Enhance performance and memory management across the codebase

- Added `Microsoft.Extensions.ObjectPool` package for improved object pooling.
- Introduced `Microsoft.NETFramework.ReferenceAssemblies.net462` for `net462` target framework.
- Updated project warnings and added `AllowUnsafeBlocks` property for specific frameworks.
- Refactored multiple `ToString` methods and other string handling to use `ValueStringBuilder`, reducing allocations and improving performance.
- Updated `SIPAuthorisationDigest` and `SIPConstants` for better memory management using `AsSpan()` and `ValueStringBuilder`.
- Enhanced `CRC32` class and JSON serialization in `JSONWriter` to utilize span-based operations for efficiency.
- Updated unit tests to reflect changes in logging and data handling.

Author: Paulo Morgado

src/SIPSorcery.csproj

@@ -21,6 +21,7 @@
     <PackageReference Include="Concentus" Version="2.2.2" />
     <PackageReference Include="BouncyCastle.Cryptography" Version="2.5.1" />
     <PackageReference Include="DnsClient" Version="1.8.0" />
+    <PackageReference Include="Microsoft.Extensions.ObjectPool" Version="8.0.16" />
     <PackageReference Include="SIPSorcery.WebSocketSharp" Version="0.0.1" />
     <PackageReference Include="SIPSorceryMedia.Abstractions" Version="8.0.10" />
     <PackageReference Include="System.Net.WebSockets.Client" Version="4.3.2" />
@@ -35,15 +36,22 @@
     <PackageReference Include="Microsoft.Bcl.HashCode" Version="6.0.0" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFramework)' == 'net462'">
+    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies.net462" Version="1.0.3">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;netstandard2.1;netcoreapp3.1;net462;net5.0;net6.0;net8.0</TargetFrameworks>
     <LangVersion>12.0</LangVersion>
     <SuppressTfmSupportBuildWarnings>true</SuppressTfmSupportBuildWarnings>
-    <NoWarn>$(NoWarn);SYSLIB0050</NoWarn>
+    <NoWarn>$(NoWarn);SYSLIB0050;CS1591;CS1573;CS1587</NoWarn>
     <TreatWarningsAsErrors>True</TreatWarningsAsErrors>
+    <WarningsNotAsErrors>$(WarningsNotAsErrors);NU1510;CS0809;CS0618;CS8632</WarningsNotAsErrors>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <!-- Disable warning for missing XML doc comments. -->
-    <NoWarn>$(NoWarn);CS1591;CS1573;CS1587</NoWarn>
     <Authors>Aaron Clauson, Christophe Irles, Rafael Soares &amp; Contributors</Authors>
     <Copyright>Copyright © 2010-2025 Aaron Clauson</Copyright>
     <PackageLicenseExpression>BSD-3-Clause</PackageLicenseExpression>
@@ -93,6 +101,7 @@
     <IncludeSymbols>true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <ContinuousIntegrationBuild Condition="'$(CI)' == 'true'">true</ContinuousIntegrationBuild>
+    <AllowUnsafeBlocks Condition="'$(TargetFramework)' == 'net462' OR '$(TargetFramework)' == 'netstandard2.0'">true</AllowUnsafeBlocks>
   </PropertyGroup>
 
 </Project>

src/core/SIP/SIPAuthorisationDigest.cs

@@ -256,24 +256,116 @@ public string GetDigest()
 
