fix(wasm): execute filter plugins in a consistent order

Before this change, execution order of filter plugins was subject to
ordering returned by the underling DB implementation of
`kong.db.plugins:each()`.

This adds an extra step that sorts all discovered filter plugins by name
so that execution order is more consistent.

kong/runloop/wasm.lua

@@ -53,6 +53,7 @@ local ipairs = ipairs
 local type = type
 local assert = assert
 local insert = table.insert
+local sort = table.sort
 local cjson_encode = cjson.encode
 local cjson_decode = cjson.decode
 local fmt = string.format
@@ -116,6 +117,21 @@ local STATUS_ENABLED = "wasm support is enabled"
 local ENABLED = false
 local STATUS = STATUS_DISABLED
 
+local function filter_plugin_compare(a, b)
+  if a.name ~= b.name then
+    return a.name < b.name
+  end
+
+  if a.updated_at and b.updated_at and a.updated_at ~= b.updated_at then
+    return a.updated_at < b.updated_at
+  end
+
+  if a.created_at and b.created_at and a.created_at ~= b.created_at then
+    return a.created_at < b.created_at
+  end
+
+  return a.id < b.id
+end
 
 local hash_chain
 do
@@ -485,28 +501,36 @@ local function rebuild_state(db, version, old_state)
 
   local plugin_pagesize = db.plugins.pagination.max_page_size
 
+  local filter_plugins = {}
+
   for plugin, err in db.plugins:each(plugin_pagesize, GLOBAL_QUERY_OPTS) do
     if err then
       return nil, "failed iterating plugins: " .. tostring(err)
     end
 
     if _M.filters_by_name[plugin.name] and plugin.enabled then
-      local chain = get_or_insert_chain(chains, {
-        id = uuid.uuid(),
-        enabled = true,
-        route = plugin.route,
-        service = plugin.service,
-        filters = {},
-      })
-
-      insert(chain.filters, {
-        name = plugin.name,
-        enabled = true,
-        config = serialize_configuration(plugin.config),
-      })
+      insert(filter_plugins, plugin)
     end
   end
 
+  sort(filter_plugins, filter_plugin_compare)
+
+  for _, plugin in ipairs(filter_plugins) do
+    local chain = get_or_insert_chain(chains, {
+      id = uuid.uuid(),
+      enabled = true,
+      route = plugin.route,
+      service = plugin.service,
+      filters = {},
+    })
+
+    insert(chain.filters, {
+      name = plugin.name,
+      enabled = true,
+      config = serialize_configuration(plugin.config),
+    })
+  end
+
   local routes = db.routes
   local select_route = routes.select
 

spec/02-integration/20-wasm/12-filters-as-plugins_spec.lua

@@ -117,10 +117,23 @@ describe("#wasm filters as plugins (#" .. strategy .. ")", function()
 
 
   lazy_setup(function()
+    assert(helpers.file.copy(FILTER_PATH .. "/tests.wasm",
+                             FILTER_PATH .. "/tests-01.wasm"))
+    assert(helpers.file.copy(FILTER_PATH .. "/tests.wasm",
+                             FILTER_PATH .. "/tests-02.wasm"))
+
     require("kong.runloop.wasm").enable({
       { name = "response_transformer",
         path = FILTER_PATH .. "/response_transformer.wasm",
       },
+      {
+        name = "tests-01",
+        path = FILTER_PATH .. "/tests-01.wasm",
+      },
+      {
+        name = "tests-02",
+        path = FILTER_PATH .. "/tests-02.wasm",
+      },
     })
 
     bp, db = helpers.get_db_utils(strategy, {
@@ -130,14 +143,14 @@ describe("#wasm filters as plugins (#" .. strategy .. ")", function()
       "plugins",
     })
 
-    helpers.start_kong({
+    assert(helpers.start_kong({
       database = strategy,
       nginx_conf = "spec/fixtures/custom_nginx.template",
       nginx_main_worker_processes = "2",
       wasm = true,
-      wasm_filters = "response_transformer",
+      wasm_filters = "response_transformer,tests-01,tests-02",
       plugins = "response-transformer",
-    })
+    }))
 
     admin = helpers.admin_client()
     proxy = helpers.proxy_client()
@@ -154,6 +167,8 @@ describe("#wasm filters as plugins (#" .. strategy .. ")", function()
     end
 
     helpers.stop_kong()
+    helpers.file.delete(FILTER_PATH .. "/tests-01.wasm")
+    helpers.file.delete(FILTER_PATH .. "/tests-02.wasm")
   end)
 
   before_each(function()
@@ -229,7 +244,6 @@ describe("#wasm filters as plugins (#" .. strategy .. ")", function()
 
         local expected = 4
         assert.equals(expected, #json.data)
-        helpers.intercept(json.data)
         local found = 0
 
