Refactor System.Net.* AppContextSwitch usage to LocalAppContextSwitches by rzikm · Pull Request #125385 · dotnet/runtime

rzikm · 2026-03-10T13:43:53Z

Replace instances of AppContextSwitchHelper with LocalAppContextSwitches across System.Net.* assemblies. This change standardizes the handling of configuration switches and improves code maintainability by adopting a consistent pattern for switch management.

This PR does not touch appcontext switches in HTTP code, as it also uses numeric values and has separate implementation in RuntimeSettingsParser helper.

Replace inline AppContext.TryGetSwitch + environment variable patterns with AppContextSwitchHelper.GetBooleanConfig() calls in: - SocketProtocolSupportPal (System.Net.Sockets, Ping, NameResolution) - SslStream.Protocol (DisableTlsResume, EnableServerAiaDownloads) - AuthenticationHelper.NtAuth (UsePortInSpn) - SslAuthenticationOptions (OCSP stapling switch) - HttpListener.Windows (EnableKernelResponseBuffering) - SslKeyLogger (EnableSslKeyLogging) - NegotiateAuthenticationPal.Unix (UseManagedNtlm) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Extend LocalAppContextSwitches.Common.cs with a GetCachedSwitchValue overload that supports environment variable fallback, and add GetBooleanEnvironmentVariable helper method. Create per-library LocalAppContextSwitches.cs files: - System.Net.Security: DisableTlsResume, EnableServerAiaDownloads, EnableOcspStapling - System.Net.Http: UsePortInSpn - System.Net.HttpListener: EnableKernelResponseBuffering This replaces the ad-hoc NullableBool caching pattern with the standard LocalAppContextSwitches pattern used across the codebase (System.Data.Common, System.Diagnostics.DiagnosticSource, etc.). NullableBool.cs is no longer needed in Http and Security. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Move DisableIPv6 from SocketProtocolSupportPal.cs to a new shared Common/src/System/Net/LocalAppContextSwitches.Net.cs file, using the GetSwitchValue + GetBooleanEnvironmentVariable pattern for single-evaluation switches with env var fallback. Move UseManagedNtlm from NegotiateAuthenticationPal.Unix.cs to the System.Net.Security LocalAppContextSwitches.cs, using the same GetSwitchValue pattern with a computed default value for platforms that default to managed NTLM. Replace AppContextSwitchHelper.cs with LocalAppContextSwitches in Sockets, Ping, and NameResolution csprojs. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Use the same GetCachedSwitchValue pattern with an int backing field as all other networking LocalAppContextSwitches properties. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Add GetCachedSwitchValue overload with a defaultValue parameter to LocalAppContextSwitches.Common.cs for switches that have a non-false default. Switch UseManagedNtlm to use the same cached int field pattern as all other networking switches. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…tches Move UseNetworkFramework and EnableSslKeyLogging switches to LocalAppContextSwitches in System.Net.Security. Move DisableConfigurationCache and AppLocalMsQuic switches to a new LocalAppContextSwitches.cs in System.Net.Quic. Remove AppContextSwitchHelper.cs from Security, Quic, and Security unit test csprojs — all networking AppContext switches now use the LocalAppContextSwitches pattern. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Delete the file and remove all remaining csproj references (WinHttpHandler src and tests had unused includes). System.Text.Json has its own local copy which is unaffected. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Move default values to call sites using the defaultValue parameter. Merge the two no-envvar GetCachedSwitchValue overloads into one with 'bool defaultValue = false'. Remove GetSwitchDefaultValue and one GetCachedSwitchValueInternal overload. Affected callers updated to pass defaultValue: true: - SerializationGuard (System.Private.CoreLib) - BinaryFormatterEnabled (System.Runtime.Serialization.Formatters) - IsNetworkingEnabledByDefault (System.Private.Xml) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Use a single GetCachedSwitchValueInternal with a nullable envVariable parameter instead of two separate overloads. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet-policy-service · 2026-03-10T13:45:36Z

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Pull request overview

This PR refactors AppContext switch handling across System.Net.* assemblies by consolidating the various patterns (manual AppContext.TryGetSwitch, NullableBool state machines, and AppContextSwitchHelper) into a unified LocalAppContextSwitches partial class pattern. The common base (LocalAppContextSwitches.Common.cs) is extended with environment variable fallback support, and each assembly defines its specific switches in a local partial class file.

Changes:

Replaced AppContextSwitchHelper and manual AppContext.TryGetSwitch/NullableBool patterns with LocalAppContextSwitches partial class pattern across System.Net.Security, System.Net.Quic, System.Net.Http, System.Net.HttpListener, and shared common code.
Extended LocalAppContextSwitches.Common.cs with environment variable fallback support and moved default value handling from a centralized GetSwitchDefaultValue method to inline defaultValue parameters at each call site.
Updated all .csproj files to reference the new common files and removed references to the now-deleted AppContextSwitchHelper.cs and unnecessary NullableBool.cs.

Reviewed changes

Copilot reviewed 33 out of 33 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
`Common/src/System/LocalAppContextSwitches.Common.cs`	Extended with env variable fallback, new overloads, and `TryGetBooleanEnvironmentVariable` helper; removed `GetSwitchDefaultValue`
`Common/src/System/Net/LocalAppContextSwitches.Net.cs`	New file: shared net-level switches (DisableIPv6, EnableSslKeyLogging)
`Common/src/System/AppContextSwitchHelper.cs`	Deleted: replaced by `LocalAppContextSwitches` pattern
`Common/src/System/Net/Security/SslKeyLogger.cs`	Replaced `#if DEBUG` / `AppContext.TryGetSwitch` with `LocalAppContextSwitches.EnableSslKeyLogging`
`Common/src/System/Net/SocketProtocolSupportPal.cs`	Replaced manual IPv6 disabled check with `LocalAppContextSwitches.DisableIPv6`
`Common/src/Interop/Unix/.../Interop.OpenSsl.cs`	Updated `DisableTlsResume` reference to `LocalAppContextSwitches`
`System.Net.Security/src/.../LocalAppContextSwitches.cs`	New file: Security-specific switches (DisableTlsResume, EnableServerAiaDownloads, EnableOcspStapling, UseManagedNtlm, UseNetworkFramework)
`System.Net.Security/src/.../SslStream.Protocol.cs`	Removed inline switch implementations; updated references
`System.Net.Security/src/.../SslStreamPal.Windows.cs`	Updated DisableTlsResume references
`System.Net.Security/src/.../SslAuthenticationOptions.cs`	Updated OCSP stapling switch usage
`System.Net.Security/src/.../SafeDeleteNwContext.cs`	Updated UseNetworkFramework switch
`System.Net.Security/src/.../NegotiateAuthenticationPal.Unix.cs`	Removed local UseManagedNtlm; uses `LocalAppContextSwitches`
`System.Net.Security/src/System.Net.Security.csproj`	Updated project references
`System.Net.Security/tests/.../System.Net.Security.Unit.Tests.csproj`	Updated test project references
`System.Net.Quic/src/.../LocalAppContextSwitches.cs`	New file: Quic-specific switches (DisableConfigurationCache, AppLocalMsQuic)
`System.Net.Quic/src/.../MsQuicConfiguration.Cache.cs`	Updated ConfigurationCacheEnabled
`System.Net.Quic/src/.../MsQuicApi.cs`	Updated ShouldUseAppLocalMsQuic
`System.Net.Quic/src/System.Net.Quic.csproj`	Updated project references
`System.Net.Http/src/.../LocalAppContextSwitches.cs`	New file: Http-specific switch (UsePortInSpn)
`System.Net.Http/src/.../AuthenticationHelper.NtAuth.cs`	Removed inline UsePortInSpn switch; uses `LocalAppContextSwitches`
`System.Net.Http/src/System.Net.Http.csproj`	Updated project references
`System.Net.Http.WinHttpHandler/src/System.Net.Http.WinHttpHandler.csproj`	Removed unused AppContextSwitchHelper reference
`System.Net.Http.WinHttpHandler/tests/.../Unit.Tests.csproj`	Removed unused AppContextSwitchHelper reference
`System.Net.HttpListener/src/.../LocalAppContextSwitches.cs`	New file: HttpListener-specific switch (EnableKernelResponseBuffering)
`System.Net.HttpListener/src/.../HttpListener.Windows.cs`	Updated reference
`System.Net.HttpListener/src/System.Net.HttpListener.csproj`	Updated project references
`System.Net.Sockets/src/System.Net.Sockets.csproj`	Added new common file references
`System.Net.Ping/src/System.Net.Ping.csproj`	Added new common file references
`System.Net.NameResolution/src/System.Net.NameResolution.csproj`	Added new common file references
`System.Net.NameResolution/tests/.../Pal.Tests.csproj`	Added new common file references
`System.Private.CoreLib/src/.../LocalAppContextSwitches.cs`	Updated SerializationGuard to use defaultValue parameter
`System.Runtime.Serialization.Formatters/src/.../LocalAppContextSwitches.cs`	Updated BinaryFormatterEnabled to use defaultValue parameter
`System.Private.Xml/src/.../LocalAppContextSwitches.cs`	Updated IsNetworkingEnabledByDefault to use defaultValue parameter

