Add internal source-mapped error logging and breakpoint debugging

This change massively improves the debuggability of Miniflare's
internal Durable Objects. Uncaught errors throws by Durable Objects
will now be source-mapped and logged. `//# sourceURL` comments are
also added to all Miniflare internal scripts, allowing for breakpoint
debugging.

packages/miniflare/src/plugins/d1/index.ts

@@ -10,6 +10,7 @@ import { SharedBindings } from "../../workers";
 import {
   PersistenceSchema,
   Plugin,
+  SERVICE_LOOPBACK,
   getPersistPath,
   kProxyNodeBinding,
   migrateDatabase,
@@ -112,6 +113,10 @@ export const D1_PLUGIN: Plugin<
               name: SharedBindings.MAYBE_SERVICE_BLOBS,
               service: { name: D1_STORAGE_SERVICE_NAME },
             },
+            {
+              name: SharedBindings.MAYBE_SERVICE_LOOPBACK,
+              service: { name: SERVICE_LOOPBACK },
+            },
           ],
         },
       };

packages/miniflare/src/plugins/kv/index.ts

@@ -10,6 +10,7 @@ import { SharedBindings } from "../../workers";
 import {
   PersistenceSchema,
   Plugin,
+  SERVICE_LOOPBACK,
   getPersistPath,
   kProxyNodeBinding,
   migrateDatabase,
@@ -118,6 +119,10 @@ export const KV_PLUGIN: Plugin<
               name: SharedBindings.MAYBE_SERVICE_BLOBS,
               service: { name: KV_STORAGE_SERVICE_NAME },
             },
+            {
+              name: SharedBindings.MAYBE_SERVICE_LOOPBACK,
+              service: { name: SERVICE_LOOPBACK },
+            },
           ],
         },
       };

packages/miniflare/src/plugins/r2/index.ts

@@ -10,6 +10,7 @@ import { SharedBindings } from "../../workers";
 import {
   PersistenceSchema,
   Plugin,
+  SERVICE_LOOPBACK,
   getPersistPath,
   kProxyNodeBinding,
   migrateDatabase,
@@ -92,6 +93,10 @@ export const R2_PLUGIN: Plugin<
               name: SharedBindings.MAYBE_SERVICE_BLOBS,
               service: { name: R2_STORAGE_SERVICE_NAME },
             },
+            {
+              name: SharedBindings.MAYBE_SERVICE_LOOPBACK,
+              service: { name: SERVICE_LOOPBACK },
+            },
           ],
         },
       };

packages/miniflare/src/workers/core/proxy.worker.ts

@@ -1,6 +1,6 @@
 import assert from "node:assert";
 import { parse } from "devalue";
-import { readPrefix } from "miniflare:shared";
+import { readPrefix, reduceError } from "miniflare:shared";
 import {
   CoreHeaders,
   ProxyAddresses,
@@ -42,22 +42,6 @@ const WORKERS_PLATFORM_IMPL: PlatformImpl<ReadableStream> = {
   },
 };
 
-interface JsonError {
-  message?: string;
-  name?: string;
-  stack?: string;
-  cause?: JsonError;
-}
-
-function reduceError(e: any): JsonError {
-  return {
-    name: e?.name,
-    message: e?.message ?? String(e),
-    stack: e?.stack,
-    cause: e?.cause === undefined ? undefined : reduceError(e.cause),
-  };
-}
-
 // Helpers taken from `devalue` (unfortunately not exported):
 // https://github.com/Rich-Harris/devalue/blob/50af63e2b2c648f6e6ea29904a14faac25a581fc/src/utils.js#L31-L51
 const objectProtoNames = Object.getOwnPropertyNames(Object.prototype)

packages/miniflare/src/workers/shared/index.worker.ts

@@ -63,5 +63,5 @@ export type { DeferredPromiseResolve, DeferredPromiseReject } from "./sync";
 export { Timers } from "./timers.worker";
 export type { TimerHandle } from "./timers.worker";
 
-export { maybeApply } from "./types";
-export type { Awaitable, ValueOf } from "./types";
+export { maybeApply, reduceError } from "./types";
+export type { Awaitable, ValueOf, JsonError } from "./types";

packages/miniflare/src/workers/shared/object.worker.ts

@@ -4,6 +4,7 @@ import { LogLevel, SharedBindings, SharedHeaders } from "./constants";
 import { Router } from "./router.worker";
 import { TypedSql, all, createTypedSql, isTypedValue } from "./sql.worker";
 import { Timers } from "./timers.worker";
+import { reduceError } from "./types";
 
 export interface MiniflareDurableObjectEnv {
   // NOTE: "in-memory" storage is never in-memory. We always back simulator
@@ -127,15 +128,38 @@ export abstract class MiniflareDurableObject<
     this.#name = name;
 
