fix(router) ensure preserve_host when no hosts

kong/core/router.lua

@@ -615,11 +615,7 @@ function _M.new(apis)
 
 
     if api_t.preserve_host then
-      if not headers then
-        headers = ngx.req.get_headers()
-      end
-
-      host_header = headers["host"]
+      host_header = ngx.var.http_host
     end
 
 

spec/01-unit/11-router_spec.lua

@@ -588,7 +588,8 @@ describe("Router", function()
       _ngx = {
         re = ngx.re,
         var = {
-          uri = uri
+          uri = uri,
+          http_host = headers["host"] or headers["Host"],
         },
         req = {
           set_uri = function(uri)
@@ -860,6 +861,25 @@ describe("Router", function()
           assert.same(use_case_apis[1], api)
           assert.equal("httpbin.org", upstream.host)
         end)
+
+        it("uses the request's Host header when `grab_header` is disabled", function()
+          local use_case_apis = {
+            {
+              name          = "api-1",
+              upstream_url  = "http://httpbin.org",
+              preserve_host = true,
+              uris          = { "/foo" },
+            }
+          }
+
+          local router = assert(Router.new(use_case_apis))
+
+          local _ngx = mock_ngx("GET", "/foo", { ["host"] = "preserve.com" })
+
+          local api, _, host_header = router.exec(_ngx)
+          assert.same(use_case_apis[1], api)
+          assert.equal("preserve.com", host_header)
+        end)
       end)
 
       describe("when preserve_host is false", function()

spec/02-integration/05-proxy/01-router_spec.lua

@@ -250,6 +250,13 @@ describe("Router", function()
           upstream_url = "http://localhost:9999/headers-inspect",
           hosts = "discarded.com",
         },
+        {
+          name = "api-3",
+          strip_uri = false,
+          preserve_host = true,
+          upstream_url = "http://localhost:9999",
+          uris = "/headers-inspect",
+        }
       }
 
       assert(helpers.start_kong {
@@ -323,6 +330,18 @@ describe("Router", function()
         local json = cjson.decode(body)
         assert.equal("preserved.com:123", json.host)
       end)
+
+      it("forwards request Host even if not matched by [hosts]", function()
+        local res = assert(client:send {
+          method = "GET",
+          path = "/headers-inspect",
+          headers = { ["Host"] = "preserved.com" },
+        })
+
+        local body = assert.res_status(200, res)
+        local json = cjson.decode(body)
+        assert.equal("preserved.com", json.host)
+      end)
     end)
   end)