Quoted non-string values remain quoted after serialization (#442)

* add failing test for environment variable and annotation yaml serialization

* simplify the test case

* initial tests passing with StringQuotingEmitter

* cleanup

* expand test

* add attribution

* run dotnet format

Author: ridhoq

src/KubernetesClient/StringQuotingEmitter.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Text.RegularExpressions;
+using YamlDotNet.Core;
+using YamlDotNet.Serialization;
+using YamlDotNet.Serialization.EventEmitters;
+
+namespace k8s
+{
+    // adapted from https://github.com/cloudbase/powershell-yaml/blob/master/powershell-yaml.psm1
+    public class StringQuotingEmitter : ChainedEventEmitter
+    {
+        // Patterns from https://yaml.org/spec/1.2/spec.html#id2804356
+        private static readonly Regex quotedRegex =
+            new Regex(@"^(\~|null|true|false|-?(0|[1-9][0-9]*)(\.[0-9]*)?([eE][-+]?[0-9]+)?)?$");
+
+        public StringQuotingEmitter(IEventEmitter next) : base(next)
+        {
+        }
+
+        /// <inheritdoc/>
+        public override void Emit(ScalarEventInfo eventInfo, IEmitter emitter)
+        {
+            var typeCode = eventInfo.Source.Value != null
+                ? Type.GetTypeCode(eventInfo.Source.Type)
+                : TypeCode.Empty;
+            switch (typeCode)
+            {
+                case TypeCode.Char:
+                    if (char.IsDigit((char)eventInfo.Source.Value))
+                    {
+                        eventInfo.Style = ScalarStyle.DoubleQuoted;
+                    }
+
+                    break;
+                case TypeCode.String:
+                    var val = eventInfo.Source.Value.ToString();
+                    if (quotedRegex.IsMatch(val))
+                    {
+                        eventInfo.Style = ScalarStyle.DoubleQuoted;
+                    }
+                    else if (val.IndexOf('\n') > -1)
+                    {
+                        eventInfo.Style = ScalarStyle.Literal;
+                    }
+
+                    break;
+            }
+
+            base.Emit(eventInfo, emitter);
+        }
+    }
+}

src/KubernetesClient/Yaml.cs

@@ -135,6 +135,7 @@ public static string SaveToString<T>(T value)
                     .WithNamingConvention(new CamelCaseNamingConvention())
                     .WithTypeInspector(ti => new AutoRestTypeInspector(ti))
                     .WithTypeConverter(new IntOrStringYamlConverter())
+                    .WithEventEmitter(e => new StringQuotingEmitter(e))
                     .BuildValueSerializer();
             emitter.Emit(new StreamStart());
             emitter.Emit(new DocumentStart());

tests/KubernetesClient.Tests/YamlTests.cs

@@ -291,5 +291,35 @@ public void SerializeIntOrString()
             var output = Yaml.SaveToString<V1Service>(obj);
             Assert.True(ToLines(output).SequenceEqual(ToLines(content)));
         }
+
+        [Fact]
+        public void QuotedValuesShouldRemainQuotedAfterSerialization()
+        {
+            var content = @"apiVersion: v1
+kind: Pod
+metadata:
+  annotations:
+    custom.annotation: ""null""
+  name: cpu-demo
+spec:
+  containers:
+  - env:
+    - name: PORT
+      value: ""3000""
+    - name: NUM_RETRIES
+      value: ""3""
+    - name: ENABLE_CACHE
+      value: ""true""
+    - name: ENABLE_OTHER
+      value: ""false""
+    image: vish/stress
+    name: cpu-demo-ctr";
+            var obj = Yaml.LoadFromString<V1Pod>(content);
+            Assert.NotNull(obj?.Spec?.Containers);
+            var container = Assert.Single(obj.Spec.Containers);
+            Assert.NotNull(container.Env);
+            var objStr = Yaml.SaveToString(obj);
+            Assert.Equal(content, objStr);
+        }
     }
 }