Export to Markdown Support (#1705)

* Adding file writer for Markdown tables. No testing yet.

* Unit tests for the markdown writer

* Wiring up the factory and and request types

* Wiring up changes for Markdown serialization in serialization service

* Couple last minute tweaks

* Changes as per PR comments

* Revert temp testing code. 🙈

* Fluent assertions in SerializationServiceTests.cs

Co-authored-by: Ben Russell <russellben@microsoft.com>

src/Microsoft.SqlTools.ServiceLayer/QueryExecution/DataStorage/SaveAsMarkdownFileStreamWriter.cs

@@ -0,0 +1,101 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Text.RegularExpressions;
+using System.Web;
+using Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.QueryExecution.DataStorage
+{
+    /// <summary>
+    /// Writer for exporting results to a Markdown table.
+    /// </summary>
+    public class SaveAsMarkdownFileStreamWriter : SaveAsStreamWriter
+    {
+        private const string Delimiter = "|";
+        private static readonly Regex NewlineRegex = new Regex(@"(\r\n|\n|\r)", RegexOptions.Compiled);
+
+        private readonly Encoding _encoding;
+        private readonly string _lineSeparator;
+
+        public SaveAsMarkdownFileStreamWriter(
+            Stream stream,
+            SaveResultsAsMarkdownRequestParams requestParams,
+            IReadOnlyList<DbColumnWrapper> columns)
+            : base(stream, requestParams, columns)
+        {
+            // Parse the request params
+            this._lineSeparator = string.IsNullOrEmpty(requestParams.LineSeparator)
+                ? Environment.NewLine
+                : requestParams.LineSeparator;
+            this._encoding = ParseEncoding(requestParams.Encoding, Encoding.UTF8);
+
+            // Output the header if requested
+            if (requestParams.IncludeHeaders)
+            {
+                // Write the column header
+                IEnumerable<string> selectedColumnNames = columns.Skip(this.ColumnStartIndex)
+                    .Take(this.ColumnCount)
+                    .Select(c => EncodeMarkdownField(c.ColumnName));
+                string headerLine = string.Join(Delimiter, selectedColumnNames);
+
+                this.WriteLine($"{Delimiter}{headerLine}{Delimiter}");
+
+                // Write the separator row
+                var separatorBuilder = new StringBuilder(Delimiter);
+                for (int i = 0; i < this.ColumnCount; i++)
+                {
+                    separatorBuilder.Append($"---{Delimiter}");
+                }
+
+                this.WriteLine(separatorBuilder.ToString());
+            }
+        }
+
+        /// <inheritdoc />
+        public override void WriteRow(IList<DbCellValue> row, IReadOnlyList<DbColumnWrapper> columns)
+        {
+            IEnumerable<string> selectedCells = row.Skip(this.ColumnStartIndex)
+                .Take(this.ColumnCount)
+                .Select(c => EncodeMarkdownField(c.DisplayValue));
+            string rowLine = string.Join(Delimiter, selectedCells);
+
+            this.WriteLine($"{Delimiter}{rowLine}{Delimiter}");
+        }
+
+        internal static string EncodeMarkdownField(string? field)
+        {
+            // Special case for nulls
+            if (field == null)
+            {
+                return "NULL";
+            }
+
+            // Escape HTML entities, since Markdown supports inline HTML
+            field = HttpUtility.HtmlEncode(field);
+
+            // Escape pipe delimiters
+            field = field.Replace(@"|", @"\|");
+
+            // @TODO: Allow option to encode multiple whitespace characters as &nbsp;
+
+            // Replace newlines with br tags, since cell values must be single line
+            field = NewlineRegex.Replace(field, @"<br />");
+
+            return field;
+        }
+
+        private void WriteLine(string line)
+        {
+            byte[] bytes = this._encoding.GetBytes(line + this._lineSeparator);
+            this.FileStream.Write(bytes);
+        }
+    }
+}