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Apple Push Notification Server for Erlang
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README.md

Apns4erl v2 Build Statuscodecov

This lib is intended to allow you to write an APNs provider for Apple Push Notificaion services (APNs) over HTTP2 in Erlang.

Copyright (c) 2017 Erlang Solutions Ltd. support@inaka.net, released under the Apache 2 license

You can find the v1 here?

Note: Apns4erl v2 is still under development. Currently it supports push notifications with certificate and authentication token.

Contact Us

If you find any bugs or have a problem while using Apns4erl, please open an issue in this repo (or a pull request :)).

Requirements

  • You must have installed an updated Openssl version or, at least, be sure it supports TLS 1.2+. New APNs server only supports connections over TLS 1.2+.
  • Erlang R19+

Important Links

How to use it?

First we have to fill our config data. There are two ways for do this, one is filling a config file. This is an example you can find at test/test.config:

{
  apns,
  [ {apple_host,       "api.development.push.apple.com"}
  , {apple_port,       443}
  , {certfile,         "priv/apns-dev-cert.pem"}
  , {keyfile,          "priv/apns-dev-key-noenc.pem"}
  , {token_keyfile,    "priv/APNsAuthKey_KEYID12345.p8"}
  , {timeout,          10000}

  %% APNs Headers

  , {apns_id,          undefined}
  , {apns_expiration,  0}
  , {apns_priority,    10}
  , {apns_topic,       "com.example.myapp"}
  , {apns_collapse_id, undefined}
  , {apns_push_type,   "alert"}

  %% Feedback
  , {feedback_host,    "feedback.push.apple.com"}
  , {feedback_port,    2195}
  ]
  ]
}

The other way is send all that info as a parameter to apns:connect/1 function encapsulated in a apns_connection:connection() structure:

#{ name       := name()
 , apple_host := host()
 , apple_port := inet:port_number()
 , certfile   => path()
 , keyfile    => path()
 , timeout    => integer()
 , type       := type()
 }.

APNs allows two connection types, one is using Provider Certificates. The first certificate option is to supply cert paths in certfile and keyfile. Alternatively, you can supply a cert binary in certdata and a keydata()-type tuple (see: https://github.com/inaka/apns4erl/blob/master/src/apns_connection.erl#L64) in keydata. Certs are the Provider Certificates and the keys are the Private Key both provided by Apple. We need them in .pem format, here is an example of how to convert them, check the certificates section.

The other way to connect against APNs is using Provider Authentication Tokens, for this choice you must fill the field token_keyfile. This is a path to the Authentication Key provided by Apple. This is in .p8 format and it doesn't need conversion.

This key will be needed in order to generate a token which will be used every time we try to push a notification. In connection's time it is not needed.

Run

apns4erl can be included as a dependency and started from yourapp.app.src. You also can run it on the shell for testing.

> rebar3 compile
> erl -pa _build/default/lib/*/ebin -config test/test.config

Don't forget your config file if you want to use apns:connect/2.

1> apns:start().
ok

Create connections

After running apns4erl app we can start creating connections. As we mentioned before there are two types of connections. Both are created using the functions apns:connect/1 and apns:connect/2.

  • apns:connect/1: This function accepts as a parameter an apns_connection:connection() structure.

    #{ name       := name()
     , apple_host := host()
     , apple_port := inet:port_number()
     , certdata   => binary()
     , certfile   => path()
     , keydata    => keydata()
     , keyfile    => path()
     , timeout    => integer()
     , type       := type()
     }.

    where the type field indicates if is certdata, cert, or token.

  • apns:connect/2: The first argument is the type and the second one is the connection's name. In order to use it successfully we have to fill the config file before, as explained in how to use it? section.

Example:

1> apns:connect(cert, my_first_connection).
{ok,<0.87.0>}
2> apns:connect(#{name => another_cert, apple_host => "api.push.apple.com", apple_port => 443,
certfile => "priv/cert.pem", keyfile => "priv/key.pem", type => cert}).
3> apns:connect(token, my_second_connection).
{ok,<0.95.0>}

Note cert and token define the type we want.

apns:connect/2 returns the connection pid.

Create Connections without name

In some scenarios we don't want to assign names to the connections instead we want working just with the pid (working with a pool of connections for example). If that is the case we use the same apns:connect/1 and apns:connect/2 functions but instead of a connection name we put undefined:

1> apns:connect(cert, undefined).
{ok,<0.127.0>}
2> apns:connect(#{name => undefined, apple_host => "api.push.apple.com", apple_port => 443,
certfile => "priv/cert2.pem", keyfile => "priv/key2-noenc.pem", type => cert}).
{ok,<0.130.0>}
3> apns:connect(token, my_second_connection).
{ok,<0.132.0>}

Push Notifications over Provider Certificate connections

In order to send Notifications over Provider Certificate connection we will use apns:push_notification/3,4.

We will need the connection, a notification, the device ID and some http2 headers. The connection is the atom we used when we executed apns:connect/2 for setting a name or its pid, the device ID is provided by Apple, the notification is a map with the data we want to send, that map will be encoded to json later and the http2 headers can be explicitly sent as a parameter using apns:push_notification/4 or can be defined at the config file, in that case we would use apns:push_notification/3.

