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kotlinlang

hi all, when uploading a file through a multipart form, we want to keep the temp file around for async virus scanning. However, in the following piece of code, the file is deleted upon JVM exit:
```    private fun writeToDisk(part: StreamingPart, bytes: ByteArray, length: Int) =
        File.createTempFile(part.fileName ?: UUID.randomUUID().toString()
        + "-", ".tmp", temporaryFileDirectory).apply {
            deleteOnExit()
            FileOutputStream(this).apply {
                write(bytes, 0, length)
                use { part.inputStream.copyTo(it, writeToDiskThreshold) }
            }
        }```
with the `deleteOnExit()` call.

We want to keep the file around even when the JVM exits (we're running on k8s so pods can always be killed).

Would it be a good idea to make this behaviour configurable, i.e. through a flag that is passed from `MultipartFormBody.from` to the `MultipartFormParser`?

If so, I'll make a merge request... Happy to hear your thoughts.

See <https://github.com/http4k/http4k/pull/798>

the alternative would be to make a copy of the temp file, but that seems a bit wasteful...

updated merge request: <https://github.com/http4k/http4k/pull/798>