azure-event-hubs-go/event.go

package eventhub

//	MIT License
//
//	Copyright (c) Microsoft Corporation. All rights reserved.
//
//	Permission is hereby granted, free of charge, to any person obtaining a copy
//	of this software and associated documentation files (the "Software"), to deal
//	in the Software without restriction, including without limitation the rights
//	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//	copies of the Software, and to permit persons to whom the Software is
//	furnished to do so, subject to the following conditions:
//
//	The above copyright notice and this permission notice shall be included in all
//	copies or substantial portions of the Software.
//
//	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//	SOFTWARE

import (
	"fmt"
	"reflect"
	"strings"
	"time"

	"github.com/Azure/azure-amqp-common-go/persist"
	"github.com/mitchellh/mapstructure"
	"pack.ag/amqp"
)

const (
	batchMessageFormat         uint32 = 0x80013700
	partitionKeyAnnotationName string = "x-opt-partition-key"
	sequenceNumberName         string = "x-opt-sequence-number"
	enqueueTimeName            string = "x-opt-enqueued-time"
)

type (
	// Event is an Event Hubs message to be sent or received
	Event struct {
		Data             []byte
		PartitionKey     *string
		Properties       map[string]interface{}
		ID               string
		message          *amqp.Message
		SystemProperties *SystemProperties
	}

	// EventBatch is a batch of Event Hubs messages to be sent
	EventBatch struct {
		Events       []*Event
		PartitionKey *string
		Properties   map[string]interface{}
		ID           string
	}

	// SystemProperties are used to store properties that are set by the system.
	SystemProperties struct {
		SequenceNumber *int64     `mapstructure:"x-opt-sequence-number"` // unique sequence number of the message
		EnqueuedTime   *time.Time `mapstructure:"x-opt-enqueued-time"`   // time the message landed in the message queue
		Offset         *int64     `mapstructure:"x-opt-offset"`
		PartitionID    *int16     `mapstructure:"x-opt-partition-id"`
		PartitionKey   *string    `mapstructure:"x-opt-partition-key"`
	}

	mapStructureTag struct {
		Name         string
		PersistEmpty bool
	}
)

// NewEventFromString builds an Event from a string message
func NewEventFromString(message string) *Event {
	return NewEvent([]byte(message))
}

// NewEvent builds an Event from a slice of data
func NewEvent(data []byte) *Event {
	return &Event{
		Data: data,
	}
}

// NewEventBatch builds an EventBatch from an array of Events
func NewEventBatch(events []*Event) *EventBatch {
	return &EventBatch{
		Events: events,
	}
}

// GetCheckpoint returns the checkpoint information on the Event
func (e *Event) GetCheckpoint() persist.Checkpoint {
	var offset string
	var enqueueTime time.Time
	var sequenceNumber int64
	if val, ok := e.message.Annotations[offsetAnnotationName]; ok {
		offset = val.(string)
	}

	if val, ok := e.message.Annotations[enqueueTimeName]; ok {
		enqueueTime = val.(time.Time)
	}

	if val, ok := e.message.Annotations[sequenceNumberName]; ok {
		sequenceNumber = val.(int64)
	}

	return persist.NewCheckpoint(offset, sequenceNumber, enqueueTime)
}

// Set will set a key in the event properties
func (e *Event) Set(key string, value interface{}) {
	if e.Properties == nil {
		e.Properties = make(map[string]interface{})
	}
	e.Properties[key] = value
}

// Get will fetch a property from the event
func (e *Event) Get(key string) (interface{}, bool) {
	if e.Properties == nil {
		return nil, false
	}

	if val, ok := e.Properties[key]; ok {
		return val, true
	}
	return nil, false
}

func (e *Event) toMsg() (*amqp.Message, error) {
	msg := e.message
	if msg == nil {
		msg = amqp.NewMessage(e.Data)
	}

	msg.Properties = &amqp.MessageProperties{
		MessageID: e.ID,
	}

	if len(e.Properties) > 0 {
		msg.ApplicationProperties = make(map[string]interface{})
		for key, value := range e.Properties {
			msg.ApplicationProperties[key] = value
		}
	}

