Octave Sockets Package, how to receive large data streams - sockets

Question

I still have problems with Octave. I need to receive large (>10M) images via a web socket connection, process the data and send it back. I work with Octave 4.2.1 in Windows 7, the sockets package is version 1.2.0 and can be found here: https://octave.sourceforge.io/sockets/
Here is the minimal code example:
pkg load sockets;
rcv_sck=socket(AF_INET, SOCK_STREAM, 0);
bind(rcv_sck,12345);
a=listen(rcv_sck,0);
b=accept(rcv_sck);
data = [];
bufflen = 4600;
total = 0;
count = 0;
while (total < 10000)
[buff,count]=recv(b, bufflen);
data = horzcat(data, buff);
total += count;
endwhile
disconnect (b);
disconnect (rcv_sck);
fileID = fopen('data.jpg','w');
fwrite('data.jpg', data);
fclose(fileID);
imshow ('data.jpg')
it can be tested with netcat
ncat.exe 127.0.0.1 12345 < test.jpg
My problem is, that I am not able to receive data bigger than 4608 bytes. If I send more data, the receive array is cut to this size. This is why i choose 4600 bytes as a buffer length. Now I try to put the chunks of small data blocks together to get the correct data.
But this has two serious issues:
1) I have to know the size of the data I am sending, a problem which can be solved by sending the size first as a parameter. In my example i have set the size to 10000 bytes.
2) More important: it is terribly slow. For a jpeg of 170kB it takes 7 seconds to send the data.
Any hints or tipps are greatly appreciated, thank you.
jan

Answer 1

If you want to read data until disconnect I would suggest
data = recv (b, Inf, MSG_WAITALL);
without any loop or horcat. And on your client side (netcat) use -q0:
netcat.exe -q0 localhost 12345 < test.jpg
Btw, if you want to store it on the server side, why don't you use
system ("netcat -l -p 12345 > data.jpg");
in the first place?