fix: add warning about wrangler dev with remote Durable Objects (#687)

Durable Objects that are being bound by `script_name` will not be isolated from the
live data during development with `wrangler dev`.
This change simply warns the developer about this, so that they can back out before
accidentally changing live data.

Fixes #319

.changeset/four-bags-admire.md

@@ -0,0 +1,12 @@
+---
+"wrangler": patch
+---
+
+fix: add warning about `wrangler dev` with remote Durable Objects
+
+Durable Objects that are being bound by `script_name` will not be isolated from the
+live data during development with `wrangler dev`.
+This change simply warns the developer about this, so that they can back out before
+accidentally changing live data.
+
+Fixes #319

packages/wrangler/src/__tests__/dev.test.tsx

@@ -9,7 +9,7 @@ import { runInTempDir } from "./helpers/run-in-tmp";
 import { runWrangler } from "./helpers/run-wrangler";
 import writeWranglerToml from "./helpers/write-wrangler-toml";
 
-describe("Dev component", () => {
+describe("wrangler dev", () => {
   mockAccountId();
   mockApiToken();
   runInTempDir();
@@ -480,6 +480,42 @@ describe("Dev component", () => {
       expect(std.err).toMatchInlineSnapshot(`""`);
     });
   });
+
+  describe("durable_objects", () => {
+    it("should warn if there is one or more remote Durable Object", async () => {
+      writeWranglerToml({
+        main: "index.js",
+        durable_objects: {
+          bindings: [
+            { name: "NAME_1", class_name: "CLASS_1" },
+            {
+              name: "NAME_2",
+              class_name: "CLASS_2",
+              script_name: "SCRIPT_A",
+            },
+            { name: "NAME_3", class_name: "CLASS_3" },
+            {
+              name: "NAME_4",
+              class_name: "CLASS_4",
+              script_name: "SCRIPT_B",
+            },
+          ],
+        },
+      });
+      fs.writeFileSync("index.js", `export default {};`);
+      await runWrangler("dev");
+      expect((Dev as jest.Mock).mock.calls[0][0].ip).toEqual("localhost");
+      expect(std.out).toMatchInlineSnapshot(`""`);
+      expect(std.warn).toMatchInlineSnapshot(`
+        "WARNING: You have Durable Object bindings, which are not defined locally in the worker being developed.
+        Be aware that changes to the data stored in these Durable Objects will be permanent and affect the live instances.
+        Remote Durable Objects that are affected:
+        - {\\"name\\":\\"NAME_2\\",\\"class_name\\":\\"CLASS_2\\",\\"script_name\\":\\"SCRIPT_A\\"}
+        - {\\"name\\":\\"NAME_4\\",\\"class_name\\":\\"CLASS_4\\",\\"script_name\\":\\"SCRIPT_B\\"}"
+      `);
+      expect(std.err).toMatchInlineSnapshot(`""`);
+    });
+  });
 });
 
 function mockGetZones(domain: string, zones: { id: string }[] = []) {

packages/wrangler/src/entry.ts

@@ -20,7 +20,7 @@ export type Entry = { file: string; directory: string; format: CfScriptFormat };
 export async function getEntry(
   args: { script?: string; format?: CfScriptFormat | undefined },
   config: Config,
-  command: string
+  command: "dev" | "publish"
 ): Promise<Entry> {
   let file: string;
   let directory = process.cwd();
@@ -49,12 +49,24 @@ export async function getEntry(
     args.format ?? config.build?.upload?.format
   );
 
-  if (format === "service-worker" && hasDurableObjectImplementations(config)) {
+  const { localBindings, remoteBindings } =
+    partitionDurableObjectBindings(config);
+
+  if (command === "dev" && remoteBindings.length > 0) {
+    console.warn(
+      "WARNING: You have Durable Object bindings, which are not defined locally in the worker being developed.\n" +
+        "Be aware that changes to the data stored in these Durable Objects will be permanent and affect the live instances.\n" +
+        "Remote Durable Objects that are affected:\n" +
+        remoteBindings.map((b) => `- ${JSON.stringify(b)}`).join("\n")
+    );
+  }
+
+  if (format === "service-worker" && localBindings.length > 0) {
     const errorMessage =
       "You seem to be trying to use Durable Objects in a Worker written with Service Worker syntax.";
     const addScriptName =
       "You can use Durable Objects defined in other Workers by specifying a `script_name` in your wrangler.toml, where `script_name` is the name of the Worker that implements that Durable Object. For example:";
-    const addScriptNameExamples = generateAddScriptNameExamples(config);
+    const addScriptNameExamples = generateAddScriptNameExamples(localBindings);
     const migrateText =
       "Alternatively, migrate your worker to ES Module syntax to implement a Durable Object in this Worker:";
     const migrateUrl =
@@ -174,29 +186,41 @@ export function fileExists(filePath: string): boolean {
   return false;
 }
 
+type DurableObjectBindings = Config["durable_objects"]["bindings"];
+
 /**
- * Returns true if the given config contains Durable Object bindings that are implemented
- * in this worker instead of being implemented elsewhere, and bound via a `script_name`
- * property in wrangler.toml
+ * Groups the durable object bindings into two lists:
+ * those that are defined locally and those that refer to a durable object defined in another script.
  */
-function hasDurableObjectImplementations(config: Config): boolean {
-  return config.durable_objects.bindings.some(
-    (binding) => binding.script_name === undefined
-  );
+function partitionDurableObjectBindings(config: Config): {
+  localBindings: DurableObjectBindings;
+  remoteBindings: DurableObjectBindings;
+} {
+  const localBindings: DurableObjectBindings = [];
+  const remoteBindings: DurableObjectBindings = [];
+  for (const binding of config.durable_objects.bindings) {
+    if (binding.script_name === undefined) {
+      localBindings.push(binding);
+    } else {
+      remoteBindings.push(binding);
+    }
+  }
+  return { localBindings, remoteBindings };
 }
 
 /**
  * Generates some help text based on the Durable Object bindings in a given
  * config indicating how the user can add a `script_name` field to bind an
  * externally defined Durable Object.
  */
-function generateAddScriptNameExamples(config: Config): string {
+function generateAddScriptNameExamples(
+  localBindings: DurableObjectBindings
+): string {
   function exampleScriptName(binding_name: string): string {
     return `${binding_name.toLowerCase().replaceAll("_", "-")}-worker`;
   }
 
-  return config.durable_objects.bindings
-    .filter((binding) => binding.script_name === undefined)
+  return localBindings
     .map(({ name, class_name }) => {
       const script_name = exampleScriptName(name);
       const currentBinding = `{ name = ${name}, class_name = ${class_name} }`;