How to remove headers form ALB response from lambda - amazon-web-services

Question

I am using ALB with Lambda Integration. My ALB gets a request from a server, forwards it to the Lambda and forwards the lambda response back to the server.
However, the server only accepts an xml body and not the whole request with headers that are added by ALB. (Please see responses below).
Is there a way for ALB to only send the body back?
The server expects something like this:
[<?xml version="1.0" encoding="UTF-8"?>
<EventMessage xmlns:hb="Heartbeat" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="Message.xsd">
...
</EventMessage>
]
ALB sends back this:
[HTTP/1.1 200 OK
Server: awselb/2.0
Date: Mon, 19 Dec 2022 14:52:01 GMT
Content-Type: application/octet-stream
Content-Length: 28
Connection: keep-alive
<EventMessage xmlns:hb="Heartbeat" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="Message.xsd">
...
</EventMessage>
]
I have no control over what the server accepts, so somehow I need to remove the headers and send back the eventMessage which can be accepted.
Here is my current return (callback) statement in the lambda:
const resFromRequestsLambda = {
"isBase64Encoded": false,
"statusCode": 200,
"body": "<EventMessage ...>...</EventMessage>,
}
callback(null, resFromRequestsLambda);
Thanks for any help!
ps. I realise this may be a very secific case, and possibly the answer is you 'can't/shouldn't'. Any way around this would be great if i can't directly change the way alb responds to the server.

Answer 1

These headers are part of the http protocol. The load balancer speaks http, so it will always include the headers. There is no way around it.
It’s exceedingly odd that the server won’t accept the headers. Perhaps you can use a custom TCP server on an EC2 instance instead of an ALB with a Lambda target. This way you can respond to requests with total control over the payload.