echo_server.py

import hashlib
import time
import xmltodict

from flask import Flask, request

app = Flask(__name__)

WECHAT_TOKEN = "wechat_token"

# Check if the message XML is valid, this simple bot handles TEXT messages only!
# To learn more about the supported types of messages and how to implement them, see:
# Common Messages: http://admin.wechat.com/wiki/index.php?title=Common_Messages
# Event Messages: http://admin.wechat.com/wiki/index.php?title=Event-based_Messages
# Speech Recognition Messages:
# http://admin.wechat.com/wiki/index.php?title=Speech_Recognition_Messages
def validate_message(message):
    return (
        message is not None and
        message['xml'] != None and
        message['xml']['MsgType'] != None and
        message['xml']['MsgType'] == 'text' and
        message['xml']['Content'] != None
    )

# Format the reply according to the WeChat XML format for synchronous replies,
# see: http://admin.wechat.com/wiki/index.php?title=Callback_Messages
def format_message(original_message, content):
    return (
        "<xml>"
        "<ToUserName><![CDATA[%s]]></ToUserName>"
        "<FromUserName><![CDATA[%s]]></FromUserName>"
        "<CreateTime>%s</CreateTime>"
        "<MsgType><![CDATA[text]]></MsgType>"
        "<Content><![CDATA[%s]]></Content>"
        "</xml>"
    ) % (
        # From and To must be inverted in replies ;)
        original_message['xml']['FromUserName'],
        original_message['xml']['ToUserName'],  # Same as above!
        time.gmtime(),
        content
    )


def verify_backend(request):
    # Get the parameters from the query string
    signature = request.args.get('signature')
    timestamp = request.args.get('timestamp')
    nonce = request.args.get('nonce')
    echostr = request.args.get('echostr')

    # Compute the signature (note that the shared token is used too)
    verification_elements = [WECHAT_TOKEN, timestamp, nonce]
    verification_elements.sort()
    verification_string = "".join(verification_elements)
    verification_string = hashlib.sha1(
        verification_string.encode('utf-8')).hexdigest()

    # If the signature is correct, output the same "echostr" provided by
    # the WeChat server as a parameter
    if signature == verification_string:
        return echostr
    else:
        return ""


@app.route('/wechat', methods=['GET', 'POST'])
def echo_server():
    error = None
    if request.method == 'GET':
        # The WeChat server will issue a GET request in order to verify the chatbot backend server upon configuration.
        return verify_backend(request)
    elif request.method == 'POST':
        # Messages will be POSTed from the WeChat server to the chatbot backend server,
        # see: http://admin.wechat.com/wiki/index.php?title=Common_Messages
        message = xmltodict.parse(request.data)

        # If the message is valid, echo it back to the user or send an error message.
        # Some kind of response, even an empty one, is *REQUIRED* by WeChat
        # within the mandatory timeout limit of 5 seconds.
        # Otherwise, the user will see an error in the app.
        if validate_message(message):
            reply = "You typed: %s" % (message['xml']['Content'])
            return format_message(message, reply)
        else:
            return "Message was sent in a wrong format."