Webflux post request: Only one connection receive subscriber allowed

Question

I try to implement a springboot app that allow me to :

• upload mp3 on S3
• extract meta data and store them on mongo DB.

If i want to extract meta data from a mp3, I have to provide MultipartFile. Unfortunatelly, we can't send Flux.

In my controller, I do pass 3 parameters:

@PostMapping
public Mono<ResponseEntity<AudioDto>> saveAudioTrack(@RequestHeader HttpHeaders headers,
                                                     @RequestHeader String fileName,
                                                     @RequestBody Flux<ByteBuffer> body) {
    return this.audioService.saveAudioTrack(headers, fileName, body);
}

Now i'm a little bit stuck in my service layer. I want to build my response, store data and post file onto S3. For storing the metadata, mp3agic.

public Mono<ResponseEntity<AudioDto>> saveAudioTrack(HttpHeaders headers, String fileName, Flux<ByteBuffer> body) {
    return Mono.from(body.flatMap(byteBuffer -> {
        Mono<MultipartFile> multipartFileMono = AppUtils.byteBufferToMultipartFile(headers, fileName, body);
        return multipartFileMono;
    }).flatMap(multipartFile -> {
        AudioEntity storedEntity = new AudioEntity();
        try {
            AudioDto audioDto = storeAudioMeta(multipartFile, headers);
            AudioEntity audioEntity = new AudioEntity();
            BeanUtils.copyProperties(audioDto, audioEntity);
            storedEntity = audioRepository.save(audioEntity).block();
        } catch (IOException | InvalidDataException | UnsupportedTagException e) {
            e.printStackTrace();
        }
        AudioDto storedAudio = new AudioDto();
        BeanUtils.copyProperties(storedEntity, storedAudio);
        ResponseEntity<AudioDto> responseEntity = ResponseEntity.status(HttpStatus.OK).body(storedAudio);
        return Mono.just(responseEntity);
    }));
}

I first try to convert byteBufffer to MultipartFile:

public static Mono<MultipartFile> byteBufferToMultipartFile(HttpHeaders headers, String fileName, Flux<ByteBuffer> body) {
    System.out.println(headers);
    return Mono.from(body.flatMap(byteBuffer -> {
        byte[] bytes = byteBuffer.array();
        MultipartFile multipartFile = new MockMultipartFile(fileName, bytes);
        return Mono.just(multipartFile);
    }));
}

Then I call a part of code that should allow me to persist meta data is called

private AudioDto storeAudioMeta(MultipartFile multipartFile, HttpHeaders headers) throws IOException, InvalidDataException, UnsupportedTagException {
    AudioDto audioDto = new AudioDto();
    if (multipartFile.isEmpty()) {
        throw new IllegalStateException("Cannot upload empty file");
    }
    //Check if the file is an image => we'll check if it's a mp3
    if(!multipartFile.getContentType().equals("audio/mpeg")) {
        throw new IllegalStateException("File uploaded is not a mp3");
    }
    InputStream initialStream = multipartFile.getInputStream();
    byte[] buffer = new byte[initialStream.available()];
    initialStream.read(buffer);
    File targetFile = new File("src/main/resources/" + multipartFile.getOriginalFilename());
    try (OutputStream outStream = new FileOutputStream(targetFile)) {
        outStream.write(buffer);
    }

    Mp3File mp3file  = new Mp3File(targetFile.getPath());
    audioDto.setLength((int) mp3file.getLengthInSeconds());
    audioDto.setBitrate(mp3file.getBitrate());
    audioDto.setSampleRate(mp3file.getSampleRate());
    if (mp3file.hasId3v1Tag()) {
        ID3v1 id3v1Tag = mp3file.getId3v1Tag();
        audioDto.setTrack(id3v1Tag.getTrack());
        audioDto.setArtist(id3v1Tag.getArtist());
        audioDto.setTitle(id3v1Tag.getTitle());
        ...
    }
    if (mp3file.hasId3v2Tag()) {
        ID3v2 id3v2Tag = mp3file.getId3v2Tag();
        audioDto.setTrack(id3v2Tag.getTrack());
        ...
        audioDto.setAlbumImage(id3v2Tag.getAlbumImage());
        byte[] albumImageData = id3v2Tag.getAlbumImage();
        if (albumImageData != null) {
            audioDto.setAlbumImageSize(albumImageData.length);
            audioDto.setAlbumImageMimeType(id3v2Tag.getAlbumImageMimeType());
        }
    }

