Make review changes to logstash input (#6299)

internal/choice/choice.go

@@ -0,0 +1,36 @@
+// Package choice provides basic functions for working with
+// plugin options that must be one of several values.
+package choice
+
+import "fmt"
+
+// Contains return true if the choice in the list of choices.
+func Contains(choice string, choices []string) bool {
+	for _, item := range choices {
+		if item == choice {
+			return true
+		}
+	}
+	return false
+}
+
+// CheckSContains returns an error if a choice is not one of
+// the available choices.
+func Check(choice string, available []string) error {
+	if !Contains(choice, available) {
+		return fmt.Errorf("unknown choice %s", choice)
+	}
+	return nil
+}
+
+// CheckSliceContains returns an error if the choices is not a subset of
+// available.
+func CheckSlice(choices, available []string) error {
+	for _, choice := range choices {
+		err := Check(choice, available)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}