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message.go
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message.go
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/*
* Copyright 2018 The Knative Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package provisioners
import (
"errors"
"regexp"
"strings"
)
const (
// MessageHistoryHeader is the header containing all channel hosts traversed by the message
// This is an experimental header: https://github.com/knative/eventing/issues/638
MessageHistoryHeader = "ce-knativehistory"
MessageHistorySeparator = "; "
)
var historySplitter = regexp.MustCompile(`\s*` + regexp.QuoteMeta(MessageHistorySeparator) + `\s*`)
var forwardHeaders = []string{
"content-type",
// tracing
"x-request-id",
}
var forwardPrefixes = []string{
// knative
"knative-",
// cloud events
"ce-",
// tracing
"x-b3-",
"x-ot-",
}
// Message represents a chunk of data within a channel dispatcher. The message contains both
// a map of string headers and a binary payload. This struct gets marshaled/unmarshaled in order to
// preserve and pass Header information to the event subscriber.
//
// A message may represent a CloudEvent.
type Message struct {
// Headers provide metadata about the message payload. All header keys
// should be lowercase.
Headers map[string]string `json:"headers,omitempty"`
// Payload is the raw binary content of the message. The payload format is
// often described by the 'content-type' header.
Payload []byte `json:"payload,omitempty"`
}
// ErrUnknownChannel is returned when a message is received by a channel dispatcher for a
// channel that does not exist.
var ErrUnknownChannel = errors.New("unknown channel")
// History returns the list of hosts where the message has been into
func (m *Message) History() []string {
if m.Headers == nil {
return nil
}
if h, ok := m.Headers[MessageHistoryHeader]; ok {
return decodeMessageHistory(h)
}
return nil
}
// AppendToHistory appends a new host at the end of the list of hosts of the message history
func (m *Message) AppendToHistory(host string) {
host = cleanupMessageHistoryItem(host)
if host == "" {
return
}
m.setHistory(append(m.History(), host))
}
// setHistory sets the message history to the given value
func (m *Message) setHistory(history []string) {
historyStr := encodeMessageHistory(history)
if m.Headers == nil {
m.Headers = make(map[string]string)
}
m.Headers[MessageHistoryHeader] = historyStr
}
func cleanupMessageHistoryItem(host string) string {
return strings.Trim(host, " ")
}
func encodeMessageHistory(history []string) string {
return strings.Join(history, MessageHistorySeparator)
}
func decodeMessageHistory(historyStr string) []string {
readHistory := historySplitter.Split(historyStr, -1)
// Filter and cleanup in-place
history := readHistory[:0]
for _, item := range readHistory {
cleanItem := cleanupMessageHistoryItem(item)
if cleanItem != "" {
history = append(history, cleanItem)
}
}
return history
}