This is the headers format:

-type headers()   :: #{ apns_id          => binary()
                      , apns_expiration  => binary()
                      , apns_priority    => binary()
                      , apns_topic       => binary()
                      , apns_collapse_id => binary()
                      , apns_push_type   => binary()
                      , apns_auth_token  => binary()
                      }.

All of them are defined by Apple here

Lets send a Notification.

1> {ok, Pid} = apns:connect(cert, my_first_connection).
{ok,<0.85.0>}
2> DeviceId = <<"a0dc63fb059cb9c13b03e5c974af3dd33d67fed4147da8c5ada0626439e18935">>.
<<"a0dc63fb059cb9c13b03e5c974af3dd33d67fed4147da8c5ada0626439e18935">>
3> Notification = #{aps => #{alert => <<"you have a message">>}}.
#{aps => #{alert => <<"you have a message">>}}
4> apns:push_notification(my_first_connection, DeviceId, Notification).
{200,
 [{<<"apns-id">>,<<"EFDE0D9D-F60C-30F4-3FF1-86F3B90BE434">>}],
 no_body}
5> apns:push_notification(Pid, DeviceId, Notification).
{200,
 [{<<"apns-id">>,<<"EFDE0D9D-F60C-30F4-3FF1-86F3B90BE654">>}],
 no_body}

The result is the response itself, its format is:

-type response()  :: { integer()          % HTTP2 Code
                     , [term()]           % Response Headers
                     , [term()] | no_body % Response Body
                     } | timeout.

And that's all.

Push Notifications over Provider Authentication Tokens connections

This is the other way APNs allows us to send notifications. In this case we don't need a certificate but we will need a p8 file with the private key we will use to sign the token. Lets assume we've got the file APNsAuthKey_KEYID12345.p8 from Apple. We then have to fill the config file key token_keyfile with the path to that file.

We will need a kid value, this is the key identifier. In our case is the last 10 chars of the file name (KEYID123456). We will need also the iss value, this is the Team Id, that can be checked on your Apple's Developer account, in our case it will be THEATEAM. And that's it.

You can find more info here

In order to push a notification we will use apns:push_notification_token/4,5. We will need the same attributes we used sending a notification over Provider Certificate connections plus a signed token. This token has a 1 hour life, so that means we can generate one token and use it many times till it expires. Lets try.

Create the token:

6> TeamId = <<"THEATEAM">>.
<<"THEATEAM">>
7> KeyID = <<"KEYID123456">>.
<<"KEYID123456">>
8> Token = apns:generate_token(TeamId, KeyID).
<<"eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6IktFWUlEMTIzNDU2In0.eyJpc3MiOiJUSEVBVEVBTSIsImlhdCI6MTQ4NjE0OTMzNH0.MEQC"...>>

Now push the notification:

12> DeviceId = <<"a0dc63fb059cb9c13b03e5c974af3dd33d67fed4147da8c5ada0626439e18935">>.
<<"a0dc63fb059cb9c13b03e5c974af3dd33d67fed4147da8c5ada0626439e18935">>
13> Notification = #{aps => #{alert => <<"you have a message">>}}.
#{aps => #{alert => <<"you have a message">>}}
14> apns:push_notification_token(my_second_connection, Token, DeviceId, Notification).
{200,
 [{<<"apns-id">>,<<"EBC03BF9-A784-FDED-34F7-5A8D859DA977">>}],
 no_body}

We can use this token for an entire hour, after that we will receive something like this:

16> apns:push_notification_token(my_second_connection, Token, DeviceId, Notification).
{403,
 [{<<"apns-id">>,<<"03FF9497-8A6B-FFD6-B32B-160ACEDE35F0">>}],
 [{<<"reason">>,<<"ExpiredProviderToken">>}]}

Pushing notifications

NOTE in order to push notifications, in both ways, we must call apns:push_notification/3,4 and apns:push_notification_token/4,5 from the same process which created the connection. If we try to do it from a different one we will get an error {error, not_connection_owner}.

Reconnection

If network goes down or something unexpected happens the gun connection with APNs will go down. In that case apns4erl will send a message {reconnecting, ServerPid} to the client process, that means apns4erl lost the connection and it is trying to reconnect. Once the connection has been recover a {connection_up, ServerPid} message will be send.

We implemented an Exponential Backoff strategy. We can set the ceiling time adding the backoff_ceiling variable on the config file. By default it is set to 10 (seconds).

Close connections

Apple recommends us to keep our connections open and avoid opening and closing very often. You can check the Best Practices for Managing Connections section.

But when closing a connection makes sense apns4erl gives us the function apns:close_connection/1 where the parameter is the connection's name or the connection's pid. After using it the name will be available for new connections again (if it was different than undefined).

Feedback

apns4erl also allows us to get feedback from APNs service. It does it thru the binary API.

In order to get feedback we would need a Provider Certificate. apns4erl provides us two functions, apns:get_feedback/0 and apns:get_feedback/1 which require some Feedback's information like url, port, timeout... We can set that info in our config file and use apns:get_feedback/0. We can also send all that configuration as a parameter to apns:get_feedback/1 where the config structure must looks like this:

#{ host     := string()
 , port     := pos_integer()
 , certfile := string()
 , keyfile  => string()
 , timeout  := pos_integer()
 }.

The response for both functions will be a list of feedback()

-type feedback() :: {calendar:datetime(), string()}.

Where the first element in the tuple is the date when the device uninstalled the app and the second element is the Device Id.

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