     // Dispatch the request to the underlying router
-    const res = await super.fetch(req);
-    // Make sure we consume the request body if specified. Otherwise, calls
-    // which make requests to this object may hang and never resolve.
-    // See https://github.com/cloudflare/workerd/issues/960.
-    // Note `Router#fetch()` should never throw, returning 500 responses for
-    // unhandled exceptions.
-    if (req.body !== null && !req.bodyUsed) {
-      await req.body.pipeTo(new WritableStream());
+    try {
+      return await super.fetch(req);
+    } catch (e) {
+      // `HttpError`s are handled by `Router`. If we threw another error log it.
+      const error = reduceError(e);
+      const fallback = error.stack ?? error.message;
+
+      const loopbackService = this.env[SharedBindings.MAYBE_SERVICE_LOOPBACK];
+      if (loopbackService !== undefined) {
+        // If we have a connected loopback service, log a source mapped error
+        void loopbackService
+          .fetch("http://localhost/core/error", {
+            method: "POST",
+            body: JSON.stringify(error),
+          })
+          .catch(() => {
+            // ...falling back to `workerd` logging (requires `--verbose` flag)
+            console.error(fallback);
+          });
+      } else {
+        // Otherwise, just use `workerd`'s logging (requires `--verbose` flag)
+        console.error(fallback);
+      }
+
+      return new Response(fallback, { status: 500 });
+    } finally {
+      // Make sure we consume the request body if specified. Otherwise, calls
+      // which make requests to this object may hang and never resolve.
+      // See https://github.com/cloudflare/workerd/issues/960.
+      if (req.body !== null && !req.bodyUsed) {
+        await req.body.pipeTo(new WritableStream());
+      }
     }
-    return res;
   }
 }

packages/miniflare/src/workers/shared/router.worker.ts

@@ -42,11 +42,11 @@ export abstract class Router {
         if (match !== null) return await handlers[key](req, match.groups, url);
       }
       return new Response(null, { status: 404 });
-    } catch (e: any) {
+    } catch (e) {
       if (e instanceof HttpError) {
         return e.toResponse();
       }
-      return new Response(e?.stack ?? String(e), { status: 500 });
+      throw e;
     }
   }
 }

packages/miniflare/src/workers/shared/types.ts

@@ -3,6 +3,22 @@ export type Awaitable<T> = T | Promise<T>;
 // { a: A, b: B, ... } => A | B | ...
 export type ValueOf<T> = T[keyof T];
 
+export interface JsonError {
+  message?: string;
+  name?: string;
+  stack?: string;
+  cause?: JsonError;
+}
+
+export function reduceError(e: any): JsonError {
+  return {
+    name: e?.name,
+    message: e?.message ?? String(e),
+    stack: e?.stack,
+    cause: e?.cause === undefined ? undefined : reduceError(e.cause),
+  };
+}
+
 export function maybeApply<From, To>(
   f: (value: From) => To,
   maybeValue: From | undefined

scripts/build.mjs

@@ -1,4 +1,3 @@
-import assert from "assert";
 import fs from "fs/promises";
 import path from "path";
 import esbuild from "esbuild";
@@ -102,6 +101,8 @@ const embedWorkersPlugin = {
           format: "esm",
           target: "esnext",
           bundle: true,
+          sourcemap: true,
+          sourcesContent: false,
           external: ["miniflare:shared", "miniflare:zod"],
           metafile: true,
           incremental: watch, // Allow `rebuild()` calls if watching
@@ -134,11 +135,12 @@ const embedWorkersPlugin = {
       const contents = `
       import fs from "fs";
       import path from "path";
+      import url from "url";
       let contents;
       export default function() {
          if (contents !== undefined) return contents;
-         const filePath = path.join(__dirname, "workers", ${outPath})
-         contents = fs.readFileSync(filePath, "utf8");
+         const filePath = path.join(__dirname, "workers", ${outPath});
+         contents = fs.readFileSync(filePath, "utf8") + "//# sourceURL=" + url.pathToFileURL(filePath);
          return contents;
       }
       `;