 
             transport = new TcpTransport(dc.IpAddress, dc.Port, handler);