fs: add support for AbortSignal in readFile

PR-URL: #35911
Backport-PR-URL: #38386
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

doc/api/fs.md

@@ -3026,6 +3026,10 @@ If `options.withFileTypes` is set to `true`, the result will contain
 <!-- YAML
 added: v0.1.29
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/35911
+    description: The options argument may include an AbortSignal to abort an
+                 ongoing readFile request.
   - version: v10.0.0
     pr-url: https://github.com/nodejs/node/pull/12562
     description: The `callback` parameter is no longer optional. Not passing
@@ -3051,6 +3055,7 @@ changes:
 * `options` {Object|string}
   * `encoding` {string|null} **Default:** `null`
   * `flag` {string} See [support of file system `flags`][]. **Default:** `'r'`.
+  * `signal` {AbortSignal} allows aborting an in-progress readFile
 * `callback` {Function}
   * `err` {Error}
   * `data` {string|Buffer}
@@ -3092,9 +3097,25 @@ fs.readFile('<directory>', (err, data) => {
 });
 ```
 
+It is possible to abort an ongoing request using an `AbortSignal`. If a
+request is aborted the callback is called with an `AbortError`:
+
+```js
+const controller = new AbortController();
+const signal = controller.signal;
+fs.readFile(fileInfo[0].name, { signal }, (err, buf) => {
+  // ...
+});
+// When you want to abort the request
+controller.abort();
+```
+
 The `fs.readFile()` function buffers the entire file. To minimize memory costs,
 when possible prefer streaming via `fs.createReadStream()`.
 
+Aborting an ongoing request does not abort individual operating
+system requests but rather the internal buffering `fs.readFile` performs.
+
 ### File descriptors
 
 1. Any specified file descriptor has to support reading.
@@ -4748,6 +4769,7 @@ added: v10.0.0
 
 * `options` {Object|string}
   * `encoding` {string|null} **Default:** `null`
+  * `signal` {AbortSignal} allows aborting an in-progress readFile
 * Returns: {Promise}
 
 Asynchronously reads the entire contents of a file.
@@ -5411,12 +5433,18 @@ print('./').catch(console.error);
 ### `fsPromises.readFile(path[, options])`
 <!-- YAML
 added: v10.0.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/35911
+    description: The options argument may include an AbortSignal to abort an
+                 ongoing readFile request.
 -->
 
 * `path` {string|Buffer|URL|FileHandle} filename or `FileHandle`
 * `options` {Object|string}
   * `encoding` {string|null} **Default:** `null`
   * `flag` {string} See [support of file system `flags`][]. **Default:** `'r'`.
+  * `signal` {AbortSignal} allows aborting an in-progress readFile
 * Returns: {Promise}
 
 Asynchronously reads the entire contents of a file.
@@ -5432,6 +5460,20 @@ platform-specific. On macOS, Linux, and Windows, the promise will be rejected
 with an error. On FreeBSD, a representation of the directory's contents will be
 returned.
 
+It is possible to abort an ongoing `readFile` using an `AbortSignal`. If a
+request is aborted the promise returned is rejected with an `AbortError`:
+
+```js
+const controller = new AbortController();
+const signal = controller.signal;
+readFile(fileName, { signal }).then((file) => { /* ... */ });
+// Abort the request
+controller.abort();
+```
+
+Aborting an ongoing request does not abort individual operating
+system requests but rather the internal buffering `fs.readFile` performs.
+
 Any specified `FileHandle` has to support reading.
 
 ### `fsPromises.readlink(path[, options])`

lib/fs.js

@@ -316,6 +316,9 @@ function readFile(path, options, callback) {
   const context = new ReadFileContext(callback, options.encoding);
   context.isUserFd = isFd(path); // File descriptor ownership
 
+  if (options.signal) {
+    context.signal = options.signal;
+  }
   if (context.isUserFd) {
     process.nextTick(function tick(context) {
       readFileAfterOpen.call({ context }, null, path);

lib/internal/fs/promises.js

@@ -30,12 +30,14 @@ const {
 } = internalBinding('constants').fs;
 const binding = internalBinding('fs');
 const { Buffer } = require('buffer');
+
+const { codes, hideStackFrames } = require('internal/errors');
 const {
   ERR_FS_FILE_TOO_LARGE,
   ERR_INVALID_ARG_TYPE,
   ERR_INVALID_ARG_VALUE,
-  ERR_METHOD_NOT_IMPLEMENTED
-} = require('internal/errors').codes;
+  ERR_METHOD_NOT_IMPLEMENTED,
+} = codes;
 const { isArrayBufferView } = require('internal/util/types');
 const { rimrafPromises } = require('internal/fs/rimraf');
 const {
@@ -83,6 +85,13 @@ const {
 const getDirectoryEntriesPromise = promisify(getDirents);
 const validateRmOptionsPromise = promisify(validateRmOptions);
 
+let DOMException;
+const lazyDOMException = hideStackFrames((message, name) => {
+  if (DOMException === undefined)
+    DOMException = internalBinding('messaging').DOMException;
+  return new DOMException(message, name);
+});
+
 class FileHandle extends JSTransferable {
   constructor(filehandle) {
     super();
@@ -260,8 +269,17 @@ async function writeFileHandle(filehandle, data) {
 }
 
 async function readFileHandle(filehandle, options) {
+  const signal = options && options.signal;
+
