AWS Lambda Function for Proxying Requests to S3

index.js

/**
 * This is a simple AWS Lambda function that will look for a given file on S3 and return it
 * passing along all of the headers of the S3 file. To make this available via a URL use
 * API Gateway with an AWS Lambda Proxy Integration.
 * 
 * Set the S3_REGION and S3_BUCKET global parameters in AWS Lambda
 * Make sure the Lambda function is passed an object with `{ pathParameters : { proxy: 'path/to/file.jpg' } }` set
 */

var AWS = require('aws-sdk');

exports.handler = function( event, context, callback ) {
	var region = process.env.S3_REGION;
	var bucket = process.env.S3_BUCKET;
	var key = decodeURI( event.pathParameters.proxy );
	
	// Basic server response
	/*
	var response = {
	    statusCode: 200,
	    headers: {
		    'Content-Type': 'text/plain',
		},
	    body: "Hello world!",
	};
	callback( null, response );
	*/
	
	// Fetch from S3
	var s3 = new AWS.S3( Object.assign({ region: region }) );
	return s3.makeUnauthenticatedRequest(
		'getObject',
		{ Bucket: bucket, Key: key },
		function(err, data) {
			if (err) {
				return err;
			}
			
			var isBase64Encoded = false;
			if ( data.ContentType.indexOf('image/') > -1 ) {
			    isBase64Encoded = true;
			}
			
            var encoding = '';
            if ( isBase64Encoded ) {
                encoding = 'base64'
            }
			var resp = {
				statusCode: 200,
				headers: {
					'Content-Type': data.ContentType,
				},
				body: new Buffer(data.Body).toString(encoding),
				isBase64Encoded: isBase64Encoded
			};

			callback(null, resp);
		}
	);
};