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Copyright IBM Corp. All Rights Reserved.
SPDX-License-Identifier: Apache-2.0
package msgprocessor
import (
ab ""
// ErrEmptyMessage is returned by the empty message filter on rejection.
var ErrEmptyMessage = errors.New("Message was empty")
// Rule defines a filter function which accepts, rejects, or forwards (to the next rule) an Envelope
type Rule interface {
// Apply applies the rule to the given Envelope, either successfully or returns error
Apply(message *ab.Envelope) error
// EmptyRejectRule rejects empty messages
var EmptyRejectRule = Rule(emptyRejectRule{})
type emptyRejectRule struct{}
func (a emptyRejectRule) Apply(message *ab.Envelope) error {
if message.Payload == nil {
return ErrEmptyMessage
return nil
// AcceptRule always returns Accept as a result for Apply
var AcceptRule = Rule(acceptRule{})
type acceptRule struct{}
func (a acceptRule) Apply(message *ab.Envelope) error {
return nil
// RuleSet is used to apply a collection of rules
type RuleSet struct {
rules []Rule
// NewRuleSet creates a new RuleSet with the given ordered list of Rules
func NewRuleSet(rules []Rule) *RuleSet {
return &RuleSet{
rules: rules,
// Apply applies the rules given for this set in order, returning nil on valid or err on invalid
func (rs *RuleSet) Apply(message *ab.Envelope) error {
for _, rule := range rs.rules {
err := rule.Apply(message)
if err != nil {
return err
return nil
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