Squashed commit of the following:

commit 7f46be64521d7cdf4d94409f979143a55acd665a
Author: Avi Zimmerman <avi.zimmerman@gmail.com>
Date:   Thu Jan 7 12:18:37 2021 +0200

    improve plugin interfaces

examples/plugins/Makefile

@@ -0,0 +1,10 @@
+PLUGINS ?=  $(patsubst %/,%,$(sort $(dir $(wildcard */))))
+
+.PHONY: $(PLUGINS)
+$(PLUGINS):
+	cd $@ && \
+		go build -o ../libgstgo$@.so -buildmode c-shared .
+	rm libgstgo$@.h
+
+clean:
+	rm -f *.so *.h

examples/plugins/filesrc/filesrc.go

@@ -90,7 +90,8 @@ func (f *fileSrc) setLocation(path string) error {
 }
 
 // The ObjectSubclass implementations below are for registering the various aspects of our
-// element and its capabilities with the type system.
+// element and its capabilities with the type system. These are the minimum methods that
+// should be implemented by an element.
 
 // Every element needs to provide its own constructor that returns an initialized
 // gst.GoElement implementation. Here we simply create a new fileSrc with zeroed settings
@@ -132,9 +133,12 @@ func (f *fileSrc) ClassInit(klass *gst.ElementClass) {
 	klass.InstallProperties(properties)
 }
 
-// Object implementations are used during the initialization of element. The
-// methods are called once the obejct is constructed and its properties are read
-// and written to.
+// Object implementations are used during the initialization of an element. The
+// methods are called once the object is constructed and its properties are read
+// and written to. These and the rest of the methods described below are documented
+// in interfaces in the bindings, however only individual methods needs from those
+// interfaces need to be implemented. When left unimplemented, the behavior of the parent
+// class is inherited.
 
 // SetProperty is called when a `value` is set to the property at index `id` in the
 // properties slice that we installed during ClassInit. It should attempt to register

gst/base/gst_base_src_impl.go

@@ -56,7 +56,7 @@ import (
 
 var (
 	// ExtendsBaseSrc is an Extendable for extending a GstBaseSrc
-	ExtendsBaseSrc gst.Extendable = &extendsBaseSrc{}
+	ExtendsBaseSrc gst.Extendable = &extendsBaseSrc{parent: gst.ExtendsElement}
 )
 
 // GstBaseSrcImpl is the documented interface for an element extending a GstBaseSrc. It does not have to
@@ -109,7 +109,7 @@ type GstBaseSrcImpl interface {
 	Fill(self *GstBaseSrc, offset uint64, size uint, buffer *gst.Buffer) gst.FlowReturn
 }
 
-type extendsBaseSrc struct{}
+type extendsBaseSrc struct{ parent gst.Extendable }
 
 func (e *extendsBaseSrc) Type() glib.Type     { return glib.Type(C.gst_base_src_get_type()) }
 func (e *extendsBaseSrc) ClassSize() int64    { return int64(C.sizeof_GstBaseSrcClass) }
@@ -118,6 +118,8 @@ func (e *extendsBaseSrc) InstanceSize() int64 { return int64(C.sizeof_GstBaseSrc
 // InitClass iterates the methods provided by the element and overrides any provided
 // in the virtual methods.
 func (e *extendsBaseSrc) InitClass(klass unsafe.Pointer, elem gst.GoElement) {
+	e.parent.InitClass(klass, elem)
+
 	class := C.toGstBaseSrcClass(klass)
 
 	if _, ok := elem.(interface {

gst/cgo_exports.go

@@ -258,6 +258,7 @@ func goClassInit(klass C.gpointer, klassData C.gpointer) {
 	data.ext.InitClass(unsafe.Pointer(klass), data.elem)
 
 	C.g_type_class_add_private(klass, C.gsize(unsafe.Sizeof(uintptr(0))))
+
 	data.elem.ClassInit(wrapElementClass(klass))
 }
 
@@ -310,13 +311,17 @@ func goURIHdlrSetURI(hdlr *C.GstURIHandler, uri *C.gchar, gerr **C.GError) C.gbo
 
 //export goObjectSetProperty
 func goObjectSetProperty(obj *C.GObject, propID C.guint, val *C.GValue, param *C.GParamSpec) {
-	iface := FromObjectUnsafePrivate(unsafe.Pointer(obj))
+	iface := FromObjectUnsafePrivate(unsafe.Pointer(obj)).(interface {
+		SetProperty(obj *Object, id uint, value *glib.Value)
+	})
 	iface.SetProperty(wrapObject(toGObject(unsafe.Pointer(obj))), uint(propID-1), glib.ValueFromNative(unsafe.Pointer(val)))
 }
 
