Liquid context debugging policy

CHANGELOG.md

@@ -31,6 +31,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Support for HTTP Proxy [THREESCALE-221](https://issues.jboss.org/browse/THREESCALE-221), [#709](https://github.com/3scale/apicast/issues/709)
 - Conditions for the limits of the rate-limit policy [PR #839](https://github.com/3scale/apicast/pull/839)
 - `bin/apicast console` to start Lua REPL with APIcast code loaded [PR #853](https://github.com/3scale/apicast/pull/853)
+- Liquid Context Debugging policy. It's a policy only meant for debugging purposes, returns the context available when evaluating liquid [PR #849](https://github.com/3scale/apicast/pull/849)
 
 ### Changed
 

gateway/src/apicast/policy/liquid_context_debug/apicast-policy.json

@@ -0,0 +1,20 @@
+{
+  "$schema": "http://apicast.io/policy-v1/schema#manifest#",
+  "name": "Liquid context debug",
+  "summary": "Inspects the available liquid context.",
+  "description": [
+    "This is a policy meant only for debugging purposes. This policy ",
+    "returns the context available when evaluating liquid. Any policy can ",
+    "modify the context that is shared between policies and that context is ",
+    "available when evaluating liquid. However, documenting what's available ",
+    "is not possible because policies can add any arbitrary field. Users who ",
+    "want to develop a policy can use this one to know the context available ",
+    "in their configuration."
+  ],
+  "version": "builtin",
+  "configuration": {
+    "type": "object",
+    "properties": {
+    }
+  }
+}

gateway/src/apicast/policy/liquid_context_debug/context_content.lua

@@ -0,0 +1,97 @@
+local type = type
+local pairs = pairs
+local tostring = tostring
+
+local _M = {}
+
+-- The context usually contains a lot of information. For example, it includes
+-- the whole service configuration. Also, some of the values are objects that
+-- we can't really use when evaluating liquid, like functions.
+-- That's why we define only a few types of keys and values to return.
+local accepted_types_for_keys = {
+  string = true,
+  number = true,
+}
+
+local accepted_types_for_values = {
+  string = true,
+  number = true,
+  table = true
+}
+
+-- In the context, there might be large integers as keys. This can be a problem
+-- when converting to JSON. Imagine an entry of the table like this:
+-- { [10000] = 'something' }. To convert that to JSON, we need an array of 1000
+-- positions with only one occupied. With arrays like these, 'cjson' raises an
+-- "Excessively sparse arrays" error:
+-- https://github.com/efelix/lua-cjson/blob/4f27182acabc435fcc220fdb710ddfaf4e648c86/README#L140
+-- For example, there is a lrucache instance with a table that maps service ids
+-- (numbers) to hosts. So we can have something like { [123456] = "127.0.0.1" }.
+-- This can be limited using a global setting of the 'cjson' library. However,
+-- we're going to implement an add-hoc solution here so we don't affect the
+-- other modules. We're going to convert those large ints to strings as a
+-- workaround.
+local max_integer_key = 1000
+
+local function key(k)
+  if type(k) ~= 'number' then return k end
+
+  if k <= max_integer_key then
+    return k
+  else
+    return tostring(k)
+  end
+end
+
+local value_from
+
+local ident = function(...) return ... end
+local value_from_fun = {
+  string = ident, number = ident,
+  table = function(table)
+    local res = {}
+    for k, v in pairs(table) do
+      local wanted_types = accepted_types_for_keys[type(k)] and
+                           accepted_types_for_values[type(v)]
+
+      if wanted_types then
+        res[key(k)] = value_from(v)
+      end
+    end
+
+    return res
+  end
+}
+
+value_from = function(object)
+  local fun = value_from_fun[type(object)]
+  if fun then return fun(object) end
+end
+
+local function add_content(object, acc)
+  if type(object) ~= 'table' then return nil end
+
+  -- The context is a list where each element has a "current" and a "next".
+  local current = object.current
+  local next = object.next
+
+  local values_of_current = value_from(current or object)
+
+  for k, v in pairs(values_of_current) do
+    if acc[key(k)] == nil then -- to return only the first occurrence
+      acc[key(k)] = v
+    end
+  end
+
+  if next then
+    add_content(next, acc)
+  end
+end
+
+function _M.from(context)
+  local res = {}
+  add_content(context, res)
+  return res
+end
+
+return _M

gateway/src/apicast/policy/liquid_context_debug/init.lua

@@ -0,0 +1 @@
+return require('liquid_context_debug')

gateway/src/apicast/policy/liquid_context_debug/liquid_context_debug.lua

@@ -0,0 +1,21 @@
+local context_content = require('context_content')
+local cjson = require('cjson')
+local policy = require('apicast.policy')
+local ngx_variable = require('apicast.policy.ngx_variable')
+local _M = policy.new('Liquid context debug')
+
+local new = _M.new
+
+function _M.new(config)
+  local self = new(config)
+  return self
+end
+
+function _M.content(_, context)
+  local liquid_context = ngx_variable.available_context(context)
+  local content = context_content.from(liquid_context)
+
+  ngx.say(cjson.encode(content))
+end
+
+return _M

gateway/src/apicast/policy/ngx_variable.lua

@@ -1,3 +1,5 @@
+local LinkedList = require('apicast.linked_list')
+
 local _M = {}
 
