Race condition custom action for Burp Repeater

race-condition-probe.java

// This will use the single-packet attack for HTTP/2, and last-byte synchronisation for HTTP/1
int NUMBER_OF_REQUESTS = 10;
var reqs = new ArrayList<HttpRequest>();
for (int i = 0; i < NUMBER_OF_REQUESTS; i++) {
    reqs.add(requestResponse.request());
}

var responses = api().http().sendRequests(reqs); 
var codes = responses.stream().map(HttpRequestResponse::response).filter(Objects::nonNull).map(HttpResponse::statusCode).toList();
logging().logToOutput(codes);