Disabling URL decoding in nginx proxy

Solution 1:

Quoting Valentin V. Bartenev (who should get the full credit for this answer):

A quote from documentation:

• If proxy_pass is specified with URI, when passing a request to the server, part of a normalized request URI matching the location is replaced by a URI specified in the directive

• If proxy_pass is specified without URI, a request URI is passed to the server in the same form as sent by a client when processing an original request

The correct configuration in your case would be:

location /foo {
   proxy_pass http://localhost:8080;
}

Solution 2:

Note that URL decoding, commonly known as $uri "normalisation" within the documentation of nginx, happens before the backend IFF:

• either any URI is specified within proxy_pass itself, even if just the trailing slash all by itself,

• or, URI is changed during the processing, e.g., through rewrite.

---

Both conditions are explicitly documented at http://nginx.org/r/proxy_pass (emphasis mine):

• If the proxy_pass directive is specified with a URI, then when a request is passed to the server, the part of a normalized request URI matching the location is replaced by a URI specified in the directive

• If proxy_pass is specified without a URI, the request URI is passed to the server in the same form as sent by a client when the original request is processed, or the full normalized request URI is passed when processing the changed URI

---

The solution is to either omit the URI as in OPs case, or, indeed, use a clever rewrite rule:

# map `/foo` to `/foo`:
location /foo {
    proxy_pass  http://localhost:8080;  # no URI -- not even just a slash
}

# map `/foo` to `/bar`:
location /foo {
    rewrite  ^  $request_uri;            # get original URI
    rewrite  ^/foo(/.*)  /bar$1  break;  # drop /foo, put /bar
    return 400;   # if the second rewrite won't match
    proxy_pass    http://localhost:8080$uri;
}

You can see it live in a related Stack Overflow answer, including control group.