AWS API Gateway and Lambda to return image

Question

Say I have this HTML:

<img src="http://example.com/pic"/>

What I would like to do is have example.com/pic map to an AWS API Gateway endpoint.

That endpoint would then call a lambda function.

That lambda function would read a random image from an s3 bucket and return it.

So my aim is to use a STANDARD HTML image tag and end up with an image from an s3 bucket but going via some decision code in the lambda to decide the image to return.

I know you can use s3 to serve static content directly (hence the lambda to make the decision about what image). I also know I could do stuff in the lambda like b64 encode the response and then handle it on the client but I am aiming to use the standard HTML IMG tag.

Is this possible?

I've tried using the ResponseStreamHandler (Java SDK) for the lambda and returning the byte array of the image and also added the API gateway config to not map the output to JSON, but nothing seems to work!

Answer 1

It seems AWS has simplified this process, so that many answers are outdated and/or overly complicated.

This is how I got Lambda to return an image through the API Gateway, as of June 2018:

1) In API Gateway, enable Use Lambda Proxy integration for your API. (This setting is located on the Integration Request section, where you had set the type to Lambda.)

2) In API Gateway, select your API and click Settings. In Binary Media Types add */*. (Note: I tried adding simply 'image/jpeg', but it seems to require */* to get all of this to work)

3) Be sure to deploy your API, otherwise your changes will not be live. (In API Gateway, select your API, then Actions > Deploy API).

4) In your Lambda code, return your image in Base64 encoding (this example is C# code):

    // set the Content-type header
    // set to whichever image type you're returning
    var headersDic = new Dictionary<string, string>();
    headersDic.Add("Content-type", "image/jpeg");

    // return the response object that APIGateway requires
    return new APIGatewayProxyResponse
    {
        StatusCode = 200,
        Headers = headersDic,
        // return the image in Base64 encoding
        Body = Convert.ToBase64String(...your image data...),
        IsBase64Encoded = true
    };

Done.

If you've setup your API to not require authentication, simply type your API link into your browser, and it will display the image. Or put the API link into an IMG tag. e.g. <img src="https://asdf.execute-api.us-east-1.amazonaws.com/live/myapi" />

Note: Even though in step 2 you set the Binary Media Types to */*, API Gateway will still return text if that is what your Lambda is returning.

Answer 2

Luckily, now AWS API Gateway supports binary data, though you also need to update your resource method through the CLI as it is not yet implemented in the Console. This is what you need to do:

1. In the Method Response of your method
   Set Content-Type as image/jpeg in HTTP 200 Status Response Header
2. In the Integration Response of your method
   Set Content-Type as 'image/jpeg' in Header Mappings. Mind the quotes!
3. With the AWS CLI, set contentHandling attribute to CONVERT_TO_BINARYon your Integration Response

Check to entire process in this great step-by step guide: https://stackoverflow.com/a/41434295/720665

Answer 3

I've run in to a similar problem. As mentioned you currently can't directly return your image in binary format from your API Gateway endpoint, which would be required for the browser to display it correctly.

However, I solved this by instead having API Gateway return a 302 Redirect, pointing to the correct file in S3. You can have your Lambda function return the url to the file, which is later on mapped to the Location header in API Gateway. The browser will follow the redirect and display the image properly.

There are several ways to implement the redirect, but I did as follow:

• Lambda returns an object with the target image like so:

  function handler(event, context) {
       context.succeed({ 
           location: "https://[bucket-name].s3-eu-west-1.amazonaws.com/myimage.png" });
       });
  }
  

• Remove the normal '200' Method Response Status from The Integration Response in API Gateway. Replace it with a '302' response status and add the 'Location' header mapped to value 'integration.response.body.location'

• Add the 302 status to the Method Response as well

Answer 4

Just to be clear, the client does two different requests:

1. The first to get the HTML (including the image url).
2. The second to fetch the image data from the url.

In other words, the image data is not inlined in the HTML.

Based on this knowledge you can have a Lambda (behind the API gateway) as you suggest. The Lambda implementation can have some logic that determines the url to the image stored in S3. However, the Lambda returns JSON data and not HTML (there are workarounds such as return the html in a variable) which makes things trickier, especially for large HTML pages.

I suggest a slightly different approach, since just receiving an image tag will not get you far. I assume you will inline the image tag in a HTML document, probably by using JavaScript. Then you might as well let the API Gateway / Lambda request return a JSON document with the image url and let the JavaScript either update an existing image tag with the new url or generate the tag for you.

Answer 5

It currently isn't possible because you cannot return binary data through the AWS API Gateway.

For this to work, the lambda function would need to return the image data as binary blob, and some meta-information such as the image content type. Then, AWS API Gateway would need to be able to map this to the HTTP response. For example:-

lambda returns: { contentType: 'image/png', image: "encoded binary data" }

then API gateway would need to map contentType to the 'content-type' header of the response, and put the image data in the body of the response with the right encoding and length.

Unfortunately, it doesn't do this right now. It only maps text encodings like application/json or application/xml as the response type (it is designed for APIs after all).

You could very easily achieve this using ElasticBeanstalk where you have a lot more control over the http response.

Answer 6

I resolved this problem be reconsidering my design. The underlying thinking is that Lambdas are good computing units and bad file servers.

I changed

• Client > APIGW > Lambda > Image

into

• Client > APIGW > Lambda > SignedURL
• then Client(SignedURL) > Image

Since my client was web based, everything was easier after that shift