feat(windows): allow open and Bun.file() with /dev/null (oven-sh#8499)

* DEV NULL

* oops

* ok

src/bun.js/node/node_fs.zig

@@ -4486,7 +4486,11 @@ pub const NodeFS = struct {
     }
 
     pub fn open(this: *NodeFS, args: Arguments.Open, comptime _: Flavor) Maybe(Return.Open) {
-        const path = args.path.sliceZ(&this.sync_error_buf);
+        const path = if (Environment.isWindows and bun.strings.eqlComptime(args.path.slice(), "/dev/null"))
+            "\\\\.\\NUL"
+        else
+            args.path.sliceZ(&this.sync_error_buf);
+
         return switch (Syscall.open(path, @intFromEnum(args.flags), args.mode)) {
             .err => |err| .{
                 .err = err.withPath(args.path.slice()),

src/bun.js/webcore/blob.zig

@@ -1519,35 +1519,41 @@ pub const Blob = struct {
         return ptr.toJS(globalObject);
     }
 
-    pub fn findOrCreateFileFromPath(path_: *JSC.Node.PathOrFileDescriptor, globalThis: *JSGlobalObject) Blob {
+    pub fn findOrCreateFileFromPath(path_or_fd: *JSC.Node.PathOrFileDescriptor, globalThis: *JSGlobalObject) Blob {
         var vm = globalThis.bunVM();
         const allocator = bun.default_allocator;
 
         const path: JSC.Node.PathOrFileDescriptor = brk: {
-            switch (path_.*) {
+            switch (path_or_fd.*) {
                 .path => {
-                    const slice = path_.path.slice();
+                    const slice = path_or_fd.path.slice();
+
+                    if (Environment.isWindows and bun.strings.eqlComptime(slice, "/dev/null")) {
+                        // it is okay to use rodata here, because the '.string' case
+                        // in PathLike.deinit does not free anything.
+                        path_or_fd.* = .{ .path = .{ .string = bun.PathString.init("\\\\.\\NUL") } };
+                    }
 
                     if (vm.standalone_module_graph) |graph| {
                         if (graph.find(slice)) |file| {
                             defer {
-                                if (path_.path != .string) {
-                                    path_.deinit();
-                                    path_.* = .{ .path = .{ .string = bun.PathString.empty } };
+                                if (path_or_fd.path != .string) {
+                                    path_or_fd.deinit();
+                                    path_or_fd.* = .{ .path = .{ .string = bun.PathString.empty } };
                                 }
                             }
 
                             return file.blob(globalThis).dupe();
                         }
                     }
 
-                    path_.toThreadSafe();
-                    const copy = path_.*;
-                    path_.* = .{ .path = .{ .string = bun.PathString.empty } };
+                    path_or_fd.toThreadSafe();
+                    const copy = path_or_fd.*;
+                    path_or_fd.* = .{ .path = .{ .string = bun.PathString.empty } };
                     break :brk copy;
                 },
                 .fd => {
-                    switch (bun.FDTag.get(path_.fd)) {
+                    switch (bun.FDTag.get(path_or_fd.fd)) {
                         .stdin => return Blob.initWithStore(
                             vm.rareData().stdin(),
                             globalThis,
@@ -1562,7 +1568,7 @@ pub const Blob = struct {
                         ),
                         else => {},
                     }
-                    break :brk path_.*;
+                    break :brk path_or_fd.*;
                 },
             }
         };

test/js/bun/shell/leak.test.ts

@@ -4,7 +4,7 @@ import { $ } from "bun";
 import { describe, expect, test } from "bun:test";
 import { bunEnv } from "harness";
 import { appendFileSync, closeSync, openSync, writeFileSync } from "node:fs";
-import { tmpdir } from "os";
+import { tmpdir, devNull } from "os";
 import { join } from "path";
 import { TestBuilder } from "./util";
 
@@ -55,13 +55,13 @@ describe("fd leak", () => {
         await builder().quiet().run();
       }
 
-      const baseline = openSync("/dev/null", "r");
+      const baseline = openSync(devNull, "r");
       closeSync(baseline);
 
       for (let i = 0; i < runs; i++) {
         await builder().quiet().run();
       }
-      const fd = openSync("/dev/null", "r");
+      const fd = openSync(devNull, "r");
       closeSync(fd);
       expect(fd).toBe(baseline);
     }, 100_000);

test/js/bun/spawn/spawn-streaming-stdin.test.ts

@@ -3,13 +3,13 @@ import { it, test, expect } from "bun:test";
 import { spawn } from "bun";
 import { bunExe, bunEnv, gcTick } from "harness";
 import { closeSync, openSync } from "fs";
-import { tmpdir } from "node:os";
+import { tmpdir, devNull } from "node:os";
 import { join } from "path";
 import { unlinkSync } from "node:fs";
 
 const N = 100;
 test("spawn can write to stdin multiple chunks", async () => {
-  const maxFD = openSync("/dev/null", "w");
+  const maxFD = openSync(devNull, "w");
   for (let i = 0; i < N; i++) {
     var exited;
     await (async function () {
@@ -59,7 +59,7 @@ test("spawn can write to stdin multiple chunks", async () => {
   }
 
   closeSync(maxFD);
-  const newMaxFD = openSync("/dev/null", "w");
+  const newMaxFD = openSync(devNull, "w");
   closeSync(newMaxFD);
 
   // assert we didn't leak any file descriptors

test/js/bun/spawn/spawn-streaming-stdout.test.ts

@@ -3,6 +3,7 @@ import { it, test, expect } from "bun:test";
 import { spawn } from "bun";
 import { bunExe, bunEnv, gcTick } from "harness";
 import { closeSync, openSync } from "fs";
+import { devNull } from "os";
 
 test("spawn can read from stdout multiple chunks", async () => {
   gcTick(true);
@@ -35,11 +36,11 @@ test("spawn can read from stdout multiple chunks", async () => {
       await proc.exited;
     })();
     if (maxFD === -1) {
-      maxFD = openSync("/dev/null", "w");
+      maxFD = openSync(devNull, "w");
       closeSync(maxFD);
     }
   }
-  const newMaxFD = openSync("/dev/null", "w");
+  const newMaxFD = openSync(devNull, "w");
   closeSync(newMaxFD);
   expect(newMaxFD).toBe(maxFD);
 }, 60_000);

test/js/bun/util/bun-file-windows.test.ts

@@ -0,0 +1,16 @@
+import { openSync, closeSync } from "fs";
+import { open } from "fs/promises";
+
+test('Bun.file("/dev/null") works on windows', async () => {
+  expect(await Bun.file("/dev/null").arrayBuffer()).toHaveLength(0);
+});
+
+test('openSync("/dev/null") works on windows', async () => {
+  const handle = openSync("/dev/null", "r");
+  closeSync(handle);
+});
+
+test('open("/dev/null") works on windows', async () => {
+  const handle = await open("/dev/null", "r");
+  await handle.close();
+});