lennykean · mrotondo · Jun 16, 2026
diff --git a/src/WcfCoreMtomEncoder.Tests/MtomCharsetTests.cs b/src/WcfCoreMtomEncoder.Tests/MtomCharsetTests.cs
@@ -0,0 +1,59 @@
+using System.IO;
+using System.ServiceModel.Channels;
+using System.Text;
+using Xunit;
+
+namespace WcfCoreMtomEncoder.Tests
+{
+    public class MtomCharsetTests
+    {
+        // Regression coverage for the charset parameter on the application/xop+xml root part.
+        // A quoted charset (e.g. charset="utf-8") is valid per RFC 7231 3.1.1.1 and is what IRS MeF
+        // sends; before the fix, GetEncoding was handed the value with the quotes still attached and
+        // threw: System.ArgumentException: '"utf-8"' is not a supported encoding name.
+        [Theory]
+        [InlineData("charset=\"utf-8\"")] // quoted, lowercase  -> the reported crash
+        [InlineData("charset=\"UTF-8\"")] // quoted, uppercase
+        [InlineData("charset=utf-8")]     // unquoted           -> must keep working
+        [InlineData("")]                  // absent             -> must fall back, not NRE
+        public void ReadMessage_decodes_xop_part_regardless_of_charset_quoting(string charsetParameter)
+        {
+            var message = ReadMtomResponse(charsetParameter);
+
+            Assert.NotNull(message);
+            Assert.Equal("Ping", message.GetReaderAtBodyContents().LocalName);
+        }
+
+        // Builds a minimal multipart/related MTOM response whose application/xop+xml root part carries
+        // the given charset token, then decodes it through MtomMessageEncoder (the path GenTax takes).
+        private static Message ReadMtomResponse(string charsetParameter)
+        {
+            MessageEncoder inner = new TextMessageEncodingBindingElement(MessageVersion.Soap11, Encoding.UTF8)
+                .CreateMessageEncoderFactory().Encoder;
+            var encoder = new MtomMessageEncoder(inner);
+
+            const string boundary = "MIMEBoundary_test";
+            var httpContentType =
+                $"multipart/related; boundary=\"{boundary}\"; type=\"application/xop+xml\"; start=\"<root>\"";
+
+            var partContentType = "application/xop+xml"
+                + (string.IsNullOrEmpty(charsetParameter) ? "" : "; " + charsetParameter)
+                + "; type=\"text/xml\"";
+
+            var body =
+                $"--{boundary}\r\n" +
+                "Content-ID: <root>\r\n" +
+                $"Content-Type: {partContentType}\r\n" +
+                "Content-Transfer-Encoding: binary\r\n" +
+                "\r\n" +
+                "<s:Envelope xmlns:s=\"http://schemas.xmlsoap.org/soap/envelope/\">" +
+                "<s:Body><Ping xmlns=\"urn:test\" /></s:Body></s:Envelope>\r\n" +
+                $"--{boundary}--\r\n";
+
+            using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(body)))
+            {
+                return encoder.ReadMessage(stream, int.MaxValue, httpContentType);
+            }
+        }
+    }
+}
diff --git a/src/WcfCoreMtomEncoder.Tests/WcfCoreMtomEncoder.Tests.csproj b/src/WcfCoreMtomEncoder.Tests/WcfCoreMtomEncoder.Tests.csproj
@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="System.ServiceModel.Primitives" Version="10.0.652802" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\WcfCoreMtomEncoder\WcfCoreMtomEncoder.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/WcfCoreMtomEncoder.sln b/src/WcfCoreMtomEncoder.sln
@@ -5,16 +5,42 @@ VisualStudioVersion = 16.0.28803.156
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "WcfCoreMtomEncoder", "WcfCoreMtomEncoder\WcfCoreMtomEncoder.csproj", "{F5F35855-99CB-44E0-9471-BC8BDE86B555}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "WcfCoreMtomEncoder.Tests", "WcfCoreMtomEncoder.Tests\WcfCoreMtomEncoder.Tests.csproj", "{53F07002-4799-4535-BE67-B2CEFDB7A50D}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
+		Debug|x64 = Debug|x64
+		Debug|x86 = Debug|x86
 		Release|Any CPU = Release|Any CPU
+		Release|x64 = Release|x64
+		Release|x86 = Release|x86
 	EndGlobalSection
 	GlobalSection(ProjectConfigurationPlatforms) = postSolution
 		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Debug|x64.Build.0 = Debug|Any CPU
+		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Debug|x86.Build.0 = Debug|Any CPU
 		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Release|Any CPU.Build.0 = Release|Any CPU
+		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Release|x64.ActiveCfg = Release|Any CPU
+		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Release|x64.Build.0 = Release|Any CPU
+		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Release|x86.ActiveCfg = Release|Any CPU
+		{F5F35855-99CB-44E0-9471-BC8BDE86B555}.Release|x86.Build.0 = Release|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Debug|x64.Build.0 = Debug|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Debug|x86.Build.0 = Debug|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Release|x64.ActiveCfg = Release|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Release|x64.Build.0 = Release|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Release|x86.ActiveCfg = Release|Any CPU
+		{53F07002-4799-4535-BE67-B2CEFDB7A50D}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

diff --git a/src/WcfCoreMtomEncoder/MtomMessageEncoder.cs b/src/WcfCoreMtomEncoder/MtomMessageEncoder.cs
@@ -128,8 +128,9 @@ where ReferenceMatch(reference.Attribute("href"), part)
 
         private static Stream CreateStream(string content, MediaTypeHeaderValue contentType)
         {
-            var encoding = !string.IsNullOrEmpty(contentType.CharSet)
-                ? Encoding.GetEncoding(contentType.CharSet)
+            var charset = contentType.CharSet?.Trim('"');
+            var encoding = !string.IsNullOrEmpty(charset)
+                ? Encoding.GetEncoding(charset)
                 : Encoding.Default;
 
             return new MemoryStream(encoding.GetBytes(content));

diff --git a/src/WcfCoreMtomEncoder/MtomPart.cs b/src/WcfCoreMtomEncoder/MtomPart.cs
@@ -50,7 +50,8 @@ public string GetStringContentForEncoder(MessageEncoder encoder)
                 throw new NotSupportedException();
             }
 
-            var encoding = ContentType.CharSet != null ? Encoding.GetEncoding(ContentType.CharSet) : Encoding.Default;
+            var charset = ContentType.CharSet?.Trim('"');
+            var encoding = !string.IsNullOrEmpty(charset) ? Encoding.GetEncoding(charset) : Encoding.Default;
 
             return encoding.GetString(GetRawContent());
         }