How can I troubleshoot and resolve the issue of “malformed lambda proxy response”?

In the context of AWS, here are the appropriate approaches given for resolving this particular issue:-

Checking lambda function response format

Try to ensure that your lambda function is returning the response in the correct format for lambda proxy Integration.

Validation of the Response Headers

You should try to verify that the response header should be correct and should have valid values.

Validation of response body

Try to ensure that the response body is a well-formed JSON object. You can use the tools like JSONint to validate the JSON structure.

Checking HTTP status code

You can try to confirm that the lambda function is returning an HTTP status code in the range of 200-299 for successful responses.

Enable logging

You can enable logging in your lambda function and API gateways for the purpose of capturing detailed logs.

Here is the example given in Python for a lambda function that would return a response in the correct lambda proxy Integration format:-

Import JSON

Def lambda_handler(event, context):
    # Process the event and generate a response body
    Response_body = {
        “message”: “Hello from Lambda!”
    }
    # Create the Lambda proxy integration response format
    Response = {
        “statusCode”: 200,  # HTTP status code for success
        “headers”: {
            “Content-Type”: “application/json”,  # Response content type
            “Access-Control-Allow-Origin”: “*”  # Allow CORS for all origins (modify as needed)
        },
        “body”: json.dumps(response_body)  # Convert response body to JSON string
    }
    Return response
Here is the example given in java for a lambda function which would return a response in the correct lambda proxy Integration format:-
Package com.example;
Import com.amazonaws.services.lambda.runtime.Context;
Import com.amazonaws.services.lambda.runtime.RequestHandler;
Import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent;
Import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent;
Import com.fasterxml.jackson.core.JsonProcessingException;
Import com.fasterxml.jackson.databind.ObjectMapper;
Import java.util.HashMap;
Import java.util.Map;
Public class HelloLambda implements RequestHandler {
    @Override
    Public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
        APIGatewayProxyResponseEvent response = new APIGatewayProxyResponseEvent();
        // Process the event and generate a response body
        Map responseBody = new HashMap<>();
        responseBody.put(“message”, “Hello from Lambda!”);
        // Create the Lambda proxy integration response format
        Response.setStatusCode(200);  // HTTP status code for success
        Map headers = new HashMap<>();
        Headers.put(“Content-Type”, “application/json”);  // Response content type
        Headers.put(“Access-Control-Allow-Origin”, “*”);  // Allow CORS for all origins (modify as needed)
        Response.setHeaders(headers);
        // Convert response body to JSON string
        ObjectMapper objectMapper = new ObjectMapper();
        Try {
            String responseBodyString = objectMapper.writeValueAsString(responseBody);
            Response.setBody(responseBodyString);
        } catch (JsonProcessingException e) {
            // Handle JSON processing exception
            Response.setStatusCode(500);  // Internal Server Error
            Response.setBody(“{”message”: ”Error processing response body”}”);
        }
        Return response;
    }
}