refactor(plugin): abstruct proxy cache related function to kong.tools (…

…#13458)

move proxy-cache plugin parse_directive_header and resource_ttl functions to kong tools for reuse in another plugin.

AG-91

(cherry picked from commit dd37fac)

kong/plugins/proxy-cache/handler.lua

@@ -17,22 +17,17 @@ local ngx              = ngx
 local kong             = kong
 local type             = type
 local pairs            = pairs
-local tostring         = tostring
-local tonumber         = tonumber
-local max              = math.max
 local floor            = math.floor
 local lower            = string.lower
-local concat           = table.concat
 local time             = ngx.time
 local resp_get_headers = ngx.resp and ngx.resp.get_headers
-local ngx_re_gmatch    = ngx.re.gmatch
 local ngx_re_sub       = ngx.re.gsub
 local ngx_re_match     = ngx.re.match
-local parse_http_time  = ngx.parse_http_time
 local parse_mime_type  = mime_type.parse_mime_type
+local parse_directive_header = require("kong.tools.http").parse_directive_header
+local calculate_resource_ttl = require("kong.tools.http").calculate_resource_ttl
 
 
-local tab_new = require("table.new")
 
 
 local STRATEGY_PATH = "kong.plugins.proxy-cache.strategies"
@@ -81,39 +76,6 @@ local function set_res_header(res, header, value, conf)
   end
 end
 
-local function parse_directive_header(h)
-  if not h then
-    return EMPTY
-  end
-
-  if type(h) == "table" then
-    h = concat(h, ", ")
-  end
-
-  local t    = {}
-  local res  = tab_new(3, 0)
-  local iter = ngx_re_gmatch(h, "([^,]+)", "oj")
-
-  local m = iter()
-  while m do
-    local _, err = ngx_re_match(m[0], [[^\s*([^=]+)(?:=(.+))?]],
-                                "oj", nil, res)
-    if err then
-      kong.log.err(err)
-    end
-
-    -- store the directive token as a numeric value if it looks like a number;
-    -- otherwise, store the string value. for directives without token, we just
-    -- set the key to true
-    t[lower(res[1])] = tonumber(res[2]) or res[2] or true
-
-    m = iter()
-  end
-
-  return t
-end
-
-
 local function req_cc()
   return parse_directive_header(ngx.var.http_cache_control)
 end
@@ -124,27 +86,6 @@ local function res_cc()
 end
 
 
-local function resource_ttl(res_cc)
-  local max_age = res_cc["s-maxage"] or res_cc["max-age"]
-
-  if not max_age then
-    local expires = ngx.var.sent_http_expires
-
-    -- if multiple Expires headers are present, last one wins
-    if type(expires) == "table" then
-      expires = expires[#expires]
-    end
-
-    local exp_time = parse_http_time(tostring(expires))
-    if exp_time then
-      max_age = exp_time - time()
-    end
-  end
-
-  return max_age and max(max_age, 0) or 0
-end
-
-
 local function cacheable_request(conf, cc)
   -- TODO refactor these searches to O(1)
   do
@@ -234,7 +175,7 @@ local function cacheable_response(conf, cc)
     return false
   end
 
-  if conf.cache_control and resource_ttl(cc) <= 0 then
+  if conf.cache_control and calculate_resource_ttl(cc) <= 0 then
     return false
   end
 
@@ -433,7 +374,7 @@ function ProxyCacheHandler:header_filter(conf)
   if cacheable_response(conf, cc) then
     -- TODO: should this use the kong.conf configured limit?
     proxy_cache.res_headers = resp_get_headers(0, true)
-    proxy_cache.res_ttl = conf.cache_control and resource_ttl(cc) or conf.cache_ttl
+    proxy_cache.res_ttl = conf.cache_control and calculate_resource_ttl(cc) or conf.cache_ttl
 
   else
     set_header(conf, "X-Cache-Status", "Bypass")

kong/tools/http.lua

@@ -22,7 +22,15 @@ local re_match      = ngx.re.match
 local join          = require("kong.tools.string").join
 local split         = require("kong.tools.string").split
 local strip         = require("kong.tools.string").strip
+local parse_http_time = ngx.parse_http_time
+local time          = ngx.time
+local ngx_re_gmatch = ngx.re.gmatch
+local ngx_re_match = ngx.re.match
+local lower         = string.lower
+local max           = math.max
+local tab_new       = require("table.new")
 
+local EMPTY = {}
 
 local _M = {}
 
@@ -562,4 +570,63 @@ do
   end
 end
 
+-- Parses a HTTP header value into a table of directives
+-- eg: Cache-Control: public, max-age=3600
+--     => { public = true, ["max-age"] = 3600 }
+-- @param h (string) the header value to parse
+-- @return table a table of directives
+function _M.parse_directive_header(h)
+  if not h then
+    return EMPTY
+  end
+
+  if type(h) == "table" then
+    h = concat(h, ", ")
+  end
+
+  local t = {}
+  local res = tab_new(3, 0)
+  local iter = ngx_re_gmatch(h, "([^,]+)", "oj")
+
+  local m = iter()
+  while m do
+    local _, err = ngx_re_match(m[0], [[^\s*([^=]+)(?:=(.+))?]], "oj", nil, res)
+    if err then
+      kong.log.err(err)
+    end
+
+    -- store the directive token as a numeric value if it looks like a number;
+    -- otherwise, store the string value. for directives without token, we just
+    -- set the key to true
+    t[lower(res[1])] = tonumber(res[2]) or res[2] or true
+
+    m = iter()
+  end
+
+  return t
+end
+
+-- Calculates resource Time-To-Live (TTL) based on Cache-Control headers
+-- @param res_cc (table) the Cache-Control headers, as parsed by `parse_directive_header`
+-- @return number the TTL in seconds
+function _M.calculate_resource_ttl(res_cc)
+  local max_age = res_cc and (res_cc["s-maxage"] or res_cc["max-age"])
+
+  if not max_age then
+    local expires = ngx.var.sent_http_expires
+
+    if type(expires) == "table" then
+      expires = expires[#expires]
+    end
+
+    local exp_time = parse_http_time(tostring(expires))
+    if exp_time then
+      max_age = exp_time - time()
+    end
+  end
+
+  return max_age and max(max_age, 0) or 0
+end
+
+
 return _M