project/
　　　　├　main.py
　　　　└　requirements.txt

import os
import base64, hashlib, hmac
import logging

from flask import abort, jsonify

from linebot import (
    LineBotApi, WebhookParser
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, TextSendMessage
)

def main(request):
    channel_secret = os.environ.get('LINE_CHANNEL_SECRET')
    channel_access_token = os.environ.get('LINE_CHANNEL_ACCESS_TOKEN')

    line_bot_api = LineBotApi(channel_access_token)
    parser = WebhookParser(channel_secret)

    body = request.get_data(as_text=True)
    hash = hmac.new(channel_secret.encode('utf-8'),
        body.encode('utf-8'), hashlib.sha256).digest()
    signature = base64.b64encode(hash).decode()

    if signature != request.headers['X_LINE_SIGNATURE']:
        return abort(405)

    try:
        events = parser.parse(body, signature)
    except InvalidSignatureError:
        return abort(405)


    for event in events:
        if not isinstance(event, MessageEvent):
            continue
        if not isinstance(event.message, TextMessage):
            continue

        line_bot_api.reply_message(
            event.reply_token,
            TextSendMessage(text=event.message.text)
        )
    return jsonify({ 'message': 'ok'})

# Function dependencies, for example:
# package>=version
line-bot-sdk

gcloud functions deploy hogehoge --trigger-http

gcloud functions deploy hogehoge --trigger-http --set-env-vars LINE_CHANNEL_SECRET=123456789qwert123456789qwert,LINE_CHANNEL_ACCESS_TOKEN=123456789qwert