google-cloud-nio: CloudStorageFileSystemProvider throws UnsupportedException when used with Webflux + MultipartFile upload

[mcgin]

Because CloudStorageFileSystemProvider does not override the newFileChannel method it throws an UnsupportedOperationException when used for Multipart file uploads with FilePart.transferto(Path path) in a reactive Spring boot application.

Environment details

1. Specify the API: google-cloud-nio
2. OS type and version: Debian 9
3. Java version: 10
4. google-cloud-nio version(s): 0.83-alpha

Steps to reproduce

1. See code sample

Code example

    @PostMapping(value = "/upload", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    public Mono<Void> multipartUpload( final @RequestPart("file") FilePart filePart
    ) {

        FileSystem fileSystem = CloudStorageFileSystem.forBucket("my-bucket");
        return filePart.transferTo(fileSystem.getPath("failed-file"));
    }

Stack trace

java.lang.UnsupportedOperationException: null
    at java.base/java.nio.file.spi.FileSystemProvider.newFileChannel(FileSystemProvider.java:524)
    at java.base/java.nio.channels.FileChannel.open(FileChannel.java:292)
    at java.base/java.nio.channels.FileChannel.open(FileChannel.java:345)
    at org.springframework.http.codec.multipart.SynchronossPartHttpMessageReader$SynchronossFilePart.transferTo(SynchronossPartHttpMessageReader.java:334)

External references such as API reference guides used

• Stackoverflow question - https://stackoverflow.com/questions/55246844/unsupportedoperationexception-with-multipart-file-upload-using-webflux-and-sprin/55248459#55248459
• Java documentation for FileServiceProvider - https://docs.oracle.com/javase/7/docs/api/java/nio/file/spi/FileSystemProvider.html#newFileChannel(java.nio.file.Path,%20java.util.Set,%20java.nio.file.attribute.FileAttribute...)
• FilePart javadoc - https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/http/codec/multipart/FilePart.html#transferTo-java.nio.file.Path-

Any additional information below

[sduskis]

@meltsufin, do you have any advice for this Spring question?

[meltsufin]

It looks like CloudStorageFileSystemProvider needs to override newFileChannel.