GET /git/sample-repository/info/refs?service=git-receive-pack HTTP/1.1

server {
  #... commond definitions such as server, root

  location / {
    error_page 418 = @queryone;
    error_page 419 = @querytwo;
    error_page 420 = @querythree;

    if ( $query_string = "service=git-receive-pack" ) { return 418; }
    if ( $args = "service=git-send-pack" ) { return 419; }
    if ( $arg_somerandomfield = "somerandomvaluetomatch" ) { return 420; }

    # do the remaining stuff
    # ex: try_files $uri =404;

  }

  location @queryone {
    # do stuff when queryone matches
  }

  location @querytwo {
    # do stuff when querytwo matches
  }

  location @querythree {
    # do stuff when querythree matches
  }
}