Nginx module: how to redirect from filter?

Question

I am writing a custom nginx module where I do some processing using filters. The setup of the filters looks like so:

static ngx_int_t ngx_http_mymodule_init(ngx_conf_t *cf)
{
    ngx_http_next_header_filter = ngx_http_top_header_filter;
    ngx_http_top_header_filter = ngx_http_mymodule_header_filter;

    ngx_http_next_body_filter = ngx_http_top_body_filter;
    ngx_http_top_body_filter = ngx_http_mymodule_body_filter;
    return NGX_OK;
}

I am processing some logic in this body filter and on a certain condition, I would like to perform a redirect in the client's browser to localhost. The filter body code looks like this:

static ngx_int_t
ngx_http_mymodule_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
    ctx = ngx_http_get_module_ctx(r, ngx_http_mymodule_module);
    if (ctx == NULL) {
        return ngx_http_next_body_filter(r, in);
    }

    bool success = __my_custom_logic(r);
    if (success == false) {
        ngx_http_set_ctx(r, NULL, ngx_http_mymodule_module);

        // Do the redirect here! How?

        // Setting the Location header and changing r->headers_out.status to 302
        // just returns an empty HTTP 200 to the client instead...
    }

    ngx_http_set_ctx(r, NULL, ngx_http_mymodule_module);
    return ngx_http_send_special(r, NGX_HTTP_LAST);
}

Things I have tried:
- Set the Location header and headers_out.status to 302, but it returns an empty response to the client
- Set headers_out.location but this still returns an empty response
- Call ngx_http_send_header(r) but this returns an NGX_ERROR response

How can I respond with a redirect to the client?