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[Mono.Android] Marshal exceptions in RegisterNativeMembers() (#6672)
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Context: dotnet/maui#4262
Context: #6675

If you run the `maui-blazor` template in a Release build:

	dotnet build -t:Run -c Release

it crashes at runtime:

	D monodroid-assembly: typemap: type with token 33555274 (0x200034a) in module {C7B4CC8F-7A03-4A3F-A34A-DC66EDC548B9} (Mono.Android) corresponds to Java type 'android/runtime/JavaProxyThrowable'
	…
	F DEBUG   : backtrace:
	F DEBUG   : #00 pc 000000000065d8fc  /apex/com.android.art/lib64/libart.so (void art::StackVisitor::WalkStack<(art::StackVisitor::CountTransitions)0>(bool)+156) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
	F DEBUG   : #1 pc 000000000069b25d  /apex/com.android.art/lib64/libart.so (art::Thread::GetCurrentMethod(unsigned int*, bool, bool) const+157) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
	F DEBUG   : #2 pc 0000000000430fed  /apex/com.android.art/lib64/libart.so (art::JNI<false>::FindClass(_JNIEnv*, char const*)+765) (BuildId: 7fbaf2a1a3317bd634b00eb90e32291e)
	F DEBUG   : #3 pc 0000000000047e5a  /data/app/~~0Qm6D1S0sO3f1lwfakN0PA==/com.companyname.mauiapp2-08UokVCH5k_PlbZEH_hhkA==/split_config.x86_64.apk!libmono-android.release.so (offset 0x11e000) (java_interop_jnienv_find_class+26) (BuildId: 3d04f8b946590175e97b89aee2e3b19ceed4b524)
	F DEBUG   : #4 pc 00000000000128ac  <anonymous:41640000>

The crash can be avoided by disabling the linker:

	dotnet build -t:Run -c Release -p:AndroidLinkMode=None
	# -or-
	dotnet build -t:Run -c Release -p:PublishTrimmed=false

However, let us return to the crash: *why* is it crashing?
This isn't a "good debugging experience"; we have no useful context.

Lots of investigation later -- all hail printf debugging -- and we
found that the cause of the crash was an unhandled exception:

 1. `Mono.Android.dll` has it's Java Callable Wrappers generated
    from the *unlinked* assembly, into `mono.android.jar` and
    `mono.android.dex` files.  The Java Callable Wrapper for
    `Android.Runtime.InputStreamAdapter` thus includes *all*
    `Read()` method overloads.

 2. When the app is built in Release configuration, linking is
    enabled, and *some* of the `InputStreamAdapter.Read()` methods
    are removed by the linker, along with the
    `Java.IO.InputStream.Read()` methods that were overridden.

 3. At runtime, we perform [Java Type Registration][0] for the
    `Android.Runtime.InputStreamAdapter` type, which eventually calls
    `AndroidTypeManager.RegisterNativeMembers()`, which eventually
    attempts to *effectively* do:

        Delegate.CreateDelegate (
	        typeof(Func<Delegate>),
	        typeof(InputStreamAdapter),
	        "GetReadHandler");

 4. Because of (2), `Java.IO.InputStream.GetReadHandler()`
    *does not exist*, and thus `Delegate.CreateDelegate()` throws an
    `ArgumentException`.

So far, so reasonable, but…

 5. `AndroidTypeManager.RegisterNativeMembers()` didn't catch any
    exceptions, nor did any other method between the original Java
    `Runtime.register()` invocation and
    `AndroidTypeManager.RegisterNativeMembers()`.  The result is that
    a C# exception was "in flight", and Mono then proceeded to
    *tear down the stack frame* as it unwound the callstack looking
    for `catch` handlers.

At this point, the process is toast: the runtime stack is FUBAR.

This is also why the `backtrace:` is "rooted" in
`JNIEnv::FindClass()`: `JNIEnv::FindClass()` invokes Java static
constructors before returning, which is how the static constructor in
the Java Callable Wrapper for `InputStreamAdapter` called
`Runtime.register()` in the first place.

