如何调试“Java NIO Socket Channel 发送和接收字节大小不匹配”？

Question

Please look at this question .

This is exact what I'm looking for but I didn't reach it yet. I'm sending multiple of images over a socketChannel. I try to attach the image size into a (cleared ByteBuffer) and attach then the image data into the same buffer (the buffer size is big enough!).

On the receiving side first the image size will be read by ByteBuffer.read(...), then ByteBuffer.flip() and ByteBuffer.getLong() (eg. imageData = readBuffer.getLong()) To read the following image data, have I do ByteBuffer.comact()? How do I realize that exact the number of bytes of imageData will be read?

No I have the following: On the sender-side:

socketChannelEntity.getWriteBuffer().clear();
            if(socketChannelEntity.getFileToProcessCounter() < fileList.size()){
                this.fileName = fileList.get(socketChannelEntity.getFileToProcessCounter()).toString();
                System.out.println("NIO_CLIENT: " + socketChannelEntity.getEntityName() + ": Send next image: " + fileName);
            } else {
                System.out.println("NIO_CLIENT: No more images to send.");
                socketChannelEntity.setSendReceiveStatus(SendReceiveStatusClient.DONE);
                socketChannel.register(this.selector, SelectionKey.OP_READ, socketChannelEntity);
                return;
            }
            Path path = Paths.get(fileName);
            long fileSize = Files.size(path);
            System.out.println(fileName + " size: " + fileSize);
            socketChannelEntity.getWriteBuffer().putLong(fileSize);
            try{
                FileChannel fileChannel = FileChannel.open(path);
                int numRead = 0;
                int counter = 0;
                while((numRead = fileChannel.read(socketChannelEntity.getWriteBuffer())) > 0){
                    counter += numRead;
                    socketChannelEntity.getWriteBuffer().flip();
                    do {
                        numRead -= socketChannel.write(socketChannelEntity.getWriteBuffer());
//                      socketChannelEntity.getWriteBuffer().clear();
                    } while (numRead > 0);
                }
                fileChannel.close();
                System.out.println("NIO_CLIENT: " + socketChannelEntity.getEntityName() + ": Image " + fileName + " sent: " + counter + " bytes long");
                socketChannelEntity.setCheckSum(fileSize);
                socketChannelEntity.setSendReceiveStatus(SendReceiveStatusClient.RECEIVE_CHECKSUM_IMAGE);
            } catch(IOException e) {
                e.printStackTrace();
            }

On the receiver side:

if(socketChannel.socket().getLocalPort() == 10000){
                outputFile =  Config.HOME_PATH_SERVER_1 + "receivedImage" + fileNameCounter + ".jpg";
            } else if(socketChannel.socket().getLocalPort() == 10001){
                outputFile =  Config.HOME_PATH_SERVER_2 + "receivedImage" + fileNameCounter + ".jpg";
            }
            Path path = Paths.get(outputFile);
            FileChannel fileChannel = FileChannel.open(path,
                    EnumSet.of(StandardOpenOption.CREATE,
                            StandardOpenOption.TRUNCATE_EXISTING,
                            StandardOpenOption.WRITE));
            int numRead = 0;
            int counter = 0;
            readBuffer.clear();
            socketChannel.read(readBuffer);
            readBuffer.flip();
            checkSum = readBuffer.getLong();
            System.out.println("Server erwartet ein Bild der Groesse: " + checkSum);
            readBuffer.limit((int)checkSum+8);
            fileChannel.write(readBuffer);
            fileChannel.close();
            if(readBuffer.hasRemaining()){
                System.out.println("Ist noch was im ReadBuffer!");
            }
            prepareWriteBuffer(checkSum);
            System.out.println("NIO_SERVER: Received image.");
            sendReceiveStatus = SendReceiveStatusServer.SEND_CHECKSUM_IMAGE;

For the first image everything works fine. The filecounter on the sender side increments and the sender tries to send the next image. The receiver side gets now: size for the next image: eg. 1591323337052742968 What is wrong?

Answer 1

Try this:
On the Client (sending) Side

1. Write the size of the image to a ByteBuffer ( ByteBuffer.putLong ).
2. Write the image data to the same ByteBuffer ( ByteBuffer.put(byte[]) ).
3. Call ByteBuffer.flip .
4. Write the ByteBuffer to the socket channel.

On the Server (receiving) Side

1. Read from the socket channel into a ByteBuffer .
2. Call ByteBuffer.flip .
3. Get the image length out of the ByteBuffer ( ByteBuffer.getLong ).
4. Allocate the image byte[] (using the image size).
5. Read the image out of the ByteBuffer ( ByteBuffer.get(byte[]) ).