fix(config) parse headers config option from .kong_env

This fixes a bug introduced in 976dd87 (#3300)
where headers config option was being overwritten
as a table. The table is not persisted in the intermediate
config file and hence the config option does not take effect.

This commit also exposes `get_running_conf` helper function to
read conf from prefix directory in use during the current test.

kong/conf_loader.lua

@@ -606,31 +606,33 @@ local function load(path, custom_conf)
 
   -- load headers configuration
   do
-    local headers_enabled = {}
+    local enabled_headers = {}
 
     for _, v in pairs(header_key_to_name) do
-      headers_enabled[v] = false
+      enabled_headers[v] = false
     end
 
     if #conf.headers > 0 and conf.headers[1] ~= "off" then
       for _, token in ipairs(conf.headers) do
         if token ~= "off" then
-          headers_enabled[header_key_to_name[string.lower(token)]] = true
+          enabled_headers[header_key_to_name[string.lower(token)]] = true
         end
       end
     end
 
-    if headers_enabled.server_tokens then
-      headers_enabled[headers.VIA] = true
-      headers_enabled[headers.SERVER] = true
+    if enabled_headers.server_tokens then
+      enabled_headers[headers.VIA] = true
+      enabled_headers[headers.SERVER] = true
     end
 
-    if headers_enabled.latency_tokens then
-      headers_enabled[headers.PROXY_LATENCY] = true
-      headers_enabled[headers.UPSTREAM_LATENCY] = true
+    if enabled_headers.latency_tokens then
+      enabled_headers[headers.PROXY_LATENCY] = true
+      enabled_headers[headers.UPSTREAM_LATENCY] = true
     end
 
-    conf.headers = headers_enabled
+    conf.enabled_headers = setmetatable(enabled_headers, {
+      __tostring = function() return "" end,
+    })
   end
 
   -- load absolute paths

kong/error_handlers.lua

@@ -58,7 +58,7 @@ return function(ngx)
   local status = ngx.status
   message = BODIES["s" .. status] and BODIES["s" .. status] or format(BODIES.default, status)
 
-  if singletons.configuration.headers[constants.HEADERS.SERVER] then
+  if singletons.configuration.enabled_headers[constants.HEADERS.SERVER] then
     ngx.header[constants.HEADERS.SERVER] = SERVER_HEADER
   end
 

kong/runloop/handler.lua

@@ -698,20 +698,20 @@ return {
       local header = ngx.header
 
       if ctx.KONG_PROXIED then
-        if singletons.configuration.headers[constants.HEADERS.UPSTREAM_LATENCY] then
+        if singletons.configuration.enabled_headers[constants.HEADERS.UPSTREAM_LATENCY] then
           header[constants.HEADERS.UPSTREAM_LATENCY] = ctx.KONG_WAITING_TIME
         end
 
-        if singletons.configuration.headers[constants.HEADERS.PROXY_LATENCY] then
+        if singletons.configuration.enabled_headers[constants.HEADERS.PROXY_LATENCY] then
           header[constants.HEADERS.PROXY_LATENCY] = ctx.KONG_PROXY_LATENCY
         end
 
-        if singletons.configuration.headers[constants.HEADERS.VIA] then
+        if singletons.configuration.enabled_headers[constants.HEADERS.VIA] then
           header[constants.HEADERS.VIA] = server_header
         end
 
       else
-        if singletons.configuration.headers[constants.HEADERS.SERVER] then
+        if singletons.configuration.enabled_headers[constants.HEADERS.SERVER] then
           header[constants.HEADERS.SERVER] = server_header
 
         else

spec/02-integration/05-proxy/13-server_tokens_spec.lua

@@ -46,6 +46,13 @@ describe("headers [#" .. strategy .. "]", function()
 
       teardown(helpers.stop_kong)
 
+      it("intermediate kong conf in prefix should contain 'headers=server_tokens,latency_tokens'", function()
+        local conf = helpers.get_running_conf()
+        assert.equal("server_tokens", conf.headers[1])
+        assert.equal("latency_tokens", conf.headers[2])
+        assert.equal(2, #conf.headers)
+      end)
+
       it("should return Kong 'Via' header but not change the 'Server' header when request was proxied", function()
         local res = assert(proxy_client:send {
           method  = "GET",
@@ -122,6 +129,12 @@ describe("headers [#" .. strategy .. "]", function()
 
       teardown(helpers.stop_kong)
 
+      it("intermediate kong conf in prefix should contain 'headers=Server'", function()
+        local conf = helpers.get_running_conf()
+        assert.equal("Server", conf.headers[1])
+        assert.equal(1, #conf.headers)
+      end)
+
       it("should not return Kong 'Via' header but not change the 'Server' header when request was proxied", function()
         local res = assert(proxy_client:send {
           method  = "GET",
@@ -160,6 +173,12 @@ describe("headers [#" .. strategy .. "]", function()
 
       teardown(helpers.stop_kong)
 
+      it("intermediate kong conf in prefix should contain 'headers=server_tokens'", function()
+        local conf = helpers.get_running_conf()
+        assert.equal("server_tokens", conf.headers[1])
+        assert.equal(1, #conf.headers)
+      end)
+
       it("should return Kong 'Via' header but not change the 'Server' header when request was proxied", function()
         local res = assert(proxy_client:send {
           method  = "GET",

spec/helpers.lua

@@ -1159,6 +1159,7 @@ return {
   clean_prefix = clean_prefix,
   wait_for_invalidation = wait_for_invalidation,
   each_strategy = each_strategy,
+  get_running_conf = get_running_conf,
 
   -- miscellaneous
   intercept = intercept,