tweak struct & improve comment (#34)

Signed-off-by: spacewander <spacewanderlzx@gmail.com>

pkg/filtermanager/api/api.go

@@ -73,12 +73,6 @@ type BufferInstance = api.BufferInstance
 type RequestTrailerMap = api.RequestTrailerMap
 type ResponseTrailerMap = api.ResponseTrailerMap
 
-type FilterConfigParser interface {
-	Parse(input interface{}, callbacks ConfigCallbackHandler) (interface{}, error)
-	Merge(parentConfig interface{}, childConfig interface{}) interface{}
-}
-type FilterConfigFactory func(config interface{}) FilterFactory
-
 type StreamInfo = api.StreamInfo
 type FilterCallbackHandler interface {
 	StreamInfo() StreamInfo
@@ -87,6 +81,7 @@ type FilterCallbackHandler interface {
 }
 
 type FilterFactory func(callbacks FilterCallbackHandler) Filter
+type FilterConfigFactory func(config interface{}) FilterFactory
 
 type DynamicMetadata = api.DynamicMetadata
 type FilterState = api.FilterState

pkg/filtermanager/filtermanager.go

@@ -17,14 +17,22 @@ var (
 	httpFilterConfigFactoryAndParser = sync.Map{}
 )
 
+// Here we introduce extra struct to avoid cyclic import between pkg/filtermanager and pkg/plugins
+type FilterConfigParser interface {
+	Parse(input interface{}, callbacks api.ConfigCallbackHandler) (interface{}, error)
+	Merge(parentConfig interface{}, childConfig interface{}) interface{}
+}
+
 type filterConfigFactoryAndParser struct {
-	configParser  api.FilterConfigParser
+	configParser  FilterConfigParser
 	configFactory api.FilterConfigFactory
 }
 
-// we can't import package below here which will cause the integration test to fail in Mac
+// We can't import package below here that will cause build failure in Mac
 // "github.com/envoyproxy/envoy/contrib/golang/filters/http/source/go/pkg/http"
-// therefore, we choice to export these fields
+// Therefore, the FilterManagerConfigParser & FilterManagerConfigFactory need to be exportable.
+// The http.RegisterHttpFilterConfigFactoryAndParser will be called in the main.go when building
+// the shared library in Linux.
 
 type FilterManagerConfigParser struct {
 }
@@ -478,7 +486,7 @@ func (m *filterManager) OnLog() {
 	}
 }
 
-func RegisterHttpFilterConfigFactoryAndParser(name string, factory api.FilterConfigFactory, parser api.FilterConfigParser) {
+func RegisterHttpFilterConfigFactoryAndParser(name string, factory api.FilterConfigFactory, parser FilterConfigParser) {
 	if factory == nil {
 		panic("config factory should not be nil")
 	}

pkg/plugins/plugins.go

@@ -70,10 +70,6 @@ func (cp *PluginConfigParser) Parse(any interface{}, callbacks api.ConfigCallbac
 // PluginMethodDefaultImpl provides reasonable implementation for optional methods
 type PluginMethodDefaultImpl struct{}
 
-func (p *PluginMethodDefaultImpl) Handle(c interface{}, callbacks api.ConfigCallbackHandler) (interface{}, error) {
-	return c, nil
-}
-
 func (p *PluginMethodDefaultImpl) Merge(parent interface{}, child interface{}) interface{} {
 	return child
 }