Formats/XmlRoundtripWriter.cs

@@ -0,0 +1,235 @@
+using System;
+using System.IO;
+using System.Text;
+using System.Text.RegularExpressions;
+using System.Xml;
+
+namespace XNeedle.Formats
+{
+    /// <summary>
+    /// An XmlWriter that round-trips XML as faithfully as possible:
+    /// - Preserves the source encoding (detected from BOM or XML declaration).
+    /// - Preserves line endings (they live in the document's whitespace text nodes).
+    /// - Optionally strips the space before self-closing tags (&lt;Tag/&gt; vs &lt;Tag /&gt;),
+    ///   auto-detected from whether the input file uses compact style.
+    /// </summary>
+    public sealed class XmlRoundtripWriter : XmlWriter
+    {
+        private readonly XmlTextWriter _inner;
+
+        public override WriteState WriteState => _inner.WriteState;
+
+        private XmlRoundtripWriter(XmlTextWriter inner)
+        {
+            _inner = inner;
+        }
+
+        /// <summary>
+        /// Creates an XmlRoundtripWriter by inspecting the input file for encoding
+        /// and self-closing tag style.
+        /// </summary>
+        public static XmlRoundtripWriter Create(string inputPath, string outputPath)
+        {
+            var rawBytes = File.ReadAllBytes(inputPath);
+            var encoding = DetectEncoding(rawBytes);
+            var rawText = encoding.GetString(rawBytes);
+
+            // Compact self-closing: <Tag/> has a non-whitespace char immediately before '/>'
+            var compact = Regex.IsMatch(rawText, @"\S/>");
+
+            // Detect DOS line endings
+            var dosLineEndings = rawText.Contains("\r\n");
+
+            // Extract verbatim encoding name from the XML declaration to preserve its exact casing
+            string? verbatimEncodingName = null;
+            var encMatch = Regex.Match(rawText, @"encoding\s*=\s*[""']([^""']+)[""']",
+                RegexOptions.IgnoreCase);
+            if (encMatch.Success)
+                verbatimEncodingName = encMatch.Groups[1].Value;
+
+            var streamWriter = new StreamWriter(outputPath, false, encoding);
+            var filterWriter = new FilteringTextWriter(streamWriter, compact, dosLineEndings, verbatimEncodingName);
+            var xmlWriter = new XmlTextWriter(filterWriter)
+            {
+                Formatting = Formatting.None
+            };
+
+            return new XmlRoundtripWriter(xmlWriter);
+        }
+
+        /// <summary>
+        /// Detects encoding from BOM first, then the XML declaration, then defaults to UTF-8.
+        /// </summary>
+        private static Encoding DetectEncoding(byte[] raw)
+        {
+            if (raw.Length >= 3 && raw[0] == 0xEF && raw[1] == 0xBB && raw[2] == 0xBF)
+                return new UTF8Encoding(encoderShouldEmitUTF8Identifier: true);
+            if (raw.Length >= 2 && raw[0] == 0xFF && raw[1] == 0xFE)
+                return Encoding.Unicode;          // UTF-16 LE
+            if (raw.Length >= 2 && raw[0] == 0xFE && raw[1] == 0xFF)
+                return Encoding.BigEndianUnicode; // UTF-16 BE
+
+            // No BOM — probe the XML declaration for an encoding= attribute
+            var probe = Encoding.ASCII.GetString(raw, 0, Math.Min(raw.Length, 256));
+            var match = Regex.Match(probe, @"encoding\s*=\s*[""']([^""']+)[""']",
+                RegexOptions.IgnoreCase);
+            if (match.Success)
+            {
+                try { return Encoding.GetEncoding(match.Groups[1].Value); }
+                catch (ArgumentException) { /* unknown name, fall through */ }
+            }
+
+            return new UTF8Encoding(encoderShouldEmitUTF8Identifier: false);
+        }
+
+        // ── XmlWriter abstract member delegation ──────────────────────────────
+
+        public override void WriteStartDocument()
+            => _inner.WriteStartDocument();
+        public override void WriteStartDocument(bool standalone)
+            => _inner.WriteStartDocument(standalone);
+        public override void WriteEndDocument()
+            => _inner.WriteEndDocument();
+        public override void WriteDocType(string name, string? pubid, string? sysid, string? subset)
+            => _inner.WriteDocType(name, pubid, sysid, subset);
+        public override void WriteStartElement(string? prefix, string localName, string? ns)
+            => _inner.WriteStartElement(prefix, localName, ns);
+        public override void WriteEndElement()
+            => _inner.WriteEndElement();
+        public override void WriteFullEndElement()
+            => _inner.WriteFullEndElement();
+        public override void WriteStartAttribute(string? prefix, string localName, string? ns)
+            => _inner.WriteStartAttribute(prefix, localName, ns);
+        public override void WriteEndAttribute()
+            => _inner.WriteEndAttribute();
+        public override void WriteCData(string? text)
+            => _inner.WriteCData(text);
+        public override void WriteComment(string? text)
+            => _inner.WriteComment(text);
+        public override void WriteProcessingInstruction(string name, string? text)
+            => _inner.WriteProcessingInstruction(name, text);
+        public override void WriteEntityRef(string name)
+            => _inner.WriteEntityRef(name);
+        public override void WriteCharEntity(char ch)
+            => _inner.WriteCharEntity(ch);
+        public override void WriteWhitespace(string? ws)
+            => _inner.WriteWhitespace(ws);
+        public override void WriteString(string? text)
+            => _inner.WriteString(text);
+        public override void WriteSurrogateCharEntity(char lowChar, char highChar)
+            => _inner.WriteSurrogateCharEntity(lowChar, highChar);
+        public override void WriteChars(char[] buffer, int index, int count)
+            => _inner.WriteChars(buffer, index, count);
+        public override void WriteRaw(string data)
+            => _inner.WriteRaw(data);
+        public override void WriteRaw(char[] buffer, int index, int count)
+            => _inner.WriteRaw(buffer, index, count);
+        public override void WriteBase64(byte[] buffer, int index, int count)
+            => _inner.WriteBase64(buffer, index, count);
+        public override string? LookupPrefix(string ns)
+            => _inner.LookupPrefix(ns);
+        public override void Flush()
+            => _inner.Flush();
+        public override void Close()
+            => _inner.Close();
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing) _inner.Close();
+            base.Dispose(disposing);
+        }
+
+        // ── FilteringTextWriter ───────────────────────────────────────────────
+
+        /// <summary>
+        /// Wraps a TextWriter and optionally converts " />" to "/>" via a state machine,
+        /// correctly spanning across multiple Write() calls.
+        /// </summary>
+        private sealed class FilteringTextWriter : TextWriter
+        {
+            private readonly TextWriter _inner;
+            private readonly bool _filter;
+            private readonly bool _dosLineEndings;
+            private readonly string? _verbatimEncodingName;
+
+            private enum State { Normal, SeenSpace, SeenSpaceSlash }
+            private State _state = State.Normal;
+            private bool _lastWasCR = false;
+
+            public FilteringTextWriter(TextWriter inner, bool filter, bool dosLineEndings, string? verbatimEncodingName)
+            {
+                _inner = inner;
+                _filter = filter;
+                _dosLineEndings = dosLineEndings;
+                _verbatimEncodingName = verbatimEncodingName;
+            }
+
+            public override Encoding Encoding => _inner.Encoding;
+
+            public override void Write(char c)
+            {
+                ProcessChar(c);
+            }
+
+            public override void Write(string? value)
+            {
+                if (value is null) return;
+                // XmlTextWriter writes the declaration in pieces; the encoding attribute
+                // arrives as a standalone " encoding="..." " string — match either form.
+                if (_verbatimEncodingName != null && value.Contains("encoding=", StringComparison.OrdinalIgnoreCase))
+                    value = Regex.Replace(value, @"encoding=[""']([^""']+)[""']",
+                        $"encoding=\"{_verbatimEncodingName}\"", RegexOptions.IgnoreCase);
+                foreach (var c in value) ProcessChar(c);
+            }
+
+            private void ProcessChar(char c)
+            {
+                // Restore DOS line endings stripped by XmlTextWriter's normalisation
+                if (_dosLineEndings && c == '\n' && !_lastWasCR)
+                {
+                    Emit('\r');
+                }
+                _lastWasCR = (c == '\r');
+
+                if (!_filter) { _inner.Write(c); return; }
+
+                switch (_state)
+                {
+                    case State.Normal:
+                        if (c == ' ') _state = State.SeenSpace;
+                        else          Emit(c);
+                        break;
+
+                    case State.SeenSpace:
+                        if (c == '/')  _state = State.SeenSpaceSlash;
+                        else         { Emit(' '); _state = State.Normal; ProcessChar(c); }
+                        break;
+
+                    case State.SeenSpaceSlash:
+                        if (c == '>') { _inner.Write("/>"); _state = State.Normal; }
+                        else         { Emit(' '); Emit('/'); _state = State.Normal; ProcessChar(c); }
+                        break;
+                }
+            }
+
+            private void Emit(char c) => _inner.Write(c);
+
+            public override void Flush()
+            {
+                // Drain any partially-matched state
+                if (_filter)
+                {
+                    if      (_state == State.SeenSpace)      { _inner.Write(' ');  _state = State.Normal; }
+                    else if (_state == State.SeenSpaceSlash) { _inner.Write(" /"); _state = State.Normal; }
+                }
+                _inner.Flush();
+            }
+
+            protected override void Dispose(bool disposing)
+            {
+                if (disposing) { Flush(); _inner.Dispose(); }
+                base.Dispose(disposing);
+            }
+        }
+    }
+}