All of this makes for a miserable debugging experience.

Fixing the "original" linker issue will be done in
#6675.

This hasn't been an issue in "Classic" Xamarin.Android, presumably
because the classic linker isn't as good as the net6 linker.

What we want to do *here* is improve this debugging experience, by
"wrapping" `AndroidTypeManager.RegisterNativeMembers()` in a
`try`/`catch` block, which can then *marshal the thrown exception*
back to Java.  This *prevents* Mono from unwinding the callstack past
a JNI boundary, and avoids the annoying-to-debug app crash.

After this change, we get a much friendlier unhandled exception crash:

	I MonoDroid: Android.Runtime.JavaProxyThrowable: Exception_WasThrown, Android.Runtime.JavaProxyThrowable
	I MonoDroid:
	I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
	I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
	I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
	I MonoDroid: --- End of stack trace from previous location ---
	I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
	I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
	I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
	I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
	I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
	I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
	I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)
	I MonoDroid:
	I MonoDroid:   --- End of managed Android.Runtime.JavaProxyThrowable stack trace ---
	I MonoDroid: android.runtime.JavaProxyThrowable: System.ArgumentException: Arg_DlgtTargMeth
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String , Boolean , Boolean )
	I MonoDroid:    at System.Delegate.CreateDelegate(Type , Type , String )
	I MonoDroid:    at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , String )
	I MonoDroid: --- End of stack trace from previous location ---
	I MonoDroid:    at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.CallStaticObjectMethod(IntPtr , IntPtr , JValue[] )
	I MonoDroid:    at Android.Runtime.JNIEnv.FindClass(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.AllocObject(String )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
	I MonoDroid:    at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter..ctor(Stream )
	I MonoDroid:    at Android.Runtime.InputStreamAdapter.ToLocalJniHandle(Stream )
	I MonoDroid:    at Android.Webkit.WebResourceResponse..ctor(String , String , Int32 , String , IDictionary`2 , Stream )
	I MonoDroid:    at Microsoft.AspNetCore.Components.WebView.Maui.WebKitWebViewClient.ShouldInterceptRequest(WebView view, IWebResourceRequest request)
	I MonoDroid:    at Android.Webkit.WebViewClient.n_ShouldInterceptRequest_Landroid_webkit_WebView_Landroid_webkit_WebResourceRequest_(IntPtr , IntPtr , IntPtr , IntPtr )
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.n_shouldInterceptRequest(Native Method)
	I MonoDroid: 	at crc64d693e2d9159537db.WebKitWebViewClient.shouldInterceptRequest(WebKitWebViewClient.java:39)
	I MonoDroid: 	at Rr.a(chromium-TrichromeWebViewGoogle.apk-stable-410410686:16)
	I MonoDroid: 	at org.chromium.android_webview.AwContentsBackgroundThreadClient.shouldInterceptRequestFromNative(chromium-TrichromeWebViewGoogle.apk-stable-410410686:2)

This is much easier to reason about, and will save us time in
the future.

[0]: https://github.com/xamarin/xamarin-android/wiki/Blueprint#java-type-registration
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@jonathanpeppers
jonathanpeppers committed Jan 27, 2022
1 parent 084be1d commit 9708548
Showing 1 changed file with 48 additions and 44 deletions.
92 changes: 48 additions & 44 deletions src/Mono.Android/Android.Runtime/AndroidRuntime.cs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -378,57 +378,61 @@ static bool CallRegisterMethodByIndex (JniNativeMethodRegistrationArguments argu

public override void RegisterNativeMembers (JniType nativeClass, Type type, string? methods)
{
if (FastRegisterNativeMembers (nativeClass, type, methods))
return;
try {
if (FastRegisterNativeMembers (nativeClass, type, methods))
return;

