# Transparent proxy which passes requests to a set of un-pooled
# application servers that are reserved for debugging, based on
# the value of the X-Wikimedia-Debug header.

# The X-Wikimedia-Debug header is made up of semicolon-separated
# fields. Each field may consist of either an attribute name or
# an attribute=value pairs. The block below extracts the value of
# the 'backend' attribute. For backward-compatibility, if the
# header does not contain a well-formed 'backend' attribute, then
# the entire header is used as the backend value.

map_hash_bucket_size 128;

# Trims the content of X-Wikimedia-Debug to be just the first flag
map $http_x_wikimedia_debug $debug_backend {
  "~backend=(?<h>[^;]+)" $h;
  default $http_x_wikimedia_debug;
}

# Checks if php7 is selected
map $http_x_wikimedia_debug $php_engine {
  "~; php7" "php7";
  default "hhvm";
}

map $debug_backend $debug_host {
  "~^((mwdebug1001|mwdebug1002)\\.eqiad\\.wmnet|(mwdebug2001|mwdebug2002)\\.codfw\\.wmnet)" $debug_backend;
  "1" "mwdebug1001.eqiad.wmnet";
  "mw1017.eqiad.wmnet" "mwdebug1001.eqiad.wmnet";
  "mw1099.eqiad.wmnet" "mwdebug1002.eqiad.wmnet";
  "mw2017.codfw.wmnet" "mwdebug2001.codfw.wmnet";
  "mw2099.codfw.wmnet" "mwdebug2002.codfw.wmnet";
  default 'invalid';
}

server {
    listen       [::]:80 ipv6only=off;
    server_name  _;
    access_log   /var/log/nginx/debug_proxy_access.log;
    error_log    /var/log/nginx/debug_proxy_error.log;
    client_max_body_size 100m;
    resolver     10.3.0.1;

    location / {
        if ($debug_host = invalid) {
            return 400;
        }
        proxy_buffering off;
        proxy_pass $scheme://$debug_host;
        proxy_pass_request_headers on;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        # Swap whatever cookie we had for PHP_ENGINE with what we extracted
        set_by_lua_block $cookies {
            local cookie_snippet_to_set = "PHP_ENGINE=" .. ngx.var.php_engine;
            local current_engine = ngx.var.cookie_PHP_ENGINE;
            if (ngx.var.http_cookie == nil) then
                return cookie_snippet_to_set;
            elseif (current_engine == nil) then
                return ngx.var.http_cookie .. ";" .. cookie_snippet_to_set;
            else
                local php_engine_cookie = "PHP_ENGINE=" .. current_engine;
                return string.gsub(ngx.var.http_cookie, php_engine_cookie, cookie_snippet_to_set);
            end
        }
        proxy_http_version 1.1;
        proxy_set_header Cookie $cookies;
        proxy_set_header Host $host;
        proxy_pass_header Server;
        proxy_read_timeout 180s;
    }
}