feat: Use XmlWriter to serialize TwiML instead of using XDocument

src/Twilio/TwiML/Fax/Receive.cs

@@ -91,7 +91,7 @@ public Receive(Uri action = null,
         /// <summary>
         /// Return the attributes of the TwiML tag
         /// </summary>
-        protected override List<XAttribute> GetElementAttributes()
+        protected override IEnumerable<XAttribute> GetElementAttributes()
         {
             var attributes = new List<XAttribute>();
             if (this.Action != null)

src/Twilio/TwiML/Messaging/Message.cs

@@ -78,7 +78,7 @@ protected override string GetElementBody()
         /// <summary>
         /// Return the attributes of the TwiML tag
         /// </summary>
-        protected override List<XAttribute> GetElementAttributes()
+        protected override IEnumerable<XAttribute> GetElementAttributes()
         {
             var attributes = new List<XAttribute>();
             if (this.To != null)

src/Twilio/TwiML/Messaging/Redirect.cs

@@ -49,7 +49,7 @@ protected override string GetElementBody()
         /// <summary>
         /// Return the attributes of the TwiML tag
         /// </summary>
-        protected override List<XAttribute> GetElementAttributes()
+        protected override IEnumerable<XAttribute> GetElementAttributes()
         {
             var attributes = new List<XAttribute>();
             if (this.Method != null)

src/Twilio/TwiML/Text.cs

@@ -1,4 +1,9 @@
-using System.Xml.Linq;
+#if !NET35
+using System.Threading;
+using System.Threading.Tasks;
+#endif
+using System.Xml;
+using System.Xml.Linq;
 
 namespace Twilio.TwiML
 {
@@ -15,5 +20,18 @@ protected override XNode ToXml()
         {
             return new XText(_content);
         }
+
+#if !NET35
+        protected override async Task WriteXml(XmlWriter writer, CancellationToken cancellationToken)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            await writer.WriteStringAsync(_content).ConfigureAwait(false);
+        }
+#endif
+
+        protected override void WriteContent(XmlWriter writer)
+        {
+            writer.WriteString(_content);
+        }
     }
-}
+}

src/Twilio/TwiML/TwiML.cs

@@ -1,44 +1,38 @@
 using System.Collections.Generic;
-using System.IO;
 using System.Linq;
-using System.Text;
 using System.Xml.Linq;
-using Twilio.Exceptions;
 
 namespace Twilio.TwiML
 {
-
     /// <summary>
     /// Base class for all TwiML Objects.
     /// </summary>
-    public class TwiML
+    public partial class TwiML
     {
         /// <summary>
         /// Tag name
         /// </summary>
         private string TagName { get; }
+
         /// <summary>
         /// Children elements
         /// </summary>
         private List<TwiML> Children { get; }
+
         /// <summary>
         /// Additional tag attributes to set on the generated xml
         /// </summary>
-        private List<KeyValuePair<string,string>> Options { get; }
-        /// <summary>
-        /// Attribute names to be transformed on the generated xml
-        /// </summary>
-        private Dictionary<string, string> AttributeNameMapper = new Dictionary<string, string> { { "for_", "for" } };
+        private List<KeyValuePair<string, string>> Options { get; }
 
         /// <summary>
         /// Base constructor to create any TwiML instance.
         /// </summary>
         /// <param name="tagName"> TwiML tag name </param>
         protected TwiML(string tagName)
         {
-            this.TagName = tagName;
-            this.Children = new List<TwiML>();
-            this.Options = new List<KeyValuePair<string,string>>();
+            TagName = tagName;
+            Children = new List<TwiML>();
+            Options = new List<KeyValuePair<string, string>>();
         }
 
         /// <summary>
@@ -52,9 +46,9 @@ protected virtual string GetElementBody()
         /// <summary>
         /// Get the TwiML element attributes.
         /// </summary>
-        protected virtual List<XAttribute> GetElementAttributes()
+        protected virtual IEnumerable<XAttribute> GetElementAttributes()
         {
-            return new List<XAttribute>();
+            return Enumerable.Empty<XAttribute>();
         }
 
