vfs: createVfsHandlers() does not implement writev(fd, buffers, position) #66532

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1. Hati- commented on Oct 5, 2026

   

   Hati-

   on Oct 5, 2026

   Last edited by Hati-

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   Workaround

   As a temporary workaround, the missing writev() VFS handler can be added at runtime using --expose-internals.

   Typescript example:

   import { createRequire } from 'node:module'
   
   export function patchVfsStateHandlers() {
     if (!process.execArgv.includes('--expose-internals')) {
       throw new Error('Node must be launched with --expose-internals')
     }
     const require = createRequire(import.meta.url)
   
     interface NodeInternalFsUtils {
       vfsState: {
         handlers: Record<string, (...args: never[]) => unknown> | null
       }
     }
     interface NodeInternalVfsFd {
       getVirtualFd(fd: number): {
         entry: {
           writev(buffers: readonly ArrayBufferView[], position: number | null): Promise<{ bytesWritten: number }>
         }
       } | undefined
     }
   
     const { vfsState } = require('internal/fs/utils') as NodeInternalFsUtils
     if (vfsState.handlers === null) return
   
     if (vfsState.handlers['writev'] === undefined) {
       const { getVirtualFd } = require('internal/vfs/fd') as NodeInternalVfsFd
   
       vfsState.handlers['writev'] = (fd, buffers, position) => {
         const vfd = getVirtualFd(fd)
   
         // Not a VFS fd: tell fs.writev() to use the native implementation.
         if (vfd === undefined) {
           return undefined
         }
   
         return vfd.entry.writev(buffers, position).then(({ bytesWritten }) => bytesWritten)
       }
     }
   }

   Non-SEA

   For a normal Node.js application, call the patch immediately after mounting a VFS and before using code that may call fs.writev():

   import vfs from 'node:vfs'
   import { patchVfsStateHandlers } from './patchVfsStateHandlers.js'
   
   const myVfs = vfs.create()
   myVfs.mount() // Cause VFS to install its fs handler
   
   patchVfsStateHandlers()
   
   // Application code can now use fs.writev(), createWriteStream(), etc.
   startApplication()

   SEA

   For an SEA built with:

   {
     ...
     "useVfs": true
     "execArgv": [
       "--expose-internals"
     ]
   }
   

   the SEA VFS is already mounted before the embedded JavaScript entrypoint starts. Therefore, the patch can be called directly at the beginning of the SEA entrypoint:

   import { patchVfsStateHandlers } from './patchVfsStateHandlers.js'
   
   patchVfsStateHandlers()
   
   // Application code can now use fs.writev(), createWriteStream(), etc.
   startApplication()