errors: set 'Retry-After' in .limits_exceeded

gateway/src/apicast/errors.lua

@@ -22,9 +22,14 @@ function _M.authorization_failed(service)
   return exit()
 end
 
-function _M.limits_exceeded(service)
+function _M.limits_exceeded(service, retry_after)
   ngx.log(ngx.INFO, 'limits exceeded for service ', service.id)
   ngx.var.cached_key = nil
+
+  if retry_after then
+    ngx.header['Retry-After'] = retry_after
+  end
+
   ngx.status = service.limits_exceeded_status
   ngx.header.content_type = service.limits_exceeded_headers
   ngx.print(service.error_limits_exceeded)

spec/errors_spec.lua

@@ -0,0 +1,27 @@
+local errors = require 'apicast.errors'
+local Service = require 'apicast.configuration.service'
+
+describe('Errors', function()
+  describe('.limits_exceeded', function()
+    before_each(function()
+      ngx.var = {}
+      ngx.header = {}
+    end)
+
+    local test_service = Service.new({ id = 1 })
+
+    it('sets the Retry-After header when a value for it is received', function()
+      local retry_after = 60
+
+      errors.limits_exceeded(test_service, retry_after)
+
+      assert.equals(retry_after, ngx.header['Retry-After'])
+    end)
+
+    it('does not set the Retry-After header when a value for it is not received', function()
+      errors.limits_exceeded(test_service)
+
+      assert.is_nil(ngx.header['Retry-After'])
+    end)
+  end)
+end)