Nginx Rewrite vs. Location: The Hidden URL Normalization Trap

When adjusting Nginx rules, I discovered that the location directive matches a normalized URL, while the URL generated by an internal rewrite is not re‑normalized, leading to mismatches.

For example, the following configuration adds an extra slash in the rewrite:

if ($request_uri ~ "/api") {
    rewrite (.*) /newapi/$1;    # extra slash
}

location /newapi/api {
    set $testapi 1;
}

location /newapi {
    # ...
}

When accessing /api, the request is rewritten to /newapi/api, but because the rewritten URL contains a double slash, the location /newapi/api block is not matched. Directly requesting /newapi//api does match.

The root cause is that the original request URL is normalized (collapsing multiple slashes, resolving “.” and “..”), whereas the URL produced by rewrite is used as‑is.

See the official Nginx documentation for details: http://nginx.org/en/docs/http/ngx_http_core_module.html