How do you determine when to use $request_uri vs $uri?

According to NGINX documentation, $request_uri is the original request (for example, /foo/bar.php?arg=baz includes arguments and can't be modified) but $uri refers to the altered URI.

If the URI doesn't change, does $uri = $request_uri?

Would it be incorrect or better or worse to use:

map $uri $new_uri {
  # do something
}

vs

map $request_uri $new_uri {
  # do something
}

$uri is not equivalent to $request_uri.

The $uri variable is set to the URI that nginx is currently processing - but it is also subject to normalisation, including:

• Removal of the ? and query string
• Consecutive / characters are replace by a single /
• URL encoded characters are decoded

The value of $request_uri is always the original URI and is not subject to any of the above normalisations.

Most of the time you would use $uri, because it is normalised. Using $request_uri in the wrong place can cause URL encoded characters to become doubly encoded.

Use $request_uri in a map directive, if you need to match the URI and its query string.