if (string.IsNullOrEmpty (methods)) {
if (jniAddNativeMethodRegistrationAttributePresent)
base.RegisterNativeMembers (nativeClass, type, methods);
return;
}
if (string.IsNullOrEmpty (methods)) {
if (jniAddNativeMethodRegistrationAttributePresent)
base.RegisterNativeMembers (nativeClass, type, methods);
return;
}

string[] members = methods!.Split ('\n');
if (members.Length < 2) {
if (jniAddNativeMethodRegistrationAttributePresent)
base.RegisterNativeMembers (nativeClass, type, methods);
return;
}
string[] members = methods!.Split ('\n');
if (members.Length < 2) {
if (jniAddNativeMethodRegistrationAttributePresent)
base.RegisterNativeMembers (nativeClass, type, methods);
return;
}

JniNativeMethodRegistration[] natives = new JniNativeMethodRegistration [members.Length-1];
for (int i = 0; i < members.Length; ++i) {
string method = members [i];
if (string.IsNullOrEmpty (method))
continue;
string[] toks = members [i].Split (new[]{':'}, 4);
Delegate callback;
if (toks [2] == "__export__") {
var mname = toks [0].Substring (2);
MethodInfo? minfo = null;
foreach (var mi in type.GetMethods (BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static))
if (mi.Name == mname && JavaNativeTypeManager.GetJniSignature (mi) == toks [1]) {
minfo = mi;
break;
JniNativeMethodRegistration[] natives = new JniNativeMethodRegistration [members.Length-1];
for (int i = 0; i < members.Length; ++i) {
string method = members [i];
if (string.IsNullOrEmpty (method))
continue;
string[] toks = members [i].Split (new[]{':'}, 4);
Delegate callback;
if (toks [2] == "__export__") {
var mname = toks [0].Substring (2);
MethodInfo? minfo = null;
foreach (var mi in type.GetMethods (BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static))
if (mi.Name == mname && JavaNativeTypeManager.GetJniSignature (mi) == toks [1]) {
minfo = mi;
break;
}

if (minfo == null)
throw new InvalidOperationException (String.Format ("Specified managed method '{0}' was not found. Signature: {1}", mname, toks [1]));
callback = CreateDynamicCallback (minfo);
} else {
Type callbackDeclaringType = type;
if (toks.Length == 4) {
callbackDeclaringType = Type.GetType (toks [3], throwOnError: true)!;
}

if (minfo == null)
throw new InvalidOperationException (String.Format ("Specified managed method '{0}' was not found. Signature: {1}", mname, toks [1]));
callback = CreateDynamicCallback (minfo);
} else {
Type callbackDeclaringType = type;
if (toks.Length == 4) {
callbackDeclaringType = Type.GetType (toks [3], throwOnError: true)!;
}
while (callbackDeclaringType.ContainsGenericParameters) {
callbackDeclaringType = callbackDeclaringType.BaseType!;
while (callbackDeclaringType.ContainsGenericParameters) {
callbackDeclaringType = callbackDeclaringType.BaseType!;
}
GetCallbackHandler connector = (GetCallbackHandler) Delegate.CreateDelegate (typeof (GetCallbackHandler),
callbackDeclaringType, toks [2]);
callback = connector ();
}
GetCallbackHandler connector = (GetCallbackHandler) Delegate.CreateDelegate (typeof (GetCallbackHandler),
callbackDeclaringType, toks [2]);
callback = connector ();
natives [i] = new JniNativeMethodRegistration (toks [0], toks [1], callback);
}
natives [i] = new JniNativeMethodRegistration (toks [0], toks [1], callback);
}

JniEnvironment.Types.RegisterNatives (nativeClass.PeerReference, natives, natives.Length);
JniEnvironment.Types.RegisterNatives (nativeClass.PeerReference, natives, natives.Length);
} catch (Exception e) {
JniEnvironment.Runtime.RaisePendingException (e);
}
}
}

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