refactor(galileo) use lua-cjson empty_table_mt

Now that openresty/lua-cjson#6 has been merged
and OpenResty has been bumped to 1.9.15.1, we can use more granular
empty array encoding for ALF serialization.

CHANGELOG.md

@@ -23,11 +23,12 @@ The main focus of this release is Kong's new CLI. With a simpler configuration f
 - `request_host`: internationalized url support; utf-8 domain names through punycode support and paths through %-encoding. [#1300](https://github.com/Mashape/kong/issues/1300)
 - Implements caching locks when fetching database configuration (APIs, Plugins...) to avoid dog pile effect on cold nodes. [#1402](https://github.com/Mashape/kong/pull/1402)
 - Plugins:
-  - Bot Detection: Added a new plugin that protects APIs by detecting common bots and crawlers. [#1413](https://github.com/Mashape/kong/pull/1413)
+  - :fireworks: **New bot-detection plugin**: protect your APIs by detecting and rejecting common bots and crawlers. [#1413](https://github.com/Mashape/kong/pull/1413)
   - correlation-id: new "tracker" generator, identifying requests per worker and connection. [#1288](https://github.com/Mashape/kong/pull/1288)
   - request/response-transformer: ability to add strings including colon characters. [#1353](https://github.com/Mashape/kong/pull/1353)
-  - Rate Limiting: support for new rate-limiting policies (`cluster`, `local` and `redis`), and for a new `limit_by` property to force rate-limiting by `consumer`, `credential` or `ip`.
-  - Response Rate Limiting: support for new rate-limiting policies (`cluster`, `local` and `redis`), and for a new `limit_by` property to force rate-limiting by `consumer`, `credential` or `ip`.
+  - rate-limiting: support for new rate-limiting policies (`cluster`, `local` and `redis`), and for a new `limit_by` property to force rate-limiting by `consumer`, `credential` or `ip`.
+  - response-rate-limiting: support for new rate-limiting policies (`cluster`, `local` and `redis`), and for a new `limit_by` property to force rate-limiting by `consumer`, `credential` or `ip`.
+  - galileo: performance improvements of ALF serialization. ALFs are not discarded when exceeding 20MBs anymore. [#1463](https://github.com/Mashape/kong/issues/1463)
 
 ### Removed
 

kong/plugins/galileo/alf.lua

@@ -19,12 +19,6 @@
 -- * bodyCaptured properties are determined using HTTP headers
 -- * timings.blocked is ignored
 -- * timings.connect is ignored
---
--- * we are waiting for lua-cjson support of granular 'empty table
---   as JSON arrays' to be released in OpenResty. Until then, we
---   have to use a workaround involving string substituion, which
---   is slower and limits the maximum size of ALFs we can deal with.
---   ALFs are thus limited to 20MB
 
 local cjson = require "cjson.safe"
 local resp_get_headers = ngx.resp.get_headers
@@ -61,18 +55,10 @@ function _M.new(log_bodies, server_addr)
   return setmetatable(alf, _mt)
 end
 
-local _empty_arr_placeholder = "__empty_array_placeholder__"
-local _empty_arr_t = {_empty_arr_placeholder}
-
 -- Convert a table such as returned by ngx.*.get_headers()
 -- to integer-indexed arrays.
--- @warn Encoding of empty arrays workaround forces us
--- to replace empty arrays with a placeholder to be substituted
--- at serialization time.
--- waiting on the releast of:
--- https://github.com/openresty/lua-cjson/pull/6
 local function hash_to_array(t)
-  local arr = {}
+  local arr = setmetatable({}, cjson.empty_array_mt)
   for k, v in pairs(t) do
     if type(v) == "table" then
       for i = 1, #v do
@@ -82,12 +68,7 @@ local function hash_to_array(t)
       arr[#arr+1] = {name = k, value = v}
     end
   end
-
-  if #arr == 0 then
-    return _empty_arr_t
-  else
-    return arr
-  end
+  return arr
 end
 
 local function get_header(t, name, default)
@@ -228,10 +209,6 @@ local buf = {
    }
  }
 
-local gsub = string.gsub
-local pat = '"'.._empty_arr_placeholder..'"'
-local _alf_max_size = 20 * 2^20
-
 --- Encode the current ALF to JSON
 -- @param[type=string] service_token The ALF `serviceToken`
 -- @param[type=string] environment (optional) The ALF `environment`
@@ -249,19 +226,7 @@ function _M:serialize(service_token, environment)
   buf.environment = environment
   buf.har.log.entries = self.entries
 
-  -- tmp workaround for empty arrays
-  -- this prevents us from dealing with ALFs
-  -- larger than a few MBs at once
-  local encoded =  cjson.encode(buf)
-
-  if #encoded > _alf_max_size then
-    return nil, "ALF too large (> 20MB)"
-  end
-
-  encoded = gsub(encoded, pat, "")
-  return gsub(encoded, "\\/", "/"), #self.entries
-
-  --return cjson.encode(buf)
+  return cjson.encode(buf)
 end
 
 --- Empty the ALF

spec/03-plugins/05-galileo/01-alf_spec.lua

@@ -463,21 +463,15 @@ describe("ALF serializer", function()
       _G.ngx.resp.get_headers = function()
         return {}
       end
+      _G.ngx.req.get_uri_args = function()
+        return {}
+      end
       reload_alf_serializer()
       local alf = alf_serializer.new()
       assert(alf:add_entry(_ngx))
       local json_encoded_alf = assert(alf:serialize("abcd"))
       assert.matches('"headers":[]', json_encoded_alf, nil, true)
-    end)
-    -- @TODO: get rid of once lua-cjson gets a release including
-    -- granular 'empty table as arrays'
-    it("limits ALF sizes to 20MB", function()
-      local alf = alf_serializer.new(true)
-      local body_12mb = string.rep(".", 21 * 2^20)
-      assert(alf:add_entry(_ngx, body_12mb))
-      local json_encoded_alf, err = alf:serialize("abcd")
-      assert.equal("ALF too large (> 20MB)", err)
-      assert.is_nil(json_encoded_alf)
+      assert.matches('"queryString":[]', json_encoded_alf, nil, true)
     end)
     it("handles nil environment", function()
       local alf = alf_serializer.new()