fix(core): reduce uninitialized variable message when nginx return 400 (

#13201)

When Kong receives abnormal traffic, it will trigger 400 responses without initializing any Nginx variable, So it will trigger report.lua error, which is unnecessary.

eg: send HTTP traffic to HTTPS port, Nginx will finalize the current request by 400 response in the TLS handshake, So it will never call any openresty HTTP processing phase, it also does not initialize any Nginx variable.

Fix #13197
https://konghq.atlassian.net/browse/FTI-6025

changelog/unreleased/kong/fix-reports-uninitialized-variable-in-400.yml

@@ -0,0 +1,4 @@
+message: |
+  Fixed an issue where unnecessary uninitialized variable error log is reported when 400 bad requests were received.
+type: bugfix
+scope: Core

kong/reports.lua

@@ -303,6 +303,12 @@ function get_current_suffix(ctx)
     return nil
   end
 
+  -- 400 case is for invalid requests, eg: if a client sends a HTTP
+  -- request to a HTTPS port, it does not initialized any Nginx variables
+  if proxy_mode == "" and kong.response.get_status() == 400 then
+    return nil
+  end
+
   log(WARN, "could not determine log suffix (scheme=", tostring(scheme),
             ", proxy_mode=", tostring(proxy_mode), ")")
 end

kong/templates/nginx_kong.lua

@@ -39,6 +39,8 @@ ssl_ciphers ${{SSL_CIPHERS}};
 $(el.name) $(el.value);
 > end
 
+uninitialized_variable_warn  off;
+
 init_by_lua_block {
 > if test and coverage then
     require 'luacov'
@@ -386,9 +388,8 @@ server {
 
     location = /kong_error_handler {
         internal;
-        default_type                 '';
 
-        uninitialized_variable_warn  off;
+        default_type                 '';
 
         rewrite_by_lua_block {;}
         access_by_lua_block  {;}

spec/02-integration/05-proxy/22-reports_spec.lua

@@ -242,6 +242,20 @@ for _, strategy in helpers.each_strategy() do
       proxy_ssl_client:close()
     end)
 
+    it("when send http request to https port, no other error in error.log", function()
+      local https_port = assert(helpers.get_proxy_port(true))
+      local proxy_client = assert(helpers.proxy_client(nil, https_port))
+      local res = proxy_client:get("/", {
+        headers = { host  = "http-service.test" }
+      })
+      reports_send_ping({port=constants.REPORTS.STATS_TLS_PORT})
+
+      assert.response(res).has_status(400)
+      assert.logfile().has.no.line("using uninitialized")
+      assert.logfile().has.no.line("could not determine log suffix (scheme=http, proxy_mode=)")
+      proxy_client:close()
+    end)
+
     it("reports h2c requests", function()
       local h2c_client = assert(helpers.proxy_client_h2c())
       local body, headers = h2c_client({