feat(core) add X-Kong-Upstream-Status header

While Kong returns the same status code as
that of the upstream when it proxies a request,
it is useful to record the real status code
returned by the upstream.

This can be used for monitoring Kong
itself if it is returning the same response
as the upstream.

kong/constants.lua

@@ -41,6 +41,7 @@ return {
     HOST_OVERRIDE = "X-Host-Override",
     PROXY_LATENCY = "X-Kong-Proxy-Latency",
     UPSTREAM_LATENCY = "X-Kong-Upstream-Latency",
+    UPSTREAM_STATUS = "X-Kong-Upstream-Status",
     CONSUMER_ID = "X-Consumer-ID",
     CONSUMER_CUSTOM_ID = "X-Consumer-Custom-ID",
     CONSUMER_USERNAME = "X-Consumer-Username",

kong/core/handler.lua

@@ -519,11 +519,18 @@ return {
   },
   header_filter = {
     before = function(ctx)
+      local var = ngx.var
+      local header = ngx.header
+
       if ctx.KONG_PROXIED then
         local now = get_now()
         ctx.KONG_WAITING_TIME = now - ctx.KONG_ACCESS_ENDED_AT -- time spent waiting for a response from upstream
         ctx.KONG_HEADER_FILTER_STARTED_AT = now
       end
+
+      if singletons.configuration.server_tokens then
+        header[constants.HEADERS.UPSTREAM_STATUS]  = var.upstream_status
+      end
     end,
     after = function(ctx)
       local header = ngx.header

spec/02-integration/05-proxy/12-server_tokens_spec.lua

@@ -83,7 +83,8 @@ describe("Server Tokens", function()
 
     teardown(helpers.stop_kong)
 
-    it("should return Kong 'Via' header but not change the 'Server' header when request was proxied", function()
+    it("should return Kong 'Via'and " .. constants.HEADERS.UPSTREAM_STATUS .. 
+      " headers but not change the 'Server' header when request was proxied", function()
       local res = assert(client:send {
         method  = "GET",
         path    = "/get",
@@ -95,9 +96,11 @@ describe("Server Tokens", function()
       assert.res_status(200, res)
       assert.not_equal(default_server_header, res.headers["server"])
       assert.equal(default_server_header, res.headers["via"])
+      assert.equal('200', res.headers[constants.HEADERS.UPSTREAM_STATUS])
     end)
 
-    it("should return Kong 'Server' header but not the Kong 'Via' header when no API matched (no proxy)", function()
+    it("should return Kong 'Server' header but not the Kong 'Via' and " .. 
+      constants.HEADERS.UPSTREAM_STATUS .. " headers when no API matched (no proxy)", function()
       local res = assert(client:send {
         method  = "GET",
         path    = "/get",
@@ -109,6 +112,7 @@ describe("Server Tokens", function()
       assert.res_status(404, res)
       assert.equal(default_server_header, res.headers["server"])
       assert.is_nil(res.headers["via"])
+      assert.is_nil(res.headers[constants.HEADERS.UPSTREAM_STATUS])
     end)
 
   end)
@@ -122,7 +126,8 @@ describe("Server Tokens", function()
 
     teardown(helpers.stop_kong)
 
-    it("should not return Kong 'Via' header but it should forward the 'Server' header when request was proxied", function()
+    it("should not return Kong 'Via' or " .. constants.HEADERS.UPSTREAM_STATUS .. 
+      " header but it should forward the 'Server' header when request was proxied", function()
       local res = assert(client:send {
         method  = "GET",
         path    = "/get",
@@ -134,6 +139,7 @@ describe("Server Tokens", function()
       assert.res_status(200, res)
       assert.response(res).has.header "server"
       assert.response(res).has_not.header "via"
+      assert.is_nil(res.headers[constants.HEADERS.UPSTREAM_STATUS])
       assert.not_equal(default_server_header, res.headers["server"])
     end)
 

spec/02-integration/05-proxy/13-upstream-status-header_spec.lua

@@ -0,0 +1,61 @@
+local helpers = require "spec.helpers"
+local constants = require "kong.constants"
+
+
+describe(constants.HEADERS.UPSTREAM_STATUS .. " header", function()
+  local client
+
+  setup(function()
+    assert(helpers.dao.apis:insert {
+      name         = "upstream-header-1",
+      hosts        = { "upstream-header-1.com" },
+      upstream_url = helpers.mock_upstream_url,
+    })
+    local api2 = assert(helpers.dao.apis:insert {
+      name         = "upstream-header-2",
+      hosts        = { "upstream-header-2.com" },
+      upstream_url = helpers.mock_upstream_url,
+    })
+    assert(helpers.dao.plugins:insert {
+      name   = "force-error",
+      api_id = api2.id,
+    })
+    assert(helpers.start_kong({
+      nginx_conf = "spec/fixtures/custom_nginx.template",
+	  custom_plugins = "force-error",
+    }))
+    client = helpers.proxy_client()
+  end)
+
+  teardown(function()
+    if client then
+      client:close()
+    end
+    helpers.stop_kong()
+  end)
+
+  it("should be same as upstream staus code", function()
+    local res = assert(client:send {
+      method  = "GET",
+      path    = "/",
+      headers = {
+        host  = "upstream-header-1.com",
+      }
+    })
+
+    assert.res_status(200, res)
+    assert.equal('200', res.headers[constants.HEADERS.UPSTREAM_STATUS])
+  end)
+
+  it("should be same as upstream staus code even if plugin changes status code", function()
+    local res = assert(client:send {
+      method  = "GET",
+      path    = "/status/200",
+      headers = {
+        ["Host"]  = "upstream-header-2.com",
+      }
+    })
+    assert.res_status(500, res)
+    assert.equal('200', res.headers[constants.HEADERS.UPSTREAM_STATUS])
+  end)
+end)

spec/fixtures/custom_plugins/kong/plugins/force-error/handler.lua

@@ -0,0 +1,19 @@
+local BasePlugin = require "kong.plugins.base_plugin"
+
+
+local ForceError = BasePlugin:extend()
+
+
+ForceError.PRIORITY = 1000
+
+
+function ForceError:new()
+  ForceError.super.new(self, "force-error")
+end
+
+function ForceError:header_filter()
+  ForceError.super.access(self)
+  ngx.status = ngx.HTTP_INTERNAL_SERVER_ERROR
+end
+
+return ForceError

spec/fixtures/custom_plugins/kong/plugins/force-error/schema.lua

@@ -0,0 +1,4 @@
+return {
+  fields = {
+  }
+}