spring webflux FilePart如何验证mime类型？

Question

@PostMapping("/users/avatar")
suspend fun uploadAvatar(@RequestPart("file") filePartMono: Mono<FilePart>) {
  filePartMono.map{ part -> part.content().map{ it.asInputStream().readAllBytes() }
    .map { it /* ??? */ }
  }
  // ...
}

在无Reactor栈上，我是这样做的：

uploadAvatar(@RequestParam("file") MultipartFile file) {
    String contentType = file.getContentType().toLowerCase();
    List<String> valid = Arrays.asList("image/jpg", "image/jpeg", "image/png");
    if (file.isEmpty() || !valid.contains(contentType)) {
        throw new UploadException("Invalid image format or empty file", HttpStatus.UNPROCESSABLE_ENTITY);
    }
    if (file.getSize() > IMAGE_MAX_FILE_SIZE) {
        throw new UploadException("Image too big (max " + (IMAGE_MAX_FILE_SIZE / 1000) + " kB )", HttpStatus.UNPROCESSABLE_ENTITY);
    }
    try {
        // try to read file as image to ensure it is an image
        ImageIO.read(file.getInputStream());
    } catch (IOException e) {
        throw new UploadException("Invalid image", HttpStatus.UNPROCESSABLE_ENTITY);
    }

    try {
        byte[] bytes = file.getBytes();
        userService.storeAvatar(bytes);
    } catch (IOException e) {
        throw new UploadException("Could not store image", HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

但是FilePart不提供相同的API（例如contentType）。

如何从filepart获取contentType和文件大小？

Answer 1

FilePart有可以像这样访问的头。

@PostMapping(value = ["/upload"], consumes = [MediaType.MULTIPART_FORM_DATA_VALUE])
suspend fun upload(@RequestPart(name = "file") file: Mono<FilePart>) {

    val filePart = file.awaitFirstOrNull() ?: throw Exception()

    println(filePart.headers().contentType)
    println(filePart.headers().contentLength)
}

但是，我认为仅仅依靠header来获取内容类型并不是一个好主意。因此，可以使用Tika库进行类型检测。考虑到您使用的是gradle，您可以这样做。

在build.gradle.kts中

implementation("org.apache.tika:tika-core:1.26")

@PostMapping(value = ["/upload"], consumes = [MediaType.MULTIPART_FORM_DATA_VALUE])
suspend fun upload(@RequestPart(name = "file") file: Mono<FilePart>) : Response {

    val filePart = file.awaitFirstOrNull() ?: throw Exception()
    val inputStream = filePart.content().awaitFirst().asInputStream()
    val detectedFileTye = getFilePartFileType(filePart.filename(), inputStream)
    ...
}

private suspend fun getFilePartFileType(fileName: String, inputStream: InputStream): String? = coroutineScope {

    val mimeTypeDeferred = async(Dispatchers.IO) {

        Tika().detect(inputStream, fileName)
    }

    mimeTypeDeferred.await()
}