CheckedInputStream + DataOutputStream problem

Question

Hi. I've been working on a simple File transfer / IM program using tcp sockets. I decided to add a checksum calc to the file transfer process, but this led into problems. Here's the problem in detail (code snippet simplified):
File sender code:
<code>
// Tcp connection through Socket fsock
byte[] buffer = new byte[1024*50];
DataOutputStream dos = new DataOutputStream(fsock.getOutputStream());
FileInputStream fis = new FileInputStream("anyfile.wtf");
CheckedInputStream cin = new CheckedInputStream(fis, new Adler32());
BufferedInputStream bis = new BufferedInputStream(cin);
int len = 0;
while ((len = bis.read(buffer)) != -1)
dos.write(buffer, 0, len);
dos.flush();
//calc checksum etc.
//close streams
</code>
File receiver code:
<code>
byte[] buffer = new byte[1024*50];
DataInputStream dis = new DataInputStream(fsock.getInputStream());
FileOutputStream fos = new FileOutputStream("anyfile.wtf");
CheckedOutputStream cout = new CheckedOutputStream(fos, new Adler32());
BufferedOutputStream bos = new BufferedOutputStream(cout);
int len = 0;
while ((len = dis.read(buffer)) != -1)
bos.write(buffer, 0, len);
bos.flush();
// calc checksum etc.
// close streams
</code>
The problem is that, for some reason, in the file receiving end, the dis.read(buffer) call blocks forever (as if it does not receive end of file) and never returns -1.
If I, however, remove the CheckedInputStream (cin) and connect BufferedInputStream (bis) and FileInputStream (fis) directly, the problem disappears.
Whats up with this?
Cheers, Jukka

Answer 1

Well. I got the program working fine. But I'm still curious as to why I was unable to make the checksum add up to 0, since it would simplify my code a bit further.
Currently I'm just comparing the checksums calculated at both the sending and receiving end...another stripped code snippet showing this below.
Sender:
// open streams
fdos.writeUTF(file.getName());
fdos.writeLong(file.length());
fdos.flush();
writeMsg("Transferring file (" + file.getName() + ")...");
int len = 0;
while ((len = bis.read(buffer)) != -1)
  fdos.write(buffer, 0, len);
fdos.writeLong(cout.getChecksum().getValue());
fdos.flush();
// close streamsReceiver:
// open streams
String fname = fdis.readUTF();
long flength = fdis.readLong();
writeMsg("Receiving file " + fname + "...");
long received = 0;
int len = 0;
while (received < flength && len != -1)
  if (flength - received < BUFFER_SIZE)
    len = fdis.read(buffer, 0, (int)(flength - received));
    bos.write(buffer, 0, len);
  else
    len = fdis.read(buffer);
    bos.write(buffer, 0, len);
  received += len;
bos.flush();
long chksumCalc = cin.getChecksum().getValue(); 
long chksumRcvd = fdis.readLong();
// close streamsAny suggestions? Or perhaps a small example that shows how the checksum really evaluates to zero?
Thanks, Jukka