Add support for binary response content

[ebekker]

As described in this AWS Developer Forum post, in order to support binary response content from a Lambda function invoked by API Gateway proxy, the Lambda response needs to include the isBase64Encoded: true flag in its JSON response payload.

The most recent revision of the APIGatewayProxyResponse response model class does not include such a flag and the furthermore, the AspNetCoreServer package would need to provide a means of triggering (and flagging) the base64-encoding when binary response content is returned from a controller action method.

[ebekker]

Adding the additional flag is trivial and would support the basic use-case when authoring C# Lambda functions that handle APIGatewayEvents.

However, the AspNetCoreServer support is a bit trickier -- a controller action method returns an IActionResult instance and its content ultimately gets serialized into a string in all cases. However, it's not always clear just from that instance, if the raw result should be encoded directly (Base64) or transformed to UTF8.

After some experimentation I'm thinking that a good compromise that would minimize the impact on the normal controller code would be to put some flags and options on the base APIGatewayProxyFunction class, since this needs to be sub-classed in any event and at a minimum that subclass would contain Lambda-specific logic such as a call to the extension method UseApiGateway().

I'm thinking about 2 possible approaches to support:

• set a global "always-on" boolean that simply indicates that all responses from all controllers actions should be treated literally and don't do any transformation on anything
• setup a collection of one or more Content-Type header values to look for that would trigger the Base64-encoding and flagging, for example, when ever a response for application/octet-stream or application/zip or some image content type -- that would trigger the raw response bytes to be transformed into a Base64-encoding, and it would set the flag isBase64Encoded to true in the Labmda response to the API Gateway.

[normj]

Closing the issue because it is being tracked in a pull request
#75

[damianh]

the AspNetCoreServer package would need to provide a means of triggering (and flagging) the base64-encoding

Came here to report the same isue. Had same problem with my https://github.com/damianh/AwsLambdaOwin