CODEWITHSUNDEEP
javaandroidudptransfernetcat
user3137385
user3137385

Reputation: 315

android, netcat: how to send more than 2048 Byte over UDP

I'm trying to implement data transfer from a Notebook (Linux) to an Android Device over UDP.

On the notebook I launch:

cat /home/me/my/file.txt | nc -u 192.168.150.3 12345

Or:

nc -u 192.168.150.3 12345 < /home/me/my/file.txt

getting same result.

On the Android Device my code is:

byte[] msg = new byte[100000];

DatagramPacket p = new DatagramPacket(msg, msg.length);
DatagramSocket s = new DatagramSocket(portNumber);
s.receive(p);

message = new String(msg, 0, p.getLength());

s.close();

If I set a breakpoint on the line with "message =" I can see msg.length = 100000. That's right. But p.getLength() is only 2048. That means only a part of my data is transferred. I mean "message" doesn't contain all data which is in "file.txt". Why does it happen? What do I do wrong?

Upvotes: 0

Views: 1351

Answers (1)

Steffen Ullrich
Steffen Ullrich

Reputation: 123531

nc does not send the whole file in a single UDP packet, so don't expect to get it in a single call to receive. You must call receive multiple times until everything is complete. Of course, with UDP you get no "end of connection", so you must have some other indicator that you got all data. And, with UDP packets can be silently lost or reordered, so there is no guarantee that you get the file the way you want.

Upvotes: 1

Related Questions