download/upload with streaming for files with fetch and s3

[dimonnwc3]

What version of Bun is running?

1.2.1

What platform is your computer?

Darwin 24.2.0 arm64 arm

What steps can reproduce the bug?

there is code for uploading or downloading files using various methods in bun
most of them buffer whole file content in memory before sending

import { file, s3, write } from "bun"

const src = "/path-to-1gb-file"
const bucket = "bucket-name"

async function uploadFileToUrl() {
  await fetch(s3.presign("key", { bucket, method: "PUT" }), {
    method: "PUT",
    body: file(src),
    verbose: true,
  })
}

async function uploadFileStreamToUrl() {
  await fetch(s3.presign("key", { bucket, method: "PUT" }), {
    method: "PUT",
    body: file(src).stream(),
    verbose: true,
  })
}

async function uploadFileToS3() {
  await write(s3.file("key", { bucket }), file(src))
}

async function downloadFileFromUrl() {
  await write(
    "downloadFileFromUrl",
    await fetch(s3.presign("key", { bucket }), {
      verbose: true,
    }),
  )
}

async function downloadFileFromS3() {
  await write(
    "downloadFileFromS3",
    s3.file("key", { bucket }),
  )
}

console.log(process.memoryUsage().rss / 1024 / 1024)

setInterval(() => {
  console.log(process.memoryUsage().rss / 1024 / 1024)
}, 300).unref()

await uploadFileToUrl()
await uploadFileStreamToUrl()
await uploadFileToS3()
await downloadFileFromUrl()
await downloadFileFromS3()

What is the expected behavior?

I intuitively expected that all operation with files and fetch/s3 will use streaming under the hood without buffering whole file in memory.

What do you see instead?

await uploadFileToUrl() <- buffers whole file in memory
await uploadFileStreamToUrl() <- fails with 411 http status, because content length is not known, even if I add header
await uploadFileToS3() <- buffers whole file in memory
await downloadFileFromUrl() <- buffers whole file in memory
await downloadFileFromS3() <- streams as expected

Additional information

No response

[cirospaciari]

Indeed the way streams are consumed today this can happen, bun will free the memory as soon it can, but it can buffer the whole file, this will be change to another implementation that is more memory efficient