fs: add fs.readv()

Fixes: #2298
PR-URL: #32356
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/fs.md

@@ -3069,6 +3069,42 @@ Returns the number of `bytesRead`.
 For detailed information, see the documentation of the asynchronous version of
 this API: [`fs.read()`][].
 
+## `fs.readv(fd, buffers[, position], callback)`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `fd` {integer}
+* `buffers` {ArrayBufferView[]}
+* `position` {integer}
+* `callback` {Function}
+  * `err` {Error}
+  * `bytesRead` {integer}
+  * `buffers` {ArrayBufferView[]}
+
+Read from a file specified by `fd` and write to an array of `ArrayBufferView`s
+using `readv()`.
+
+`position` is the offset from the beginning of the file from where data
+should be read. If `typeof position !== 'number'`, the data will be read
+from the current position.
+
+The callback will be given three arguments: `err`, `bytesRead`, and
+`buffers`. `bytesRead` is how many bytes were read from the file.
+
+## `fs.readvSync(fd, buffers[, position])`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `fd` {integer}
+* `buffers` {ArrayBufferView[]}
+* `position` {integer}
+* Returns: {number} The number of bytes read.
+
+For detailed information, see the documentation of the asynchronous version of
+this API: [`fs.readv()`][].
+
 ## `fs.realpath(path[, options], callback)`
 <!-- YAML
 added: v0.1.31
@@ -4445,6 +4481,25 @@ If one or more `filehandle.read()` calls are made on a file handle and then a
 position till the end of the file. It doesn't always read from the beginning
 of the file.
 
+#### `filehandle.readv(buffers[, position])`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `buffers` {ArrayBufferView[]}
+* `position` {integer}
+* Returns: {Promise}
+
+Read from a file and write to an array of `ArrayBufferView`s
+
+The `Promise` is resolved with an object containing a `bytesRead` property
+identifying the number of bytes read, and a `buffers` property containing
+a reference to the `buffers` input.
+
+`position` is the offset from the beginning of the file where this data
+should be read from. If `typeof position !== 'number'`, the data will be read
+from the current position.
+
 #### `filehandle.stat([options])`
 <!-- YAML
 added: v10.0.0
@@ -5655,6 +5710,7 @@ the file contents.
 [`fs.readFileSync()`]: #fs_fs_readfilesync_path_options
 [`fs.readdir()`]: #fs_fs_readdir_path_options_callback
 [`fs.readdirSync()`]: #fs_fs_readdirsync_path_options
+[`fs.readv()`]: #fs_fs_readv_fd_buffers_position_callback
 [`fs.realpath()`]: #fs_fs_realpath_path_options_callback
 [`fs.rmdir()`]: #fs_fs_rmdir_path_options_callback
 [`fs.stat()`]: #fs_fs_stat_path_options_callback

lib/fs.js

@@ -564,6 +564,39 @@ function readSync(fd, buffer, offset, length, position) {
   return result;
 }
 
+function readv(fd, buffers, position, callback) {
+  function wrapper(err, read) {
+    callback(err, read || 0, buffers);
+  }
+
+  validateInt32(fd, 'fd', /* min */ 0);
+  validateBufferArray(buffers);
+
+  const req = new FSReqCallback();
+  req.oncomplete = wrapper;
+
+  callback = maybeCallback(callback || position);
+
+  if (typeof position !== 'number')
+    position = null;
+
+  return binding.readBuffers(fd, buffers, position, req);
+}
+
+function readvSync(fd, buffers, position) {
+  validateInt32(fd, 'fd', 0);
+  validateBufferArray(buffers);
+
+  const ctx = {};
+
+  if (typeof position !== 'number')
+    position = null;
+
+  const result = binding.readBuffers(fd, buffers, position, undefined, ctx);
+  handleErrorFromBinding(ctx);
+  return result;
+}
+
 // usage:
 //  fs.write(fd, buffer[, offset[, length[, position]]], callback);
 // OR
@@ -1928,6 +1961,8 @@ module.exports = fs = {
   readdirSync,
   read,
   readSync,
+  readv,
+  readvSync,
   readFile,
   readFileSync,
   readlink,

lib/internal/fs/promises.js

@@ -101,6 +101,10 @@ class FileHandle {
     return read(this, buffer, offset, length, position);
   }
 
+  readv(buffers, position) {
+    return readv(this, buffers, position);
+  }
+
   readFile(options) {
     return readFile(this, options);
   }
@@ -253,6 +257,18 @@ async function read(handle, buffer, offset, length, position) {
   return { bytesRead, buffer };
 }
 
