CSHARP-1730: Added IsApplicationNameValid method.

Author: rstam

src/MongoDB.Driver.Core/Core/Configuration/ConnectionString.cs

@@ -493,14 +493,12 @@ private void ParseOption(string name, string value)
             switch (name.ToLower())
             {
                 case "appname":
-                    try
+                    string invalidApplicationNameMessage;
+                    if (!ApplicationNameHelper.IsApplicationNameValid(value, out invalidApplicationNameMessage))
                     {
-                        _applicationName = ApplicationNameHelper.EnsureApplicationNameIsValid(value, nameof(value));
-                    }
-                    catch (Exception ex)
-                    {
-                        throw new MongoConfigurationException(ex.Message, ex);
+                        throw new MongoConfigurationException(invalidApplicationNameMessage);
                     }
+                    _applicationName = value;
                     break;
                 case "authmechanism":
                     _authMechanism = value;

src/MongoDB.Shared/ApplicationNameHelper.cs

@@ -21,17 +21,30 @@ namespace MongoDB.Shared
     internal static class ApplicationNameHelper
     {
         public static string EnsureApplicationNameIsValid(string applicationName, string paramName)
+        {
+            string message;
+            if (!IsApplicationNameValid(applicationName, out message))
+            { 
+                throw new ArgumentException(message, paramName);
+            }
+
+            return applicationName;
+        }
+
+        public static bool IsApplicationNameValid(string applicationName, out string message)
         {
             if (applicationName != null)
             {
                 var utf8 = Utf8Encodings.Strict.GetBytes(applicationName);
                 if (utf8.Length > 128)
                 {
-                    throw new ArgumentException("Application name exceeds 128 bytes after encoding to UTF8.", paramName);
+                    message = "Application name exceeds 128 bytes after encoding to UTF8.";
+                    return false;
                 }
             }
 
-            return applicationName;
+            message = null;
+            return true;
         }
     }
 }