	if e.SystemProperties != nil {
		sysPropMap, err := encodeStructureToMap(e.SystemProperties)
		if err != nil {
			return nil, err
		}
		msg.Annotations = annotationsFromMap(sysPropMap)
	}

	if e.PartitionKey != nil {
		msg.Annotations = make(amqp.Annotations)
		msg.Annotations[partitionKeyAnnotationName] = e.PartitionKey
	}

	return msg, nil
}

func (b *EventBatch) toEvent() (*Event, error) {
	msg := &amqp.Message{
		Data: make([][]byte, len(b.Events)),
		Properties: &amqp.MessageProperties{
			MessageID: b.ID,
		},
		Format: batchMessageFormat,
	}

	if b.PartitionKey != nil {
		msg.Annotations = make(amqp.Annotations)
		msg.Annotations[partitionKeyAnnotationName] = b.PartitionKey
	}

	for idx, event := range b.Events {
		innerMsg, err := event.toMsg()
		if err != nil {
			return nil, err
		}

		bin, err := innerMsg.MarshalBinary()
		if err != nil {
			return nil, err
		}
		msg.Data[idx] = bin
	}

	return eventFromMsg(msg)
}

func eventFromMsg(msg *amqp.Message) (*Event, error) {
	return newEvent(msg.Data[0], msg)
}

func newEvent(data []byte, msg *amqp.Message) (*Event, error) {
	event := &Event{
		Data:    data,
		message: msg,
	}

	if msg.Properties != nil {
		if id, ok := msg.Properties.MessageID.(string); ok {
			event.ID = id
		}
	}

	if msg.Annotations != nil {
		if val, ok := msg.Annotations[partitionKeyAnnotationName]; ok {
			if valStr, ok := val.(string); ok {
				event.PartitionKey = &valStr
			}
		}
	}

	if msg.Annotations != nil {
		if err := mapstructure.WeakDecode(msg.Annotations, &event.SystemProperties); err != nil {
			fmt.Println("error decoding...", err)
			return event, err
		}
	}

	if msg != nil {
		event.Properties = msg.ApplicationProperties
	}

	return event, nil
}

func encodeStructureToMap(structPointer interface{}) (map[string]interface{}, error) {
	valueOfStruct := reflect.ValueOf(structPointer)
	s := valueOfStruct.Elem()
	if s.Kind() != reflect.Struct {
		return nil, fmt.Errorf("must provide a struct")
	}

	encoded := make(map[string]interface{})
	for i := 0; i < s.NumField(); i++ {
		f := s.Field(i)
		if f.IsValid() && f.CanSet() {
			tf := s.Type().Field(i)
			tag, err := parseMapStructureTag(tf.Tag)
			if err != nil {
				return nil, err
			}

			if tag != nil {
				switch f.Kind() {
				case reflect.Ptr:
					if !f.IsNil() || tag.PersistEmpty {
						if f.IsNil() {
							encoded[tag.Name] = nil
						} else {
							encoded[tag.Name] = f.Elem().Interface()
						}
					}
				default:
					if f.Interface() != reflect.Zero(f.Type()).Interface() || tag.PersistEmpty {
						encoded[tag.Name] = f.Interface()
					}
				}
			}
		}
	}

	return encoded, nil
}

func parseMapStructureTag(tag reflect.StructTag) (*mapStructureTag, error) {
	str, ok := tag.Lookup("mapstructure")
	if !ok {
		return nil, nil
	}

	mapTag := new(mapStructureTag)
	split := strings.Split(str, ",")
	mapTag.Name = strings.TrimSpace(split[0])

	if len(split) > 1 {
		for _, tagKey := range split[1:] {
			switch tagKey {
			case "persistempty":
				mapTag.PersistEmpty = true
			default:
				return nil, fmt.Errorf("key %q is not understood", tagKey)
			}
		}
	}
	return mapTag, nil
}

func annotationsFromMap(m map[string]interface{}) amqp.Annotations {
	a := make(amqp.Annotations)
	for key, val := range m {
		a[key] = val
	}
	return a
}