Apple Push Notifications with Go language

I started to familiarize myself to the Go language, and decided to do the usual try out, i.e. sending Apple Push Notifications. It’s my personal usability benchmark for new programming environments. So far in the series

• Push notifications with Node.js
• Push notifications with Erlang

Step 1. Prerequisites

Get and build Go. Example here was done on Ubuntu 10.04 LTS x64 with Go installed based on instructions here at Go getting started guide.

• Read introduction to Apple Push here and get application and private key sandbox certificates as .pem files.
• And of course you need to have 32 byte push token from your iOS application.

Step 2. The Code.

The code here is complete, copy it to file apn.go or get it from Github.

Make sure you change the certificate files (cert.pem and key-noenc.pem) to point to your own certificate files. Also, replace the push token with your own push token, it’s written as hexadecimal string in this example for clarity.

package main

import (
   "crypto/tls"
   "fmt"
   "net"
   "json"
   "os"
   "time"
   "bytes"
   "encoding/hex"
   "encoding/binary"
)

func main() {

   // load certificates and setup config
   cert, err := tls.LoadX509KeyPair("cert.pem", "key-noenc.pem")
   if err != nil {
       fmt.Printf("error: %s\n", err.String())
       os.Exit(1)
   }
   conf := &tls.Config {
        Certificates: []tls.Certificate{cert},
   }

   // connect to the APNS and wrap socket to tls client
   conn, err := net.Dial("tcp", "", "gateway.sandbox.push.apple.com:2195")
   if err != nil {
      fmt.Printf("tcp error: %s\n", err.String())
      os.Exit(1)
   }
   tlsconn := tls.Client(conn, conf)

   // Force handshake to verify successful authorization.
   // Handshake is handled otherwise automatically on first
   // Read/Write attempt
   err = tlsconn.Handshake()
   if err != nil {
      fmt.Printf("tls error: %s\n", err.String())
      os.Exit(1)
   }
   // informational debugging stuff
   state := tlsconn.ConnectionState()
   fmt.Printf("conn state %v\n", state)

   // prepare binary payload from JSON structure
   payload := make(map[string]interface{})
   payload["aps"] = map[string]string{"alert": "Hello Push"}
   bpayload, err := json.Marshal(payload)

   // decode hexadecimal push device token to binary byte array
   btoken, _ := hex.DecodeString("6b4628de9317c80edd1c791640b58fdfc46d21d0d2d1351687239c44d8e30ab1") 

   // build the actual pdu
   buffer := bytes.NewBuffer([]byte{})
   // command
   binary.Write(buffer, binary.BigEndian, uint8(1))

   // transaction id, optional
   binary.Write(buffer, binary.BigEndian, uint32(1))

   // expiration time, 1 hour
   binary.Write(buffer, binary.BigEndian, uint32(time.Seconds() + 60*60))

   // push device token
   binary.Write(buffer, binary.BigEndian, uint16(len(btoken)))
   binary.Write(buffer, binary.BigEndian, btoken)

   // push payload
   binary.Write(buffer, binary.BigEndian, uint16(len(bpayload)))
   binary.Write(buffer, binary.BigEndian, bpayload)
   pdu := buffer.Bytes()

   // write pdu
   _, err = tlsconn.Write(pdu)
   if err != nil {
      fmt.Printf("write error: %s\n", err.String())
      os.Exit(1)
   }

   // wait for 5 seconds error pdu from the socket
   tlsconn.SetReadTimeout(5*1E9)

   readb := [6]byte{}
   n, err := tlsconn.Read(readb[:])
   if n > 0 {
     fmt.Printf("received: %s\n", hex.EncodeToString(readb[:n]))
   }

   tlsconn.Close()
}


Step 3. Compile and Run

Simple

$ 6g apn.go
$ 6l apn.6
$ ./6.out
conn state {true 47}
$

If everything went fine, the program exits within few seconds and  you’ll see your push notification appear on your iPhone.