         for _, plugin in ipairs(json.data) do
@@ -339,6 +353,186 @@ describe("#wasm filters as plugins (#" .. strategy .. ")", function()
       assert.equals(fc_value, assert.response(res).has.header(FILTER_CHAIN_HEADER))
     end)
   end)
+
+  describe("order of execution", function()
+    it("filter plugins execute at the end of any existing filter chain", function()
+      local lua_plugin = {
+        name = "response-transformer",
+        route = { id = route.id },
+        config = {
+          add = {
+            headers = {
+              "X-Added-By-Lua-Plugin:1",
+              "X-Replace-Me:lua",
+              "X-Append-Me:lua",
+              "X-Remove-Me:lua",
+            },
+          }
+        }
+      }
+
+      local plugin = {
+        name = "response_transformer",
+        route = { id = route.id },
+        config = cjson.encode({
+          add = {
+            headers = {
+              "X-Added-First:plugin",
+              "X-Added-By-Filter-Plugin:1",
+              "X-Not-Removed-By-Filter-Chain:plugin",
+            },
+          },
+          append = {
+            headers = {
+              "X-Append-Me:plugin",
+            },
+          },
+          replace = {
+            headers = {
+              "X-Replace-Me:plugin",
+              "X-Replaced-By-Filter-Plugin:plugin",
+            },
+          },
+          remove = {
+            headers = {
+              "X-Remove-Me",
+              "X-Removed-By-Filter-Plugin",
+            },
+          },
+        }),
+      }
+
+      local res, header, assert_no_header
+      do
+        function header(name)
+          return assert.response(res).has.header(name)
+        end
+
+        function assert_no_header(name)
+          return assert.response(res).has.no.header(name)
+        end
+      end
+
+      create_plugin(plugin)
+      create_plugin(lua_plugin)
+
+      helpers.wait_for_all_config_update()
+      res = proxy:get("/status/200")
+      assert.response(res).has.status(200)
+
+      -- sanity
+      assert.equals("1", header("X-Added-By-Filter-Plugin"))
+      assert.equals("1", header("X-Added-By-Lua-Plugin"))
+      assert_no_header("X-Remove-Me")
+
+      assert.equals("plugin", header("X-Added-First"))
+
+      -- added by Lua plugin, filter plugin appends
+      assert.same({ "lua", "plugin" }, header("X-Append-Me"))
+
+      -- replaced last by filter plugin
+      assert.same("plugin", header("X-Replace-Me"))
+
+      -- not replaced, because it was not added
+      assert_no_header("X-Replaced-By-Filter-Plugin")
+
+      local filter_chain = {
+        route = { id = route.id },
+        filters = {
+          {
+            name = "response_transformer",
+            config = cjson.encode({
+              add = {
+                headers = {
+                  "X-Added-First:filter-chain",
+                  "X-Added-By-Filter-Chain:1",
+                  "X-Removed-By-Filter-Plugin:filter-chain",
+                  "X-Replaced-By-Filter-Plugin:filter-chain",
+                },
+              },
+              append = {
+                headers = {
+                  "X-Append-Me:filter-chain",
+                },
+              },
+              replace = {
+                headers = {
+                  "X-Replace-Me:filter-chain",
+                  "X-Replaced-By-Filter-Chain:filter-chain",
+                },
+              },
+              remove = {
+                headers = {
+                  "X-Not-Removed-By-Filter-Chain",
+                },
+              },
+            }),
+          }
+        }
+      }
+
+      create_filter_chain(filter_chain)
+      helpers.wait_for_all_config_update()
+      res = proxy:get("/status/200")
+      assert.response(res).has.status(200)
+
+      -- sanity
+      assert.equals("1", header("X-Added-By-Filter-Plugin"))
+      assert.equals("1", header("X-Added-By-Lua-Plugin"))
+      assert.equals("1", header("X-Added-By-Filter-Chain"))
+      assert_no_header("X-Remove-Me")
+
+      -- added first by the filter chain
+      assert.equals("filter-chain", header("X-Added-First"))
+
+      -- added by Lua, appended to by filter chain and filter plugin
+      assert.same({ "lua", "filter-chain", "plugin" }, header("X-Append-Me"))
+      -- added after the filter chain tried to remove it
+      assert.same("plugin", header("X-Not-Removed-By-Filter-Chain"))
+
+      -- replaced last by filter plugin
+      assert.same("plugin", header("X-Replace-Me"))
+
+      assert_no_header("X-Removed-By-Filter-Plugin")
+      assert.same("plugin", header("X-Replaced-By-Filter-Plugin"))
+    end)
+
+    it("filter plugins execute in a consistent order", function()
+      -- should always run first because `tests-01` < `tests-02`
+      local plugin_1 = {
+        name = "tests-01",
+        config = "name=first",
+        route = { id = route.id },
+      }
+
+      local plugin_2 = {
+        name = "tests-02",
+        config = "name=last",
+        route = { id = route.id },
+      }
+
+      for _, order_added in ipairs({
+        { plugin_1, plugin_2 },
+        { plugin_2, plugin_1 },
+      }) do
+        bp.plugins:truncate()
+
+        create_plugin(order_added[1])
+        create_plugin(order_added[2])
+
+        helpers.wait_for_all_config_update()
+        local res = proxy:get("/status/200", {
+          headers = {
+            ["X-PW-Phase"] = "request_headers",
+            ["X-PW-Test"] = "dump_config",
+          }
+        })
+
+        local body = assert.res_status(200, res)
+        assert.equals("name=first", body)
+      end
+    end)
+  end)
 end)
 
 end -- each strategy

spec/fixtures/proxy_wasm_filters/tests/src/test_http.rs

@@ -160,6 +160,10 @@ impl TestHttp {
                         return self.send_http_dispatch(config);
                     }
                     "update_metrics" => self.update_metrics(),
+                    "dump_config" => {
+                        let res = self.config.as_ref().map(|config| config.to_string());
+                        self.send_plain_response(StatusCode::OK, res.as_deref());
+                    }
                     _ => (),
                 }
             }

spec/fixtures/proxy_wasm_filters/tests/src/types.rs

@@ -19,6 +19,16 @@ impl FromStr for TestConfig {
     }
 }
 
+impl std::fmt::Display for TestConfig {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut values: Vec<String> = self.map.iter().map(|(k, v)| format!("{k}={v}")).collect();
+
+        values.sort();
+
+        write!(f, "{}", values.join(" "))
+    }
+}
+
 #[derive(Debug, Eq, PartialEq, enum_utils::FromStr)]
 #[enumeration(rename_all = "snake_case")]
 pub enum TestPhase {