    //get file metadata
    Map<String, String> metadata = new HashMap<>();
    metadata.put("Content-Type", audioDto.getFile().getContentType());
    metadata.put("Content-Length", String.valueOf(audioDto.getFile().getSize()));
    String bucketName = environment.getProperty("amazon.aws.s3.audioBucket");
    String path = String.format("%s/%s", bucketName, UUID.randomUUID());
    String fileName = String.format("%s", audioDto.getFile().getOriginalFilename());
    // try {
    //     fileStore.upload(path, fileName, Optional.of(metadata), 
    audioDto.getFile().getInputStream());
    // } catch (IOException e) {
        throw new IllegalStateException("Failed to upload file", e);
    //}
    audioDto.setFileName(fileName);
    audioDto.setFilePath(path);
    return audioDto;
}

I have error message returned:

java.lang.IllegalStateException: Only one connection receive subscriber allowed.
    at reactor.netty.channel.FluxReceive.startReceiver(FluxReceive.java:182) ~[reactor-netty-core-1.0.12.jar:1.0.12]
    Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
    *__checkpoint ⇢ Handler com.myapp.api.mediastreaming.ui.controller.AudioController#saveAudioTrack(HttpHeaders, String, Flux) [DispatcherHandler]
    *__checkpoint ⇢ HTTP POST "/audio/tracks" [ExceptionHandlingWebHandler]
Stack trace:
        at reactor.netty.channel.FluxReceive.startReceiver(FluxReceive.java:182) ~[reactor-netty-core-1.0.12.jar:1.0.12]
        at reactor.netty.channel.FluxReceive.subscribe(FluxReceive.java:143) ~[reactor-netty-core-1.0.12.jar:1.0.12]
        at reactor.core.publisher.InternalFluxOperator.subscribe(InternalFluxOperator.java:62) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.netty.ByteBufFlux.subscribe(ByteBufFlux.java:339) ~[reactor-netty-core-1.0.12.jar:1.0.12]
        at reactor.core.publisher.InternalFluxOperator.subscribe(InternalFluxOperator.java:62) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.netty.ByteBufFlux.subscribe(ByteBufFlux.java:339) ~[reactor-netty-core-1.0.12.jar:1.0.12]
        at reactor.core.publisher.Mono.subscribe(Mono.java:4399) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.core.publisher.FluxFlatMap$FlatMapMain.onNext(FluxFlatMap.java:426) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:74) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onNext(FluxOnErrorResume.java:79) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:120) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:120) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.core.publisher.FluxPeek$PeekSubscriber.onNext(FluxPeek.java:200) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:120) ~[reactor-core-3.4.11.jar:3.4.11]
        at reactor.netty.channel.FluxReceive.drainReceiver(FluxReceive.java:279) ~[reactor-netty-core-1.0.12.jar:1.0.12]
        at reactor.netty.channel.FluxReceive.onInboundNext(FluxReceive.java:388) ~[reactor-netty-core-1.0.12.jar:1.0.12]
        at reactor.netty.channel.ChannelOperations.onInboundNext(ChannelOperations.java:404) ~[reactor-netty-core-1.0.12.jar:1.0.12]
        at reactor.netty.http.server.HttpServerOperations.onInboundNext(HttpServerOperations.java:584) ~[reactor-netty-http-1.0.12.jar:1.0.12]
        at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:93) ~[reactor-netty-core-1.0.12.jar:1.0.12]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at reactor.netty.http.server.HttpTrafficHandler.channelRead(HttpTrafficHandler.java:261) ~[reactor-netty-http-1.0.12.jar:1.0.12]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324) ~[netty-codec-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:296) ~[netty-codec-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:719) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493) ~[netty-transport-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986) ~[netty-common-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.69.Final.jar:4.1.69.Final]
        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.69.Final.jar:4.1.69.Final]
        at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]

