From 1855894e1a8f11beb421d07c60f7e177ea5e9014 Mon Sep 17 00:00:00 2001
From: Jonathan Peppers <jonathan.peppers@microsoft.com>
Date: Thu, 6 Mar 2025 13:06:26 -0600
Subject: [PATCH] [nativeaot] set `$HOME` and `$TMPDIR`

Context: https://github.com/dotnet/runtime/blob/d09a42b9149e14a37c8ef8363cdb7e17bb922c37/src/libraries/System.Private.CoreLib/src/System/IO/Path.Unix.cs#L83

`System.IO.Path.GetTempPath()` doesn't work under NativeAOT as seen by
the test failure:

    Mono.Android.NET_Tests, Android.RuntimeTests.InputStreamInvokerTest.InputStreamTest / Release
    System.IO.DirectoryNotFoundException : IO_PathNotFound_Path, /tmp/
    at Interop.ThrowExceptionForIoErrno(Interop.ErrorInfo, String, Boolean) + 0x11
    at Interop.CheckIo(Int64, String, Boolean) + 0x5d
    at System.IO.Path.GetTempFileName() + 0x14d
    at Android.RuntimeTests.InputStreamInvokerTest.InputStreamTest() + 0x18
    at libMono.Android.NET-Tests!<BaseAddress>+0x1483023
    at System.Reflection.DynamicInvokeInfo.Invoke(Object, IntPtr, Object[], BinderBundle, Boolean) + 0xf3

On Unix-like systems, the BCL just reads `$TMPDIR` and falls back to
`/tmp/` if it doesn't exist. `$TMPDIR` is *not* set by default in
Android applications.

To fix this, we can set `$TMPDIR` to `context.getCacheDir()` just as
we do in Mono:

https://github.com/dotnet/android/blob/04cd6f40989a8fad30d9a9759aec02d540cc9478/src/java-runtime/java/mono/android/MonoPackageManager.java#L53-L54

https://github.com/dotnet/android/blob/04cd6f40989a8fad30d9a9759aec02d540cc9478/src/native/mono/monodroid/monodroid-glue.cc#L1444-L1445

I think we can simply read these values in Java at startup, and call
`Os.setenv()` to set them. There does not seem to be a need to pass
these paths into managed code.

The `Android.RuntimeTests.InputStreamInvokerTest.InputStreamTest()`
test now passes with these changes.

I fixed `$HOME` as well, as it will be used by other APIs in the BCL.
---
 .../Resources/NativeAotRuntimeProvider.java        | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/Xamarin.Android.Build.Tasks/Resources/NativeAotRuntimeProvider.java b/src/Xamarin.Android.Build.Tasks/Resources/NativeAotRuntimeProvider.java
index f437be4ca28..a3acd8935af 100644
--- a/src/Xamarin.Android.Build.Tasks/Resources/NativeAotRuntimeProvider.java
+++ b/src/Xamarin.Android.Build.Tasks/Resources/NativeAotRuntimeProvider.java
@@ -1,5 +1,7 @@
 package net.dot.jni.nativeaot;
 
+import android.system.ErrnoException;
+import android.system.Os;
 import android.util.Log;
 import net.dot.android.ApplicationRegistration;
 
@@ -24,6 +26,18 @@ public void attachInfo(android.content.Context context, android.content.pm.Provi
         if (context instanceof android.app.Application) {
             ApplicationRegistration.Context = context;
         }
+
+        // Set environment variables
+        try {
+            String filesDir = context.getFilesDir().getAbsolutePath();
+            String cacheDir = context.getCacheDir().getAbsolutePath();
+            Os.setenv("HOME", filesDir, true);
+            Os.setenv("TMPDIR", cacheDir, true);
+        } catch (ErrnoException e) {
+            Log.e(TAG, "Failed to set environment variables", e);
+        }
+
+        // Initialize .NET runtime
         JavaInteropRuntime.init();
         // NOTE: only required for custom applications
         ApplicationRegistration.registerApplications();