webhooks.py

import logging
from sys import stderr, hexversion
import hmac
from hashlib import sha1
from json import loads, dumps
from subprocess import Popen, PIPE
from tempfile import mkstemp
from os import access, X_OK, remove, fdopen
from os.path import isfile, abspath, normpath, dirname, join, basename

import requests
from ipaddress import ip_address, ip_network
from flask import Flask, request, abort

logging.basicConfig(stream=stderr)

application = Flask(__name__)


@application.route('/', methods=['GET', 'POST'])
def index():
    """
    Main WSGI application entry.
    """
    path = normpath(abspath(dirname(__file__)))
    # Only POST is implemented
    if request.method != 'POST':
        abort(501, "only POST is supported")

    # Load the config file
    with open(join(path, 'config.json'), 'r') as cfg:
        config = loads(cfg.read())

    hooks = config.get('hooks_path', join(path, 'hooks'))
    # Allow Github IPs only
    if config.get('github_ips_only', True):
        src_ip = ip_address(u'{}'.format(request.remote_addr))
        whitelist = requests.get('https://api.github.com/meta').json()['hooks']
        for valid_ip in whitelist:
            if src_ip in ip_network(valid_ip):
                break
            else:
                abort(403, "Unable to validate source IP")

    # Enforce secret, so not just anybody can trigger these hooks
    secret = config.get('enforce_secret', '')
    if secret:
        # Only SHA1 is supported
        header_signature = request.headers.get('X-Hub-Signature')
        if header_signature is None:
            abort(403, "No header signature found")

        sha_name, signature = header_signature.split('=')
        if sha_name != 'sha1':
            abort(501, "Only SHA1 is supported")

        # HMAC requires the key to be bytes, but data is string
        mac = hmac.new(str(secret), msg=request.data, digestmod='sha1')

        # Python does not have hmac.compare_digest prior to 2.7.7
        if hexversion >= 0x020707F0:
            if not hmac.compare_digest(str(mac.hexdigest()), str(signature)):
                abort(403)
        else:
            # What compare_digest provides is protection against timing
            # attacks; we can live without this protection for a web-based
            # application
            if not str(mac.hexdigest()) == str(signature):
                abort(403)

    # Implement ping
    event = request.headers.get('X-GitHub-Event', 'ping')
    if event == 'ping':
        return dumps({'msg': 'pong'})

    # Gather data
    try:
        payload = request.get_json()
    except Exception:
        logging.warning('Request parsing failed')
        abort(400, "Request parsing failed")

    # Determining the branch can be tricky, as it only appears for certain event
    # types, and at different levels
    branch = None
    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:
            # This is the TARGET branch for the pull-request, not the source
            # branch
            branch = payload['pull_request']['base']['ref']

        elif event in ['push']:
            # Push events provide a full Git ref in 'ref' and not a 'ref_type'.
            branch = payload['ref'].split('/', 2)[2]

    except KeyError:
        # If the payload structure isn't what we expect, we'll live without
        # the branch name
        pass

    # All current events have a repository, but some legacy events do not,
    # so let's be safe
    name = payload['repository']['name'] if 'repository' in payload else None
    meta = {
        'name': name,
        'branch': branch,
        'event': event
    }
    logging.info('Metadata:\n{}'.format(dumps(meta)))
    # Skip push-delete
    if event == 'push' and payload['deleted']:
        logging.info('Skipping push-delete event for {}'.format(dumps(meta)))
        return dumps({'status': 'skipped'})

    # Possible hooks
    scripts = []
    if branch and name:
        scripts.append(join(hooks, '{event}-{name}-{branch}'.format(**meta)))
    if name:
        scripts.append(join(hooks, '{event}-{name}'.format(**meta)))
    scripts.append(join(hooks, '{event}'.format(**meta)))
    scripts.append(join(hooks, 'all'))

    # Check permissions
    scripts = [s for s in scripts if isfile(s) and access(s, X_OK)]
    if not scripts:
        return dumps({'status': 'nop'})

    # Save payload to temporal file
    osfd, tmpfile = mkstemp()
    with fdopen(osfd, 'w') as pf:
        pf.write(dumps(payload))

    # Run scripts
    ran = {}
    for s in scripts:
        proc = Popen(
            [s, tmpfile, event],
            stdout=PIPE, stderr=PIPE
        )
        stdout, stderr = proc.communicate()
        ran[basename(s)] = {
            'returncode': proc.returncode,
            'stdout': stdout.decode('utf-8'),
            'stderr': stderr.decode('utf-8'),
        }
        # Log errors if a hook failed
        if proc.returncode != 0:
            logging.error('{} : {} \n{}'.format(
                s, proc.returncode, stderr
            ))

    # Remove temporal file
    remove(tmpfile)
    info = config.get('return_scripts_info', False)
    if not info:
        return dumps({'status': 'done'})

    output = dumps(ran, sort_keys=True, indent=4)
    logging.info(output)
    return output


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