+  if (signal && signal.aborted) {
+    throw lazyDOMException('The operation was aborted', 'AbortError');
+  }
   const statFields = await binding.fstat(filehandle.fd, false, kUsePromises);
 
+  if (signal && signal.aborted) {
+    throw lazyDOMException('The operation was aborted', 'AbortError');
+  }
+
   let size;
   if ((statFields[1/* mode */] & S_IFMT) === S_IFREG) {
     size = statFields[8/* size */];
@@ -278,6 +296,9 @@ async function readFileHandle(filehandle, options) {
     MathMin(size, kReadFileMaxChunkSize);
   let endOfFile = false;
   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);

lib/internal/fs/read_file_context.js

@@ -8,6 +8,16 @@ const { Buffer } = require('buffer');
 
 const { FSReqCallback, close, read } = internalBinding('fs');
 
+const { hideStackFrames } = require('internal/errors');
+
+
+let DOMException;
+const lazyDOMException = hideStackFrames((message, name) => {
+  if (DOMException === undefined)
+    DOMException = internalBinding('messaging').DOMException;
+  return new DOMException(message, name);
+});
+
 // Use 64kb in case the file type is not a regular file and thus do not know the
 // actual file size. Increasing the value further results in more frequent over
 // allocation for small files and consumes CPU time and memory that should be
@@ -74,13 +84,19 @@ class ReadFileContext {
     this.pos = 0;
     this.encoding = encoding;
     this.err = null;
+    this.signal = undefined;
   }
 
   read() {
     let buffer;
     let offset;
     let length;
 
+    if (this.signal && this.signal.aborted) {
+      return this.close(
+        lazyDOMException('The operation was aborted', 'AbortError')
+      );
+    }
     if (this.size === 0) {
       buffer = Buffer.allocUnsafeSlow(kReadFileUnknownBufferLength);
       offset = 0;

lib/internal/fs/utils.js

@@ -37,6 +37,7 @@ const {
 const { once } = require('internal/util');
 const { toPathIfFileURL } = require('internal/url');
 const {
+  validateAbortSignal,
   validateBoolean,
   validateInt32,
   validateUint32
@@ -297,6 +298,10 @@ function getOptions(options, defaultOptions) {
 
   if (options.encoding !== 'buffer')
     assertEncoding(options.encoding);
+
+  if (options.signal !== undefined) {
+    validateAbortSignal(options.signal, 'options.signal');
+  }
   return options;
 }
 

test/parallel/test-fs-promises-readfile.js

@@ -1,3 +1,4 @@
+// Flags: --experimental-abortcontroller
 'use strict';
 
 const common = require('../common');
@@ -10,18 +11,21 @@ tmpdir.refresh();
 
 const fn = path.join(tmpdir.path, 'large-file');
 
-async function validateReadFile() {
-  // Creating large buffer with random content
-  const buffer = Buffer.from(
-    Array.apply(null, { length: 16834 * 2 })
-      .map(Math.random)
-      .map((number) => (number * (1 << 8)))
-  );
+// Creating large buffer with random content
+const largeBuffer = Buffer.from(
+  Array.apply(null, { length: 16834 * 2 })
+    .map(Math.random)
+    .map((number) => (number * (1 << 8)))
+);
 
+async function createLargeFile() {
   // Writing buffer to a file then try to read it
-  await writeFile(fn, buffer);
+  await writeFile(fn, largeBuffer);
+}
+
+async function validateReadFile() {
   const readBuffer = await readFile(fn);
-  assert.strictEqual(readBuffer.equals(buffer), true);
+  assert.strictEqual(readBuffer.equals(largeBuffer), true);
 }
 
 async function validateReadFileProc() {
@@ -39,6 +43,28 @@ async function validateReadFileProc() {
   assert.ok(hostname.length > 0);
 }
 
-validateReadFile()
-  .then(() => validateReadFileProc())
-  .then(common.mustCall());
+function validateReadFileAbortLogicBefore() {
+  const controller = new AbortController();
+  const signal = controller.signal;
+  controller.abort();
+  assert.rejects(readFile(fn, { signal }), {
+    name: 'AbortError'
+  });
+}
+
+function validateReadFileAbortLogicDuring() {
+  const controller = new AbortController();
+  const signal = controller.signal;
+  process.nextTick(() => controller.abort());
+  assert.rejects(readFile(fn, { signal }), {
+    name: 'AbortError'
+  });
+}
+
+(async () => {
+  await createLargeFile();
+  await validateReadFile();
+  await validateReadFileProc();
+  await validateReadFileAbortLogicBefore();
+  await validateReadFileAbortLogicDuring();
+})().then(common.mustCall());

test/parallel/test-fs-readfile.js

@@ -1,3 +1,4 @@
+// Flags: --experimental-abortcontroller
 'use strict';
 const common = require('../common');
 
@@ -57,3 +58,21 @@ for (const e of fileInfo) {
     assert.deepStrictEqual(buf, e.contents);
   }));
 }
+{
+  // Test cancellation, before
+  const controller = new AbortController();
+  const signal = controller.signal;
+  controller.abort();
+  fs.readFile(fileInfo[0].name, { signal }, common.mustCall((err, buf) => {
+    assert.strictEqual(err.name, 'AbortError');
+  }));
+}
+{
+  // Test cancellation, during read
+  const controller = new AbortController();
+  const signal = controller.signal;
+  fs.readFile(fileInfo[0].name, { signal }, common.mustCall((err, buf) => {
+    assert.strictEqual(err.name, 'AbortError');
+  }));
+  process.nextTick(() => controller.abort());
+}