Fix logging for Android (#188)

* Remove logging configuration from logcat init script

Eliminated the use of the logging module and related configuration from the _logcatInitScript in cpython.dart. This simplifies the script and avoids unnecessary logging setup during initialization.

* Refactor Python FFI execution and isolate handling

Simplifies sync and async execution paths for running Python programs via FFI. Moves core execution logic to a private function, improves error handling, and ensures proper resource cleanup in async mode. Removes redundant message passing and streamlines isolate communication.

* Serialize Python runs and improve async execution

Introduces a queue to serialize Python execution requests, preventing concurrent runs. Refactors async execution to use Isolate.run for better port lifecycle management and adds debug logging for run tracking.

* Improve Python logging and format async code

Configures Python logging to use a StreamHandler with a custom formatter and replaces all root handlers. Also reformats async Isolate.run() calls for better readability.

* Add logging import to logcat init script

Added the 'logging' module import to the logcat initialization script to ensure logging functionality is available during script execution.

* Set root logger level in embedded Python logging config

Adds a line to explicitly set the root logger's level to its effective level in the embedded Python logging configuration. This ensures consistent logging behavior when initializing the logger.

* Set Python root logger level to DEBUG

Changed the root logger's level from its effective level to DEBUG in the embedded Python logging configuration. This ensures all debug messages are captured during execution.

* Update logcat logger configuration in cpython.dart

Switches logging from the root logger to a dedicated 'logcat' logger, disables propagation, and sets the log level to ERROR instead of DEBUG. This change improves log handling and reduces log verbosity.

* Remove logcat propagate setting in Python logging config

Deleted the line setting 'logcat.propagate = False' from the embedded Python logging configuration. This may allow log messages to propagate to ancestor loggers, aligning with default logging behavior.

* Use root logger for logcat configuration

Replaces the use of the 'logcat' logger with the root logger when configuring logging in the embedded Python script. This ensures that all logging output is handled consistently at the ERROR level.

* Improve Python error handling and memory management

Enhanced getPythonError to handle null pointers, memory allocation failures, and fallback error formatting. Replaced Py_DecRef with malloc.free for native strings and ensured proper reference counting and cleanup to prevent memory leaks.

* Refactor Python error formatting and cleanup

Simplifies and improves Python exception formatting by extracting logic into helper functions and using more robust error handling. Removes unused run sequence tracking and an obsolete isolate runner. Enhances debug logging and clarifies error messages for better maintainability.

* Remove redundant debug log in async Python runner

Eliminated an unnecessary debug statement before the async Python execution to reduce log verbosity and improve code clarity.

* Bump version to 0.9.8 and fix Android logging

Update all packages to version 0.9.8 and add changelog entries for fixing logging on Android. Also update build.gradle and podspec files to reflect the new version.

Author: FeodorFitsner

src/serious_python/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.9.8
+
+* Fix logging on Android.
+
 ## 0.9.7
 
 * Fix app restart on Android 10.

src/serious_python/pubspec.yaml

@@ -2,7 +2,7 @@ name: serious_python
 description: A cross-platform plugin for adding embedded Python runtime to your Flutter apps.
 homepage: https://flet.dev
 repository: https://github.com/flet-dev/serious-python
-version: 0.9.7
+version: 0.9.8
 
 platforms:
   ios:

src/serious_python_android/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.9.8
+
+* Fix logging on Android.
+
 ## 0.9.7
 
 * Fix app restart on Android 10.

src/serious_python_android/android/build.gradle

@@ -1,5 +1,5 @@
 group 'com.flet.serious_python_android'
-version '0.9.7'
+version '0.9.8'
 
 def python_version = '3.12'
 

src/serious_python_android/lib/src/cpython.dart

@@ -12,8 +12,22 @@ export 'gen.dart';
 
 CPython? _cpython;
 String? _logcatForwardingError;
+Future<void> _pythonRunQueue = Future<void>.value();
+
+Future<T> _enqueuePythonRun<T>(Future<T> Function() action) {
+  final completer = Completer<T>();
+  _pythonRunQueue = _pythonRunQueue.then((_) async {
+    try {
+      completer.complete(await action());
+    } catch (e, st) {
+      completer.completeError(e, st);
+    }
+  });
+  return completer.future;
+}
+
 const _logcatInitScript = r'''
-import sys, logging
+import logging,sys
 
 # Make this init idempotent across Dart isolate restarts.
 if not getattr(sys, "__serious_python_logcat_configured__", False):
@@ -41,7 +55,7 @@ if not getattr(sys, "__serious_python_logcat_configured__", False):
     handler.setFormatter(logging.Formatter("%(levelname)s %(message)s"))
     root = logging.getLogger()
     root.handlers[:] = [handler]
-    root.setLevel(logging.DEBUG)
+    root.setLevel(logging.ERROR)
 ''';
 
