fetch: reject file: URLs whose path cannot be read

src/runtime/webcore/fetch.rs

@@ -224,6 +224,42 @@ fn data_url_response(data_url_: DataURL, global_this: &JSGlobalObject) -> JSValu
     )
 }
 
+// ──────────────────────────────────────────────────────────────────────────
+// file: URLs
+// ──────────────────────────────────────────────────────────────────────────
+
+/// The `Response` for a `file:` URL wraps a blob that opens the file lazily, so
+/// `fetch()` itself has to check the path; otherwise a path that cannot be read
+/// still gets a 200 and the error only surfaces from the body reader. Returns
+/// the JS error for `fetch()` to reject with.
+///
+/// Only conditions under which the read is certain to fail are checked (the
+/// path does not stat, or is a directory). `stat` rather than an eager `open`:
+/// opening a FIFO or a device has side effects, and nothing here needs the fd.
+/// Files embedded in a standalone executable come back as byte-backed blobs,
+/// which have nothing on disk to check.
+fn file_url_unreadable_error(file_blob: &Blob, global_this: &JSGlobalObject) -> Option<JSValue> {
+    let store = file_blob.store()?;
+    let blob::store::Data::File(file) = &store.data else {
+        return None;
+    };
+    let PathOrFileDescriptor::Path(path) = &file.pathlike else {
+        return None;
+    };
+
+    let mut path_buf = bun_paths::path_buffer_pool::get();
+    let err = match bun_sys::stat(path.slice_z(&mut path_buf)) {
+        Ok(stat) if bun_sys::S::ISDIR(stat.st_mode as bun_sys::Mode) => {
+            bun_sys::Error::from_code(bun_sys::E::EISDIR, bun_sys::Tag::read)
+        }
+        Ok(_) => return None,
+        Err(err) => err,
+    };
+    // `stat` attached the scratch copy of the path (`\\?\`-prefixed on
+    // Windows); report the path as the blob holds it.
+    Some(err.with_path(path.slice()).to_js(global_this))
+}
+
 // ──────────────────────────────────────────────────────────────────────────
 // Bun__fetchPreconnect
 // ──────────────────────────────────────────────────────────────────────────
@@ -1553,8 +1589,6 @@ fn fetch_impl<const ALLOW_GET_BODY: bool>(
                 }
             };
 
-            url_string = jsc::URL::file_url_from_string(BunString::borrow_utf8(temp_file_path));
-
             // `find_or_create_file_from_path` is typed against the
             // `crate::webcore::node_types` stub (until it's swapped to a
             // re-export of `crate::node::types`); construct that variant here.
@@ -1564,7 +1598,17 @@ fn fetch_impl<const ALLOW_GET_BODY: bool>(
                 )),
             );
 
-            break 'blob Blob::find_or_create_file_from_path(&mut pathlike, global_this, true);
+            let file_blob = Blob::find_or_create_file_from_path(&mut pathlike, global_this, true);
+
+            if let Some(err) = file_url_unreadable_error(&file_blob, global_this) {
+                return Ok(JSPromise::rejected_promise(global_this, err).to_js());
+            }
+
+            // A bare +1 ref that only `Response::init` below releases, so it is
+            // created after the early return above.
+            url_string = jsc::URL::file_url_from_string(BunString::borrow_utf8(temp_file_path));
+
+            break 'blob file_blob;
         };
 
         let response = bun_core::heap::into_raw(Box::new(Response::init(

test/bundler/bundler_compile.test.ts

@@ -316,6 +316,21 @@ describe("bundler", () => {
     outfile: "dist/out",
     run: { stdout: "Hello, world!" },
   });
+  // fetch() rejects a file: URL whose path is not on disk. An embedded file
+  // only exists inside the executable, so it has to keep resolving.
+  itBundled("compile/FetchFileURLOfEmbeddedFile", {
+    compile: true,
+    files: {
+      "/entry.ts": /* js */ `
+        import { pathToFileURL } from "node:url";
+        import embedded from './foo.file' with {type: "file"};
+        const response = await fetch(pathToFileURL(embedded));
+        console.log(response.status, (await response.text()).trim());
+      `,
+      "/foo.file": `abcd`,
+    },
+    run: { stdout: "200 abcd" },
+  });
   itBundled("compile/WorkerRelativePathNoExtension", {
     backend: "cli",
     compile: true,

