Sending file with custom attributes over a network

I 开发者_开发百科want to create a client-server program that allows the client to send a file to the server along with some information about the file (sender name, description, etc.).

The file could potentially be quite large as it could be either a text, picture, audio or video file, and because of that I do not want to have to read the whole file into a byte array before sending, I would rather read the file in blocks, sending them over the network and then allowing the server to append the blocks to the file at it's end.

However I am faced with the problem of how to best send the file along with a few bits of information about the file itself. I would like at a minimum to send the sender's name and a description both of which will be input to the client program by the user, but this may change in the future so should be flexible.

What is a good way of doing this that would also allow me to "stream" the file being sent rather than reading it in as a whole and then sending?

Sockets are natively streams of bytes so you shouldn't have a problem there. I suggest you have a protocol which looks like this.

This will allow you to send arbitrary properties as long as the total length is less than 64 KB. Followed by the file which can be any 63-bit length and is sent a block at a time. (with a buffer of 8 KB)

The Socket can be used to send more files if you wish.

DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
Properties fileProperties = new Properties();
File file = new File(filename);

// send the properties
StringWriter writer = new StringWriter();
fileProperties.store(writer, "");
writer.close();
dos.writeUTF(writer.toString());

// send the length of the file
dos.writeLong(file.length());

// send the file.
byte[] bytes = new byte[8*1024];
FileInputStream fis = new FileInputStream(file);
int len;
while((len = fis.read(bytes))>0) {
    dos.write(bytes, 0, len);
}
fis.close();
dos.flush();

to read

DataInputStream dis = new DataInputStream(socket.getInputStream());
String propertiesText = dis.readUTF();
Properties properties = new Properties();
properties.load(new StringReader(propertiesText));
long lengthRemaining = dis.readLong();
FileOutputStream fos = new FileOutputStream(outFilename);
int len;
while(lengthRemaining > 0 
   && (len = dis.read(bytes,0, (int) Math.min(bytes.length, lengthRemaining))) > 0) {
      fos.write(bytes, 0, len);
      lengthRemaining -= len;
}
fos.close();

You could build up program around a well known protocol as FTP. And to send the meta information you could just create a special file with a unique name that contains the info. Afterwards transfer both the user file and the meta file with FTP.

Otherwise, again using FTP for the file you could transfer the meta data in the client-server stream of your hand-written program.

I recommend using the http protocol for this. The server can be implemented using a servlet and Apache HttpClient can be used for the client. This article has some good examples. You can send both the file and the parameters in the same request. And that too with very little code!