webhook-handler.py

import settings
import actions
import hmac
from json import loads, dumps, dump
from flask import Flask, request, abort
from hashlib import sha1


application = Flask(__name__)


@application.route('/github', methods=['POST'])
def handle_web_hook():
    # If settigs tell us to check signature, do it
    if settings.check_signature:
        header_signature = request.headers.get('X-Hub-Signature')
        if header_signature is None:
            print "No github signature found!"
            abort(403)
        sha_name, signature = header_signature.split('=')
        # Only SHA1 is supported
        if sha_name != 'sha1':
            abort(501)
        # HMAC requires the key to be bytes, but data is string
        mac = hmac.new(str(settings.secret), msg=request.data, digestmod=sha1)
        if not str(mac.hexdigest()) == str(signature):
            print "Invalid github signature"
            abort(403)
    event = request.headers.get('X-GitHub-Event', 'ping')
    # Handle ping event
    if event == 'ping':
        return dumps({'msg': 'pong'})
    # Gather data
    try:
        payload = loads(request.data)
    except ValueError:
        abort(400)
    # Get repository name and branch
    name, branch = get_branch_parameters(payload, event)
    # Dump payload, if necessary
    if settings.dump_payload:
        write_payload(payload)
    # Execute action according to recieved event
    execute_action(event, name, branch, payload)
    # Make a response. It is not really important
    response = {
        "name": name,
        "branch": branch,
        "event": event,
    }
    return dumps(response)


# Given a payload and an event,
#   it returns a tuple with repository name and branch
def get_branch_parameters(payload, event):
    try:
        # Case 1: a ref_type indicates the type of ref.
        # This true for create and delete events.
        if 'ref_type' in payload:
            if payload['ref_type'] == 'branch':
                branch = payload['ref']
        # Case 2: a pull_request object is involved. This is pull_request and
        # pull_request_review_comment events.
        elif 'pull_request' in payload:
            branch = payload['pull_request']['head']['ref']
        elif event in ['push']:
            # Push events provide a full Git ref in 'ref' and not a 'ref_type'.
            branch = payload['ref'].split('/')[2]
        else:
            branch = None
    except KeyError:
        # If the payload structure isn't what we expect, we'll live without
        # the branch name
        branch = None
    # All current events have a repository, but some legacy events do not,
    # so let's be safe
    try:
        name = payload['repository']['name']
    except KeyError:
        name = None
    return (name, branch)


# It will write a payload in a file.
# The file path is given in settings.dump_payload_file
def write_payload(payload):
    with open(settings.dump_payload_file, 'a') as json_file:
        dump(payload, json_file, indent=2)


# Perform an action, according to event type
def execute_action(event, name, branch, payload):
    defined_actions = {
        "push": actions.push,
        "pull_request": actions.pull_request,
    }
    try:
        action = defined_actions[event]
    except KeyError:
        print "Ignoring undefined event: '%s'" % event
        return None
    print "Executing action for event: '%s'" % event
    return action(name, branch, payload)

if __name__ == '__main__':
    application.run(debug=True, host='0.0.0.0')