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package apns
import (
"bytes"
"encoding/binary"
"encoding/hex"
"encoding/json"
"errors"
"math/rand"
"strconv"
"time"
)
// Push commands always start with command value 2.
const pushCommandValue = 2
// Your total notification payload cannot exceed 2 KB.
const MaxPayloadSizeBytes = 2048
// Every push notification gets a pseudo-unique identifier;
// this establishes the upper boundary for it. Apple will return
// this identifier if there is an issue sending your notification.
const IdentifierUbound = 9999
// Constants related to the payload fields and their lengths.
const (
deviceTokenItemid = 1
payloadItemid = 2
notificationIdentifierItemid = 3
expirationDateItemid = 4
priorityItemid = 5
deviceTokenLength = 32
notificationIdentifierLength = 4
expirationDateLength = 4
priorityLength = 1
)
// Payload contains the notification data for your request.
//
// Alert is an interface here because it supports either a string
// or a dictionary, represented within by an AlertDictionary struct.
type Payload struct {
Alert interface{} `json:"alert,omitempty"`
Badge int `json:"badge,omitempty"`
Sound string `json:"sound,omitempty"`
ContentAvailable int `json:"content-available,omitempty"`
Category string `json:"category,omitempty"`
}
// NewPayload creates and returns a Payload structure.
func NewPayload() *Payload {
return new(Payload)
}
// AlertDictionary is a more complex notification payload.
//
// From the APN docs: "Use the ... alert dictionary in general only if you absolutely need to."
// The AlertDictionary is suitable for specific localization needs.
type AlertDictionary struct {
Body string `json:"body,omitempty"`
ActionLocKey string `json:"action-loc-key,omitempty"`
LocKey string `json:"loc-key,omitempty"`
LocArgs []string `json:"loc-args,omitempty"`
LaunchImage string `json:"launch-image,omitempty"`
}
// NewAlertDictionary creates and returns an AlertDictionary structure.
func NewAlertDictionary() *AlertDictionary {
return new(AlertDictionary)
}
// PushNotification is the wrapper for the Payload.
// The length fields are computed in ToBytes() and aren't represented here.
type PushNotification struct {
Identifier int32
Expiry uint32
DeviceToken string
payload map[string]interface{}
Priority uint8
}
// NewPushNotification creates and returns a PushNotification structure.
// It also initializes the pseudo-random identifier.
func NewPushNotification() (pn *PushNotification) {
pn = new(PushNotification)
pn.payload = make(map[string]interface{})
pn.Identifier = rand.New(rand.NewSource(time.Now().UnixNano())).Int31n(IdentifierUbound)
pn.Priority = 10
return
}
// AddPayload sets the "aps" payload section of the request. It also
// has a hack described within to deal with specific zero values.
func (pn *PushNotification) AddPayload(p *Payload) {
// This deserves some explanation.
//
// Setting an exported field of type int to 0
// triggers the omitempty behavior if you've set it.
// Since the badge is optional, we should omit it if
// it's not set. However, we want to include it if the
// value is 0, so there's a hack in push_notification.go
// that exploits the fact that Apple treats -1 for a
// badge value as though it were 0 (i.e. it clears the
// badge but doesn't stop the notification from going
// through successfully.)
//
// Still a hack though :)
if p.Badge == 0 {
p.Badge = -1
}
pn.Set("aps", p)
}
// Get returns the value of a payload key, if it exists.
func (pn *PushNotification) Get(key string) interface{} {
return pn.payload[key]
}
// Set defines the value of a payload key.
func (pn *PushNotification) Set(key string, value interface{}) {
pn.payload[key] = value
}
// PayloadJSON returns the current payload in JSON format.
func (pn *PushNotification) PayloadJSON() ([]byte, error) {
return json.Marshal(pn.payload)
}
// PayloadString returns the current payload in string format.
func (pn *PushNotification) PayloadString() (string, error) {
j, err := pn.PayloadJSON()
return string(j), err
}
// ToBytes returns a byte array of the complete PushNotification
// struct. This array is what should be transmitted to the APN Service.
func (pn *PushNotification) ToBytes() ([]byte, error) {
token, err := hex.DecodeString(pn.DeviceToken)
if err != nil {
return nil, err
}
if len(token) != deviceTokenLength {
return nil, errors.New("device token has incorrect length")
}
payload, err := pn.PayloadJSON()
if err != nil {
return nil, err
}
if len(payload) > MaxPayloadSizeBytes {
return nil, errors.New("payload is larger than the " + strconv.Itoa(MaxPayloadSizeBytes) + " byte limit")
}
frameBuffer := new(bytes.Buffer)
binary.Write(frameBuffer, binary.BigEndian, uint8(deviceTokenItemid))
binary.Write(frameBuffer, binary.BigEndian, uint16(deviceTokenLength))
binary.Write(frameBuffer, binary.BigEndian, token)
binary.Write(frameBuffer, binary.BigEndian, uint8(payloadItemid))
binary.Write(frameBuffer, binary.BigEndian, uint16(len(payload)))
binary.Write(frameBuffer, binary.BigEndian, payload)
binary.Write(frameBuffer, binary.BigEndian, uint8(notificationIdentifierItemid))
binary.Write(frameBuffer, binary.BigEndian, uint16(notificationIdentifierLength))
binary.Write(frameBuffer, binary.BigEndian, pn.Identifier)
binary.Write(frameBuffer, binary.BigEndian, uint8(expirationDateItemid))
binary.Write(frameBuffer, binary.BigEndian, uint16(expirationDateLength))
binary.Write(frameBuffer, binary.BigEndian, pn.Expiry)
binary.Write(frameBuffer, binary.BigEndian, uint8(priorityItemid))
binary.Write(frameBuffer, binary.BigEndian, uint16(priorityLength))
binary.Write(frameBuffer, binary.BigEndian, pn.Priority)
buffer := bytes.NewBuffer([]byte{})
binary.Write(buffer, binary.BigEndian, uint8(pushCommandValue))
binary.Write(buffer, binary.BigEndian, uint32(frameBuffer.Len()))
binary.Write(buffer, binary.BigEndian, frameBuffer.Bytes())
return buffer.Bytes(), nil
}
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