fs: refactor stats array to be more generic

- Pass kFsStatsFieldsLength between JS and C++ instead of using the
  magic number 14
- Pass the global stats array to the completion callback of
  asynchronous FSReqWrap similar to how the stats arrays are passed
  to the FSReqPromise resolvers
- Abstract the stats converter and take an offset to compute the
  old stats in fs.watchFile
- Use templates in node::FillStatsArray and FSReqPromise in preparation
  for BigInt intergration
- Put the global stat array filler in node_internals.h because it is
  shared by node_file.cc and node_stat_watcher.cc

PR-URL: #19714
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: joyeecheung

lib/fs.js

@@ -43,7 +43,7 @@ const {
 } = errors.codes;
 const { Readable, Writable } = require('stream');
 const EventEmitter = require('events');
-const { FSReqWrap, statValues } = binding;
+const { FSReqWrap, statValues, kFsStatsFieldsLength } = binding;
 const { FSEvent } = process.binding('fs_event_wrap');
 const internalFS = require('internal/fs');
 const { getPathFromURL } = require('internal/url');
@@ -56,7 +56,8 @@ const {
   nullCheck,
   preprocessSymlinkDestination,
   Stats,
-  statsFromValues,
+  getStatsFromBinding,
+  getStatsFromGlobalBinding,
   stringToFlags,
   stringToSymlinkType,
   toUnixTimestamp,
@@ -145,9 +146,9 @@ function makeStatsCallback(cb) {
     throw new ERR_INVALID_CALLBACK();
   }
 
-  return function(err) {
+  return function(err, stats) {
     if (err) return cb(err);
-    cb(err, statsFromValues());
+    cb(err, getStatsFromBinding(stats));
   };
 }
 
@@ -891,7 +892,7 @@ fs.fstatSync = function(fd) {
   const ctx = { fd };
   binding.fstat(fd, undefined, ctx);
   handleErrorFromBinding(ctx);
-  return statsFromValues();
+  return getStatsFromGlobalBinding();
 };
 
 fs.lstatSync = function(path) {
@@ -900,7 +901,7 @@ fs.lstatSync = function(path) {
   const ctx = { path };
   binding.lstat(pathModule.toNamespacedPath(path), undefined, ctx);
   handleErrorFromBinding(ctx);
-  return statsFromValues();
+  return getStatsFromGlobalBinding();
 };
 
 fs.statSync = function(path) {
@@ -909,7 +910,7 @@ fs.statSync = function(path) {
   const ctx = { path };
   binding.stat(pathModule.toNamespacedPath(path), undefined, ctx);
   handleErrorFromBinding(ctx);
-  return statsFromValues();
+  return getStatsFromGlobalBinding();
 };
 
 fs.readlink = function(path, options, callback) {
@@ -1420,15 +1421,6 @@ function emitStop(self) {
   self.emit('stop');
 }
 
-function statsFromPrevValues() {
-  return new Stats(statValues[14], statValues[15], statValues[16],
-                   statValues[17], statValues[18], statValues[19],
-                   statValues[20] < 0 ? undefined : statValues[20],
-                   statValues[21], statValues[22],
-                   statValues[23] < 0 ? undefined : statValues[23],
-                   statValues[24], statValues[25], statValues[26],
-                   statValues[27]);
-}
 function StatWatcher() {
   EventEmitter.call(this);
 
@@ -1439,13 +1431,14 @@ function StatWatcher() {
   // the sake of backwards compatibility
   var oldStatus = -1;
 
-  this._handle.onchange = function(newStatus) {
+  this._handle.onchange = function(newStatus, stats) {
     if (oldStatus === -1 &&
         newStatus === -1 &&
         statValues[2/* new nlink */] === statValues[16/* old nlink */]) return;
 
     oldStatus = newStatus;
-    self.emit('change', statsFromValues(), statsFromPrevValues());
+    self.emit('change', getStatsFromBinding(stats),
+              getStatsFromBinding(stats, kFsStatsFieldsLength));
   };
 
   this._handle.onstop = function() {

lib/fs/promises.js

@@ -23,11 +23,11 @@ const { isUint8Array } = require('internal/util/types');
 const {
   copyObject,
   getOptions,
+  getStatsFromBinding,
   isUint32,
   modeNum,
   nullCheck,
   preprocessSymlinkDestination,
-  statsFromValues,
   stringToFlags,
   stringToSymlinkType,
   toUnixTimestamp,
@@ -332,21 +332,24 @@ async function symlink(target, path, type_) {
 
 async function fstat(handle) {
   validateFileHandle(handle);
-  return statsFromValues(await binding.fstat(handle.fd, kUsePromises));
+  const result = await binding.fstat(handle.fd, kUsePromises);
+  return getStatsFromBinding(result);
 }
 
