[Android] Bridge SocketsHttpHandler to java.net.ProxySelector

[simonrozsival]

Note

This pull request (description and code) was drafted with the assistance of GitHub Copilot CLI.

Summary

Adds an AndroidPlatformProxy : IWebProxy that resolves the system proxy chain for SocketsHttpHandler on Android by JNI-calling java.net.ProxySelector.getDefault().select(URI.create(url)).

This brings the Android system proxy — Wi-Fi proxy, MDM-deployed proxy, PAC scripts, per-network and VPN-attached ProxyInfo — to the managed HTTP stack, matching the behavior HttpURLConnection / AndroidMessageHandler exhibit today. Closes the largest behavioral regression apps would face when flipping the default HttpClientHandler backend from AndroidMessageHandler to SocketsHttpHandler on net*-android* (SystemProxyInfo.Unix.cs currently honors only env vars on Android).

Implementation lives entirely in dotnet/runtime — no dependency on dotnet/android, no [UnsafeAccessor] into Mono.Android.

Background

HttpClient.DefaultProxy on Android currently resolves to HttpEnvironmentProxy (env-var only) via the shared Unix path:

runtime/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SystemProxyInfo.Unix.cs

In contrast, java.net.HttpURLConnection (and therefore AndroidMessageHandler) defers to java.net.ProxySelector.getDefault(), which on Android consults system properties, ConnectivityManager.getDefaultProxy(), per-network LinkProperties.getHttpProxy(), and PAC scripts (via the privileged PacProxyService). All of that is silently lost when an app switches to SocketsHttpHandler today.

What this PR changes

Native PAL (System.Security.Cryptography.Native.Android)

• pal_proxy.{h,c} — AndroidCryptoNative_GetProxyForUrl / AndroidCryptoNative_FreeProxyResult.
  • Pure C/JNI; no .java helper (we're just calling APIs, not implementing a Java interface).
  • Uses the existing pal_jni.h macros (INIT_LOCALS, RELEASE_LOCALS, ON_EXCEPTION_PRINT_AND_GOTO) for leak-safe local-ref handling on every exception path.
  • Per-iteration INIT_LOCALS(iter, …) + RELEASE_LOCALS on every continue to prevent local-ref-table overflow on large proxy lists.
• pal_jni.{h,c} — global refs added for java.net.ProxySelector, Proxy, Proxy$Type (HTTP/SOCKS jfieldIDs), InetSocketAddress, URI, java.util.List. All populated once in InitializeJObjectsForPal.
• pal_jni.{h,c} — promotes AllocateString (previously private to pal_sslstream.c) into a shared PAL helper. It returns a NUL-terminated UTF-16 buffer that managed code reads via Marshal.PtrToStringUni (zero-conversion memcpy: both Java and .NET strings are internally UTF-16). pal_sslstream.c is updated to use the shared helper.
• CMakeLists.txt — pal_proxy.c added to NATIVECRYPTO_SOURCES.

Managed (System.Net.Http)

• AndroidPlatformProxy.Android.cs — IWebProxy implementation (same shape as MacProxy).
  • GetProxy(uri) P/Invokes the PAL, takes the first non-DIRECT entry, falls back to direct on any failure.
  • IsBypassed(_) => false (matches HttpWindowsProxy.cs:349–360 rationale: computing the real answer costs the same as GetProxy, so we let SHH call GetProxy exactly once per pool key).
  • Credentials exists (required by IWebProxy) but is never populated by us — Android's proxy APIs do not surface credentials. Users authenticate via HttpClientHandler.DefaultProxyCredentials, the same as on macOS (MacProxy has the same limitation tracked as Use system proxy configuration on macOS #24799).
• SystemProxyInfo.Android.cs — env vars first (HttpEnvironmentProxy), then AndroidPlatformProxy, then HttpNoProxy. Gated by a new FeatureSwitchDefinition("System.Net.Http.UseAndroidSystemProxy") with default true.
• Interop.Proxy.cs — [LibraryImport] declarations.
• System.Net.Http.csproj — new <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'android'"> adds the three managed files and the Android Interop.Libraries.cs. The existing fall-through ItemGroup is updated to exclude Android.

Feature switch: System.Net.Http.UseAndroidSystemProxy

Defaults to true. Apps can opt out via <RuntimeHostConfigurationOption> (or by setting the property name in runtimeconfig.json):

<RuntimeHostConfigurationOption
    Include="System.Net.Http.UseAndroidSystemProxy"
    Value="false" Trim="true" />

Three legitimate reasons to disable:

1. Back-compat with apps that previously ran on SocketsHttpHandler and got env-var-only behavior — honoring the system proxy could change which server their HTTP requests reach.
2. Trimming — the linker can trim AndroidPlatformProxy and the P/Invokes when set to false at publish time.
3. Test/debug isolation where pure env-var behavior is required.

SOCKS support

ProxySelector may return Proxy.Type.SOCKS (transport-level proxy protocol per RFC 1928; tunnels arbitrary TCP at the socket layer). On modern Android Proxy.Type.SOCKS maps to SOCKS5. We translate to a socks5://host:port URI; SocketsHttpHandler accepts that scheme via HttpUtilities.IsSupportedProxyScheme.

Verification

• ✅ ./build.sh libs.native -os android -arch arm64 — 0 warnings, 0 errors.
• ✅ dotnet build src/libraries/System.Net.Http/src/System.Net.Http.csproj /p:TargetOS=android /p:TargetArchitecture=arm64 — 0 warnings, 0 errors across all RIDs (also confirmed pal_sslstream.c still links cleanly after moving AllocateString out).
• ✅ nm -D libSystem.Security.Cryptography.Native.Android.so confirms both AndroidCryptoNative_GetProxyForUrl and AndroidCryptoNative_FreeProxyResult are exported.

What this PR does NOT do (follow-ups)

• No tests yet. A device-test APK modeled on the AndroidPlatformTrustTests from [Android] Respect platform trust manager in SslStream #124173 is the right follow-up. The test matrix should cover: Wi-Fi system proxy honored, Settings.Global.HTTP_PROXY honored, PAC script evaluated, no-proxy fall-through, bypass list, UseProxy=false skips, explicit handler Proxy overrides, DefaultProxyCredentials flows to Proxy-Authorization, feature switch off.
• No lib rename. The new code lives in System.Security.Cryptography.Native.Android even though the lib's scope is now broader than crypto. Renaming it (e.g. System.Net.Native.Android) is a separate, mechanical refactor.
• pal_eckey.c and pal_x509chain.c still have inline duplicates of the AllocateString pattern. Hoisting them to use the shared helper is a separate cleanup.
• No MAUI/Android SDK MSBuild wiring for a per-app $(UseAndroidSystemProxy) property. The runtime config switch can be set explicitly today via <RuntimeHostConfigurationOption>; SDK-level wiring can come in dotnet/android.

Microsoft Reviewers: Open in CodeFlow

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[Copilot]

Pull request overview

This PR adds Android-specific system proxy support for SocketsHttpHandler by introducing a managed AndroidPlatformProxy : IWebProxy backed by a new native PAL entrypoint that queries java.net.ProxySelector via JNI, and wires it into SystemProxyInfo with a feature switch.

Changes:

• Add native JNI/PAL support (AndroidCryptoNative_GetProxyForUrl / ...FreeProxyResult) to query ProxySelector.select(URI), returning HTTP/SOCKS proxy entries.
• Add managed AndroidPlatformProxy and Android-specific SystemProxyInfo implementation to prefer env-var proxy first, then Android platform proxy (feature-switchable).
• Update build glue (CMake + System.Net.Http.csproj) and add Android interop declarations for the new PAL exports.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/native/libs/System.Security.Cryptography.Native.Android/pal_sslstream.c	Removes the file-local AllocateString helper in favor of a shared PAL helper.
src/native/libs/System.Security.Cryptography.Native.Android/pal_proxy.h	Defines native proxy result structs/enums and PAL export signatures.
src/native/libs/System.Security.Cryptography.Native.Android/pal_proxy.c	Implements ProxySelector-based proxy resolution and result marshalling.
src/native/libs/System.Security.Cryptography.Native.Android/pal_jni.h	Adds cached JNI class/method/field IDs for proxy-related Java types and exposes AllocateString.
src/native/libs/System.Security.Cryptography.Native.Android/pal_jni.c	Defines/initializes the new JNI caches and provides the shared AllocateString implementation.
src/native/libs/System.Security.Cryptography.Native.Android/CMakeLists.txt	Adds pal_proxy.c to the native build sources.
src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SystemProxyInfo.Android.cs	Android-specific proxy construction order + System.Net.Http.UseAndroidSystemProxy feature switch.
src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/AndroidPlatformProxy.Android.cs	Managed IWebProxy implementation calling into the native PAL and mapping to http/socks5 URIs.
src/libraries/System.Net.Http/src/System.Net.Http.csproj	Includes Android-only proxy files + Android interop sources; excludes Android from the Unix fallback item group.
src/libraries/Common/src/Interop/Android/System.Security.Cryptography.Native.Android/Interop.Proxy.cs	Adds [LibraryImport] declarations and the blittable native result struct.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.