Ban transformer: Take three on fixing out of bounds

We were modifying the array we were iterating over, which caused some
rather interesting bugs. Take a copy instead.

We also trim the array at the end to leave a tidier end result.

transformer/ban.go

@@ -11,37 +11,34 @@ type Ban struct {
 }
 
 func (b *Ban) Transform(c *skogul.Container) error {
+
 	for pathKey, pathValue := range b.LookupData {
-		for k, mi := range c.Metrics {
+		newMetrics := make([]*skogul.Metric, 0, len(c.Metrics))
+		for _, mi := range c.Metrics {
 			var ptr interface{}
-
 			ptr, _ = jsonptr.Get(mi.Data, pathKey)
 
-			if ptr == pathValue {
-				if k == len(c.Metrics)-1 {
-					c.Metrics = c.Metrics[:k]
-				} else {
-					c.Metrics = append(c.Metrics[:k], c.Metrics[k+1:]...)
-				}
+			if ptr != pathValue {
+				newMetrics = append(newMetrics, mi)
 			}
 		}
+		c.Metrics = newMetrics
 	}
 
 	for pathKey, pathValue := range b.LookupMetadata {
-		for k, mi := range c.Metrics {
+		newMetrics := make([]*skogul.Metric, 0, len(c.Metrics))
+		for _, mi := range c.Metrics {
 			var ptr interface{}
 
 			ptr, _ = jsonptr.Get(mi.Metadata, pathKey)
-			if ptr == pathValue {
-				if k == len(c.Metrics)-1 {
-					c.Metrics = c.Metrics[:k]
-				} else {
-					c.Metrics = append(c.Metrics[:k], c.Metrics[k+1:]...)
-				}
-				continue
+			if ptr != pathValue {
+				newMetrics = append(newMetrics, mi)
 			}
 		}
+		c.Metrics = newMetrics
 	}
-
+	newMetrics := make([]*skogul.Metric, len(c.Metrics))
+	copy(newMetrics, c.Metrics)
+	c.Metrics = newMetrics
 	return nil
 }

transformer/ban_test.go

@@ -99,11 +99,20 @@ func TestBan(t *testing.T) {
 			"funny": "notfunny",
 		},
 	}
+	metric5 := skogul.Metric{
+		Metadata: map[string]interface{}{
+			"funny": "",
+		},
+	}
+	metric6 := skogul.Metric{
+		Metadata: map[string]interface{}{
+			"funny": "",
+		},
+	}
 
 	c := skogul.Container{}
-	c.Metrics = []*skogul.Metric{&metric, &metric2, &metric3, &metric4}
+	c.Metrics = []*skogul.Metric{&metric, &metric2, &metric3, &metric4, &metric5, &metric6}
 
-	originalMetricsCount := len(c.Metrics)
 	ban := &transformer.Ban{}
 
 	ban.LookupData = map[string]interface{}{
@@ -113,16 +122,17 @@ func TestBan(t *testing.T) {
 	}
 
 	ban.LookupMetadata = map[string]interface{}{
-		"/funny": "notfunny",
+		"/funny": "",
 	}
 
 	err := ban.Transform(&c)
 	if err != nil {
 		t.Fatalf("error occurred %v", err.Error())
 	}
-
-	if originalMetricsCount == len(c.Metrics) {
-		t.Fatal("Metrics slice has same length even after the banning of values")
+	if len(c.Metrics) != 1 {
+		t.Fatalf("expected exactly 1 metric to remain, got %d", len(c.Metrics))
+	}
+	if cap(c.Metrics) != 1 {
+		t.Fatalf("expected exactly len(metrics) == 1, got %d", cap(c.Metrics))
 	}
-
 }