 CPython getCPython(String dynamicLibPath) {
@@ -50,31 +64,33 @@ CPython getCPython(String dynamicLibPath) {
 
 Future<String> runPythonProgramFFI(bool sync, String dynamicLibPath,
     String pythonProgramPath, String script) async {
-  final receivePort = ReceivePort();
-  if (sync) {
-    // sync run
-    return await runPythonProgramInIsolate(
-        [receivePort.sendPort, dynamicLibPath, pythonProgramPath, script]);
-  } else {
-    var completer = Completer<String>();
-    // async run
-    final isolate = await Isolate.spawn(runPythonProgramInIsolate,
-        [receivePort.sendPort, dynamicLibPath, pythonProgramPath, script]);
-    receivePort.listen((message) {
-      receivePort.close();
-      isolate.kill();
-      completer.complete(message);
-    });
-    return completer.future;
-  }
+  return _enqueuePythonRun(() async {
+    spDebug(
+        "Python run start (sync=$sync, script=${script.isNotEmpty}, program=$pythonProgramPath)");
+    if (sync) {
+      // Sync run: do not involve ports (avoids GC/close races).
+      final result =
+          _runPythonProgram(dynamicLibPath, pythonProgramPath, script);
+      spDebug("Python run done (resultLength=${result.length})");
+      return result;
+    } else {
+      // Async run: use Isolate.run() to avoid manual port lifecycle issues.
+      try {
+        final result = await Isolate.run(
+            () => _runPythonProgram(dynamicLibPath, pythonProgramPath, script));
+        spDebug("Python run done (resultLength=${result.length})");
+        return result;
+      } catch (e, st) {
+        final message = "Dart error running Python: $e\n$st";
+        spDebug(message);
+        return message;
+      }
+    }
+  });
 }
 
-Future<String> runPythonProgramInIsolate(List<Object> arguments) async {
-  final sendPort = arguments[0] as SendPort;
-  final dynamicLibPath = arguments[1] as String;
-  final pythonProgramPath = arguments[2] as String;
-  final script = arguments[3] as String;
-
+String _runPythonProgram(
+    String dynamicLibPath, String pythonProgramPath, String script) {
   var programDirPath = p.dirname(pythonProgramPath);
   var programModuleName = p.basenameWithoutExtension(pythonProgramPath);
 
@@ -85,8 +101,8 @@ Future<String> runPythonProgramInIsolate(List<Object> arguments) async {
   final cpython = getCPython(dynamicLibPath);
   spDebug("CPython loaded");
   if (cpython.Py_IsInitialized() != 0) {
-    spDebug("Python already initialized, skipping execution.");
-    sendPort.send("");
+    spDebug(
+        "Python already initialized and another program is running, skipping execution.");
     return "";
   }
 
@@ -98,7 +114,6 @@ Future<String> runPythonProgramInIsolate(List<Object> arguments) async {
   final logcatSetupError = _setupLogcatForwarding(cpython);
   if (logcatSetupError != null) {
     cpython.Py_Finalize();
-    sendPort.send(logcatSetupError);
     return logcatSetupError;
   }
 
@@ -124,53 +139,88 @@ Future<String> runPythonProgramInIsolate(List<Object> arguments) async {
   cpython.Py_Finalize();
   spDebug("after Py_Finalize()");
 
-  sendPort.send(result);
-
   return result;
 }
 
 String getPythonError(CPython cpython) {
-  // get error object
-  var exPtr = cpython.PyErr_GetRaisedException();
+  final exPtr = cpython.PyErr_GetRaisedException();
+  if (exPtr == nullptr) return "Unknown Python error (no exception set).";
+
+  try {
+    final formatted = _formatPythonException(cpython, exPtr);
+    if (formatted != null && formatted.isNotEmpty) return formatted;
+
+    final fallback = _pyObjectToDartString(cpython, exPtr);
+    return fallback ?? "Unknown Python error (failed to stringify exception).";
+  } finally {
+    cpython.Py_DecRef(exPtr);
+    // Defensive: formatting can set a new Python error.
+    cpython.PyErr_Clear();
+  }
+}
 