         /// <summary>
@@ -63,13 +57,13 @@ protected virtual List<XAttribute> GetElementAttributes()
         /// <param name="childElem"> Child TwiML element to add </param>
         public virtual TwiML Append(TwiML childElem)
         {
-            this.Children.Add(childElem);
+            Children.Add(childElem);
             return this;
         }
 
         public TwiML AddText(string text)
         {
-            this.Children.Add(new Text(text));
+            Children.Add(new Text(text));
             return this;
         }
 
@@ -79,7 +73,7 @@ public TwiML AddText(string text)
         /// <param name="childElem"> Child TwiML element to add </param>
         public T Nest<T>(T childElem) where T : TwiML
         {
-            this.Children.Add(childElem);
+            Children.Add(childElem);
             return childElem;
         }
 
@@ -89,7 +83,7 @@ public T Nest<T>(T childElem) where T : TwiML
         /// <param name="tagName"> TwiML tag name </param>
         public TwiML AddChild(string tagName)
         {
-            return this.Nest(new TwiML(tagName));
+            return Nest(new TwiML(tagName));
         }
 
         /// <summary>
@@ -99,12 +93,12 @@ public TwiML AddChild(string tagName)
         /// <param name="value"> Option value </param>
         public TwiML SetOption(string key, object value)
         {
-            if (this.Options.Exists(e => e.Key.Equals(key)))
+            if (Options.Exists(e => e.Key.Equals(key)))
             {
-                this.Options.Remove(this.Options.Find(e => e.Key.Equals(key)));
+                Options.Remove(Options.Find(e => e.Key.Equals(key)));
             }
 
-            this.Options.Add(new KeyValuePair<string, string>(key, value.ToString()));
+            Options.Add(new KeyValuePair<string, string>(key, value.ToString()));
             return this;
         }
 
@@ -114,77 +108,7 @@ public TwiML SetOption(string key, object value)
         /// <param name="key"> Option key </param>
         public virtual string GetOption(string key)
         {
-            return this.Options.Find(e => e.Key.Equals(key)).Value;
-        }
-
-        /// <summary>
-        /// Generate XElement from TwiML object
-        /// </summary>
-        protected virtual XNode ToXml()
-        {
-            var elem = new XElement(this.TagName, this.GetElementBody());
-
-            this.GetElementAttributes().ForEach(attr =>
-            {
-                string transformedAttr = attr.Name.LocalName;
-                if (AttributeNameMapper.TryGetValue(attr.Name.LocalName, out transformedAttr))
-                {
-                    elem.Add(new XAttribute(transformedAttr, attr.Value));
-                }
-                else
-                {
-                    elem.Add(attr);
-                }
-            });
-
-            this.Options.ForEach(e =>
-            {
-                if (e.Key.StartsWith("xml:"))
-                {
-                    var attribute = new XAttribute(XNamespace.Xml + e.Key.Substring(4), e.Value);
-                    elem.Add(attribute);
-                }
-                else
-                {
-                    elem.Add(new XAttribute(e.Key, e.Value));
-                }
-            });
-
-            this.Children.ForEach(child => elem.Add(child.ToXml()));
-
-            return elem;
-        }
-
-        /// <summary>
-        /// Generate XDocument from TwiML object
-        /// </summary>
-        public XDocument ToXDocument()
-        {
-            var declaration = new XDeclaration("1.0", "utf-8", null);
-            var elem = this.ToXml();
-            var document = new XDocument(declaration, elem);
-            return document;
-        }
-
-        /// <summary>
-        /// Generate XML string from TwiML object
-        /// </summary>
-        /// <param name="formattingOptions"> Change generated string format. </param>
-        public string ToString(SaveOptions formattingOptions = SaveOptions.None)
-        {
-            var document = this.ToXDocument();
-            var writer = new Utf8StringWriter();
-            document.Save(writer, formattingOptions);
-            return writer.GetStringBuilder().ToString();
+            return Options.Find(e => e.Key.Equals(key)).Value;
         }
     }
-
-    /// <summary>
-    /// StringWriter which overrides default encoding to use UTF8.
-    /// </summary>
-    public class Utf8StringWriter : StringWriter
-    {
-        public override Encoding Encoding => Encoding.UTF8;
-    }
-
 }