+async function readv(handle, buffers, position) {
+  validateFileHandle(handle);
+  validateBufferArray(buffers);
+
+  if (typeof position !== 'number')
+    position = null;
+
+  const bytesRead = (await binding.readBuffers(handle.fd, buffers, position,
+                                               kUsePromises)) || 0;
+  return { bytesRead, buffers };
+}
+
 async function write(handle, buffer, offset, length, position) {
   validateFileHandle(handle);
 

src/node_file.cc

@@ -1976,6 +1976,52 @@ static void Read(const FunctionCallbackInfo<Value>& args) {
 }
 
 
+// Wrapper for readv(2).
+//
+// bytesRead = fs.readv(fd, buffers[, position], callback)
+// 0 fd        integer. file descriptor
+// 1 buffers   array of buffers to read
+// 2 position  if integer, position to read at in the file.
+//             if null, read from the current position
+static void ReadBuffers(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+
+  const int argc = args.Length();
+  CHECK_GE(argc, 3);
+
+  CHECK(args[0]->IsInt32());
+  const int fd = args[0].As<Int32>()->Value();
+
+  CHECK(args[1]->IsArray());
+  Local<Array> buffers = args[1].As<Array>();
+
+  int64_t pos = GetOffset(args[2]);  // -1 if not a valid JS int
+
+  MaybeStackBuffer<uv_buf_t> iovs(buffers->Length());
+
+  // Init uv buffers from ArrayBufferViews
+  for (uint32_t i = 0; i < iovs.length(); i++) {
+    Local<Value> buffer = buffers->Get(env->context(), i).ToLocalChecked();
+    CHECK(Buffer::HasInstance(buffer));
+    iovs[i] = uv_buf_init(Buffer::Data(buffer), Buffer::Length(buffer));
+  }
+
+  FSReqBase* req_wrap_async = GetReqWrap(env, args[3]);
+  if (req_wrap_async != nullptr) {  // readBuffers(fd, buffers, pos, req)
+    AsyncCall(env, req_wrap_async, args, "read", UTF8, AfterInteger,
+              uv_fs_read, fd, *iovs, iovs.length(), pos);
+  } else {  // readBuffers(fd, buffers, undefined, ctx)
+    CHECK_EQ(argc, 5);
+    FSReqWrapSync req_wrap_sync;
+    FS_SYNC_TRACE_BEGIN(read);
+    int bytesRead = SyncCall(env, /* ctx */ args[4], &req_wrap_sync, "read",
+                             uv_fs_read, fd, *iovs, iovs.length(), pos);
+    FS_SYNC_TRACE_END(read, "bytesRead", bytesRead);
+    args.GetReturnValue().Set(bytesRead);
+  }
+}
+
+
 /* fs.chmod(path, mode);
  * Wrapper for chmod(1) / EIO_CHMOD
  */
@@ -2239,6 +2285,7 @@ void Initialize(Local<Object> target,
   env->SetMethod(target, "open", Open);
   env->SetMethod(target, "openFileHandle", OpenFileHandle);
   env->SetMethod(target, "read", Read);
+  env->SetMethod(target, "readBuffers", ReadBuffers);
   env->SetMethod(target, "fdatasync", Fdatasync);
   env->SetMethod(target, "fsync", Fsync);
   env->SetMethod(target, "rename", Rename);

