esm: improve getFormatOfExtensionlessFile perf.

lib/internal/modules/esm/formats.js

@@ -1,12 +1,11 @@
 'use strict';
 
-const {
-  RegExpPrototypeExec,
-  Uint8Array,
-} = primordials;
+const { RegExpPrototypeExec } = primordials;
 const { getOptionValue } = require('internal/options');
-
-const { closeSync, openSync, readSync } = require('fs');
+const { getValidatedPath } = require('internal/fs/utils');
+const pathModule = require('path');
+const fsBindings = internalBinding('fs');
+const { fs: fsConstants } = internalBinding('constants');
 
 const experimentalWasmModules = getOptionValue('--experimental-wasm-modules');
 
@@ -47,20 +46,14 @@ function mimeToFormat(mime) {
 function getFormatOfExtensionlessFile(url) {
   if (!experimentalWasmModules) { return 'module'; }
 
-  const magic = new Uint8Array(4);
-  let fd;
-  try {
-    // TODO(@anonrig): Optimize the following by having a single C++ call
-    fd = openSync(url);
-    readSync(fd, magic, 0, 4); // Only read the first four bytes
-    if (magic[0] === 0x00 && magic[1] === 0x61 && magic[2] === 0x73 && magic[3] === 0x6d) {
+  const path = pathModule.toNamespacedPath(getValidatedPath(url));
+
+  switch (fsBindings.getFormatOfExtensionlessFile(path)) {
+    case fsConstants.EXTENSIONLESS_FORMAT_WASM:
       return 'wasm';
-    }
-  } finally {
-    if (fd !== undefined) { closeSync(fd); }
+    default:
+      return 'module';
   }
-
-  return 'module';
 }
 
 module.exports = {

src/node_constants.cc

@@ -1058,6 +1058,10 @@ void DefineSystemConstants(Local<Object> target) {
   NODE_DEFINE_CONSTANT(target, UV_DIRENT_CHAR);
   NODE_DEFINE_CONSTANT(target, UV_DIRENT_BLOCK);
 
+  // Define module specific constants
+  NODE_DEFINE_CONSTANT(target, EXTENSIONLESS_FORMAT_JAVASCRIPT);
+  NODE_DEFINE_CONSTANT(target, EXTENSIONLESS_FORMAT_WASM);
+
   NODE_DEFINE_CONSTANT(target, S_IFMT);
   NODE_DEFINE_CONSTANT(target, S_IFREG);
   NODE_DEFINE_CONSTANT(target, S_IFDIR);

src/node_constants.h

@@ -27,6 +27,9 @@
 #include "node.h"
 #include "v8.h"
 
+#define EXTENSIONLESS_FORMAT_JAVASCRIPT (0)
+#define EXTENSIONLESS_FORMAT_WASM (1)
+
 #if HAVE_OPENSSL
 
 #ifndef RSA_PSS_SALTLEN_DIGEST

src/node_file.cc

@@ -2978,6 +2978,51 @@ static void Mkdtemp(const FunctionCallbackInfo<Value>& args) {
   }
 }
 
