Return binary media from a Lambda proxy integration in API Gateway

To return binary media from an AWS Lambda proxy integration, base64 encode the response from your Lambda function. You must also configure your API's binary media types. The payload size limit is 10 MB.

Note

To use a web browser to invoke an API with this example integration, set your API's binary media types to */*. API Gateway uses the first Accept header from clients to determine if a response should return binary media. To return binary media when you can't control the order of Accept header values, such as requests from a browser, set your API's binary media types to */* (for all content types).

The following example Lambda function can return a binary image from Amazon S3 or text to clients. The function's response includes a Content-Type header to indicate to the client the type of data that it returns. The function conditionally sets the isBase64Encoded property in its response, depending on the type of data that it returns.

Node.js

import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3"

const client = new S3Client({region: 'us-east-2'});

export const handler = async (event) => {

  var randomint = function(max) {
    return Math.floor(Math.random() * max);
  }
  var number = randomint(2);
  if (number == 1){ 
    const input = {
      "Bucket" : "bucket-name",
      "Key" : "image.png"
      }
    try {
      const command = new GetObjectCommand(input)
      const response = await client.send(command);
      var str = await response.Body.transformToByteArray();
    } catch (err) {
      console.error(err);
    }
    const base64body = Buffer.from(str).toString('base64');
    return {
      'headers': { "Content-Type": "image/png" },
      'statusCode': 200,
      'body': base64body,
      'isBase64Encoded': true
      }
    } else {
        return {
        'headers': { "Content-Type": "text/html" },
        'statusCode': 200,
        'body': "<h1>This is text</h1>",
        }
    }
}

Python

import base64
import boto3
import json
import random

s3 = boto3.client('s3')

def lambda_handler(event, context):
    number = random.randint(0,1)
    if number == 1:
        response = s3.get_object(
            Bucket='bucket-name',
            Key='image.png',
        )
        image = response['Body'].read()
        return {
            'headers': { "Content-Type": "image/png" },
            'statusCode': 200,
            'body': base64.b64encode(image).decode('utf-8'),
            'isBase64Encoded': True
        }
    else:
        return {
            'headers': { "Content-type": "text/html" },
            'statusCode': 200,
            'body': "<h1>This is text</h1>",
        }

To learn more about binary media types, see Binary media types for REST APIs in API Gateway.