 async function lstat(path) {
   path = getPathFromURL(path);
   validatePath(path);
-  return statsFromValues(
-    await binding.lstat(pathModule.toNamespacedPath(path), kUsePromises));
+  const result = await binding.lstat(pathModule.toNamespacedPath(path),
+                                     kUsePromises);
+  return getStatsFromBinding(result);
 }
 
 async function stat(path) {
   path = getPathFromURL(path);
   validatePath(path);
-  return statsFromValues(
-    await binding.stat(pathModule.toNamespacedPath(path), kUsePromises));
+  const result = await binding.stat(pathModule.toNamespacedPath(path),
+                                    kUsePromises);
+  return getStatsFromBinding(result);
 }
 
 async function link(existingPath, newPath) {

lib/internal/fs.js

@@ -134,6 +134,10 @@ function preprocessSymlinkDestination(path, type, linkPath) {
   }
 }
 
+function dateFromNumeric(num) {
+  return new Date(num + 0.5);
+}
+
 // Constructor for file stats.
 function Stats(
   dev,
@@ -165,10 +169,10 @@ function Stats(
   this.mtimeMs = mtim_msec;
   this.ctimeMs = ctim_msec;
   this.birthtimeMs = birthtim_msec;
-  this.atime = new Date(atim_msec + 0.5);
-  this.mtime = new Date(mtim_msec + 0.5);
-  this.ctime = new Date(ctim_msec + 0.5);
-  this.birthtime = new Date(birthtim_msec + 0.5);
+  this.atime = dateFromNumeric(atim_msec);
+  this.mtime = dateFromNumeric(mtim_msec);
+  this.ctime = dateFromNumeric(ctim_msec);
+  this.birthtime = dateFromNumeric(birthtim_msec);
 }
 
 Stats.prototype._checkModeProperty = function(property) {
@@ -203,11 +207,18 @@ Stats.prototype.isSocket = function() {
   return this._checkModeProperty(S_IFSOCK);
 };
 
-function statsFromValues(stats = statValues) {
-  return new Stats(stats[0], stats[1], stats[2], stats[3], stats[4], stats[5],
-                   stats[6] < 0 ? undefined : stats[6], stats[7], stats[8],
-                   stats[9] < 0 ? undefined : stats[9], stats[10], stats[11],
-                   stats[12], stats[13]);
+function getStatsFromBinding(stats, offset = 0) {
+  return new Stats(stats[0 + offset], stats[1 + offset], stats[2 + offset],
+                   stats[3 + offset], stats[4 + offset], stats[5 + offset],
+                   stats[6 + offset] < 0 ? undefined : stats[6 + offset],
+                   stats[7 + offset], stats[8 + offset],
+                   stats[9 + offset] < 0 ? undefined : stats[9 + offset],
+                   stats[10 + offset], stats[11 + offset],
+                   stats[12 + offset], stats[13 + offset]);
+}
+
+function getStatsFromGlobalBinding(offset = 0) {
+  return getStatsFromBinding(statValues, offset);
 }
 
 function stringToFlags(flags) {
@@ -424,7 +435,8 @@ module.exports = {
   nullCheck,
   preprocessSymlinkDestination,
   realpathCacheKey: Symbol('realpathCacheKey'),
-  statsFromValues,
+  getStatsFromBinding,
+  getStatsFromGlobalBinding,
   stringToFlags,
   stringToSymlinkType,
   Stats,

src/env.cc

@@ -104,7 +104,7 @@ Environment::Environment(IsolateData* isolate_data,
 #endif
       handle_cleanup_waiting_(0),
       http_parser_buffer_(nullptr),
-      fs_stats_field_array_(isolate_, kFsStatsFieldsLength),
+      fs_stats_field_array_(isolate_, kFsStatsFieldsLength * 2),
       context_(context->GetIsolate(), context) {
   // We'll be creating new objects so make sure we've entered the context.
   v8::HandleScope handle_scope(isolate());

src/env.h

@@ -644,6 +644,10 @@ class Environment {
 
   inline AliasedBuffer<double, v8::Float64Array>* fs_stats_field_array();
 
+  // stat fields contains twice the number of entries because `fs.StatWatcher`
+  // needs room to store data for *two* `fs.Stats` instances.
+  static const int kFsStatsFieldsLength = 14;
+
   inline std::vector<std::unique_ptr<fs::FileHandleReadWrap>>&
       file_handle_read_wrap_freelist();
 
@@ -822,9 +826,6 @@ class Environment {
   bool http_parser_buffer_in_use_ = false;
   std::unique_ptr<http2::http2_state> http2_state_;
 
-  // stat fields contains twice the number of entries because `fs.StatWatcher`
-  // needs room to store data for *two* `fs.Stats` instances.
-  static const int kFsStatsFieldsLength = 2 * 14;
   AliasedBuffer<double, v8::Float64Array> fs_stats_field_array_;
 
   std::vector<std::unique_ptr<fs::FileHandleReadWrap>>