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

@@ -0,0 +1,67 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const path = require('path');
+const fs = require('fs').promises;
+const tmpdir = require('../common/tmpdir');
+
+tmpdir.refresh();
+
+const expected = 'ümlaut. Лорем 運務ホソモ指及 आपको करने विकास 紙読決多密所 أضف';
+const exptectedBuff = Buffer.from(expected);
+
+let cnt = 0;
+function getFileName() {
+  return path.join(tmpdir.path, `readv_promises_${++cnt}.txt`);
+}
+
+const allocateEmptyBuffers = (combinedLength) => {
+  const bufferArr = [];
+  // Allocate two buffers, each half the size of exptectedBuff
+  bufferArr[0] = Buffer.alloc(Math.floor(combinedLength / 2)),
+  bufferArr[1] = Buffer.alloc(combinedLength - bufferArr[0].length);
+
+  return bufferArr;
+};
+
+(async () => {
+  {
+    const filename = getFileName();
+    await fs.writeFile(filename, exptectedBuff);
+    const handle = await fs.open(filename, 'r');
+    // const buffer = Buffer.from(expected);
+    const bufferArr = allocateEmptyBuffers(exptectedBuff.length);
+    const expectedLength = exptectedBuff.length;
+
+    let { bytesRead, buffers } = await handle.readv([Buffer.from('')],
+                                                    null);
+    assert.deepStrictEqual(bytesRead, 0);
+    assert.deepStrictEqual(buffers, [Buffer.from('')]);
+
+    ({ bytesRead, buffers } = await handle.readv(bufferArr, null));
+    assert.deepStrictEqual(bytesRead, expectedLength);
+    assert.deepStrictEqual(buffers, bufferArr);
+    assert(Buffer.concat(bufferArr).equals(await fs.readFile(filename)));
+    handle.close();
+  }
+
+  {
+    const filename = getFileName();
+    await fs.writeFile(filename, exptectedBuff);
+    const handle = await fs.open(filename, 'r');
+    // const buffer = Buffer.from(expected);
+    const bufferArr = allocateEmptyBuffers(exptectedBuff.length);
+    const expectedLength = exptectedBuff.length;
+
+    let { bytesRead, buffers } = await handle.readv([Buffer.from('')]);
+    assert.deepStrictEqual(bytesRead, 0);
+    assert.deepStrictEqual(buffers, [Buffer.from('')]);
+
+    ({ bytesRead, buffers } = await handle.readv(bufferArr));
+    assert.deepStrictEqual(bytesRead, expectedLength);
+    assert.deepStrictEqual(buffers, bufferArr);
+    assert(Buffer.concat(bufferArr).equals(await fs.readFile(filename)));
+    handle.close();
+  }
+})();

test/parallel/test-fs-readv-sync.js

@@ -0,0 +1,92 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const fs = require('fs');
+const tmpdir = require('../common/tmpdir');
+
+tmpdir.refresh();
+
+const expected = 'ümlaut. Лорем 運務ホソモ指及 आपको करने विकास 紙読決多密所 أضف';
+
+const exptectedBuff = Buffer.from(expected);
+const expectedLength = exptectedBuff.length;
+
+const filename = 'readv_sync.txt';
+fs.writeFileSync(filename, exptectedBuff);
+
+const allocateEmptyBuffers = (combinedLength) => {
+  const bufferArr = [];
+  // Allocate two buffers, each half the size of exptectedBuff
+  bufferArr[0] = Buffer.alloc(Math.floor(combinedLength / 2)),
+  bufferArr[1] = Buffer.alloc(combinedLength - bufferArr[0].length);
+
+  return bufferArr;
+};
+
+// fs.readvSync with array of buffers with all parameters
+{
+  const fd = fs.openSync(filename, 'r');
+
+  const bufferArr = allocateEmptyBuffers(exptectedBuff.length);
+
+  let read = fs.readvSync(fd, [Buffer.from('')], 0);
+  assert.deepStrictEqual(read, 0);
+
+  read = fs.readvSync(fd, bufferArr, 0);
+  assert.deepStrictEqual(read, expectedLength);
+
+  fs.closeSync(fd);
+
+  assert(Buffer.concat(bufferArr).equals(fs.readFileSync(filename)));
+}
+
+// fs.readvSync with array of buffers without position
+{
+  const fd = fs.openSync(filename, 'r');
+
+  const bufferArr = allocateEmptyBuffers(exptectedBuff.length);
+
+  let read = fs.readvSync(fd, [Buffer.from('')]);
+  assert.deepStrictEqual(read, 0);
+
+  read = fs.readvSync(fd, bufferArr);
+  assert.deepStrictEqual(read, expectedLength);
+
+  fs.closeSync(fd);
+
+  assert(Buffer.concat(bufferArr).equals(fs.readFileSync(filename)));
+}
+
+/**
+ * Testing with incorrect arguments
+ */
+const wrongInputs = [false, 'test', {}, [{}], ['sdf'], null, undefined];
+
+{
+  const fd = fs.openSync(filename, 'r');
+
+  wrongInputs.forEach((wrongInput) => {
+    assert.throws(
+      () => fs.readvSync(fd, wrongInput, null), {
+        code: 'ERR_INVALID_ARG_TYPE',
+        name: 'TypeError'
+      }
+    );
+  });
+
+  fs.closeSync(fd);
+}
+
+{
+  // fs.readv with wrong fd argument
+  wrongInputs.forEach((wrongInput) => {
+    assert.throws(
+      () => fs.readvSync(wrongInput),
+      {
+        code: 'ERR_INVALID_ARG_TYPE',
+        name: 'TypeError'
+      }
+    );
+  });
+}