         public override string ToString()
         {
-            string authHeader = AuthHeaders.AUTH_DIGEST_KEY + " ";
-
-            authHeader += (Username != null && Username.Trim().Length != 0) ? AuthHeaders.AUTH_USERNAME_KEY + "=\"" + Username + "\"" : null;
-            authHeader += (authHeader.IndexOf('=') != -1) ? "," + AuthHeaders.AUTH_REALM_KEY + "=\"" + Realm + "\"" : AuthHeaders.AUTH_REALM_KEY + "=\"" + Realm + "\"";
-            authHeader += (Nonce != null) ? "," + AuthHeaders.AUTH_NONCE_KEY + "=\"" + Nonce + "\"" : null;
-            authHeader += (URI != null && URI.Trim().Length != 0) ? "," + AuthHeaders.AUTH_URI_KEY + "=\"" + URI + "\"" : null;
-            authHeader += (Response != null && Response.Length != 0) ? "," + AuthHeaders.AUTH_RESPONSE_KEY + "=\"" + Response + "\"" : null;
-            authHeader += (Cnonce != null) ? "," + AuthHeaders.AUTH_CNONCE_KEY + "=\"" + Cnonce + "\"" : null;
-            authHeader += (NonceCount != 0) ? "," + AuthHeaders.AUTH_NONCECOUNT_KEY + "=" + GetPaddedNonceCount(NonceCount) : null;
-            authHeader += (Qop != null) ? "," + AuthHeaders.AUTH_QOP_KEY + "=" + Qop : null;
-            authHeader += (Opaque != null) ? "," + AuthHeaders.AUTH_OPAQUE_KEY + "=\"" + Opaque + "\"" : null;
-
-            string algorithmID = (DigestAlgorithm == DigestAlgorithmsEnum.SHA256) ? SHA256_ALGORITHM_ID : DigestAlgorithm.ToString();
-            authHeader += (Response != null) ? "," + AuthHeaders.AUTH_ALGORITHM_KEY + "=" + algorithmID : null;
-
-            return authHeader;
+            var builder = new ValueStringBuilder();
+
+            try
+            {
+                ToString(ref builder);
+
+                return builder.ToString();
+            }
+            finally
+            {
+                builder.Dispose();
+            }
+        }
+
+        internal void ToString(ref ValueStringBuilder builder)
+        {
+            builder.Append(AuthHeaders.AUTH_DIGEST_KEY);
+            builder.Append(' ');
+
+            bool hasUsername = !string.IsNullOrWhiteSpace(Username);
+            if (hasUsername)
+            {
+                builder.Append(AuthHeaders.AUTH_USERNAME_KEY);
+                builder.Append("=\"");
+                builder.Append(Username);
+                builder.Append('"');
+            }
+
+            builder.Append(hasUsername ? ',' : '\0');
+            builder.Append(AuthHeaders.AUTH_REALM_KEY);
+            builder.Append("=\"");
+            builder.Append(Realm);
+            builder.Append('"');
+
+            if (Nonce != null)
+            {
+                builder.Append(',');
+                builder.Append(AuthHeaders.AUTH_NONCE_KEY);
+                builder.Append("=\"");
+                builder.Append(Nonce);
+                builder.Append('"');
+            }
+
+            if (!string.IsNullOrWhiteSpace(URI))
+            {
+                builder.Append(',');
+                builder.Append(AuthHeaders.AUTH_URI_KEY);
+                builder.Append("=\"");
+                builder.Append(URI);
+                builder.Append('"');
+            }
+
+            if (!string.IsNullOrEmpty(Response))
+            {
+                builder.Append(',');
+                builder.Append(AuthHeaders.AUTH_RESPONSE_KEY);
+                builder.Append("=\"");
+                builder.Append(Response);
+                builder.Append('"');
+            }
+
+            if (Cnonce != null)
+            {
+                builder.Append(',');
+                builder.Append(AuthHeaders.AUTH_CNONCE_KEY);
+                builder.Append("=\"");
+                builder.Append(Cnonce);
+                builder.Append('"');
+            }
+
+            if (NonceCount != 0)
+            {
+                builder.Append(',');
+                builder.Append(AuthHeaders.AUTH_NONCECOUNT_KEY);
+                builder.Append('=');
+                builder.Append(GetPaddedNonceCount(NonceCount));
+        }
+
+            if (Qop != null)
+            {
+                builder.Append(',');
+                builder.Append(AuthHeaders.AUTH_QOP_KEY);
+                builder.Append('=');
+                builder.Append(Qop);
+            }
+
+            if (Opaque != null)
+            {
+                builder.Append(',');
+                builder.Append(AuthHeaders.AUTH_OPAQUE_KEY);
+                builder.Append("=\"");
+                builder.Append(Opaque);
+                builder.Append('"');
+            }
+
+            if (Response != null)
+            {
+                builder.Append(',');
+                builder.Append(AuthHeaders.AUTH_ALGORITHM_KEY);
+                builder.Append('=');
+
+                string algorithmID = (DigestAlgorithm == DigestAlgorithmsEnum.SHA256)
+                ? SHA256_ALGORITHM_ID
+                : DigestAlgorithm.ToString();
+
+                builder.Append(algorithmID);
+            }
         }
 