test/js/web/fetch/fetch-leak.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test";
-import { bunEnv, bunExe, tls as COMMON_CERT, gc, isASAN, isCI, isDebug } from "harness";
+import { bunEnv, bunExe, tls as COMMON_CERT, gc, isASAN, isCI, isDebug, tempDir } from "harness";
 import { once } from "node:events";
 import { createServer } from "node:http";
 import net from "node:net";
@@ -526,28 +526,36 @@ test.concurrent(
   async () => {
     // The leaked impl is "file://<resolved abs path>", and fetch_impl decodes
     // url.path into a stack PathBuffer that is 1024 bytes on macOS/BSD, 4096 on
-    // Linux, ~98 KiB on Windows. Use a ~900-byte path so decode_into succeeds on
-    // every platform and url_string is actually assigned, with enough iterations
-    // for the small per-call leak to show in RSS.
+    // Linux, ~98 KiB on Windows. Use a ~850-byte path so decode_into succeeds on
+    // every platform, with enough iterations for the small per-call leak to
+    // show in RSS. The file has to exist: fetch() rejects for a path that does
+    // not stat before url_string is ever created.
+    using dir = tempDir("fetch-file-url-leak", {});
     const script = /* js */ `
-    const pad = Buffer.alloc(900, "a").toString();
-    // Windows strips the leading "/" then asserts is_absolute_windows() in
-    // PosixToWinNormalizer under debug_assertions, which needs a drive letter.
-    const prefix = process.platform === "win32" ? "file:///C:/" : "file:///";
+    import { mkdirSync, writeFileSync } from "node:fs";
+    import { join } from "node:path";
+    import { pathToFileURL } from "node:url";
+
+    const component = Buffer.alloc(200, "a").toString();
+    const parent = join(process.cwd(), component, component, component, component);
+    mkdirSync(parent, { recursive: true });
+    const file = join(parent, "file.txt");
+    writeFileSync(file, "hello");
+    const url = pathToFileURL(file).href;
+
     const rss = process.platform === "darwin" && typeof Bun.unsafe.memoryFootprint === "function" ? Bun.unsafe.memoryFootprint : process.memoryUsage.rss;
-    async function hit(i) {
-      // Fresh path per iteration so each leaked ref pins a distinct impl.
-      // The file does not exist; the Response is created (with url_string set)
-      // and the lazy Blob body is never read, so no fs I/O happens.
-      await fetch(prefix + i + pad);
+    async function hit() {
+      // Every call builds a fresh url_string impl for the Response. The lazy
+      // Blob body is never read, so the Response is the only thing created.
+      await fetch(url);
     }
-    for (let i = 0; i < 200; i++) { try { await hit(-i); } catch {} }
+    for (let i = 0; i < 200; i++) await hit();
     Bun.gc(true);
     const baseline = rss();
 
     const ITERS = 20000;
     for (let i = 0; i < ITERS; i++) {
-      try { await hit(i); } catch {}
+      await hit();
       if ((i & 1023) === 0) Bun.gc(true);
     }
     Bun.gc(true);
@@ -559,15 +567,16 @@ test.concurrent(
       finalMB: (final / 1024 / 1024) | 0,
       deltaMB: Math.round(deltaMB * 10) / 10,
     }));
-    // ~0.9 KiB × 20000 ≈ 18 MiB raw leak (measured ~32 MiB on debug+ASAN)
-    // when the extra ref is dropped on the floor; ~12 MiB noise with the fix.
+    // ~0.85 KiB × 20000 ≈ 17 MiB raw leak (measured ~26 MiB on debug+ASAN)
+    // when the extra ref is dropped on the floor; ~11 MiB noise with the fix.
     if (deltaMB > 20) {
       throw new Error("fetch(file://) leaked " + deltaMB.toFixed(1) + " MB over " + ITERS + " iterations");
     }
   `;
 
     await using proc = Bun.spawn({
       cmd: [bunExe(), "--smol", "-e", script],
+      cwd: String(dir),
       env: {
         ...bunEnv,
         ASAN_OPTIONS: [bunEnv.ASAN_OPTIONS, "quarantine_size_mb=0"].filter(Boolean).join(":"),

test/js/web/fetch/fetch.test.ts

@@ -16,6 +16,7 @@ import {
   isWindows,
   rss,
   runFixtureMaxRSS,
+  tempDir,
   tls,
   tmpdirSync,
   withoutAggressiveGC,
@@ -27,6 +28,7 @@ import type { AddressInfo } from "net";
 import net from "net";
 import { join } from "path";
 import { Readable } from "stream";
+import { pathToFileURL } from "url";
 import { gzipSync } from "zlib";
 
 const tmp_dir = tmpdirSync();
@@ -1789,6 +1791,64 @@ it("fetch() file:// works", async () => {
   expect(fileResponseText).toEqual(bunFileText);
   gc(true);
 });
+
+describe.concurrent("fetch() file:// that cannot be read", () => {
+  // The file: branch keeps the URL's forward slashes in the path it reports,
+  // which only differs from path.join() on Windows.
+  const reportedPath = (p: string) => (isWindows ? p.replaceAll("\\", "/") : p);
+
+  it("rejects with ENOENT when the file does not exist", async () => {
+    using dir = tempDir("fetch-file-url", { "exists.txt": "exists" });
+    const missing = join(String(dir), "missing.txt");
+    const url = pathToFileURL(missing);
+
+    for (const input of [url.href, url, new Request(url)]) {
+      await expect(fetch(input)).rejects.toMatchObject({
+        code: "ENOENT",
+        syscall: "stat",
+        path: reportedPath(missing),
+      });
+    }
+
+    // A sibling that does exist is unaffected.
+    const response = await fetch(pathToFileURL(join(String(dir), "exists.txt")));
+    expect([response.status, await response.text()]).toEqual([200, "exists"]);
+  });
+
+  it("rejects with EISDIR when the path is a directory", async () => {
+    using dir = tempDir("fetch-file-url-dir", {});
+
+    await expect(fetch(pathToFileURL(String(dir)))).rejects.toMatchObject({
+      code: "EISDIR",
+      syscall: "read",
+      path: reportedPath(String(dir)),
+    });
+  });
+
+  it.skipIf(isWindows)("still resolves for special files such as /dev/null", async () => {
+    const response = await fetch("file:///dev/null");
+    expect([response.status, await response.text()]).toEqual([200, ""]);
+  });
+
+  it("reports the rejection as unhandled when nothing catches it", async () => {
+    using dir = tempDir("fetch-file-url-unhandled", {});
+    const missing = join(String(dir), "missing.txt");
+
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "-e", `fetch(${JSON.stringify(pathToFileURL(missing).href)});`],
+      env: bunEnv,
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+    expect(stdout).toBe("");
+    expect(stderr).toContain("ENOENT");
+    expect(stderr).toContain(reportedPath(missing));
+    expect(exitCode).toBe(1);
+  });
+});
+
 it("cloned response headers are independent before accessing", () => {
   const response = new Response("hello", {
     headers: {