Attach image in S3 bucket to send with SendGrid - node.js

Question

I am writing an iOS app in Swift 2.2 using Xcode 7.3.1. Then, for backend services I am using AWS Mobilehub (S3 and Lambda)
What the app should do: Take a screenshot, send it to an AWS S3 bucket, send the screenshot through SendGrid by using an AWS Lambda function trigger.
My problem: I can't seem to attach the damn image in the S3 bucket to the email. Locally it works fine, but when uploaded to Lambda is throws the following error:
Error: ENOENT: no such file or directory, open '...'
Using the following code:
'use strict';
var fs = require('fs');
console.log('Loading function');
let aws = require('aws-sdk');
let s3 = new aws.S3({ apiVersion: '2006-03-01' });
exports.handler = (event, context, callback) => {
// Get the object from the event and show its content type
const key = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, ' '));
var helper = require('sendgrid').mail;
let from_email = new helper.Email("from#gmail.com");
let to_email = new helper.Email("to#gmail.com");
let subject = "Hello World from the SendGrid Node.js Library";
let content = new helper.Content("text/plain", "Email content");
let mail = new helper.Mail(from_email, subject, to_email, content);
var bse64 = base64_encode(INeedThisFrigginPath);
let attachment = new helper.Attachment();
attachment.setContent(bse64);
attachment.setType("image/png");
attachment.setFilename(key);
attachment.setDisposition("attachment");
mail.addAttachment(attachment);
var sg = require('sendgrid')('SG.sengridkey');
var requestBody = mail.toJSON();
var emptyRequest = require('sendgrid-rest').request;
var requestPost = JSON.parse(JSON.stringify(emptyRequest));
requestPost.method = 'POST';
requestPost.path = '/v3/mail/send';
requestPost.body = requestBody;
sg.API(requestPost,
function (error, response)
{
console.log(response.statusCode);
console.log(response.body);
console.log(response.headers);
}
);
};
// function to encode file data to base64 encoded string
function base64_encode(file)
{
// read binary data
var bitmap = fs.readFileSync(file);
// convert binary data to base64 encoded string
return new Buffer(bitmap).toString('base64');
}
Specifically this line:
var bse64 = base64_encode(INeedThisFrigginPath);
It's quite obvious what the problem is, so what I need to know is, what is the correct path to my image.
I have tried using the key value, and the image link:
https://s3.eu-central-1.amazonaws.com/bucketname/public/test0.png
No luck.
It would be great if anyone can help me by supplying code, a tutorial or just general pointers to boost me into the right direction. Maybe using AWS S3, AWS Lambda and SendGrid isn't necessarily the best technologies to use here?
Thanks a bunch!

Answer 1

You are trying to build a path to that file and then you are trying to open it as a local file. The file isn't local, it's on S3, so you can't do that. You have two options:
Download the file from S3 to Lambda first (into the /tmp directory) and then refer to the local path when you open the file.
Open a ReadStream to the file using the AWS S3 SDK.