Program.cs

@@ -6,6 +6,7 @@ using Sprache;
 using XNeedle.Parser;
 using XNeedle.Parser.Elements;
 using XNeedle.Transformation;
+using XNeedle.Formats;
 
 namespace XNeedle
 {
@@ -37,33 +38,11 @@ namespace XNeedle
             var masterRule = (Rule)XnParser.RuleObject.Parse(File.ReadAllText(opts.XnDefinition));
             var doc = XDocument.Load(opts.Input, LoadOptions.PreserveWhitespace);
             masterRule.Transform(doc);
-            doc.Save(opts.Output, SaveOptions.DisableFormatting);
-            
+            using var writer = XmlRoundtripWriter.Create(opts.Input, opts.Output);
+            doc.WriteTo(writer);
             Console.WriteLine($"Applied \"{opts.XnDefinition}\" to \"{opts.Input}\" and saved result to \"{opts.Output}\"");
         }
 
         static void HandleParseError(IEnumerable<Error> errs) {}
     }
-
-    public static class DocumentExtensions
-    {
-        public static XmlDocument ToXmlDocument(this XDocument xDocument)
-        {
-            var xmlDocument = new XmlDocument();
-            using(var xmlReader = xDocument.CreateReader())
-            {
-                xmlDocument.Load(xmlReader);
-            }
-            return xmlDocument;
-        }
-
-        public static XDocument ToXDocument(this XmlDocument xmlDocument)
-        {
-            using (var nodeReader = new XmlNodeReader(xmlDocument))
-            {
-                nodeReader.MoveToContent();
-                return XDocument.Load(nodeReader);
-            }
-        }
-    }
 }