Refactor STUN code for clarity and consistency (#1653)

Replaced manual string comparisons with StringComparison.OrdinalIgnoreCase and placed constants first in comparisons. Refactored switch statements to use switch expressions with spans. Updated header concatenation to use string interpolation. Used string.IsNullOrWhiteSpace for null/whitespace checks. Changed method overrides to use override instead of new where appropriate.

Author: paulomorgado

src/SIPSorcery/net/STUN/STUNAppState.cs

@@ -40,7 +40,7 @@ public static string PrintBuffer(byte[] buffer)
 
                 if (byteStr.Length == 1)
                 {
-                    bufferStr += "0" + byteStr;
+                    bufferStr += $"0{byteStr}";
                 }
                 else
                 {

src/SIPSorcery/net/STUN/STUNAttributes/STUNAddressAttribute.cs

@@ -95,7 +95,7 @@ public override int ToByteBuffer(byte[] buffer, int startIndex)
 
         public override string ToString()
         {
-            string attrDescrStr = "STUN Attribute: " + base.AttributeType + ", address=" + Address.ToString() + ", port=" + Port + ".";
+            string attrDescrStr = $"STUN Attribute: {base.AttributeType}, address={Address.ToString()}, port={Port}.";
 
             return attrDescrStr;
         }

src/SIPSorcery/net/STUN/STUNAttributes/STUNAttribute.cs

@@ -220,7 +220,7 @@ public static List<STUNAttribute> ParseMessageAttributes(byte[] buffer, int star
 
                     attributes.Add(attribute);
 
-                    // Attributes start on 32 bit word boundaries so where an attribute length is not a multiple of 4 it gets padded. 
+                    // Attributes start on 32 bit word boundaries so where an attribute length is not a multiple of 4 it gets padded.
                     int padding = (stunAttributeLength % 4 != 0) ? 4 - (stunAttributeLength % 4) : 0;
 
                     startAttIndex = startAttIndex + 4 + stunAttributeLength + padding;
@@ -258,7 +258,7 @@ public virtual int ToByteBuffer(byte[] buffer, int startIndex)
 
         public new virtual string ToString()
         {
-            string attrDescrString = "STUN Attribute: " + AttributeType.ToString() + ", length=" + PaddedLength + ".";
+            string attrDescrString = $"STUN Attribute: {AttributeType.ToString()}, length={PaddedLength}.";
 
             return attrDescrString;
         }

src/SIPSorcery/net/STUN/STUNAttributes/STUNChangeRequestAttribute.cs

@@ -53,7 +53,7 @@ public STUNChangeRequestAttribute(byte[] attributeValue)
 
         public override string ToString()
         {
-            string attrDescrStr = "STUN Attribute: " + STUNAttributeTypesEnum.ChangeRequest.ToString() + ", key byte=" + m_changeRequestByte.ToString("X") + ", change address=" + ChangeAddress + ", change port=" + ChangePort + ".";
+            string attrDescrStr = $"STUN Attribute: {STUNAttributeTypesEnum.ChangeRequest.ToString()}, key byte={m_changeRequestByte.ToString("X")}, change address={ChangeAddress}, change port={ChangePort}.";
 
             return attrDescrStr;
         }

src/SIPSorcery/net/STUN/STUNAttributes/STUNConnectionIdAttribute.cs

@@ -44,7 +44,7 @@ public STUNConnectionIdAttribute(uint connectionId)
 
         public override string ToString()
         {
-            string attrDescrStr = "STUN CONNECTION_ID Attribute: value=" + ConnectionId + ".";
+            string attrDescrStr = $"STUN CONNECTION_ID Attribute: value={ConnectionId}.";
 
             return attrDescrStr;
         }

src/SIPSorcery/net/STUN/STUNAttributes/STUNErrorCodeAttribute.cs

@@ -60,7 +60,7 @@ private static byte[] BuildValue(int errorCode, string reasonPhrase)
 
         public override string ToString()
         {
-            string attrDescrStr = "STUN ERROR_CODE_ADDRESS Attribute: error code=" + ErrorCode + ", reason phrase=" + ReasonPhrase + ".";
+            string attrDescrStr = $"STUN ERROR_CODE_ADDRESS Attribute: error code={ErrorCode}, reason phrase={ReasonPhrase}.";
 
             return attrDescrStr;
         }

src/SIPSorcery/net/STUN/STUNAttributes/STUNXORAddressAttribute.cs

@@ -133,7 +133,7 @@ public override int ToByteBuffer(byte[] buffer, int startIndex)
 
         public override string ToString()
         {
-            string attrDescrStr = "STUN XOR_MAPPED_ADDRESS Attribute: " + base.AttributeType + ", address=" + Address.ToString() + ", port=" + Port + ".";
+            string attrDescrStr = $"STUN XOR_MAPPED_ADDRESS Attribute: {base.AttributeType}, address={Address.ToString()}, port={Port}.";
 
             return attrDescrStr;
         }

src/SIPSorcery/net/STUN/STUNMessage.cs

@@ -198,13 +198,13 @@ public byte[] ToByteBuffer(byte[] messageIntegrityKey, bool addFingerprint)
             return buffer;
         }
 
-        public new string ToString()
+        public override string ToString()
         {
-            string messageDescr = "STUN Message: " + Header.MessageType.ToString() + ", length=" + Header.MessageLength;
+            string messageDescr = $"STUN Message: {Header.MessageType.ToString()}, length={Header.MessageLength}";
 
             foreach (STUNAttribute attribute in Attributes)
             {
-                messageDescr += "\n " + attribute.ToString();
+                messageDescr += $"\n {attribute.ToString()}";
             }
 
             return messageDescr;