Limitate speed of a socket-based data transferring

[Tim Williams]

On 14/09/06, Diez B. Roggisch <deets at nospam.web.de> wrote:
> billie schrieb:
> > Hi all. I'm writing a TCP-based application that I will use to trasfer
> > binary files through the network. This piece of code represents how do
> > I get a file from a remote peer and save it on my local hard drive:
> >
> > file_obj = open('downloaded.ext', 'wb')
> > while 1:
> >     buf = sock.recv(2048)
> >     if len(buf) == 0:
> >          break
> >     file_obj.write(buf)
> > file_obj.close()
> > sock.close()
> >
> > I would like to know how could be possible to limit the file transfer
> > speed (for example: don't write more than 50 Kb/sec).
> > Some ideas?
>
> If you are on unix, use trickle. If you must limit it from within your
> own code, I can only assume that computing the transfer rate so far and
> introducing timeouts might help - but I never did such a thing, nor do I
> know what that means for example for the  network stack.
>
> But maybe even then trickle may help you to get an idea, as it is a
> user-space program AFAIK. So they might have some information (at least
> the code... ) out there that could be of use.

You could wrap  buf = sock.recv(xxx) in a data counter and sleep loop
so that you burst to no more than 50KB/s average.

Completely untestest and for illustration only :)

file_obj = open('downloaded.ext', 'wb')
interval = 1.0 #  seconds  eg. 0.5 or 2.0
# smaller the interval, the less bursty and smoother the throughput
max_speed = 51200   # 50k * 1024 =  bytes
data_count = 0   # keep track of the amount of data transferred
time_next = time.time() + interval
while 1:
   buf = sock.recv(512) # smaller chunks = smoother, more accurate
   if len(buf) == 0:
        break
   data_count += len(buf)
   if data_count >= max_speed * interval:
       data_count = 0
       sleep_for =  time_next - time.time()
       if sleep_for > 0:
            time.sleep(sleep_for)
            time_next = time.time() + interval
   file_obj.write(buf)
file_obj.close()
sock.close()