Fix TCP stats failure on Azure (#94)

Author: flobernd

src/Elastic.Transport/Diagnostics/TcpStats.cs

@@ -15,21 +15,40 @@ namespace Elastic.Transport.Diagnostics;
 internal static class TcpStats
 {
 	private static readonly int StateLength = Enum.GetNames(typeof(TcpState)).Length;
+	private static readonly ReadOnlyDictionary<TcpState, int> Empty = new(new Dictionary<TcpState, int>());
 
 	/// <summary>
 	/// Gets the active TCP connections
 	/// </summary>
-	/// <returns></returns>
-	public static TcpConnectionInformation[] GetActiveTcpConnections() =>
-		IPGlobalProperties.GetIPGlobalProperties().GetActiveTcpConnections();
+	/// <returns>TcpConnectionInformation[]</returns>
+	/// <remarks>Can return `null` when there is a permissions issue retrieving TCP connections.</remarks>
+	public static TcpConnectionInformation[]? GetActiveTcpConnections()
+	{
+		try
+		{
+			return IPGlobalProperties.GetIPGlobalProperties().GetActiveTcpConnections();
+		}
+		catch (NetworkInformationException) // host might not allow this information to be fetched.
+		{
+			// ignored
+		}
+
+		return null;			
+	}
 
 	/// <summary>
 	/// Gets the sum for each state of the active TCP connections
 	/// </summary>
 	public static ReadOnlyDictionary<TcpState, int> GetStates()
 	{
-		var states = new Dictionary<TcpState, int>(StateLength);
 		var connections = GetActiveTcpConnections();
+		if (connections is null)
+		{
+			return Empty;
+		}
+
+		var states = new Dictionary<TcpState, int>(StateLength);
+
 		for (var index = 0; index < connections.Length; index++)
 		{
 			var connection = connections[index];