Ftp uses TCP as its delivery mechanism so it is intrinisically
stream-based. UDP is more for delivery of blocks or packets of some fixed
length.

As Daniel mentioned, I don't think setting the TCP stack's send buf size
will really accomplish what you want to achieve. Setting the sendbuf
doesn't force the TCP implementation to send only certain size chunks onto
the wire at any one time, it is just a suggestion for how much the TCP
stack will buffer in its pending send queue, and even there, it is only a
suggestion to the stack, it does not need to abide by it on many
implementations.

You probably would need to implement some rate-limiting algorithm that
would possibly work by blocking in your read_callback function, i.e. you
maybe have some timer and keep a tally of bytes read by curl (and assume
they have been put on the wire although this may not technically be true,
e.g. when you write() to a TCP socket, the return value indicates the
amount of data the underlying stack has accepted for delivery but it does
not mean it has actually successfully deleivered it to the perr yet).
Anyway, if your algorithm determines that data is being written "too fast"
you could put a sleep() of some value in your read_callback() to slow down
the transmission.

This is just a theory, not really sure if it is all that clean or how
accurate your algorithm could be to make this useful. Any other thoughts
as I have been kicking around the idea of possibly trying to "rate-limit"
transmissions as well. Ideally, TCP's windowing mechanisms should provide
enough built in flow control and tuning, but some people want the ability
to further tune the i/o usage of individual applications for whatever
purpose.

"Guido Reina" <guidoreina_at_isdn-si.com>
Sent by: curl-library-admin_at_lists.sourceforge.net
10/18/2002 03:15 AM
Please respond to curl-library

 
        To: <curl-library_at_lists.sourceforge.net>
        cc:
        Subject: Re: How to set the size of the send buffer?

I want to send to the FTP server blocks no bigger than <n> bytes (in case
the FTP server has a slow line), does libcurl do it automatically?

Thank you very much for all your effort, you cannot imagine how much you
are
helping me.

Guido Reina.

----- Original Message -----
From: "Daniel Stenberg" <daniel_at_haxx.se>
To: "libcurl Mailing list" <curl-library_at_lists.sourceforge.net>
Sent: Friday, October 18, 2002 9:03 AM
Subject: Re: How to set the size of the send buffer?

> On Thu, 17 Oct 2002, Guido Reina wrote:
>
> > Is there a way to set the size of the send buffer (for FTP)? I have
seen
> > that I can set the size of the receive buffer but not of the send, is
this
> > possible?
>
> Hm, can you please elaborate on what you want to achieve? You return the
data
> that curl uses for upload, why do you need to care how big its internal
> buffer is? Changing the upload buffer size wouldn't change much.
>
> --
> Daniel Stenberg -- curl, cURL, Curl, CURL. Groks URLs.
>
>
>
> -------------------------------------------------------
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Received on 2002-10-18