perf(api): export YAML with string.buffer (#11706)

kong/api/routes/config.lua

@@ -1,3 +1,4 @@
+local buffer = require("string.buffer")
 local declarative = require("kong.db.declarative")
 local reports = require("kong.reports")
 local errors = require("kong.db.errors")
@@ -6,7 +7,6 @@ local errors = require("kong.db.errors")
 local kong = kong
 local ngx = ngx
 local type = type
-local table = table
 local tostring = tostring
 
 
@@ -27,14 +27,15 @@ end
 local function truthy(val)
   if type(val) == "string" then
     val = val:lower()
+
+    return val == "true"
+        or val == "1"
+        or val == "on"
+        or val == "yes"
   end
 
   return val == true
       or val == 1
-      or val == "true"
-      or val == "1"
-      or val == "on"
-      or val == "yes"
 end
 
 
@@ -93,9 +94,9 @@ return {
       end
 
       local file = {
-        buffer = {},
+        buf = buffer.new(),
         write = function(self, str)
-          self.buffer[#self.buffer + 1] = str
+          self.buf:put(str)
         end,
       }
 
@@ -105,7 +106,7 @@ return {
         return kong.response.exit(500, { message = "An unexpected error occurred" })
       end
 
-      return kong.response.exit(200, { config = table.concat(file.buffer) })
+      return kong.response.exit(200, { config = file.buf:get() })
     end,
     POST = function(self, db)
       if kong.db.strategy ~= "off" then