common/logging_backend: Introduce Python backend

CMakeLists.txt

@@ -61,7 +61,7 @@ endif()
 # With 'syslog' backend, we enable all logs (ie: up to level debug) and we leave the
 # application to set the level using 'setlogmask()'
 set(GATTLIB_LOG_LEVEL 3 CACHE STRING "Define the minimum logging level for Gattlib (0=error, 1=warning, 2=info, 3=debug)")
-set(GATTLIB_LOG_BACKEND syslog CACHE STRING "Define logging backend: syslog, printf (default: syslog)")
+set(GATTLIB_LOG_BACKEND syslog CACHE STRING "Define logging backend: syslog, printf, python (default: syslog)")
 
 if (GATTLIB_DBUS)
   # Build dbus-based gattlib

common/logging_backend/python/gattlib_logging.c

@@ -0,0 +1,56 @@
+/*
+ * SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0-or-later
+ *
+ * Copyright (c) 2024, Olivier Martin <olivier@labapart.org>
+ */
+
+#include <syslog.h>
+
+#include "gattlib_internal.h"
+
+static PyObject* m_logging_func;
+
+void gattlib_log_init(PyObject* logging_func) {
+	m_logging_func = logging_func;
+}
+
+void gattlib_log(int level, const char *format, ...) {
+	va_list args;
+	va_start(args, format);
+
+	if (m_logging_func == NULL) {
+		FILE *stream = stdout;
+
+		if (level == GATTLIB_ERROR) {
+			stream = stderr;
+		}
+
+		vfprintf(stream, format, args);
+		fprintf(stream, "\n");
+	} else {
+		PyGILState_STATE d_gstate;
+		PyObject *result;
+		char string[400];
+
+		vsnprintf(string, sizeof(string), format, args);
+
+		d_gstate = PyGILState_Ensure();
+
+		PyObject *arglist = Py_BuildValue("Is", level, string);
+#if PYTHON_VERSION >= PYTHON_VERSIONS(3, 9)
+		result = PyObject_Call(m_logging_func, arglist, NULL);
+#else
+		result = PyEval_CallObject(m_logging_func, arglist);
+#endif
+		Py_DECREF(arglist);
+
+		if (result == NULL) {
+			GATTLIB_LOG(GATTLIB_ERROR, "Python notification handler has raised an exception.");
+			PyErr_Print();
+		}
+
+		PyGILState_Release(d_gstate);
+	}
+
+	va_end(args);
+}

gattlib-py/gattlib/__init__.py

@@ -11,6 +11,28 @@ logger = logging.getLogger(__name__)
 
 gattlib = CDLL("libgattlib.so")
 
+def native_logging(level: int, string: str):
+    if level == 3:
+        logger.debug(string)
+    elif level == 2:
+        logger.info(string)
+    elif level == 1:
+        logger.warning(string)
+    elif level == 0:
+        logger.error(string)
+    else:
+        logger.debug(string)
+
+try:
+    # void gattlib_log_init(PyObject* logging_func)
+    gattlib_log_init = gattlib.gattlib_log_init
+    gattlib_log_init.argtypes = [py_object]
+
+    # Declare Python function for logging native string
+    gattlib_log_init(native_logging)
+except AttributeError:
+    # Excepted when using a Gattlib logging backend without 'gattlib_log_init'
+    pass
 
 # typedef struct {
 #    uint8_t data[16];

gattlib-py/setup.py

@@ -78,7 +78,10 @@ class CMakeBuild(build_ext):
             cmake_args += [item for item in os.environ["CMAKE_ARGS"].split(" ") if item]
 
         # In this example, we pass in the version to C++. You might not need to.
-        cmake_args += [f"-DEXAMPLE_VERSION_INFO={self.distribution.get_version()}", "-DGATTLIB_BUILD_EXAMPLES=NO"]
+        cmake_args += [
+            f"-DEXAMPLE_VERSION_INFO={self.distribution.get_version()}",
+            "-DGATTLIB_BUILD_EXAMPLES=NO",
+            "-DGATTLIB_LOG_BACKEND=python"]
 
         if self.compiler.compiler_type != "msvc":
             # Using Ninja-build since it a) is available as a wheel and b)