无法流式传输到已取消链接的文件

Question

I'm creating a system in which I need to cache a file in a short amount of time, and then delete it. I'm running into an error that if I try to cache the same deleted file after deletion, I get a permission error.

I have made a reproduction of my problem, and it looks like this:

//@ts-check
const fs = require("fs")
const promisify = require("util").promisify
const unlink = promisify(fs.unlink)

const SOURCE = "a.txt"
const DESTINATION = "b.txt"

function init() {
  console.info("Running operation")

  const sourceStream = fs.createReadStream(SOURCE)
  const destinationStream = fs.createWriteStream(DESTINATION)

  sourceStream.on("close", async () => {
    await unlink(DESTINATION)
    init()
  })

  sourceStream.pipe(destinationStream)
}

init()

Upon running, this is what is logged to console:

Running operation
Running operation
Running operation
events.js:167
      throw er; // Unhandled 'error' event
      ^

Error: EPERM: operation not permitted, open 'D:\Projects\test\b.txt'
Emitted 'error' event at:
    at WriteStream.onerror (_stream_readable.js:690:12)
    at WriteStream.emit (events.js:182:13)
    at lazyFs.open (internal/fs/streams.js:273:12)
    at FSReqWrap.oncomplete (fs.js:141:20)

Even weirder, the amount of times it can run the same operation before throwing the error varies. Sometimes it'll fail after 3, sometimes after 5.

So what's going on here?

Answer 1

You need to wait for the destinationStream to end before reading again. Try doing this:

 destinationStream.on("close", async () => {
      await unlink(DESTINATION)
      init()
 })

Answer 2

If I'm getting the problem right, perhaps you should look for finish event.

Change this:

const sourceStream = fs.createReadStream(SOURCE)
const destinationStream = fs.createWriteStream(DESTINATION)

sourceStream.on("close", async () => {
  await unlink(DESTINATION)
  init()
})

sourceStream.pipe(destinationStream)

To this:

const sourceStream = fs.createReadStream(SOURCE)
const destinationStream = fs.createWriteStream(DESTINATION)

sourceStream.pipe(destinationStream)
   .on('finish', async () => {
     await unlink(DESTINATION);
     console.log('Done');
     init()
   })