Add literal style support for OpenApiYamlWriter

src/Microsoft.OpenApi/Writers/OpenApiWriterBase.cs

@@ -23,7 +23,7 @@ public abstract class OpenApiWriterBase : IOpenApiWriter
         /// <summary>
         /// The indentation string to prepand to each line for each indentation level.
         /// </summary>
-        private const string IndentationString = "  ";
+        protected const string IndentationString = "  ";
 
         /// <summary>
         /// Scope of the Open API element - object, array, property.

src/Microsoft.OpenApi/Writers/OpenApiYamlWriter.cs

@@ -27,6 +27,8 @@ public OpenApiYamlWriter(TextWriter textWriter, OpenApiWriterSettings settings)
         {
         }
 
+        public bool UseLiteralStyle { get; set; }
+
         /// <summary>
         /// Base Indentation Level.
         /// This denotes how many indentations are needed for the property in the base object.
@@ -163,11 +165,105 @@ public override void WritePropertyName(string name)
         /// <param name="value">The string value.</param>
         public override void WriteValue(string value)
         {
-            WriteValueSeparator();
+            if (!UseLiteralStyle || value.IndexOfAny(new [] { '\n', '\r' }) == -1)
+            {
+                WriteValueSeparator();
 
-            value = value.GetYamlCompatibleString();
+                value = value.GetYamlCompatibleString();
 
-            Writer.Write(value);
+                Writer.Write(value);
+            }
+            else
+            {
+                if (CurrentScope() != null)
+                {
+                    WriteValueSeparator();
+                }
+
+                Writer.Write("|");
+
+                WriteChompingIndicator(value);
+
+                // Write indentation indicator when it starts with spaces
+                if (value.StartsWith(" "))
+                {
+                    Writer.Write(IndentationString.Length);
+                }
+
+                Writer.WriteLine();
+
+                IncreaseIndentation();
+
+                using (var reader = new StringReader(value))
+                {
+                    bool firstLine = true;
+                    while (reader.ReadLine() is var line && line != null)
+                    {
+                        if (firstLine)
+                            firstLine = false;
+                        else
+                            Writer.WriteLine();
+
+                        // Indentations for empty lines aren't needed.
+                        if (line.Length > 0)
+                        {
+                            WriteIndentation();
+                        }
+
+                        Writer.Write(line);
+                    }
+                }
+
+                DecreaseIndentation();
+            }
+        }
+
+        private void WriteChompingIndicator(string value)
+        {
+            var trailingNewlines = 0;
+            var end = value.Length - 1;
+            // We only need to know whether there are 0, 1, or more trailing newlines
+            while (end >= 0 && trailingNewlines < 2)
+            {
+                var found = value.LastIndexOfAny(new[] { '\n', '\r' }, end, 2);
+                if (found == -1 || found != end)
+                {
+                    // does not ends with newline
+                    break;
+                }
+
+                if (value[end] == '\r')
+                {
+                    // ends with \r
+                    end--;
+                }
+                else if (end > 0 && value[end - 1] == '\r')
+                {
+                    // ends with \r\n
+                    end -= 2;
+                }
+                else
+                {
+                    // ends with \n
+                    end -= 1;
+                }
+                trailingNewlines++;
+            }
+
+            switch (trailingNewlines)
+            {
+                case 0:
+                    // "strip" chomping indicator
+                    Writer.Write("-");
+                    break;
+                case 1:
+                    // "clip"
+                    break;
+                default:
+                    // "keep" chomping indicator
+                    Writer.Write("+");
+                    break;
+            }
         }
 
         /// <summary>

test/Microsoft.OpenApi.Tests/Writers/OpenApiWriterSpecialCharacterTests.cs

@@ -75,5 +75,59 @@ public void WriteStringWithSpecialCharactersAsYamlWorks(string input, string exp
             // Assert
             actual.Should().Be(expected);
         }
+
+        [Theory]
+        [InlineData("multiline\r\nstring", "test: |-\n  multiline\n  string")]
+        [InlineData("ends with\r\nline break\r\n", "test: |\n  ends with\n  line break")]
+        [InlineData("ends with\r\n2 line breaks\r\n\r\n", "test: |+\n  ends with\n  2 line breaks\n")]
+        [InlineData("ends with\r\n3 line breaks\r\n\r\n\r\n", "test: |+\n  ends with\n  3 line breaks\n\n")]
+        [InlineData("  starts with\nspaces", "test: |-2\n    starts with\n  spaces")]
+        [InlineData("  starts with\nspaces, and ends with line break\n", "test: |2\n    starts with\n  spaces, and ends with line break")]
+        [InlineData("contains\n\n\nempty lines", "test: |-\n  contains\n\n\n  empty lines")]
+        [InlineData("no line breaks fallback ", "test: 'no line breaks fallback '")]
+        public void WriteStringWithNewlineCharactersInObjectAsYamlWorks(string input, string expected)
+        {
+            // Arrange
+            var outputStringWriter = new StringWriter(CultureInfo.InvariantCulture);
+            var writer = new OpenApiYamlWriter(outputStringWriter) { UseLiteralStyle = true, };
+
+            // Act
+            writer.WriteStartObject();
+            writer.WritePropertyName("test");
+            writer.WriteValue(input);
+            writer.WriteEndObject();
+            var actual = outputStringWriter.GetStringBuilder().ToString()
+                // Normalize newline for cross platform
+                .Replace("\r", "");
+
+            // Assert
+            actual.Should().Be(expected);
+        }
+
+        [Theory]
+        [InlineData("multiline\r\nstring", "- |-\n  multiline\n  string")]
+        [InlineData("ends with\r\nline break\r\n", "- |\n  ends with\n  line break")]
+        [InlineData("ends with\r\n2 line breaks\r\n\r\n", "- |+\n  ends with\n  2 line breaks\n")]
+        [InlineData("ends with\r\n3 line breaks\r\n\r\n\r\n", "- |+\n  ends with\n  3 line breaks\n\n")]
+        [InlineData("  starts with\nspaces", "- |-2\n    starts with\n  spaces")]
+        [InlineData("  starts with\nspaces, and ends with line break\n", "- |2\n    starts with\n  spaces, and ends with line break")]
+        [InlineData("contains\n\n\nempty lines", "- |-\n  contains\n\n\n  empty lines")]
+        [InlineData("no line breaks fallback ", "- 'no line breaks fallback '")]
+        public void WriteStringWithNewlineCharactersInArrayAsYamlWorks(string input, string expected)
+        {
+            // Arrange
+            var outputStringWriter = new StringWriter(CultureInfo.InvariantCulture);
+            var writer = new OpenApiYamlWriter(outputStringWriter) { UseLiteralStyle = true, };
+
+            // Act
+            writer.WriteStartArray();
+            writer.WriteValue(input);
+            var actual = outputStringWriter.GetStringBuilder().ToString()
+                // Normalize newline for cross platform
+                .Replace("\r", "");
+
+            // Assert
+            actual.Should().Be(expected);
+        }
     }
 }