Github Webhooks => Mixpanel Annotations

githubWebhooksToMixpanelAnnotations.js

// GitHub to Mixpanel Annotations
// by AK
// ak@mixpanel.com
// purpose: ingest github webhooks; create Mixpanel annotations

//deps
const crypto = require('crypto');
const http = require("https");


/* 
    ! IMPORTANT NOTE !
it is NOT a good practice to store secrets in code as we have done here
creds are just here for ease of illustration
the best way to store secrets in a cloud function is to use Google's secret manager
https://cloud.google.com/functions/docs/configuring/secrets

*/

const creds = {
    github: `{{ your github secret }}`,
    mpUser: `{{ your mixpanel service account user }}`,
    mpSecret: `{{ your mixpanel service account secret }}`,
    workspace_id: `{{ your mixpanel workspace_id }}`
}

//entry point for cloud function
exports.start = async (req, res) => {
    console.log('RUNNING!')
    //grab body + sig
    const body = req.body
    const sig = req.headers['x-hub-signature-256']

    //run our program
    await main(body, sig).then((response) => {
        res.status(200).send(response);
        console.log('FINISHED!')
    })

};

async function main(body = {}, sig = ``) {

    //verify github signature!
    const isVerified = verifyPostData(sig, body, creds.github)
    if (isVerified) {
        const annotationData = {
            date: ``,
            description: `${body.release.tag_name} - ${body.release.name}`
        }
        
        //make the date match mixpanel's format and add time
        const published_at = new Date(body.release.published_at);
        const UTCOffset = 5 //EST
        published_at.setHours(published_at.getHours() + UTCOffset);
        const dateTimeString = `${published_at.getFullYear().toString().padStart(4, '0')}-${(published_at.getMonth()+1).toString().padStart(2, '0')}-${published_at.getDate().toString().padStart(2, '0')} ${published_at.getHours().toString().padStart(2, '0')}:${published_at.getMinutes().toString().padStart(2, '0')}:${published_at.getSeconds().toString().padStart(2, '0')}`;         
        annotationData.date = dateTimeString;
        
        
        //create the annotation
        const response = await makeAnnotation(annotationData, creds)
        if (response.statusCode === 200) {
            console.log(`created annotation!`)
            return `👍`
        } else {
            console.log(`failed to create annotation!`)
            return `👎`
        }

    } else {
        console.log(`message was not signed correctly!`)
        return `👎`
    }

}

//UTILITIES

//verify github actually sent the message
function verifyPostData(signature, body, secret) {
    const sigHeaderName = 'X-Hub-Signature-256'
    const sigHashAlg = 'sha256'
    const sig = Buffer.from(signature || '', 'utf8')
    const hmac = crypto.createHmac(sigHashAlg, secret)
    const digest = Buffer.from(sigHashAlg + '=' + hmac.update(JSON.stringify(body)).digest('hex'), 'utf8')
    if (sig.length !== digest.length || !crypto.timingSafeEqual(digest, sig)) {
        return false;
    } else {
        return true;
    }
}

//call the annotations API
async function makeAnnotation(data, creds) {
    const auth = Buffer.from(`${creds.mpUser}:${creds.mpSecret}`).toString('base64')
    const options = {
        hostname: 'mixpanel.com',
        path: `/api/app/workspaces/${creds.workspace_id}/annotations`,
        method: 'POST',
        headers: {
            Accept: 'application/json',
            Authorization: `Basic ${auth}`            
        }
    };
    const response = await fetch(options, data)
    return response;
}

//promise-aware version of fetch() using http.request
function fetch(params, postData) {
    return new Promise(function(resolve, reject) {
        const req = http.request(params, function(res) {
            // reject on bad status
            if (res.statusCode < 200 || res.statusCode >= 300) {
                return reject(new Error('statusCode=' + res.statusCode));
            }
            // cumulate data
            let body = [];
            res.on('data', function(chunk) {
                body.push(chunk);
            });
            // resolve on end
            res.on('end', function() {
                try {
                    body = JSON.parse(Buffer.concat(body).toString());
                } catch (e) {
                    reject(e);
                }
                resolve(body);
            });
        });
        // reject on request error
        req.on('error', function(err) {
            // This is not a "Second reject", just a different sort of failure
            reject(err);
        });
        if (postData) {
            req.write(postData);
        }
        // IMPORTANT
        req.end();
    });
}