In Nginx How to handle HTTP requests without the leading slash "/"?

I have an Nginx proxy in front my application. I recently learned that, HTTP requests can be made without a leading slash also.

For Example:

POST acme/_search HTTP/1.1

In cases like this, Nginx always returns 400 Bad Request. I would like to handle this case by either modifying the request_uri or rewriting the request path with a leading slash.

So that the request_uri acme/_search will be rewritten as /acme/_search . Any requests with the leading slash are working fine and returns 200.

I've tried handling it using a rewrite statement in the server block like below:

server {
    listen 9000;

    if ($request_uri ~* ^[^\/]) {
      rewrite ^(.*)$ /$1 break;
    }

    location / {
        proxy_pass http://upstream_http;
        allow all;
    }
 }

^ What I'm trying to do in the above block is, Check if the request_uri doesn't start with a leading slash & if yes, rewrite the path with a leading slash.

But this configuration is not working. I still get the 400 Bad Request message logged & returned by Nginx.

I'm using to telnet to make the example request:

telnet localhost 9000

POST acme/_search HTTP/1.1

Would like to know how these kind of HTTP requests without a leading slash can be handled using Nginx as a proxy.