src: throw error in LoadBuiltinModuleSource when reading fails

- Move the file reading code in LoadBuiltinModuleSource into
  util.h so that it can be reused by other C++ code, and
  return an error code from it when there is a failure for
  the caller to generate an error.
- Throw an error when reading local builtins fails in
  LoadBulitinModuleSource.

src/node_native_module.cc

@@ -205,33 +205,17 @@ MaybeLocal<String> NativeModuleLoader::LoadBuiltinModuleSource(Isolate* isolate,
 #ifdef NODE_BUILTIN_MODULES_PATH
   std::string filename = OnDiskFileName(id);
 
-  uv_fs_t req;
-  uv_file file =
-      uv_fs_open(nullptr, &req, filename.c_str(), O_RDONLY, 0, nullptr);
-  CHECK_GE(req.result, 0);
-  uv_fs_req_cleanup(&req);
-
-  auto defer_close = OnScopeLeave([file]() {
-    uv_fs_t close_req;
-    CHECK_EQ(0, uv_fs_close(nullptr, &close_req, file, nullptr));
-    uv_fs_req_cleanup(&close_req);
-  });
-
   std::string contents;
-  char buffer[4096];
-  uv_buf_t buf = uv_buf_init(buffer, sizeof(buffer));
-
-  while (true) {
-    const int r =
-        uv_fs_read(nullptr, &req, file, &buf, 1, contents.length(), nullptr);
-    CHECK_GE(req.result, 0);
-    uv_fs_req_cleanup(&req);
-    if (r <= 0) {
-      break;
-    }
-    contents.append(buf.base, r);
+  int r = ReadFileSync(&contents, filename.c_str());
+  if (r != 0) {
+    const std::string buf = SPrintF("Cannot read local builtin. %s: %s \"%s\"",
+                                    uv_err_name(r),
+                                    uv_strerror(r),
+                                    filename);
+    Local<String> message = OneByteString(isolate, buf.c_str());
+    isolate->ThrowException(v8::Exception::Error(message));
+    return MaybeLocal<String>();
   }
-
   return String::NewFromUtf8(
       isolate, contents.c_str(), v8::NewStringType::kNormal, contents.length());
 #else

src/util.cc

@@ -221,6 +221,39 @@ int WriteFileSync(v8::Isolate* isolate,
   return WriteFileSync(path, buf);
 }
 
+int ReadFileSync(std::string* result, const char* path) {
+  uv_fs_t req;
+  uv_file file = uv_fs_open(nullptr, &req, path, O_RDONLY, 0, nullptr);
+  if (req.result < 0) {
+    return req.result;
+  }
+  uv_fs_req_cleanup(&req);
+
+  auto defer_close = OnScopeLeave([file]() {
+    uv_fs_t close_req;
+    CHECK_EQ(0, uv_fs_close(nullptr, &close_req, file, nullptr));
+    uv_fs_req_cleanup(&close_req);
+  });
+
+  *result = std::string("");
+  char buffer[4096];
+  uv_buf_t buf = uv_buf_init(buffer, sizeof(buffer));
+
+  while (true) {
+    const int r =
+        uv_fs_read(nullptr, &req, file, &buf, 1, result->length(), nullptr);
+    if (req.result < 0) {
+      return req.result;
+    }
+    uv_fs_req_cleanup(&req);
+    if (r <= 0) {
+      break;
+    }
+    result->append(buf.base, r);
+  }
+  return 0;
+}
+
 void DiagnosticFilename::LocalTime(TIME_TYPE* tm_struct) {
 #ifdef _WIN32
   GetLocalTime(tm_struct);

src/util.h

@@ -812,6 +812,10 @@ std::unique_ptr<T> static_unique_pointer_cast(std::unique_ptr<U>&& ptr) {
 }
 
 #define MAYBE_FIELD_PTR(ptr, field) ptr == nullptr ? nullptr : &(ptr->field)
+
+// Returns a non-zero code if it fails to open or read the file,
+// aborts if it fails to close the file.
+int ReadFileSync(std::string* result, const char* path);
 }  // namespace node
 
 #endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS