Barker is a python module for notifying other servers using the webhook protocol. Webhooks are a way for a web server to communicate out to another server without direct user interaction. They can be used for notifications or triggers to start other services.

To use Barker, initialize the Webhook object:

from barker import Webhook
hook = Webhook()

The Webhook object has a number of attributes set by the user (either in the initialization call or afterwards):

1. url: the url you want to send the webhook notification
2. data: the information you want to post in the webhook
3. timeout: the number of seconds to wait for a server response
4. key: the hashing key used to verify message data. If not given, it defaults to BARKER.

Additionally, some attributes are set by Barker:

1. headers: custom HTTP headers containing information for message verification (BARKER_SIGNATURE and BARKER_TIMESTAMP)
2. response: the response received from the server as a requests.Response object

Once the object is populated with url and data at a minimum, it can be sent by calling the send method:

hook.send()
print(hook.response)

When a webhook is sent, it will include a signature in a header (BARKER_SIGNATURE) that is an HMAC hash of the time the webhook was generated (also a header, BARKER_TIMESTAMP) and the data joined by a ";". Local verification ensures the message is both correct and current.

Here is a snippet of code that can be used to verify message integrity. This assumes you have set the received headers to a headers variable, received data to a data variable, and hash key provided to the sender to hash_key (or the string 'BARKER' if none supplied).

hash = hmac.new(bytes(hash_key, 'utf-8'))
hash.update(bytes(";".join((headers['BARKER_TIMESTAMP'], data.decode('utf-8'))), 'utf-8'))
print(hmac.compare_digest(headers['BARKER_SIGNATURE'], hash.hexdigest()))