[wasm][net] System.Net.Mail should not throw PNSE for full assembly.

src/libraries/System.Net.Mail/Directory.Build.props

@@ -3,6 +3,5 @@
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
-    <UnsupportedOSPlatforms>browser</UnsupportedOSPlatforms>
   </PropertyGroup>
-</Project>
+</Project>

src/libraries/System.Net.Mail/ref/System.Net.Mail.cs

@@ -165,6 +165,7 @@ public enum MailPriority
         High = 2,
     }
     public delegate void SendCompletedEventHandler(object sender, System.ComponentModel.AsyncCompletedEventArgs e);
+    [System.Runtime.Versioning.UnsupportedOSPlatformAttribute("browser")]
     public partial class SmtpClient : System.IDisposable
     {
         public SmtpClient() { }

src/libraries/System.Net.Mail/src/Resources/Strings.resx

@@ -334,7 +334,4 @@
   <data name="SmtpGetIisPickupDirectoryNotSupported" xml:space="preserve">
     <value>IIS delivery is not supported.</value>
   </data>
-  <data name="SystemNetMail_PlatformNotSupported" xml:space="preserve">
-    <value>System.Net.Mail is not supported on this platform.</value>
-  </data>
 </root>

src/libraries/System.Net.Mail/src/System.Net.Mail.csproj

@@ -5,10 +5,7 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
-  <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemNetMail_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
-  </PropertyGroup>
-  <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
+  <ItemGroup>
     <Compile Include="System\Net\Base64Stream.cs" />
     <Compile Include="System\Net\Mime\MimePart.cs" />
     <Compile Include="System\Net\Mime\Base64WriteStateInfo.cs" />
@@ -43,42 +40,22 @@
     <Compile Include="System\Net\Mail\Attachment.cs" />
     <Compile Include="System\Net\Mail\AttachmentCollection.cs" />
     <Compile Include="System\Net\BufferedReadStream.cs" />
-    <Compile Include="System\Net\Mail\ISmtpAuthenticationModule.cs" />
     <Compile Include="System\Net\Mail\LinkedResource.cs" />
     <Compile Include="System\Net\Mail\LinkedResourceCollection.cs" />
     <Compile Include="System\Net\Mail\MailAddress.cs" />
     <Compile Include="System\Net\Mail\MailAddressCollection.cs" />
-    <Compile Include="System\Net\Mail\NetEventSource.Mail.cs" />
     <Compile Include="System\Net\Mail\MailMessage.cs" />
     <Compile Include="System\Net\Mail\MailPriority.cs" />
-    <Compile Include="System\Net\Mail\MailWriter.cs" />
     <Compile Include="System\Net\Mime\MimeMultiPart.cs" />
     <Compile Include="System\Net\Mime\MimeMultiPartType.cs" />
     <Compile Include="System\Net\Mime\MimeWriter.cs" />
-    <Compile Include="System\Net\Mail\SmtpAuthenticationManager.cs" />
-    <Compile Include="System\Net\Mail\SmtpClient.cs" />
-    <Compile Include="System\Net\Mail\SmtpCommands.cs" />
-    <Compile Include="System\Net\Mail\SmtpConnection.cs" />
-    <Compile Include="System\Net\Mail\SmtpConnection.Auth.cs" />
     <Compile Include="System\Net\Mail\SmtpException.cs" />
     <Compile Include="System\Net\Mail\SmtpFailedRecipientException.cs" />
     <Compile Include="System\Net\Mail\SmtpFailedRecipientsException.cs" />
-    <Compile Include="System\Net\Mail\SmtpReplyReader.cs" />
-    <Compile Include="System\Net\Mail\SmtpReplyReaderFactory.cs" />
     <Compile Include="System\Net\Mail\SmtpStatusCode.cs" />
-    <Compile Include="System\Net\Mail\SmtpTransport.cs" />
-    <Compile Include="System\Net\Mail\SmtpLoginAuthenticationModule.cs" />
-    <Compile Include="System\Net\Mail\SmtpNegotiateAuthenticationModule.cs" />
-    <Compile Include="System\Net\Mail\SmtpNtlmAuthenticationModule.cs" />
     <Compile Include="System\Net\DelegatedStream.cs" />
-    <Compile Include="$(CommonPath)System\Net\TlsStream.cs"
-             Link="Common\System\Net\TlsStream.cs" />
-    <Compile Include="$(CommonPath)System\Net\InternalException.cs"
-             Link="Common\System\Net\InternalException.cs" />
     <Compile Include="$(CommonPath)System\Net\LazyAsyncResult.cs"
              Link="Common\System\Net\LazyAsyncResult.cs" />
-    <Compile Include="$(CommonPath)System\Net\ContextAwareResult.cs"
-             Link="Common\System\Net\ContextAwareResult.cs" />
     <Compile Include="$(CommonPath)System\Net\Mail\MailBnfHelper.cs"
              Link="Common\System\Net\Mail\MailBnfHelper.cs" />
     <Compile Include="$(CommonPath)System\Net\Logging\NetEventSource.Common.cs"
@@ -95,16 +72,48 @@
              Link="Common\System\Net\Mail\QuotedPairReader.cs" />
