StreamedFile is not consumed

[abishai]

Expected Behavior

Usercase: receiving big entries from database I try to compress them and return as a StreamedFile with minimal memory usage.

@Controller
class Controller {

    @Get("/download", produces = [MediaType.APPLICATION_OCTET_STREAM])
    suspend fun download(): StreamedFile = coroutineScope {
        provide()
    }

    suspend fun provide(): StreamedFile = coroutineScope {
        val inputStream = PipedInputStream(1024 * 10)
        val outputStream = PipedOutputStream(inputStream)

        launch(Dispatchers.Default) {
            outputStream.use { stream ->
                ZipOutputStream(stream).use { stream ->
                    (0 until 1000).forEach { i ->
                        println("Processing entry $i")
                        stream.putNextEntry(ZipEntry("$i.txt"))
                        ByteArrayInputStream(getRandomString(1024).toByteArray()).use { it.copyTo(stream) }
                        stream.closeEntry()
                        println("Processing entry $i complete")
                    }
                }
            }

            println("Coroutine complete.")
        }

        println("Returning streaming file stub")
        StreamedFile(inputStream, MediaType.APPLICATION_OCTET_STREAM_TYPE)
            .attach("export.zip")
    }

    private fun getRandomString(length: Int): String {
        val allowedChars = ('A'..'Z') + ('a'..'z') + ('0'..'9') + ' '
        return String(CharArray(length) { allowedChars.random() })
    }
}

Actual Behaviour

Stream is not read, leading to PipedInputStream overflow, hanging the entire process.

Steps To Reproduce

Start the attached project and try to download file from /download If generated content doesn't fit PipedInputStream, the process hangs.

• Returning streaming file stub is visible, meaning that stream is passed and data pump has started in another thread
• Several Processing entry $i complete is visible. Corresponds to buffer size and entries size
• Coroutine complete. is not visible

Environment Information

FreeBSD 14.3
OpenJDK21

Example Application

hanging-pipe.zip

Version

4.9.3