Answer 1

I finally found out a solution, highly inspired by this tutorial: https://www.vinsguru.com/spring-webflux-file-upload/

In my controller :

@PostMapping(consumes = MediaType.MULTIPART_FORM_DATA_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Mono<AudioDto>> saveAudioTrack(@RequestPart("file") Mono<FilePart> filePartMono) {
    return new ResponseEntity<>(this.audioService.saveAudioTrack(filePartMono), HttpStatus.CREATED);
}

In my service layer :

@Override
public Mono<AudioDto> saveAudioTrack(Mono<FilePart> filePartMono) {
    Path basePath = Paths.get("./src/main/resources/upload/");
    return filePartMono
            .doOnNext(fp -> System.out.println("Received File : " + fp.filename()))
            .flatMap(fp -> fp.transferTo(basePath.resolve(fp.filename())))
            .then(
                    filePartMono
                            .flatMap(fp -> Mono.just(new File(String.valueOf(basePath.resolve(fp.filename())))))
                            .map(file -> {
                                try {
                                    return getAudioMetadata(file);
                                } catch (InvalidDataException | UnsupportedTagException | IOException e) {
                                    e.printStackTrace();
                                    throw new RuntimeException(e.getLocalizedMessage());
                                }
                            })
            );

}

I also manage to get meta data and upload file to S3 bucket:

I call my method to create metadata

private AudioDto getAudioMetadata(File file) throws InvalidDataException, UnsupportedTagException, IOException {
    Mp3File mp3file  = new Mp3File(file.getPath());
    AudioDto audioDto = new AudioDto();
   ...
    if (mp3file.hasId3v1Tag()) {
        ID3v1 id3v1Tag = mp3file.getId3v1Tag();
        audioDto.setTrack(id3v1Tag.getTrack());
        ...   
    }
    if (mp3file.hasId3v2Tag()) {
        ID3v2 id3v2Tag = mp3file.getId3v2Tag();
        audioDto.setTrack(id3v2Tag.getTrack());
        ...
        audioDto.setAlbumImage(id3v2Tag.getAlbumImage());
        byte[] albumImageData = id3v2Tag.getAlbumImage();
        if (albumImageData != null) {
            audioDto.setAlbumImageSize(albumImageData.length);
            audioDto.setAlbumImageMimeType(id3v2Tag.getAlbumImageMimeType());
        }
    }

    //get file metadata
    Map<String, String> metadata = new HashMap<>();
    Tika tika = new Tika();

    metadata.put("Content-Type", tika.detect(file));
    metadata.put("Content-Length", String.valueOf(file.length()));
    String path = String.format("%s/%s", environment.getProperty("amazon.aws.s3.audioBucket"), UUID.randomUUID());
    //String fileName = String.format("%s", audioDto.getFile().getOriginalFilename());
    try {
        InputStream inputSteam = new FileInputStream(file);
        fileStore.upload(path, file.getName(), Optional.of(metadata), inputSteam);
    } catch (IOException e) {
        throw new IllegalStateException("Failed to upload file", e);
    }
    audioDto.setFileName(file.getName());
    ...
    ModelMapper modelMapper = new ModelMapper();
    modelMapper.getConfiguration().setMatchingStrategy(MatchingStrategies.STRICT);
    AudioEntity audioFileEntity = modelMapper.map(audioDto, AudioEntity.class);
    AudioEntity storedEntity = audioRepository.save(audioFileEntity);

    return modelMapper.map(storedEntity, AudioDto.class);
}

here is my upload method:

private final AmazonS3 amazonS3;

public void upload(String path,
                   String fileName,
                   Optional<Map<String, String>> optionalMetaData,
                   InputStream inputStream) {
    ObjectMetadata objectMetadata = new ObjectMetadata();
    optionalMetaData.ifPresent(map -> {
        if (!map.isEmpty()) {
            map.forEach(objectMetadata::addUserMetadata);
        }
    });
    try {
        amazonS3.putObject(path, fileName, inputStream, objectMetadata);
    } catch (AmazonServiceException e) {
        throw new IllegalStateException("Failed to upload the file", e);
    }
}

Not the most elegant way, but functionnal. there 's some workout before telling it's fully operational but nothing tricky. :)