 //export goObjectGetProperty
 func goObjectGetProperty(obj *C.GObject, propID C.guint, value *C.GValue, param *C.GParamSpec) {
-	iface := FromObjectUnsafePrivate(unsafe.Pointer(obj))
+	iface := FromObjectUnsafePrivate(unsafe.Pointer(obj)).(interface {
+		GetProperty(obj *Object, id uint) *glib.Value
+	})
 	val := iface.GetProperty(wrapObject(toGObject(unsafe.Pointer(obj))), uint(propID-1))
 	if val == nil {
 		return
@@ -326,7 +331,9 @@ func goObjectGetProperty(obj *C.GObject, propID C.guint, value *C.GValue, param
 
 //export goObjectConstructed
 func goObjectConstructed(obj *C.GObject) {
-	iface := FromObjectUnsafePrivate(unsafe.Pointer(obj))
+	iface := FromObjectUnsafePrivate(unsafe.Pointer(obj)).(interface {
+		Constructed(*Object)
+	})
 	iface.Constructed(wrapObject(toGObject(unsafe.Pointer(obj))))
 }
 

gst/g_object.go

@@ -0,0 +1,78 @@
+package gst
+
+/*
+#include "gst.go.h"
+
+extern void            goObjectSetProperty  (GObject * object, guint property_id, const GValue * value, GParamSpec *pspec);
+extern void            goObjectGetProperty  (GObject * object, guint property_id, GValue * value, GParamSpec * pspec);
+extern void            goObjectConstructed  (GObject * object);
+extern void            goObjectFinalize     (GObject * object, gpointer klass);
+
+void objectFinalize (GObject * object)
+{
+	GObjectClass *parent = g_type_class_peek_parent((G_OBJECT_GET_CLASS(object)));
+	goObjectFinalize(object, G_OBJECT_GET_CLASS(object));
+	parent->finalize(object);
+}
+
+void objectConstructed (GObject * object)
+{
+	GObjectClass *parent = g_type_class_peek_parent((G_OBJECT_GET_CLASS(object)));
+	goObjectConstructed(object);
+	parent->constructed(object);
+}
+
+void  setGObjectClassSetProperty  (void * klass)  { ((GObjectClass *)klass)->set_property = goObjectSetProperty; }
+void  setGObjectClassGetProperty  (void * klass)  { ((GObjectClass *)klass)->get_property = goObjectGetProperty; }
+void  setGObjectClassConstructed  (void * klass)  { ((GObjectClass *)klass)->constructed = objectConstructed; }
+void  setGObjectClassFinalize     (void * klass)  { ((GObjectClass *)klass)->finalize = objectFinalize; }
+
+*/
+import "C"
+import (
+	"unsafe"
+
+	"github.com/gotk3/gotk3/glib"
+)
+
+// GoObject is an interface that abstracts on the GObject. In most cases at least SetProperty and GetProperty
+// should be implemented by elements built from the go bindings.
+type GoObject interface {
+	// SetProperty should set the value of the property with the given id. ID is the index+1 of the parameter
+	// in the order it was registered.
+	SetProperty(obj *Object, id uint, value *glib.Value)
+	// GetProperty should retrieve the value of the property with the given id. ID is the index+1 of the parameter
+	// in the order it was registered.
+	GetProperty(obj *Object, id uint) *glib.Value
+	// Constructed is called when the Object has finished setting up.
+	Constructed(*Object)
+}
+
+// ExtendsObject signifies a GoElement that extends a GObject.
+var ExtendsObject Extendable = &extendObject{}
+
+type extendObject struct{}
+
+func (e *extendObject) Type() glib.Type     { return glib.Type(C.g_object_get_type()) }
+func (e *extendObject) ClassSize() int64    { return int64(C.sizeof_GObjectClass) }
+func (e *extendObject) InstanceSize() int64 { return int64(C.sizeof_GObject) }
+
+func (e *extendObject) InitClass(klass unsafe.Pointer, elem GoElement) {
+	C.setGObjectClassFinalize(klass)
+
+	if _, ok := elem.(interface {
+		SetProperty(obj *Object, id uint, value *glib.Value)
+	}); ok {
+		C.setGObjectClassSetProperty(klass)
+	}
+	if _, ok := elem.(interface {
+		GetProperty(obj *Object, id uint) *glib.Value
+	}); ok {
+		C.setGObjectClassGetProperty(klass)
+	}
+	if _, ok := elem.(interface {
+		Constructed(*Object)
+	}); ok {
+		C.setGObjectClassConstructed(klass)
+	}
+}

gst/g_parameter_spec.go

@@ -11,9 +11,7 @@ import (
 )
 
 // ParameterSpec is a go representation of a C GParamSpec
-type ParameterSpec struct {
-	paramSpec *C.GParamSpec
-}
+type ParameterSpec struct{ paramSpec *C.GParamSpec }
 
