feat(var): add three variables that are indexed by default

README.md

@@ -100,6 +100,9 @@ index *commonly used variables* as follows:
 - `$http_x_forwarded_port`
 - `$http_x_forwarded_prefix`
 - `$http_x_forwarded_proto`
+- `$http_x_kong_request_debug`
+- `$http_x_kong_request_debug_token`
+- `$http_x_kong_request_debug_log`
 - `$https`
 - `$http2`
 - `$realip_remote_addr`

src/ngx_http_lua_kong_var_index.c

@@ -44,6 +44,11 @@ static ngx_str_t default_vars[] = {
     ngx_string("http_x_forwarded_prefix"),
     ngx_string("http_x_forwarded_proto"),
 
+    /* for request-debugging */
+    ngx_string("http_x_kong_request_debug"),
+    ngx_string("http_x_kong_request_debug_token"),
+    ngx_string("http_x_kong_request_debug_log"),
+
     /* --with-http_ssl_module */
 #if (NGX_HTTP_SSL)
     ngx_string("https"),

t/006-default_indexed-var.t

@@ -411,3 +411,36 @@ get variable value '0' by index
 [error]
 [crit]
 [alert]
+
+=== TEST 13: variable $http_x_kong_request_debug, $http_x_kong_request_debug_token, $http_x_kong_request_debug_log
+--- http_config
+    lua_package_path "../lua-resty-core/lib/?.lua;lualib/?.lua;;";
+    lua_kong_load_var_index default;
+    init_by_lua_block {
+        require("resty.kong.var").patch_metatable()
+    }
+
+--- config
+    location = /test {
+        content_by_lua_block {
+            ngx.say(ngx.var.http_x_kong_request_debug, " ",
+                    ngx.var.http_x_kong_request_debug_token, " ",
+                    ngx.var.http_x_kong_request_debug_log)
+        }
+    }
+--- request
+GET /test
+--- more_headers
+x-kong-request-debug: true
+x-kong-request-debug-token: 12345
+x-kong-request-debug-log: false
+--- response_body
+true 12345 false
+--- error_log
+get variable value 'true' by index
+get variable value '12345' by index
+get variable value 'false' by index
+--- no_error_log
+[error]
+[crit]
+[alert]