Comments suppressed due to low confidence (1)

src/libraries/Common/src/System/LocalAppContextSwitches.Common.cs:63

The out parameter value is not assigned on the false return path (line 63). C# requires all out parameters to be definitely assigned before the method returns. This will cause a compilation error.

Add value = false; before return false;.


            return false;

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src/libraries/Common/src/System/LocalAppContextSwitches.Common.cs

MihaZupan · 2026-03-10T14:04:52Z

src/libraries/Common/src/System/Net/LocalAppContextSwitches.Net.cs

+        private static int s_disableIPv6;
+        internal static bool DisableIPv6
+        {
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            get => GetCachedSwitchValue("System.Net.DisableIPv6", "DOTNET_SYSTEM_NET_DISABLEIPV6", ref s_disableIPv6);
+        }


While we're changing things, can we use a pattern more like this?

public static bool DisableIPv6 { get; } = GetSwitchValue("System.Net.DisableIPv6", "DOTNET_SYSTEM_NET_DISABLEIPV6");

This way the JIT can see that the value can't change, and completely remove unreachable branches when tiering up.

This pattern defeats the purpose of TestSwitch.LocalAppContext.DisableCaching that allows caching to be disabled and turn the appcontext switch on/off without restarting the process.

Also, this pattern is not friendly for startup and trimming: It will read all switches eagerly, even if they are not used by the app. This startup performance hit may be acceptable for System.Net.*, but we would not want to spread it everywhere (CoreLib in particular).

Add missing return statement and fast-path cache check in the GetCachedSwitchValue overload without envVariable parameter. Also fix missing out parameter assignment in TryGetBooleanEnvironmentVariable. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

rzikm and others added 9 commits March 10, 2026 11:36

Use cached int field pattern for DisableIPv6 switch

accd589

Use the same GetCachedSwitchValue pattern with an int backing field as all other networking LocalAppContextSwitches properties. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Remove Common AppContextSwitchHelper.cs

2e01303

Delete the file and remove all remaining csproj references (WinHttpHandler src and tests had unused includes). System.Text.Json has its own local copy which is unaffected. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Merge GetCachedSwitchValueInternal overloads

1cd5696

Use a single GetCachedSwitchValueInternal with a nullable envVariable parameter instead of two separate overloads. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings March 10, 2026 13:43

rzikm changed the title ~~Refactor AppContextSwitch usage to LocalAppContextSwitches~~ Refactor System.Net.* AppContextSwitch usage to LocalAppContextSwitches Mar 10, 2026

dotnet-policy-service bot assigned rzikm Mar 10, 2026

github-actions bot added the area-System.Net label Mar 10, 2026

rzikm requested a review from a team March 10, 2026 13:44

Copilot started reviewing on behalf of rzikm March 10, 2026 13:45 View session

Fix typo

f9eac54

Copilot AI reviewed Mar 10, 2026

View reviewed changes

src/libraries/Common/src/System/LocalAppContextSwitches.Common.cs Show resolved Hide resolved

MihaZupan reviewed Mar 10, 2026

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rzikm and others added 2 commits March 10, 2026 15:39

One more ifdef

2b1e9ef

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Refactor System.Net.* AppContextSwitch usage to LocalAppContextSwitches#125385

Refactor System.Net.* AppContextSwitch usage to LocalAppContextSwitches#125385
rzikm wants to merge 12 commits intodotnet:mainfrom
rzikm:system-net-appctx-switches

rzikm commented Mar 10, 2026 •

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rzikm commented Mar 10, 2026 •

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