From ea69fbc04d17326260180df2afed99ab3e199413 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
---
 lib/internal/fs/promises.js                   | 50 +++++++++++++------
 .../test-fs-promises-file-handle-readFile.js  | 15 ++++--
 2 files changed, 45 insertions(+), 20 deletions(-)

diff --git a/lib/internal/fs/promises.js b/lib/internal/fs/promises.js
index 32ad2123d47db0..aa927a3dff575d 100644
--- a/lib/internal/fs/promises.js
+++ b/lib/internal/fs/promises.js
@@ -4,9 +4,8 @@
 // See https://github.com/libuv/libuv/pull/1501.
 const kIoMaxLength = 2 ** 31 - 1;
 
-// Note: This is different from kReadFileBufferLength used for non-promisified
-// fs.readFile.
-const kReadFileMaxChunkSize = 2 ** 14;
+const kReadFileBufferLength = 512 * 1024;
+const kReadFileUnknownBufferLength = 64 * 1024;
 const kWriteFileMaxChunkSize = 2 ** 14;
 
 const {
@@ -316,25 +315,46 @@ async function readFileHandle(filehandle, options) {
   if (size > kIoMaxLength)
     throw new ERR_FS_FILE_TOO_LARGE(size);
 
-  const chunks = [];
-  let isFirstChunk = true;
-  const firstChunkSize = size === 0 ? kReadFileMaxChunkSize : size;
-  const chunkSize = MathMin(firstChunkSize, kReadFileMaxChunkSize);
   let endOfFile = false;
+  let totalRead = 0;
+  const noSize = size === 0;
+  const buffers = [];
+  const fullBuffer = noSize ? undefined : Buffer.allocUnsafeSlow(size);
   do {
     if (signal?.aborted) {
       throw lazyDOMException('The operation was aborted', 'AbortError');
     }
-    const buf = Buffer.alloc(isFirstChunk ? firstChunkSize : chunkSize);
-    const { bytesRead, buffer } =
-      await read(filehandle, buf, 0, buf.length, -1);
-    endOfFile = bytesRead === 0;
-    if (bytesRead > 0)
-      ArrayPrototypePush(chunks, buffer.slice(0, bytesRead));
-    isFirstChunk = false;
+    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 d1e724d201ee71..66dc8f0fb0e0a1 100644
--- a/test/parallel/test-fs-promises-file-handle-readFile.js
+++ b/test/parallel/test-fs-promises-file-handle-readFile.js
@@ -10,7 +10,7 @@ const {
   open,
   readFile,
   writeFile,
-  truncate
+  truncate,
 } = fs.promises;
 const path = require('path');
 const tmpdir = require('../common/tmpdir');
@@ -64,6 +64,7 @@ async function doReadAndCancel() {
     await assert.rejects(readFile(fileHandle, { signal }), {
       name: 'AbortError'
     });
+    await fileHandle.close();
   }
 
   // Signal aborted on first tick
@@ -74,10 +75,11 @@ 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
@@ -90,10 +92,12 @@ 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
@@ -111,6 +115,7 @@ async function doReadAndCancel() {
       name: 'RangeError',
       code: 'ERR_FS_FILE_TOO_LARGE'
     });
+    await fileHandle.close();
   }
 }