 // NewStringParameter returns a new ParameterSpec that will hold a string value.
 func NewStringParameter(name, nick, blurb string, defaultValue *string, flags ParameterFlags) *ParameterSpec {

gst/gst_buffer.go

@@ -598,6 +598,7 @@ func (b *Buffer) Unmap() {
 		return
 	}
 	C.gst_buffer_unmap(b.Instance(), (*C.GstMapInfo)(b.mapInfo.Instance()))
+	C.free(unsafe.Pointer(b.mapInfo.Instance()))
 }
 
 // MapRange maps the info of length merged memory blocks starting at idx in buffer.

gst/gst_debug.go

@@ -19,6 +19,7 @@ import "C"
 import (
 	"path"
 	"runtime"
+	"unsafe"
 )
 
 // DebugColorFlags are terminal style flags you can use when creating your debugging
@@ -98,14 +99,20 @@ func NewDebugCategory(name string, color DebugColorFlags, description string) *D
 
 func (d *DebugCategory) logDepth(level DebugLevel, message string, depth int, obj *C.GObject) {
 	function, file, line, _ := runtime.Caller(depth)
+	cFile := C.CString(path.Base(file))
+	cFunc := C.CString(runtime.FuncForPC(function).Name())
+	cMsg := C.CString(message)
+	defer C.free(unsafe.Pointer(cFile))
+	defer C.free(unsafe.Pointer(cFunc))
+	defer C.free(unsafe.Pointer(cMsg))
 	C.cgoDebugLog(
 		d.ptr,
 		C.GstDebugLevel(level),
-		C.CString(path.Base(file)),
-		(C.CString(runtime.FuncForPC(function).Name())),
+		(*C.gchar)(cFile),
+		(*C.gchar)(cFunc),
 		C.gint(line),
 		obj,
-		C.CString(message),
+		(*C.gchar)(cMsg),
 	)
 }
 

gst/gst_element.go

@@ -384,3 +384,16 @@ func (e *Element) URIHandler() URIHandler {
 	}
 	return &gstURIHandler{ptr: e.Instance()}
 }
+
+// ExtendsElement signifies a GoElement that extends a GstElement.
+var ExtendsElement Extendable = &extendElement{parent: ExtendsObject}
+
+type extendElement struct{ parent Extendable }
+
+func (e *extendElement) Type() glib.Type     { return glib.Type(C.gst_element_get_type()) }
+func (e *extendElement) ClassSize() int64    { return int64(C.sizeof_GstElementClass) }
+func (e *extendElement) InstanceSize() int64 { return int64(C.sizeof_GstElement) }
+
+func (e *extendElement) InitClass(klass unsafe.Pointer, elem GoElement) {
+	e.parent.InitClass(klass, elem)
+}

gst/gst_memory.go

@@ -109,6 +109,7 @@ func (m *Memory) Unmap() {
 		return
 	}
 	C.gst_memory_unmap(m.Instance(), (*C.GstMapInfo)(m.mapInfo.Instance()))
+	C.free(unsafe.Pointer(m.mapInfo.Instance()))
 }
 
 // Bytes will return a byte slice of the data inside this memory if it is readable.

gst/interfaces.go

@@ -6,40 +6,8 @@ package gst
 extern void   goClassInit     (gpointer g_class, gpointer class_data);
 extern void   goInstanceInit  (GTypeInstance * instance, gpointer g_class);
 
-extern void            goObjectSetProperty  (GObject * object, guint property_id, const GValue * value, GParamSpec *pspec);
-extern void            goObjectGetProperty  (GObject * object, guint property_id, GValue * value, GParamSpec * pspec);
-extern void            goObjectConstructed  (GObject * object);
-extern void            goObjectFinalize     (GObject * object, gpointer klass);
-
-void objectFinalize (GObject * object)
-{
-	GObjectClass *parent = g_type_class_peek_parent((G_OBJECT_GET_CLASS(object)));
-	goObjectFinalize(object, G_OBJECT_GET_CLASS(object));
-	parent->finalize(object);
-}
-
-void objectConstructed (GObject * object)
-{
-	GObjectClass *parent = g_type_class_peek_parent((G_OBJECT_GET_CLASS(object)));
-	goObjectConstructed(object);
-	parent->constructed(object);
-}
-
-void cgoClassInit (gpointer g_class, gpointer class_data)
-{
-	((GObjectClass *)g_class)->set_property = goObjectSetProperty;
-	((GObjectClass *)g_class)->get_property = goObjectGetProperty;
-	((GObjectClass *)g_class)->constructed = objectConstructed;
-	((GObjectClass *)g_class)->finalize = objectFinalize;
-
-	goClassInit(g_class, class_data);
-}
-
-void cgoInstanceInit (GTypeInstance * instance, gpointer g_class)
-{
-	goInstanceInit(instance, g_class);
-}
-
+void  cgoClassInit     (gpointer g_class, gpointer class_data)       { goClassInit(g_class, class_data); }
+void  cgoInstanceInit  (GTypeInstance * instance, gpointer g_class)  { goInstanceInit(instance, g_class); }
 */
 import "C"
 
@@ -51,45 +19,28 @@ import (
 	gopointer "github.com/mattn/go-pointer"
 )
 
+// GoElement is an interface to be implemented by GStreamer elements built using the
+// go bindings. Select methods from other interfaces can be overridden and declared via
+// the Extendable properties.
+//
+// Typically, at the very least, an element will want to implement methods from the Element
+// Extendable (and by extension the GoObject).
+type GoElement interface{ GoObjectSubclass }
+
 // Extendable is an interface implemented by extendable classes. It provides
 // the methods necessary to setup the vmethods on the object it represents.
 type Extendable interface {
+	// Type should return the type of the extended object
 	Type() glib.Type
+	// ClasSize should return the size of the extended class
 	ClassSize() int64
+	// InstanceSize should return the size of the object itself
 	InstanceSize() int64
+	// InitClass should take a pointer to a new subclass and a GoElement and override any
+	// methods implemented by the GoElement in the subclass.
 	InitClass(unsafe.Pointer, GoElement)
 }
 
-type extendElement struct{}
-
-func (e *extendElement) Type() glib.Type                                { return glib.Type(C.gst_element_get_type()) }
-func (e *extendElement) ClassSize() int64                               { return int64(C.sizeof_GstElementClass) }
-func (e *extendElement) InstanceSize() int64                            { return int64(C.sizeof_GstElement) }
-func (e *extendElement) InitClass(klass unsafe.Pointer, elem GoElement) {}
-
-// ExtendsElement signifies a GoElement that extends a GstElement.
-var ExtendsElement Extendable = &extendElement{}
-
-// GoElement is an interface to be implemented by GStreamer elements built using the
-// go bindings. The various methods are called throughout the lifecycle of the plugin.
-type GoElement interface {
-	GoObjectSubclass
-	GoObject
-}
-
-// privateFromObj returns the actual value of the address we stored in the object's private data.
-func privateFromObj(obj unsafe.Pointer) unsafe.Pointer {
-	private := C.g_type_instance_get_private((*C.GTypeInstance)(obj), C.objectGType((*C.GObject)(obj)))
-	privAddr := (*unsafe.Pointer)(unsafe.Pointer(private))
-	return *privAddr
-}
-
-// FromObjectUnsafePrivate will return the GoElement addressed in the private data of the given GObject.
-func FromObjectUnsafePrivate(obj unsafe.Pointer) GoElement {
-	ptr := gopointer.Restore(privateFromObj(obj))
-	return ptr.(GoElement)
-}
-
 // GoObjectSubclass is an interface that abstracts on the GObjectClass. It should be implemented
 // by plugins using the go bindings.
 type GoObjectSubclass interface {
@@ -99,21 +50,14 @@ type GoObjectSubclass interface {
 	// element should add any interfaces it plans to implement.
 	TypeInit(*TypeInstance)
 	// ClassInit is called on the element after registering it with GStreamer. This is when the element
-	// should  install any properties and pad templates it has.
+	// should install its properties and pad templates.
 	ClassInit(*ElementClass)
 }
 
-// GoObject is an interface that abstracts on the GObject. It should be implemented by plugins using
-// the gobindings.
-type GoObject interface {
-	// SetProperty should set the value of the property with the given id. ID is the index+1 of the parameter
-	// in the order it was registered.
-	SetProperty(obj *Object, id uint, value *glib.Value)
-	// GetProperty should retrieve the value of the property with the given id. ID is the index+1 of the parameter
-	// in the order it was registered.
-	GetProperty(obj *Object, id uint) *glib.Value
-	// Constructed is called when the Object has finished setting up.
-	Constructed(*Object)
+// FromObjectUnsafePrivate will return the GoElement addressed in the private data of the given GObject.
+func FromObjectUnsafePrivate(obj unsafe.Pointer) GoElement {
+	ptr := gopointer.Restore(privateFromObj(obj))
+	return ptr.(GoElement)
 }
 
 type classData struct {
@@ -156,3 +100,10 @@ func gtypeForGoElement(name string, elem GoElement, extendable Extendable) C.GTy
 	registeredTypes[reflect.TypeOf(elem).String()] = gtype
 	return gtype
 }
+
+// privateFromObj returns the actual value of the address we stored in the object's private data.
+func privateFromObj(obj unsafe.Pointer) unsafe.Pointer {
+	private := C.g_type_instance_get_private((*C.GTypeInstance)(obj), C.objectGType((*C.GObject)(obj)))
+	privAddr := (*unsafe.Pointer)(unsafe.Pointer(private))
+	return *privAddr
+}