 local function context_values()
@@ -10,7 +12,7 @@ local function context_values()
 end
 
 function _M.available_context(policies_context)
-  return setmetatable(context_values(), { __index = policies_context })
+  return LinkedList.readonly(context_values(), policies_context)
 end
 
 return _M

spec/policy/liquid_context_debug/context_content_spec.lua

@@ -0,0 +1,74 @@
+local LinkedList = require 'apicast.linked_list'
+local context_content = require 'apicast.policy.liquid_context_debug.context_content'
+
+describe('Context content', function()
+  describe('.from', function()
+    it('returns the content from a context with one node', function()
+      local t = { a = 1, b = 2 }
+      local context = LinkedList.readonly(t)
+
+      local content = context_content.from(context)
+
+      assert.contains(t, content)
+    end)
+
+    it('returns the content from a context with several nodes', function()
+      local context = LinkedList.readonly(
+        { a = 1 },
+        LinkedList.readonly(
+          { b = 2, c = 3 },
+          LinkedList.readonly(
+            { d = 4 },
+            { e = 5, f = 6 }
+          )
+        )
+      )
+
+      local content = context_content.from(context)
+
+      local expected = { a = 1, b = 2, c = 3, d = 4, e = 5, f = 6 }
+      assert.contains(expected, content)
+    end)
+
+    it('returns only the first value of a repeated element', function()
+      local context = LinkedList.readonly(
+        { a = 1 },
+        LinkedList.readonly(
+          { a = 2 },
+          LinkedList.readonly(
+            { a = 3 },
+            { a = 4 }
+          )
+        )
+      )
+
+      local content = context_content.from(context)
+
+      assert.equals(1, content.a)
+    end)
+
+    it('ignores keys that are not strings or numbers', function()
+      local context = LinkedList.readonly(
+        { a = 1, [function() end] = 2, [{}] = 3 }
+      )
+
+      local content = context_content.from(context)
+
+      assert.contains({ a = 1 }, content)
+    end)
+
+    it('ignores values that are not strings, numbers or tables', function()
+      local context = LinkedList.readonly(
+        { a = 1, b = {}, c = function() end }
+      )
+
+      local content = context_content.from(context)
+
+      assert.contains({ a = 1, b = {} }, content)
+    end)
+
+    it('returns empty if the context is empty', function()
+      assert.same({}, context_content.from({}))
+    end)
+  end)
+end)

spec/policy/liquid_context_debug/liquid_context_debug_spec.lua

@@ -0,0 +1,32 @@
+local ngx_variable = require('apicast.policy.ngx_variable')
+local LinkedList = require('apicast.linked_list')
+local context_content = require('apicast.policy.liquid_context_debug.context_content')
+local cjson = require('cjson')
+
+local LiquidContextDebug = require 'apicast.policy.liquid_context_debug'
+
+describe('Liquid context debug policy', function()
+  describe('.content', function()
+    before_each(function()
+      stub(ngx, 'say')
+    end)
+
+    it('calls ngx.say with the "ngx_variable" available context in JSON', function()
+      -- Return something simple with just headers instead of mocking all the
+      -- ngx.var.* needed.
+      stub(ngx_variable, 'available_context', function(policies_context)
+        return LinkedList.readonly({ headers = { some_header = 'some_val' } },
+          policies_context)
+      end)
+      local policies_context = { a = 1 }
+
+      LiquidContextDebug.new():content(policies_context)
+
+      local expected_content = context_content.from(
+        ngx_variable.available_context(policies_context)
+      )
+      local expected_json = cjson.encode(expected_content)
+      assert.stub(ngx.say).was_called_with(expected_json)
+    end)
+  end)
+end)

spec/policy/ngx_variable_spec.lua

@@ -13,7 +13,23 @@ describe('ngx_variable', function()
 
       local context = ngx_variable.available_context()
 
-      assert('some_val', context.headers['some_header'])
+      assert.equals('some_val', context.headers['some_header'])
+    end)
+
+    it('gives precedence to what is exposed in "ngx_variable"', function()
+      local headers_in_ngx_variable = { some_header = 'some_val' }
+      local headers_in_context = { some_header = 'different_val' }
+
+      stub(ngx.req, 'get_headers', function()
+        return headers_in_ngx_variable
+      end)
+
+      local policies_context = { headers = headers_in_context }
+
+      local liquid_context = ngx_variable.available_context(policies_context)
+
+      assert.equals(headers_in_ngx_variable.some_header,
+                    liquid_context.headers.some_header)
     end)
   end)
 end)

t/apicast-policy-liquid-context-debug.t

@@ -0,0 +1,33 @@
+use lib 't';
+use Test::APIcast::Blackbox 'no_plan';
+
+run_tests();
+
+__DATA__
+
+=== TEST 1: liquid_context_debug policy does not crash
+If there's a problem while parsing the context or converting it to JSON, this
+will crash.
+--- configuration
+{
+  "services": [
+    {
+      "id": 42,
+      "proxy": {
+        "policy_chain": [
+          {
+            "name": "liquid_context_debug",
+            "configuration": {}
+          }
+        ],
+        "proxy_rules": [
+        ]
+      }
+    }
+  ]
+}
+--- request
+GET /
+--- error_code: 200
+--- no_error_log
+[error]