+
         public SIPAuthorisationDigest CopyOf()
         {
             var copy = new SIPAuthorisationDigest(AuthorisationType, Realm, Username, Password, URI, Nonce, RequestType, DigestAlgorithm);
@@ -385,21 +477,21 @@ public static string GetHashHex(DigestAlgorithmsEnum hashAlg, string val)
                 case DigestAlgorithmsEnum.SHA256:
                     using (var hash = new SHA256CryptoServiceProvider())
                     {
-                        return hash.ComputeHash(Encoding.UTF8.GetBytes(val)).HexStr().ToLower();
+                        return hash.ComputeHash(Encoding.UTF8.GetBytes(val)).AsSpan().HexStr(lowercase: true);
                     }
                 // This is commented because RFC8760 does not have an SHA-512 option. Instead it's HSA-512-sess which
                 // means the SIP request body needs to be included in the digest as well. Including the body will require 
                 // some additional changes that can be done at a later date.
                 //case DigestAlgorithmsEnum.SHA512:
                 //    using (var hash = new SHA512CryptoServiceProvider())
                 //    {
-                //        return hash.ComputeHash(Encoding.UTF8.GetBytes(val)).HexStr().ToLower();
+                //        return hash.ComputeHash(Encoding.UTF8.GetBytes(val)).HexStr(lowercase: false);
                 //    }
                 case DigestAlgorithmsEnum.MD5:
                 default:
                     using (var hash = new MD5CryptoServiceProvider())
                     {
-                        return hash.ComputeHash(Encoding.UTF8.GetBytes(val)).HexStr().ToLower();
+                        return hash.ComputeHash(Encoding.UTF8.GetBytes(val)).AsSpan().HexStr(lowercase: true);
                     }
             }
 #pragma warning restore SYSLIB0021

src/core/SIP/SIPConstants.cs

@@ -541,17 +541,68 @@ public static string SIPURIUserUnescape(string escapedString)
 
         public static string SIPURIParameterEscape(string unescapedString)
         {
-            string result = unescapedString;
-            if (!result.IsNullOrBlank())
+            // Characters that need escaping
+            ReadOnlySpan<char> specialChars = stackalloc char[] { ';', '?', '@', '=', ',', ' ' };
+
+            // Early exit if no special characters are found
+            var unescapedSpan = unescapedString.AsSpan();
+            int nextIndex = unescapedSpan.IndexOfAny(specialChars);
+            if (nextIndex == -1)
             {
-                result = result.Replace(";", "%3B");
-                result = result.Replace("?", "%3F");
-                result = result.Replace("@", "%40");
-                result = result.Replace("=", "%3D");
-                result = result.Replace(",", "%2C");
-                result = result.Replace(" ", "%20");
+                // No escaping needed
+                return unescapedString;
+            }
+
+            var builder = new ValueStringBuilder();
+
+            try
+            {
+                SIPURIParameterEscape(ref builder, unescapedSpan);
+
+                return builder.ToString();
+            }
+            finally
+            {
+                builder.Dispose();
+            }
+        }
+
+        internal static void SIPURIParameterEscape(ref ValueStringBuilder builder, ReadOnlySpan<char> unescapedSpan)
+        {
+            // Characters that need escaping
+            ReadOnlySpan<char> specialChars = stackalloc char[] { ';', '?', '@', '=', ',', ' ' };
+
+            var currentIndex = 0;
+            var nextIndex = unescapedSpan.IndexOfAny(specialChars);
+            while (nextIndex != -1)
+            {
+                // Append everything before the special character
+                builder.Append(unescapedSpan.Slice(currentIndex, nextIndex - currentIndex));
+
+                // Escape the special character
+                switch (unescapedSpan[nextIndex])
+                {
+                    case ';': builder.Append("%3B"); break;
+                    case '?': builder.Append("%3F"); break;
+                    case '@': builder.Append("%40"); break;
+                    case '=': builder.Append("%3D"); break;
+                    case ',': builder.Append("%2C"); break;
+                    case ' ': builder.Append("%20"); break;
+                }
+
+                currentIndex = nextIndex + 1;
+                nextIndex = unescapedSpan.Slice(currentIndex).IndexOfAny(specialChars);
+                if (nextIndex != -1)
+                {
+                    nextIndex += currentIndex; // Adjust relative index to absolute
+                }
+            }
+
+            // Append the remaining part
+            if (currentIndex < unescapedSpan.Length)
+            {
+                builder.Append(unescapedSpan.Slice(currentIndex));
             }
-            return result;
         }
 
         public static string SIPURIParameterUnescape(string escapedString)