Repository navigation
vfs: mounted fs.readSync(fd, ..., null) treats position as -1 and throws #64162
Description
Version
main
Platform
macOS 26.5.0
Subsystem
vfs
What steps will reproduce the bug?
import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';
import vfs from 'node:vfs';
const mountPoint = fs.mkdtempSync(path.join(os.tmpdir(), 'vfs-mount-'));
const mounted = vfs
.create({ emitExperimentalWarning: false })
.mount(mountPoint);
try {
const file = path.join(mountPoint, 'file.txt');
fs.writeFileSync(file, 'abcdef');
const fd = fs.openSync(file, 'r');
const buffer = Buffer.alloc(2);
try {
const bytesRead = fs.readSync(fd, buffer, 0, buffer.length, null);
console.log('bytesRead:', bytesRead);
console.log('buffer:', buffer.toString());
} finally {
fs.closeSync(fd);
}
} finally {
mounted.unmount();
fs.rmSync(mountPoint, { recursive: true, force: true });
}How often does it reproduce? Is there a required condition?
Always
What is the expected behavior? Why is that the expected behavior?
bytesRead: 2
buffer: abIn fs.readSync, position: null means read from and advance the descriptor’s current file position, so VFS should translate the internal sentinel back to “no explicit position.”
What do you see instead?
node:buffer:253
throw new ERR_OUT_OF_RANGE('sourceStart', `>= 0 && <= ${source.byteLength}`, sourceStart);
^
RangeError [ERR_OUT_OF_RANGE]: The value of "sourceStart" is out of range. It must be >= 0 && <= 6. Received -1
at copyImpl (node:buffer:253:13)
at Buffer.copy (node:buffer:894:12)
at MemoryFileHandle.readSync (node:internal/vfs/file_handle:479:13)
at Object.readSync (node:internal/vfs/setup:360:33)
at Object.readSync (node:fs:892:22)
at file:///Users/trivikram/workspace/test-repro/repro.js:20:26
at ModuleJob.run (node:internal/modules/esm/module_job:447:25)
at async node:internal/modules/esm/loader:646:26
at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:101:5) {
code: 'ERR_OUT_OF_RANGE'
}VFS receives -1 as the position and treats it as an explicit negative offset.
Additional information
Native repro
import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';
const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'native-readsync-'));
try {
const file = path.join(dir, 'file.txt');
fs.writeFileSync(file, 'abcdef');
const fd = fs.openSync(file, 'r');
const buffer = Buffer.alloc(2);
try {
const bytesRead = fs.readSync(fd, buffer, 0, buffer.length, null);
console.log('bytesRead:', bytesRead);
console.log('buffer:', buffer.toString());
} finally {
fs.closeSync(fd);
}
} finally {
fs.rmSync(dir, { recursive: true, force: true });
}
Activity
vfs: handle current-position sentinel in memory files
vfs: handle current-position sentinel in memory files