     <Compile Include="$(CommonPath)System\Net\Mail\DomainLiteralReader.cs"
              Link="Common\System\Net\Mail\DomainLiteralReader.cs" />
-    <Compile Include="$(CommonPath)System\Net\SecurityProtocol.cs"
-             Link="Common\System\Net\SecurityProtocol.cs" />
     <Compile Include="$(CommonPath)System\StringExtensions.cs"
              Link="Common\System\StringExtensions.cs" />
+    <Compile Include="$(CommonPath)System\HexConverter.cs"
+             Link="Common\System\HexConverter.cs" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetsBrowser)' == 'true'">
+    <Compile Include="System\Net\Mail\SmtpClient.Browser.cs" />
+  </ItemGroup>
+
+  <!-- Non Browser specific files - internal and security -->
+  <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
+    <Compile Include="System\Net\Mail\SmtpClient.cs" />
+    <Compile Include="System\Net\Mail\ISmtpAuthenticationModule.cs" />
+    <Compile Include="System\Net\Mail\SmtpAuthenticationManager.cs" />
+    <Compile Include="System\Net\Mail\SmtpCommands.cs" />
+    <Compile Include="System\Net\Mail\SmtpConnection.cs" />
+    <Compile Include="System\Net\Mail\SmtpConnection.Auth.cs" />
+    <Compile Include="System\Net\Mail\SmtpReplyReader.cs" />
+    <Compile Include="System\Net\Mail\SmtpReplyReaderFactory.cs" />
+    <Compile Include="System\Net\Mail\SmtpTransport.cs" />
+    <Compile Include="System\Net\Mail\SmtpLoginAuthenticationModule.cs" />
+    <Compile Include="System\Net\Mail\SmtpNegotiateAuthenticationModule.cs" />
+    <Compile Include="System\Net\Mail\SmtpNtlmAuthenticationModule.cs" />
+    <Compile Include="System\Net\Mail\MailWriter.cs" />
+    <Compile Include="System\Net\Mail\NetEventSource.Mail.cs" />
+    <Compile Include="$(CommonPath)System\Net\ContextAwareResult.cs"
+             Link="Common\System\Net\ContextAwareResult.cs" />
+    <Compile Include="$(CommonPath)System\Net\NTAuthentication.Common.cs"
+             Link="Common\System\Net\NTAuthentication.Common.cs" />
+    <Compile Include="$(CommonPath)System\Net\Security\SSPIHandleCache.cs"
+             Link="Common\System\Net\Security\SSPIHandleCache.cs" />
     <Compile Include="$(CommonPath)System\Net\DebugCriticalHandleMinusOneIsInvalid.cs"
              Link="Common\System\Net\DebugCriticalHandleMinusOneIsInvalid.cs" />
     <Compile Include="$(CommonPath)System\Net\DebugCriticalHandleZeroOrMinusOneIsInvalid.cs"
              Link="Common\System\Net\DebugCriticalHandleZeroOrMinusOneIsInvalid.cs" />
     <Compile Include="$(CommonPath)System\Net\DebugSafeHandle.cs"
              Link="Common\System\Net\DebugSafeHandle.cs" />
+    <Compile Include="$(CommonPath)System\Net\TlsStream.cs"
+             Link="Common\System\Net\TlsStream.cs" />
+    <Compile Include="$(CommonPath)System\Net\InternalException.cs"
+             Link="Common\System\Net\InternalException.cs" />
     <Compile Include="$(CommonPath)System\Net\ExceptionCheck.cs"
              Link="Common\System\Net\ExceptionCheck.cs" />
     <Compile Include="$(CommonPath)System\Collections\Generic\BidirectionalDictionary.cs"
@@ -115,19 +124,16 @@
              Link="Common\System\Net\ContextFlagsPal.cs" />
     <Compile Include="$(CommonPath)System\Net\NegotiationInfoClass.cs"
              Link="Common\System\Net\NegotiationInfoClass.cs" />
-    <Compile Include="$(CommonPath)System\Net\NTAuthentication.Common.cs"
-             Link="Common\System\Net\NTAuthentication.Common.cs" />
     <Compile Include="$(CommonPath)System\Net\SecurityStatusPal.cs"
              Link="Common\System\Net\SecurityStatusPal.cs" />
-    <Compile Include="$(CommonPath)System\Net\Security\SSPIHandleCache.cs"
-             Link="Common\System\Net\Security\SSPIHandleCache.cs" />
     <Compile Include="$(CommonPath)System\Net\Security\NetEventSource.Security.cs"
              Link="Common\System\Net\Security\NetEventSource.Security.cs" />
-    <Compile Include="$(CommonPath)System\HexConverter.cs"
-             Link="Common\System\HexConverter.cs" />
+    <Compile Include="$(CommonPath)System\Net\SecurityProtocol.cs"
+             Link="Common\System\Net\SecurityProtocol.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.UNICODE_STRING.cs"
              Link="Common\Interop\Windows\Interop.UNICODE_STRING.cs" />
   </ItemGroup>
+
   <!-- Unix specific files -->
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
     <Compile Include="$(CommonPath)System\Net\ContextAwareResult.Unix.cs"

