src/ProtocolBuffers/Serialization/XmlFormatWriter.cs

using System;
using System.IO;
using System.Text;
using System.Xml;
using Google.ProtocolBuffers.Descriptors;

namespace Google.ProtocolBuffers.Serialization
{
    /// <summary>
    /// Writes a proto buffer to an XML document or fragment.  .NET 3.5 users may also
    /// use this class to produce Json by setting the options to support Json and providing
    /// an XmlWriter obtained from <see cref="System.Runtime.Serialization.Json.JsonReaderWriterFactory"/>.
    /// </summary>
    public class XmlFormatWriter : AbstractTextWriter
    {
        public const string DefaultRootElementName = "root";
        private const int NestedArrayFlag = 0x0001;
        private readonly XmlWriter _output;
        private string _rootElementName;

        static XmlWriterSettings DefaultSettings(Encoding encoding)
        {
            return new XmlWriterSettings() 
            { 
                CheckCharacters = false, 
                NewLineHandling = NewLineHandling.Entitize, 
                OmitXmlDeclaration = true,
                Encoding = encoding, 
            };
        }

        /// <summary>
        /// Constructs the XmlFormatWriter to write to the given TextWriter
        /// </summary>
        public static XmlFormatWriter CreateInstance(TextWriter output) { return new XmlFormatWriter(XmlWriter.Create(output, DefaultSettings(output.Encoding))); }
        /// <summary>
        /// Constructs the XmlFormatWriter to write to the given stream
        /// </summary>
        public static XmlFormatWriter CreateInstance(Stream output) { return new XmlFormatWriter(XmlWriter.Create(output, DefaultSettings(Encoding.UTF8))); }
        /// <summary>
        /// Constructs the XmlFormatWriter to write to the given stream
        /// </summary>
        public static XmlFormatWriter CreateInstance(Stream output, Encoding encoding) { return new XmlFormatWriter(XmlWriter.Create(output, DefaultSettings(encoding))); }
        /// <summary>
        /// Constructs the XmlFormatWriter to write to the given XmlWriter
        /// </summary>
        public static XmlFormatWriter CreateInstance(XmlWriter output) { return new XmlFormatWriter(output); }

        protected XmlFormatWriter(XmlWriter output)
        {
            _output = output;
            _rootElementName = DefaultRootElementName;
        }

        /// <summary>
        /// Closes the underlying XmlTextWriter
        /// </summary>
        protected override void Dispose(bool disposing)
        {
            if(disposing)
                _output.Close();
        }

        /// <summary>
        /// Gets or sets the default element name to use when using the Merge&lt;TBuilder>()
        /// </summary>
        public string RootElementName
        {
            get { return _rootElementName; }
            set { ThrowHelper.ThrowIfNull(value, "RootElementName"); _rootElementName = value; }
        }

        /// <summary>
        /// Gets or sets the options to use while generating the XML
        /// </summary>
        public XmlWriterOptions Options { get; set; }
        /// <summary>
        /// Sets the options to use while generating the XML
        /// </summary>
        public XmlFormatWriter SetOptions(XmlWriterOptions options) { Options = options; return this; }

        private bool TestOption(XmlWriterOptions option) { return (Options & option) != 0; }

        /// <summary>
        /// Writes a message as an element using the name defined in <see cref="RootElementName"/>
        /// </summary>
        public override void WriteMessage(IMessageLite message)
        { WriteMessage(_rootElementName, message); }

        /// <summary>
        /// Writes a message as an element with the given name
        /// </summary>
        public void WriteMessage(string elementName, IMessageLite message)
        {
            if (TestOption(XmlWriterOptions.OutputJsonTypes))
            {
                _output.WriteStartElement("root"); // json requires this is the root-element
                _output.WriteAttributeString("type", "object");
            }
            else
                _output.WriteStartElement(elementName);

            message.WriteTo(this);
            _output.WriteEndElement();
            _output.Flush();
        }

        /// <summary>
        /// Writes a message
        /// </summary>
        protected override void WriteMessageOrGroup(string field, IMessageLite message)
        {
            _output.WriteStartElement(field);

            if (TestOption(XmlWriterOptions.OutputJsonTypes))
                _output.WriteAttributeString("type", "object");

            message.WriteTo(this);
            _output.WriteEndElement();
        }

        /// <summary>
        /// Writes a String value
        /// </summary>
        protected override void WriteAsText(string field, string textValue, object typedValue)
        {
            _output.WriteStartElement(field);

            if (TestOption(XmlWriterOptions.OutputJsonTypes))
            {
                if (typedValue is int || typedValue is uint || typedValue is long || typedValue is ulong || typedValue is double || typedValue is float)
                    _output.WriteAttributeString("type", "number");
                else if (typedValue is bool)
                    _output.WriteAttributeString("type", "boolean");
            }
            _output.WriteString(textValue);

            //Empty strings should not be written as empty elements '<item/>', rather as '<item></item>'
            if (_output.WriteState == WriteState.Element)
                _output.WriteRaw("");

            _output.WriteEndElement();
        }

        /// <summary>
        /// Writes an array of field values
        /// </summary>
        protected override void WriteArray(FieldType fieldType, string field, System.Collections.IEnumerable items)
        {
            //see if it's empty
            System.Collections.IEnumerator eitems = items.GetEnumerator();
            try { if (!eitems.MoveNext()) return; }
            finally
            { if (eitems is IDisposable) ((IDisposable) eitems).Dispose(); }

            if (TestOption(XmlWriterOptions.OutputNestedArrays | XmlWriterOptions.OutputJsonTypes))
            {
                _output.WriteStartElement(field);
                if (TestOption(XmlWriterOptions.OutputJsonTypes))
                    _output.WriteAttributeString("type", "array");

                base.WriteArray(fieldType, "item", items);
                _output.WriteEndElement();
            }
            else
                base.WriteArray(fieldType, field, items);
        }

        /// <summary>
        /// Writes a System.Enum by the numeric and textual value
        /// </summary>
        protected override void WriteEnum(string field, int number, string name)
        {
            _output.WriteStartElement(field);

            if (!TestOption(XmlWriterOptions.OutputJsonTypes) && TestOption(XmlWriterOptions.OutputEnumValues))
                _output.WriteAttributeString("value", XmlConvert.ToString(number));

            _output.WriteString(name);
            _output.WriteEndElement();
        }
    }
}