+static void GetFormatOfExtensionlessFile(
+    const FunctionCallbackInfo<Value>& args) {
+  CHECK_EQ(args.Length(), 1);
+  CHECK(args[0]->IsString());
+
+  Environment* env = Environment::GetCurrent(args);
+  node::Utf8Value input(args.GetIsolate(), args[0]);
+
+  THROW_IF_INSUFFICIENT_PERMISSIONS(
+      env, permission::PermissionScope::kFileSystemRead, input.ToStringView());
+
+  uv_fs_t req;
+  FS_SYNC_TRACE_BEGIN(open)
+  uv_file file = uv_fs_open(nullptr, &req, input.out(), O_RDONLY, 0, nullptr);
+  FS_SYNC_TRACE_END(open);
+
+  if (req.result < 0) {
+    return args.GetReturnValue().Set(EXTENSIONLESS_FORMAT_JAVASCRIPT);
+  }
+
+  auto cleanup = OnScopeLeave([&req, &file]() {
+    FS_SYNC_TRACE_BEGIN(close);
+    CHECK_EQ(0, uv_fs_close(nullptr, &req, file, nullptr));
+    FS_SYNC_TRACE_END(close);
+    uv_fs_req_cleanup(&req);
+  });
+
+  char buffer[4];
+  uv_buf_t buf = uv_buf_init(buffer, sizeof(buffer));
+  int err = uv_fs_read(nullptr, &req, file, &buf, 1, 0, nullptr);
+
+  if (err < 0) {
+    return args.GetReturnValue().Set(EXTENSIONLESS_FORMAT_JAVASCRIPT);
+  }
+
+  // We do this by taking advantage of the fact that all Wasm files start with
+  // the header `0x00 0x61 0x73 0x6d`
+  if (buffer[0] == 0x00 && buffer[1] == 0x61 && buffer[2] == 0x73 &&
+      buffer[3] == 0x6d) {
+    return args.GetReturnValue().Set(EXTENSIONLESS_FORMAT_WASM);
+  }
+
+  return args.GetReturnValue().Set(EXTENSIONLESS_FORMAT_JAVASCRIPT);
+}
+
 static bool FileURLToPath(
     Environment* env,
     const ada::url_aggregator& file_url,
@@ -3390,6 +3435,10 @@ static void CreatePerIsolateProperties(IsolateData* isolate_data,
                                        Local<ObjectTemplate> target) {
   Isolate* isolate = isolate_data->isolate();
 
+  SetMethod(isolate,
+            target,
+            "getFormatOfExtensionlessFile",
+            GetFormatOfExtensionlessFile);
   SetMethod(isolate, target, "access", Access);
   SetMethod(isolate, target, "accessSync", AccessSync);
   SetMethod(isolate, target, "close", Close);
@@ -3518,6 +3567,7 @@ void RegisterExternalReferences(ExternalReferenceRegistry* registry) {
   StatWatcher::RegisterExternalReferences(registry);
   BindingData::RegisterExternalReferences(registry);
 
+  registry->Register(GetFormatOfExtensionlessFile);
   registry->Register(Close);
   registry->Register(CloseSync);
   registry->Register(ExistsSync);

typings/internalBinding/constants.d.ts

@@ -186,6 +186,8 @@ export interface ConstantsBinding {
     COPYFILE_FICLONE: 2;
     UV_FS_COPYFILE_FICLONE_FORCE: 4;
     COPYFILE_FICLONE_FORCE: 4;
+    EXTENSIONLESS_FORMAT_JAVASCRIPT: 0;
+    EXTENSIONLESS_FORMAT_WASM: 1;
   };
   crypto: {
     OPENSSL_VERSION_NUMBER: 269488319;

typings/internalBinding/fs.d.ts

@@ -1,3 +1,5 @@
+import { ConstantsBinding } from './constants';
+
 declare namespace InternalFSBinding {
   class FSReqCallback<ResultType = unknown> {
     constructor(bigint?: boolean);
@@ -218,6 +220,8 @@ declare namespace InternalFSBinding {
   function writeString(fd: number, value: string, pos: unknown, encoding: unknown, req: FSReqCallback<number>): void;
   function writeString(fd: number, value: string, pos: unknown, encoding: unknown, req: undefined, ctx: FSSyncContext): number;
   function writeString(fd: number, value: string, pos: unknown, encoding: unknown, usePromises: typeof kUsePromises): Promise<number>;
+
+  function getFormatOfExtensionlessFile(url: string): ConstantsBinding['fs'];
 }
 
 export interface FsBinding {
@@ -269,4 +273,6 @@ export interface FsBinding {
   writeBuffer: typeof InternalFSBinding.writeBuffer;
   writeBuffers: typeof InternalFSBinding.writeBuffers;
   writeString: typeof InternalFSBinding.writeString;
+
+  getFormatOfExtensionlessFile: typeof InternalFSBinding.getFormatOfExtensionlessFile;
 }