src/libraries/System.Net.Mail/src/System/Net/Mail/SmtpClient.Browser.cs

@@ -0,0 +1,160 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.ComponentModel;
+using System.Runtime.Versioning;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Mail
+{
+    public delegate void SendCompletedEventHandler(object sender, AsyncCompletedEventArgs e);
+
+    public enum SmtpDeliveryMethod
+    {
+        Network,
+        SpecifiedPickupDirectory,
+        PickupDirectoryFromIis
+    }
+
+    // EAI Settings
+    public enum SmtpDeliveryFormat
+    {
+        SevenBit = 0, // Legacy
+        International = 1, // SMTPUTF8 - Email Address Internationalization (EAI)
+    }
+
+    [UnsupportedOSPlatform("browser")]
+    public class SmtpClient : IDisposable
+    {
+#pragma warning disable CS0067      // Field is not used
+        public event SendCompletedEventHandler? SendCompleted;
+#pragma warning restore CS0067
+        public SmtpClient()
+        {
+            Initialize();
+        }
+
+        public SmtpClient(string? host)
+        {
+            Initialize();
+        }
+
+        public SmtpClient(string? host, int port)
+        {
+            Initialize();
+        }
+
+        private void Initialize()
+        {
+            throw new PlatformNotSupportedException();
+        }
+
+        public string? Host
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        public int Port
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        public bool UseDefaultCredentials
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        public ICredentialsByHost? Credentials
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        public int Timeout
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        public ServicePoint ServicePoint
+        {
+            get => throw new PlatformNotSupportedException();
+        }
+
+        public SmtpDeliveryMethod DeliveryMethod
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        public SmtpDeliveryFormat DeliveryFormat
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        public string? PickupDirectoryLocation
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        /// <summary>
+        ///    <para>Set to true if we need SSL</para>
+        /// </summary>
+        public bool EnableSsl
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        /// <summary>
+        /// Certificates used by the client for establishing an SSL connection with the server.
+        /// </summary>
+        public X509CertificateCollection ClientCertificates => throw new PlatformNotSupportedException();
+
+        public string? TargetName
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        private bool ServerSupportsEai => throw new PlatformNotSupportedException();
+
+        public void Send(string from, string recipients, string? subject, string? body) => throw new PlatformNotSupportedException();
+
+        public void Send(MailMessage message) => throw new PlatformNotSupportedException();
+
+        public void SendAsync(string from, string recipients, string? subject, string? body, object? userToken) => throw new PlatformNotSupportedException();
+
+        public void SendAsync(MailMessage message, object? userToken) => throw new PlatformNotSupportedException();
+
+        public void SendAsyncCancel()  => throw new PlatformNotSupportedException();
+
+        //************* Task-based async public methods *************************
+        public Task SendMailAsync(string from, string recipients, string? subject, string? body) => throw new PlatformNotSupportedException();
+
+        public Task SendMailAsync(MailMessage message) => throw new PlatformNotSupportedException();
+
+        public Task SendMailAsync(string from, string recipients, string? subject, string? body, CancellationToken cancellationToken) => throw new PlatformNotSupportedException();
+
+        public Task SendMailAsync(MailMessage message, CancellationToken cancellationToken) => throw new PlatformNotSupportedException();
+
+        protected void OnSendCompleted(AsyncCompletedEventArgs e) => throw new PlatformNotSupportedException();
+
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+
+        protected virtual void Dispose(bool disposing)
+        { }
+    }
+}

