slack-police.js

// Sample event data for a proxy request
// {
//     "resource": "Resource path",
//     "path": "Path parameter",
//     "httpMethod": "Incoming request's method name"
//     "headers": {Incoming request headers}
//     "queryStringParameters": {query string parameters }
//     "pathParameters": {path parameters}
//     "stageVariables": {Applicable stage variables}
//     "requestContext": {Request context, including authorizer-returned key-value pairs}
//     "body": "A JSON string of the request payload."
//     "isBase64Encoded": "A boolean flag to indicate if the applicable request payload is Base64-encode"
// }

const url = require('url');
const https = require('https');
const querystring = require('querystring');

const SLACK_INCOMING_WEBHOOK_URL = process.env.SLACK_INCOMING_WEBHOOK_URL;
const SLACK_VERIFICATION_TOKEN = process.env.SLACK_VERIFICATION_TOKEN;

async function postToWebhook(webhookUrl, payload) {
    return new Promise((resolve, reject) => {
        const body = JSON.stringify(payload);

        // Setup request options
        const options = url.parse(webhookUrl);
        options.method = 'POST';
        options.headers = {
            'Content-Type': 'application/json',
            'Content-Length': Buffer.byteLength(body),
        };

        // Request with response handler
        console.log('Making chat.postMessage API request');
        const req = https.request(options, (res) => {
            res.setEncoding('utf8');

            let json = '';
            res.on('data', (chunk) => { json += chunk; });
            res.on('end', () => {
                if (res.statusCode === 200) {
                    console.log('Webhook request was successful!');
                    resolve();
                } else {
                    console.log('Webhook request failed!');
                    reject(new Error(res.statusMessage))
                }
            });
        });

        // Generic request error handling
        req.on('error', e => reject(e));

        req.write(body);
        req.end();
    });
}

function messageText(payload) {
    if (payload.text && payload.text.indexOf(' ') != -1) {
        return payload.text;
    } else {
        const intro = "Okay folks, let's move this conversation";

        const channel = ('#' + payload.text).replace(/##/, '#');
        const to = (payload.text ? channel : 'elsewhere');

        return `${intro} ${to}.`;
    }
}

exports.handler = async (event) => {
    // The Slack slash command request body is URL encoded
    const payload = querystring.parse(event.body);

    if (payload.token !== SLACK_VERIFICATION_TOKEN) {
        // Invalid Slack verification token on payload
        throw 'Invalid verification token';
    }

    try {
        await postToWebhook(SLACK_INCOMING_WEBHOOK_URL, {
            channel: `#${payload.channel_name}`,
            text: messageText(payload),
            link_names: 1,
            mrkdwn: true
        });

        // Returning an empty body to the Slack slash command request will
        // preventany message from being posted to the channel (we've already
        // sent our message using the incoming webhook).
        return { statusCode: 200, headers: {}, body: '' };
    } catch (e) {
        throw e;
    }
};