refactor(router): categorize router fields to simplify logic (#11411)

Summary

Categorize atc fields to fields header_fields query_fields,
then we can simplify the logic in select().

kong/router/atc.lua

@@ -158,35 +158,34 @@ local function add_atc_matcher(inst, route, route_id,
 end
 
 
-local function is_http_headers_field(field)
-  return field:sub(1, 13) == "http.headers."
-end
-
+local function categorize_fields(fields)
 
-local function has_header_matching_field(fields)
-  for _, field in ipairs(fields) do
-    if is_http_headers_field(field) then
-      return true
-    end
+  if not is_http then
+    return fields, nil, nil
   end
 
-  return false
-end
+  local basic = {}
+  local headers = {}
+  local queries = {}
 
+  -- 13 bytes, same len for "http.queries."
+  local PREFIX_LEN = 13 -- #"http.headers."
 
-local function is_http_queries_field(field)
-  return field:sub(1, 13) == "http.queries."
-end
+  for _, field in ipairs(fields) do
+    local prefix = field:sub(1, PREFIX_LEN)
 
+    if prefix == "http.headers." then
+      headers[field:sub(PREFIX_LEN + 1)] = field
 
-local function has_query_matching_field(fields)
-  for _, field in ipairs(fields) do
-    if is_http_queries_field(field) then
-      return true
+    elseif prefix == "http.queries." then
+      queries[field:sub(PREFIX_LEN + 1)] = field
+
+    else
+      table.insert(basic, field)
     end
   end
 
-  return false
+  return basic, headers, queries
 end
 
 
@@ -230,18 +229,16 @@ local function new_from_scratch(routes, get_exp_and_priority)
     yield(true, phase)
   end
 
-  local fields = inst:get_fields()
-  local match_headers = has_header_matching_field(fields)
-  local match_queries = has_query_matching_field(fields)
+  local fields, header_fields, query_fields = categorize_fields(inst:get_fields())
 
   return setmetatable({
       schema = CACHED_SCHEMA,
       router = inst,
       routes = routes_t,
       services = services_t,
       fields = fields,
-      match_headers = match_headers,
-      match_queries = match_queries,
+      header_fields = header_fields,
+      query_fields = query_fields,
       updated_at = new_updated_at,
       rebuilding = false,
     }, _MT)
@@ -325,11 +322,11 @@ local function new_from_previous(routes, get_exp_and_priority, old_router)
     yield(true, phase)
   end
 
-  local fields = inst:get_fields()
+  local fields, header_fields, query_fields = categorize_fields(inst:get_fields())
 
   old_router.fields = fields
-  old_router.match_headers = has_header_matching_field(fields)
-  old_router.match_queries = has_query_matching_field(fields)
+  old_router.header_fields = header_fields
+  old_router.query_fields = query_fields
   old_router.updated_at = new_updated_at
   old_router.rebuilding = false
 
@@ -455,12 +452,16 @@ function _M:select(req_method, req_uri, req_host, req_scheme,
         return nil, err
       end
 
-    elseif is_http_headers_field(field) then
-      if not req_headers then
-        goto continue
-      end
+    else  -- unknown field
+      error("unknown router matching schema field: " .. field)
+
+    end -- if field
+
+  end   -- for self.fields
+
+  if req_headers then
+    for h, field in pairs(self.header_fields) do
 
-      local h = field:sub(14)
       local v = req_headers[h]
 
       if type(v) == "string" then
@@ -478,14 +479,14 @@ function _M:select(req_method, req_uri, req_host, req_scheme,
         end
       end -- if type(v)
 
-      -- if v is nil or others, goto continue
+      -- if v is nil or others, ignore
 
-    elseif is_http_queries_field(field) then
-      if not req_queries then
-        goto continue
-      end
+    end   -- for self.header_fields
+  end   -- req_headers
+
+  if req_queries then
+    for n, field in pairs(self.query_fields) do
 
-      local n = field:sub(14)
       local v = req_queries[n]
 
       -- the query parameter has only one value, like /?foo=bar
@@ -514,15 +515,10 @@ function _M:select(req_method, req_uri, req_host, req_scheme,
         end
       end -- if type(v)
 
-      -- if v is nil or others, goto continue
+      -- if v is nil or others, ignore
 
-    else  -- unknown field
-      error("unknown router matching schema field: " .. field)
-
-    end -- if field
-
-    ::continue::
-  end   -- for self.fields
+    end   -- for self.query_fields
+  end   -- req_queries
 
   local matched = self.router:execute(c)
   if not matched then
@@ -642,7 +638,7 @@ function _M:exec(ctx)
   local sni = server_name()
 
   local headers, headers_key
-  if self.match_headers then
+  if not is_empty_field(self.header_fields) then
     headers = get_http_params(get_headers, "headers", "lua_max_req_headers")
 
     headers["host"] = nil
@@ -651,7 +647,7 @@ function _M:exec(ctx)
   end
 
   local queries, queries_key
-  if self.match_queries then
+  if not is_empty_field(self.query_fields) then
     queries = get_http_params(get_uri_args, "queries", "lua_max_uri_args")
 
     queries_key = get_queries_key(queries)