bindings: bind ILogger and setLogger()

This will allow users of the parameter-framework bindings to set a logger;
without it, the parameter-framework wasn't able to log anything.

Some SWIG features and workarounds must be activated in order to:

 - Support nested classes;
 - Derive bound classes and allow C++ to call back the user-created objects;
 - Properly handle exceptions that may be raised upon errors happening on the
   user side.

Change-Id: I955152a4658eff3307ad595f175f2624a3acfa8c
Signed-off-by: David Wagner <david.wagner@intel.com>

4 files changed, 68 insertions, 5 deletions

diff --git a/bindings/python/Android.mk b/bindings/python/Android.mk
index 2cfd13d..296d4bc 100644
--- a/bindings/python/Android.mk
+++ b/bindings/python/Android.mk
@@ -48,7 +48,11 @@ LOCAL_C_INCLUDES := \
 
 # The 'unused-but-set-variable' warning must be disabled because SWIG generates
 # files that do not respect that constraint.
-LOCAL_CFLAGS := -Wno-unused-but-set-variable -fexceptions
+# '-DSWIG_PYTHON_SILENT_MEMLEAK' is needed because the "memleak" warning
+# pollutes the standard output. At the time of writing, the only warning is
+# spurious anyway, as it relates to "ILogger *" which is an abstract
+# class/interface class and as such cannot be destroyed.
+LOCAL_CFLAGS := -Wno-unused-but-set-variable -fexceptions -DSWIG_PYTHON_SILENT_MEMLEAK
 
 # Undefined symbols will be resolved at runtime
 LOCAL_ALLOW_UNDEFINED_SYMBOLS := true
diff --git a/bindings/python/CMakeLists.txt b/bindings/python/CMakeLists.txt
index 535c920..e9016b1 100644
--- a/bindings/python/CMakeLists.txt
+++ b/bindings/python/CMakeLists.txt
@@ -48,9 +48,13 @@ endif(NOT PYTHONLIBS_FOUND)
 
 include_directories(${PROJECT_SOURCE_DIR}/parameter/include ${PYTHON_INCLUDE_DIRS})
 
-# Add some exceptions because files generated by SWIG are not
-# "-Wextra"-compliant
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unused-but-set-variable")
+# The 'unused-but-set-variable' warning must be disabled because SWIG generates
+# files that do not respect that contraint.
+# '-DSWIG_PYTHON_SILENT_MEMLEAK' is needed because the "memleak" warning
+# pollutes the standard output. At the time of writing, the only warning is
+# spurious anyway, as it relates to "ILogger *" which is an abstract
+# class/interface class and as such cannot be destroyed.
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unused-but-set-variable -DSWIG_PYTHON_SILENT_MEMLEAK")
 
 install(TARGETS _PyPfw LIBRARY DESTINATION lib)
 
diff --git a/bindings/python/pfw.i b/bindings/python/pfw.i
index c029d13..da01cdc 100644
--- a/bindings/python/pfw.i
+++ b/bindings/python/pfw.i
@@ -27,7 +27,22 @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
-%module PyPfw
+// The generated python module will be named "PyPfw"
+// the "directors" feature is used to derive Python classes and make them look
+// like derived C++ classes (calls to virtual methods will be properly
+// forwarded to Python) - only on classes for which is it specified, see
+// ILogger below..
+%module(directors="1") PyPfw
+
+%feature("director:except") {
+    if ($error != NULL) {
+        throw Swig::DirectorMethodException();
+    }
+}
+%exception {
+    try { $action }
+    catch (Swig::DirectorException &e) { SWIG_fail; }
+}
 
 %include "std_string.i"
 %include "std_vector.i"
@@ -63,6 +78,8 @@ public:
 
     bool start(std::string& strError);
 
+    void setLogger(ILogger* pLogger);
+
     ISelectionCriterionTypeInterface* createSelectionCriterionType(bool bIsInclusive);
     ISelectionCriterionInterface* createSelectionCriterion(const std::string& strName,
             const ISelectionCriterionTypeInterface* pSelectionCriterionType);
@@ -155,6 +172,25 @@ public:
 %clear std::string& strResult;
 };
 
+// SWIG nested class support is not complete - cf.
+// http://swig.org/Doc2.0/SWIGPlus.html#SWIGPlus_nested_classes
+// This link also explains how to trick SWIG and pretend that
+// ILogger is a toplevel class (whereas it actually is an inner class of
+// CParameterMgrFullConnector
+// Logger interface
+%feature("director") ILogger;
+%nestedworkaround CParameterMgrFullConnector::ILogger;
+class ILogger
+{
+    public:
+        virtual void log(bool bIsWarning, const std::string& strLog) = 0;
+    protected:
+        virtual ~ILogger() {}
+};
+%{
+typedef CParameterMgrFullConnector::ILogger ILogger;
+%}
+
 class ISelectionCriterionTypeInterface
 {
 %{
diff --git a/bindings/python/sample.py b/bindings/python/sample.py
index f33ddeb..1208fc9 100755
--- a/bindings/python/sample.py
+++ b/bindings/python/sample.py
@@ -29,9 +29,28 @@
 
 import PyPfw
 import sys
+import logging
+
+class MyLogger(PyPfw.ILogger):
+    def __init__(self):
+        # Calling the base constructor is necessary: if you don't, MyLogger
+        # won't be recognised as a derived class of PyPfw.ILogger
+        super(MyLogger, self).__init__()
+
+    def log(self, is_warning, log):
+        log_func = logging.warning if is_warning else logging.info
+        log_func(log)
+
+
+logging.root.setLevel(logging.INFO)
 
 pfw = PyPfw.ParameterFramework(sys.argv[1])
 
+# warning: don't pass MyLogger() directly as argument to setLogger() or it will
+# be garbage collected
+mylogger = MyLogger()
+pfw.setLogger(mylogger);
+
 moodType = pfw.createSelectionCriterionType(False)
 for numerical, literal in enumerate(["mad", "sad", "glad"]):
     moodType.addValuePair(numerical, literal)