How to send a push notification using Erlang? - erlang

Question

I'm trying to send a push notification to APNs using Erlang.
This is the code I came up with so far:
-module(apnstest2).
-export([connect/0]).
connect() ->
application:start(ssl),
ssl:seed("someseedstring"),
Address = "gateway.sandbox.push.apple.com",
Port = 2195,
Cert = "/path/to/Certificate.pem",
Key = "/path/to/Key.unenc.pem",
Options = [{certfile, Cert}, {keyfile, Key}, {mode, binary}],
Timeout = 1000,
{ok, Socket} = ssl:connect(Address, Port, Options, Timeout),
Token = "195ec05a962b24954693c0b638b6216579a0d1d74b3e1c6f534c6f8fd0d50d03",
Payload = "{\"aps\":{\"alert\":\"Just testing.\",\"sound\":\"chime\", \"badge\":10}}",
TokenLength = length(Token),
PayloadLength = length(Payload),
Packet = [<<0:8, TokenLength, Token, PayloadLength, Payload>>],
ssl:send(Socket, list_to_binary(Packet)),
ssl:close(Socket).
The code doesn't take advantage of Erlang's concurrency but is just a prototype. I only want to test if I can send the push in the most simple way.
I think the problem is in the packet being sent to the APNs.
This is the binary format of a push notification:
alt text http://developer.apple.com/IPhone/library/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Art/aps_provider_binary.jpg
How should I create such a packet in Erlang?
Could someone please take a look at my code and tell me where the problem is?
Also I used Erlang's SSL application to create the connection and send the data and I don't know if this is the problem or the packet.
Thanks!

Answer 1

To start with, there is no need for creating a list of a single binary and then calling list_to_binary/1 on it. You can just send the binary itself.
Also, make sure the field lengths and values are appropriate according to the protocol:
TokenLength = 32 = length(Token),
Packet = <<0:8, TokenLength:16/big, Token, PayloadLength:16/big, Payload>>,
ssl:send(Socket, Packet),
Now that we have gotten this far, we will see that length(Token) is in fact 64, not 32:
You forgot to convert the hex string for Token to a binary, so you are sending a 64 byte hex character string instead of 32 binary bytes.
So... making Payload a binary from the start, and making Token a numeric constant, you can do something like the following:
Payload = <<"{\"aps\":{\"alert\":\"Just testing.\",\"sound\":\"chime\", \"badge\":10}}">>,
PayloadLength = size(Payload),
Packet = <<0:8, 32:16/big,
16#195ec05a962b24954693c0b638b6216579a0d1d74b3e1c6f534c6f8fd0d50d03:256/big,
PayloadLength:16/big, Payload/binary>>,
ssl:send(Socket, Packet),
Thanks to Christian for pointing out a number of mistakes in the former revisions of this answer.

Answer 2

I see two mistakes:
Token should be passed in binary and not in hex ascii.
You can't use the binary syntax to turn lists into binaries.
For parsing hex to an integer and then down to binary use something like this:
Token = "dead",
TokenNum = erlang:list_to_integer(Token, 16),
TokenBin = <<TokenNum:32/integer-unit:8>>,
Build the protocol packet with something like this:
TokenBin = ...,
Payload = <<"Payload">>,
PayloadSize = byte_size(Payload),
Packet = <<0:8, 32:16, TokenBin/binary, PayloadSize:16, Payload/binary>>,

Answer 3

Try use a simple library epns(Erlang Push Notifications)
This library can send push notification as APNS and FCM by Erlang side. How use epns(Erlang Push Notifications) library - you can read in README.md. This liblary can used as 3-rd party in project, or you can run it locally for see how this library works:
$ git clone https://github.com/vkatsuba/epns.git
$ cd epns
$ make
Retested on Erlang 20~21