From 2ffa9c59371b408b52c930a0ad59df43c146809e Mon Sep 17 00:00:00 2001
From: Nitzan Uziely <linkgoron@gmail.com>
Date: Fri, 5 Mar 2021 13:27:56 +0200
Subject: [PATCH] fs: improve fsPromises readFile performance

Improve the fsPromises readFile performance
by allocating only one buffer, when size is known,
increase the size of the readbuffer chunks,
and dont read more data if size bytes have been read

Refs: https://github.com/nodejs/node/issues/37583
PR-URL: https://github.com/nodejs/node/pull/37608
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
---
 lib/internal/fs/promises.js                   | 45 ++++++++++++++-----
 .../test-fs-promises-file-handle-readFile.js  | 15 ++++---
 2 files changed, 44 insertions(+), 16 deletions(-)

diff --git a/lib/internal/fs/promises.js b/lib/internal/fs/promises.js
index 733d3f2c99285d..a3de33c45c52d0 100644
--- a/lib/internal/fs/promises.js
+++ b/lib/internal/fs/promises.js
@@ -3,6 +3,7 @@
 const kWriteFileMaxChunkSize = 2 ** 14;
 
 const {
+  ArrayPrototypePush,
   Error,
   MathMax,
   MathMin,
@@ -292,24 +293,46 @@ async function readFileHandle(filehandle, options) {
   if (size > kIoMaxLength)
     throw new ERR_FS_FILE_TOO_LARGE(size);
 
-  const chunks = [];
-  const chunkSize = size === 0 ?
-    kReadFileMaxChunkSize :
-    MathMin(size, kReadFileMaxChunkSize);
   let endOfFile = false;
+  let totalRead = 0;
+  const noSize = size === 0;
+  const buffers = [];
+  const fullBuffer = noSize ? undefined : Buffer.allocUnsafeSlow(size);
   do {
     if (signal && signal.aborted) {
       throw lazyDOMException('The operation was aborted', 'AbortError');
     }
-    const buf = Buffer.alloc(chunkSize);
-    const { bytesRead, buffer } =
-      await read(filehandle, buf, 0, chunkSize, -1);
-    endOfFile = bytesRead === 0;
-    if (bytesRead > 0)
-      chunks.push(buffer.slice(0, bytesRead));
+    let buffer;
+    let offset;
+    let length;
+    if (noSize) {
+      buffer = Buffer.allocUnsafeSlow(kReadFileUnknownBufferLength);
+      offset = 0;
+      length = kReadFileUnknownBufferLength;
+    } else {
+      buffer = fullBuffer;
+      offset = totalRead;
+      length = MathMin(size - totalRead, kReadFileBufferLength);
+    }
+
+    const bytesRead = (await binding.read(filehandle.fd, buffer, offset,
+                                          length, -1, kUsePromises)) || 0;
+    totalRead += bytesRead;
+    endOfFile = bytesRead === 0 || totalRead === size;
+    if (noSize && bytesRead > 0) {
+      const isBufferFull = bytesRead === kReadFileUnknownBufferLength;
+      const chunkBuffer = isBufferFull ? buffer : buffer.slice(0, bytesRead);
+      ArrayPrototypePush(buffers, chunkBuffer);
+    }
   } while (!endOfFile);
 
-  const result = chunks.length === 1 ? chunks[0] : Buffer.concat(chunks);
+  let result;
+  if (size > 0) {
+    result = totalRead === size ? fullBuffer : fullBuffer.slice(0, totalRead);
+  } else {
+    result = buffers.length === 1 ? buffers[0] : Buffer.concat(buffers,
+                                                               totalRead);
+  }
 
   return options.encoding ? result.toString(options.encoding) : result;
 }
diff --git a/test/parallel/test-fs-promises-file-handle-readFile.js b/test/parallel/test-fs-promises-file-handle-readFile.js
index 367391244eace9..3a178f7f37ff25 100644
--- a/test/parallel/test-fs-promises-file-handle-readFile.js
+++ b/test/parallel/test-fs-promises-file-handle-readFile.js
@@ -11,7 +11,7 @@ const {
   open,
   readFile,
   writeFile,
-  truncate
+  truncate,
 } = fs.promises;
 const path = require('path');
 const tmpdir = require('../common/tmpdir');
@@ -65,6 +65,7 @@ async function doReadAndCancel() {
     await assert.rejects(readFile(fileHandle, { signal }), {
       name: 'AbortError'
     });
+    await fileHandle.close();
   }
 
   // Signal aborted on first tick
@@ -75,10 +76,11 @@ async function doReadAndCancel() {
     fs.writeFileSync(filePathForHandle, buffer);
     const controller = new AbortController();
     const { signal } = controller;
-    tick(1, () => controller.abort());
+    process.nextTick(() => controller.abort());
     await assert.rejects(readFile(fileHandle, { signal }), {
       name: 'AbortError'
-    });
+    }, 'tick-0');
+    await fileHandle.close();
   }
 
   // Signal aborted right before buffer read
@@ -91,10 +93,12 @@ async function doReadAndCancel() {
 
     const controller = new AbortController();
     const { signal } = controller;
-    tick(2, () => controller.abort());
+    tick(1, () => controller.abort());
     await assert.rejects(fileHandle.readFile({ signal, encoding: 'utf8' }), {
       name: 'AbortError'
-    });
+    }, 'tick-1');
+
+    await fileHandle.close();
   }
 
   // Validate file size is within range for reading
@@ -112,6 +116,7 @@ async function doReadAndCancel() {
       name: 'RangeError',
       code: 'ERR_FS_FILE_TOO_LARGE'
     });
+    await fileHandle.close();
   }
 }