Fix filtering when both pass and drop match an item (#3036)

Adjust logic in functions responsible for passing metrics in order to be able
to process them correctly in case where pass and drop are defined together.

docs/CONFIGURATION.md

@@ -134,8 +134,8 @@ is tested on points after they have passed the `namepass` test.
 An array of glob pattern strings.  Only fields whose field key matches a
 pattern in this list are emitted.  Not available for outputs.
 * **fielddrop**:
-The inverse of `fieldpass`. Fields with a field key matching one of the
-patterns will be discarded from the point.  Not available for outputs.
+The inverse of `fieldpass`.  Fields with a field key matching one of the
+patterns will be discarded from the point.  This is tested on points after they have passed the `fieldpass` test.  Not available for outputs.
 * **tagpass**:
 A table mapping tag keys to arrays of glob pattern strings.  Only points
 that contain a tag key in the table and a tag value matching one of its

internal/models/filter.go

@@ -132,51 +132,74 @@ func (f *Filter) Apply(
 	return true
 }
 
+// IsActive checking if filter is active
 func (f *Filter) IsActive() bool {
 	return f.isActive
 }
 
 // shouldNamePass returns true if the metric should pass, false if should drop
 // based on the drop/pass filter parameters
 func (f *Filter) shouldNamePass(key string) bool {
-	if f.namePass != nil {
+
+	pass := func(f *Filter) bool {
 		if f.namePass.Match(key) {
 			return true
 		}
 		return false
 	}
 
-	if f.nameDrop != nil {
+	drop := func(f *Filter) bool {
 		if f.nameDrop.Match(key) {
 			return false
 		}
+		return true
 	}
+
+	if f.namePass != nil && f.nameDrop != nil {
+		return pass(f) && drop(f)
+	} else if f.namePass != nil {
+		return pass(f)
+	} else if f.nameDrop != nil {
+		return drop(f)
+	}
+
 	return true
 }
 
 // shouldFieldPass returns true if the metric should pass, false if should drop
 // based on the drop/pass filter parameters
 func (f *Filter) shouldFieldPass(key string) bool {
-	if f.fieldPass != nil {
+
+	pass := func(f *Filter) bool {
 		if f.fieldPass.Match(key) {
 			return true
 		}
 		return false
 	}
 
-	if f.fieldDrop != nil {
+	drop := func(f *Filter) bool {
 		if f.fieldDrop.Match(key) {
 			return false
 		}
+		return true
 	}
+
+	if f.fieldPass != nil && f.fieldDrop != nil {
+		return pass(f) && drop(f)
+	} else if f.fieldPass != nil {
+		return pass(f)
+	} else if f.fieldDrop != nil {
+		return drop(f)
+	}
+
 	return true
 }
 
 // shouldTagsPass returns true if the metric should pass, false if should drop
 // based on the tagdrop/tagpass filter parameters
 func (f *Filter) shouldTagsPass(tags map[string]string) bool {
 
-	tagPass := func(f *Filter) bool {
+	pass := func(f *Filter) bool {
 		for _, pat := range f.TagPass {
 			if pat.filter == nil {
 				continue
@@ -190,7 +213,7 @@ func (f *Filter) shouldTagsPass(tags map[string]string) bool {
 		return false
 	}
 
-	tagDrop := func(f *Filter) bool {
+	drop := func(f *Filter) bool {
 		for _, pat := range f.TagDrop {
 			if pat.filter == nil {
 				continue
@@ -209,11 +232,11 @@ func (f *Filter) shouldTagsPass(tags map[string]string) bool {
 	if f.TagPass != nil && f.TagDrop != nil {
 		// return true only in case when tag pass and won't be dropped (true, true).
 		// in case when the same tag should be passed and dropped it will be dropped (true, false).
-		return tagPass(f) && tagDrop(f)
+		return pass(f) && drop(f)
 	} else if f.TagPass != nil {
-		return tagPass(f)
+		return pass(f)
 	} else if f.TagDrop != nil {
-		return tagDrop(f)
+		return drop(f)
 	}
 
 	return true

internal/models/filter_test.go

@@ -358,6 +358,46 @@ func TestFilter_FilterTagsMatches(t *testing.T) {
 	}, pretags)
 }
 
+// TestFilter_FilterNamePassAndDrop used for check case when
+// both parameters were defined
+// see: https://github.com/influxdata/telegraf/issues/2860
+func TestFilter_FilterNamePassAndDrop(t *testing.T) {
+
+	inputData := []string{"name1", "name2", "name3", "name4"}
+	expectedResult := []bool{false, true, false, false}
+
+	f := Filter{
+		NamePass: []string{"name1", "name2"},
+		NameDrop: []string{"name1", "name3"},
+	}
+
+	require.NoError(t, f.Compile())
+
+	for i, name := range inputData {
+		assert.Equal(t, f.shouldNamePass(name), expectedResult[i])
+	}
+}
+
+// TestFilter_FilterFieldPassAndDrop used for check case when
+// both parameters were defined
+// see: https://github.com/influxdata/telegraf/issues/2860
+func TestFilter_FilterFieldPassAndDrop(t *testing.T) {
+
+	inputData := []string{"field1", "field2", "field3", "field4"}
+	expectedResult := []bool{false, true, false, false}
+
+	f := Filter{
+		FieldPass: []string{"field1", "field2"},
+		FieldDrop: []string{"field1", "field3"},
+	}
+
+	require.NoError(t, f.Compile())
+
+	for i, field := range inputData {
+		assert.Equal(t, f.shouldFieldPass(field), expectedResult[i])
+	}
+}
+
 // TestFilter_FilterTagsPassAndDrop used for check case when
 // both parameters were defined
 // see: https://github.com/influxdata/telegraf/issues/2860