-  // use 'traceback' module to format exception
+String? _formatPythonException(
+    CPython cpython, Pointer<PyObject> exceptionPtr) {
+  // Uses `traceback.format_exception(exc)` (Python 3.10+ signature).
   final tracebackModuleNamePtr = "traceback".toNativeUtf8();
-  var tracebackModulePtr =
+  final tracebackModulePtr =
       cpython.PyImport_ImportModule(tracebackModuleNamePtr.cast<Char>());
-  cpython.Py_DecRef(tracebackModuleNamePtr.cast());
-
-  if (tracebackModulePtr != nullptr) {
-    //spDebug("Traceback module loaded");
-
-    final formatFuncName = "format_exception".toNativeUtf8();
-    final pFormatFunc = cpython.PyObject_GetAttrString(
-        tracebackModulePtr, formatFuncName.cast());
-    cpython.Py_DecRef(tracebackModuleNamePtr.cast());
-
-    if (pFormatFunc != nullptr && cpython.PyCallable_Check(pFormatFunc) != 0) {
-      // call `traceback.format_exception()` method
-      final pArgs = cpython.PyTuple_New(1);
-      cpython.PyTuple_SetItem(pArgs, 0, exPtr);
-
-      // result is a list
-      var listPtr = cpython.PyObject_CallObject(pFormatFunc, pArgs);
-
-      // get and combine list items
-      var exLines = [];
-      var listSize = cpython.PyList_Size(listPtr);
-      for (var i = 0; i < listSize; i++) {
-        var itemObj = cpython.PyList_GetItem(listPtr, i);
-        var itemObjStr = cpython.PyObject_Str(itemObj);
-        var s =
-            cpython.PyUnicode_AsUTF8(itemObjStr).cast<Utf8>().toDartString();
-        exLines.add(s);
+  malloc.free(tracebackModuleNamePtr);
+  if (tracebackModulePtr == nullptr) return null;
+
+  try {
+    final formatFuncNamePtr = "format_exception".toNativeUtf8();
+    final formatFuncPtr = cpython.PyObject_GetAttrString(
+        tracebackModulePtr, formatFuncNamePtr.cast());
+    malloc.free(formatFuncNamePtr);
+    if (formatFuncPtr == nullptr) return null;
+
+    try {
+      if (cpython.PyCallable_Check(formatFuncPtr) == 0) return null;
+
+      final listPtr = cpython.PyObject_CallOneArg(formatFuncPtr, exceptionPtr);
+      if (listPtr == nullptr) return null;
+
+      try {
+        final listSize = cpython.PyList_Size(listPtr);
+        if (listSize < 0) return null;
+
+        final buffer = StringBuffer();
+        for (var i = 0; i < listSize; i++) {
+          final itemObj = cpython.PyList_GetItem(listPtr, i); // borrowed ref
+          if (itemObj == nullptr) continue;
+
+          final line = _pyUnicodeToDartString(cpython, itemObj) ??
+              _pyObjectToDartString(cpython, itemObj);
+          if (line == null) continue;
+          buffer.write(line);
+        }
+        return buffer.toString();
+      } finally {
+        cpython.Py_DecRef(listPtr);
       }
-      return exLines.join("");
-    } else {
-      return "traceback.format_exception() method not found.";
+    } finally {
+      cpython.Py_DecRef(formatFuncPtr);
     }
-  } else {
-    return "Error loading traceback module.";
+  } finally {
+    cpython.Py_DecRef(tracebackModulePtr);
+  }
+}
+
+String? _pyUnicodeToDartString(
+    CPython cpython, Pointer<PyObject> unicodeObjPtr) {
+  final cStr = cpython.PyUnicode_AsUTF8(unicodeObjPtr);
+  if (cStr == nullptr) return null;
+  return cStr.cast<Utf8>().toDartString();
+}
+
+String? _pyObjectToDartString(CPython cpython, Pointer<PyObject> objPtr) {
+  final strObj = cpython.PyObject_Str(objPtr);
+  if (strObj == nullptr) return null;
+  try {
+    return _pyUnicodeToDartString(cpython, strObj);
+  } finally {
+    cpython.Py_DecRef(strObj);
   }
 }
 

src/serious_python_android/pubspec.yaml

@@ -2,7 +2,7 @@ name: serious_python_android
 description: Android implementation of the serious_python plugin
 homepage: https://flet.dev
 repository: https://github.com/flet-dev/serious-python
-version: 0.9.7
+version: 0.9.8
 
 environment:
   sdk: ">=3.0.0 <4.0.0"

src/serious_python_darwin/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.9.8
+
+* Fix logging on Android.
+
 ## 0.9.7
 
 * Fix app restart on Android 10.

src/serious_python_darwin/darwin/serious_python_darwin.podspec

@@ -4,7 +4,7 @@
 #
 Pod::Spec.new do |s|
   s.name             = 'serious_python_darwin'
-  s.version          = '0.9.7'
+  s.version          = '0.9.8'
   s.summary          = 'A cross-platform plugin for adding embedded Python runtime to your Flutter apps.'
   s.description      = <<-DESC
   A cross-platform plugin for adding embedded Python runtime to your Flutter apps.

src/serious_python_darwin/pubspec.yaml

@@ -2,7 +2,7 @@ name: serious_python_darwin
 description: iOS and macOS implementations of the serious_python plugin
 homepage: https://flet.dev
 repository: https://github.com/flet-dev/serious-python
-version: 0.9.7
+version: 0.9.8
 
 environment:
   sdk: ">=3.0.0 <4.0.0"

src/serious_python_linux/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.9.8
+
+* Fix logging on Android.
+
 ## 0.9.7
 
 * Fix app restart on Android 10.