Improve JsonEncoder.EscapeString and fix test warnings for ToString()

Stack/Opc.Ua.Core/Types/Encoders/JsonEncoder.cs

@@ -16,6 +16,7 @@ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 using System.IO;
 using System.Runtime.CompilerServices;
 using System.Text;
+using System.Threading;
 using System.Xml;
 
 namespace Opc.Ua
@@ -35,6 +36,8 @@ public class JsonEncoder : IJsonEncoder
         private static readonly char s_rightCurlyBrace = '}';
         private static readonly char s_leftSquareBracket = '[';
         private static readonly char s_rightSquareBracket = ']';
+        private StringBuilder m_stringBuilder = new StringBuilder();
+        private static readonly UTF8Encoding s_utf8Encoding = new UTF8Encoding(false);
         private Stream m_stream;
         private MemoryStream m_memoryStream;
         private StreamWriter m_writer;
@@ -87,12 +90,12 @@ public JsonEncoder(
             if (m_stream == null)
             {
                 m_memoryStream = new MemoryStream();
-                m_writer = new StreamWriter(m_memoryStream, new UTF8Encoding(false), streamSize, false);
+                m_writer = new StreamWriter(m_memoryStream, s_utf8Encoding, streamSize, false);
                 m_leaveOpen = false;
             }
             else
             {
-                m_writer = new StreamWriter(m_stream, new UTF8Encoding(false), streamSize, m_leaveOpen);
+                m_writer = new StreamWriter(m_stream, s_utf8Encoding, streamSize, m_leaveOpen);
             }
 
             InitializeWriter();
@@ -117,7 +120,7 @@ public JsonEncoder(
             if (m_writer == null)
             {
                 m_stream = new MemoryStream();
-                m_writer = new StreamWriter(m_stream, new UTF8Encoding(false), kStreamWriterBufferSize);
+                m_writer = new StreamWriter(m_stream, s_utf8Encoding, kStreamWriterBufferSize);
             }
 
             InitializeWriter();
@@ -293,11 +296,11 @@ public int Close()
             {
                 if (m_topLevelIsArray)
                 {
-                    m_writer.Write("]");
+                    m_writer.Write(']');
                 }
                 else
                 {
-                    m_writer.Write("}");
+                    m_writer.Write('}');
                 }
             }
 
@@ -498,38 +501,45 @@ public void PopNamespace()
             m_namespaces.Pop();
         }
 
-        private static readonly char[] m_specialChars = new char[] { s_quotation, s_backslash, '\n', '\r', '\t', '\b', '\f', };
-        private static readonly char[] m_substitution = new char[] { s_quotation, s_backslash, 'n', 'r', 't', 'b', 'f' };
+        private static readonly Dictionary<char, string> m_substitution = new Dictionary<char, string>
+        {
+            { s_quotation, "\\\"" },
+            { s_backslash, "\\\\" },
+            { '\n', "\\n" },
+            { '\r', "\\r" },
+            { '\t', "\\t" },
+            { '\b', "\\b" },
+            { '\f', "\\f" }
+        };
 
+        /// <summary>
+        /// Escapes a string and writes it to the stream.
+        /// </summary>
+        /// <param name="value"></param>
         private void EscapeString(string value)
         {
+            m_stringBuilder.Clear();
+            m_stringBuilder.EnsureCapacity(value.Length * 2);
+
             foreach (char ch in value)
             {
-                bool found = false;
-
-                for (int ii = 0; ii < m_specialChars.Length; ii++)
+                // Check if ch is present in the dictionary
+                if (m_substitution.TryGetValue(ch, out string escapeSequence))
                 {
-                    if (m_specialChars[ii] == ch)
-                    {
-                        m_writer.Write(s_backslash);
-                        m_writer.Write(m_substitution[ii]);
-                        found = true;
-                        break;
-                    }
+                    m_stringBuilder.Append(escapeSequence);
                 }
-
-                if (!found)
+                else if (ch < 32)
                 {
-                    if (ch < 32)
-                    {
-                        m_writer.Write("\\u");
-                        m_writer.Write("{0:X4}", (int)ch);
-                        continue;
-                    }
-
-                    m_writer.Write(ch);
+                    m_stringBuilder.Append("\\u");
+                    m_stringBuilder.Append(((int)ch).ToString("X4", CultureInfo.InvariantCulture));
+                }
+                else
+                {
+                    m_stringBuilder.Append(ch);
                 }
             }
+
+            m_writer.Write(m_stringBuilder);
         }
 
         private void WriteSimpleField(string fieldName, string value, bool quotes)