[SpringBoot + Kotlin + WebFlux] cannot fetch data in the frontend

[vapid rivet]

hey, I meet a problem when using spring-boot-starter-webflux, here is my code relevant
in controller,

@GetMapping("/download")
suspend fun downloadFile(@RequestBody request: DownloadRequest,
                         response: ServerHttpResponse) {
    val databuffer = response.bufferFactory().allocateBuffer(bufferSize)
    val outputStream = databuffer.asOutputStream()

    // outputStream.write here
    sambaUtils.downloadFile(request.path, request.filename, outputStream)
}

I have logged the writing bytes,

[frosty lark]

Detected code, here are some useful tools:

<@&1008423204219531294> please have a look, thanks.

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oad")
fun download(): Mono<ResponseEntity<Resource>> {
val file = File("path/to/file")
val resource = FileSystemResource(file)

return Mono.just(ResponseEntity.ok()
        .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=${file.name}")
        .contentType(MediaType.APPLICATION_OCTET_STREAM)
        .body(resource))

}

in frontend,

```javascript
fetch('/download')
  .then(response => response.blob())
  .then(blob => {
    const url = window.URL.createObjectURL(blob);
    const a = document.createElement('a');
    a.style.display = 'none';
    a.href = url;
    a.download = 'file.txt';
    document.body.appendChild(a);
    a.click();
    window.URL.revokeObjectURL(url);
  });

but it seems that the frontend cannot fetch the data correctly, what's wrong with my code?