src/libraries/System.Net.Mail/src/System/Net/Mail/SmtpClient.cs

@@ -6,6 +6,7 @@
 using System.Globalization;
 using System.IO;
 using System.Net.NetworkInformation;
+using System.Runtime.Versioning;
 using System.Security;
 using System.Security.Authentication;
 using System.Security.Cryptography.X509Certificates;
@@ -31,6 +32,7 @@ public enum SmtpDeliveryFormat
         International = 1, // SMTPUTF8 - Email Address Internationalization (EAI)
     }
 
+    [UnsupportedOSPlatform("browser")]
     public class SmtpClient : IDisposable
     {
         private string? _host;

src/libraries/System.Net.Mail/src/System/Net/Mail/SmtpFailedRecipientException.cs

@@ -12,7 +12,10 @@ namespace System.Net.Mail
     public class SmtpFailedRecipientException : SmtpException, ISerializable
     {
         private readonly string? _failedRecipient;
+
+#pragma warning disable CS0649      // Browser - never assigned to
         internal bool fatal;
+#pragma warning restore CS0649
 
         public SmtpFailedRecipientException() : base() { }
 

src/libraries/System.Net.Mail/tests/Functional/AssemblyInfo.cs

@@ -4,4 +4,3 @@
 using Xunit;
 
 [assembly: ActiveIssue("https://github.com/dotnet/runtime/issues/34690", TestPlatforms.Windows, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
-[assembly: SkipOnMono("System.Net.Mail is not supported on wasm", TestPlatforms.Browser)]

src/libraries/System.Net.Mail/tests/Functional/LoggingTest.cs

@@ -9,6 +9,7 @@
 
 namespace System.Net.Mail.Tests
 {
+    [PlatformSpecific(~TestPlatforms.Browser)]  // SmtpClient is not supported on Browser
     public class LoggingTest
     {
         [Fact]

src/libraries/System.Net.Mail/tests/Functional/MailMessageTest.cs

@@ -146,6 +146,7 @@ public void SubjectAndEncodingTest()
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // Not passing as internal System.Net.Mail.MailWriter stripped from build
         public void SentSpecialLengthMailAttachment_Base64Decode_Success()
         {
             // The special length follows pattern: (3N - 1) * 0x4400 + 1

src/libraries/System.Net.Mail/tests/Functional/SmtpClientCredentialsTest.cs

@@ -11,10 +11,11 @@
 
 namespace System.Net.Mail.Functional.Tests
 {
+    [PlatformSpecific(~TestPlatforms.Browser)]  // SmtpClient is not supported on Browser
     public class SmtpClientCredentialsTest
     {
         private readonly string UserName = "user";
-        private readonly string Password = Guid.NewGuid().ToString(); 
+        private readonly string Password = Guid.NewGuid().ToString();
 
         [Fact]
         public void Credentials_Unset_Null()

src/libraries/System.Net.Mail/tests/Functional/SmtpClientTest.cs

@@ -19,6 +19,7 @@
 
 namespace System.Net.Mail.Tests
 {
+    [PlatformSpecific(~TestPlatforms.Browser)]  // SmtpClient is not supported on Browser
     public class SmtpClientTest : FileCleanupTestBase
     {
         private SmtpClient _smtp;

src/libraries/System.Net.Mail/tests/Functional/System.Net.Mail.Functional.Tests.csproj

@@ -2,8 +2,6 @@
   <PropertyGroup>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
-    <!-- Doesn't run tests on Browser since it is not supported. -->
-    <IgnoreForCI Condition="'$(TargetOS)' == 'Browser'">true</IgnoreForCI>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AlternateViewCollectionTest.cs" />
@@ -31,4 +29,4 @@
     <Compile Include="$(CommonTestPath)System\Threading\Tasks\TaskTimeoutExtensions.cs"
              Link="Common\System\Threading\Tasks\TaskTimeoutExtensions.cs" />
   </ItemGroup>
-</Project>
+</Project>