src: report libuv error when openAsBlob cannot stat

`FdEntry::Create()` returned nullptr for any failed `uv_fs_stat()`,
discarding the status, and `BlobFromFilePath()` turned that into
`ERR_INVALID_ARG_VALUE: Unable to open file as blob`. A missing file is
not a malformed argument, and the resulting `TypeError` carried no
`errno`, `syscall`, or `path`, so ENOENT could not be told apart from
any other reason the path was unusable.

Thread the libuv status out of `CreateFdEntry()` and throw a
`UVException` instead, so `fs.openAsBlob()` reports the same error
`fs.stat()` does for the same path.

Fixes: #65514
Signed-off-by: Paul Bouchon <mail@bitpshr.net>
PR-URL: #65517
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: bitpshr

src/dataqueue/queue.cc

@@ -868,13 +868,19 @@ class FdEntry final : public EntryImpl {
   // the race
   //   condition described in the comment above.
  public:
-  static std::unique_ptr<FdEntry> Create(Environment* env, Local<Value> path) {
+  static std::unique_ptr<FdEntry> Create(Environment* env,
+                                         Local<Value> path,
+                                         int* status) {
     // We're only going to create the FdEntry if the file exists.
     uv_fs_t req = uv_fs_t();
     auto cleanup = OnScopeLeave([&] { uv_fs_req_cleanup(&req); });
 
     auto buf = std::make_shared<BufferValue>(env->isolate(), path);
-    if (uv_fs_stat(nullptr, &req, buf->out(), nullptr) < 0) return nullptr;
+    int err = uv_fs_stat(nullptr, &req, buf->out(), nullptr);
+    if (err < 0) {
+      if (status != nullptr) *status = err;
+      return nullptr;
+    }
 
     return std::make_unique<FdEntry>(
         env, std::move(buf), req.statbuf, 0, req.statbuf.st_size);
@@ -1183,8 +1189,9 @@ std::unique_ptr<DataQueue::Entry> DataQueue::CreateDataQueueEntry(
 }
 
 std::unique_ptr<DataQueue::Entry> DataQueue::CreateFdEntry(Environment* env,
-                                                           Local<Value> path) {
-  return FdEntry::Create(env, path);
+                                                           Local<Value> path,
+                                                           int* status) {
+  return FdEntry::Create(env, path, status);
 }
 
 void DataQueue::Initialize(Environment* env, v8::Local<v8::Object> target) {

src/dataqueue/queue.h

@@ -226,8 +226,11 @@ class DataQueue : public MemoryRetainer {
   static std::unique_ptr<Entry> CreateDataQueueEntry(
       std::shared_ptr<DataQueue> data_queue);
 
+  // Returns nullptr if the file cannot be stat'd. When `status` is given, it
+  // is set to the libuv error code so callers can report why.
   static std::unique_ptr<Entry> CreateFdEntry(Environment* env,
-                                              v8::Local<v8::Value> path);
+                                              v8::Local<v8::Value> path,
+                                              int* status = nullptr);
 
   // Creates a Reader for the given queue. If the queue is idempotent,
   // any number of readers can be created, all of which are guaranteed

src/node_blob.cc

@@ -110,9 +110,12 @@ void BlobFromFilePath(const FunctionCallbackInfo<Value>& args) {
   ToNamespacedPath(env, &path);
   THROW_IF_INSUFFICIENT_PERMISSIONS(
       env, permission::PermissionScope::kFileSystemRead, path.ToStringView());
-  auto entry = DataQueue::CreateFdEntry(env, args[0]);
+  int status = 0;
+  auto entry = DataQueue::CreateFdEntry(env, args[0], &status);
   if (entry == nullptr) {
-    return THROW_ERR_INVALID_ARG_VALUE(env, "Unable to open file as blob");
+    // The file could not be stat'd. Report the libuv error so callers can tell
+    // ENOENT apart from any other reason the path could not be used.
+    return env->ThrowUVException(status, "stat", nullptr, *path);
   }
 
   std::vector<std::unique_ptr<DataQueue::Entry>> entries;

test/parallel/test-blob-file-backed.js

@@ -129,6 +129,19 @@ writeFileSync(testfile5, '');
   await unlink(testfile5);
 })().then(common.mustCall());
 
+(async () => {
+  // A path that cannot be stat'd reports the underlying libuv error rather
+  // than a generic argument error, so ENOENT can be told apart from any other
+  // reason the file could not be used.
+  // Refs: https://github.com/nodejs/node/issues/65514
+  const missing = tmpdir.resolve('does-not-exist.txt');
+  await assert.rejects(async () => openAsBlob(missing), {
+    code: 'ENOENT',
+    syscall: 'stat',
+    path: missing,
+  });
+})().then(common.mustCall());
+
 (async () => {
   // We currently do not allow File-backed blobs to be cloned or transferred
   // across worker threads. This is largely because the underlying FdEntry