On Thu, 27 Mar 2008, Cloutier, Joseph (Joseph) wrote:

> We have a slow throughput problem with curl for uplink (from a W2K sniffer)
> to FTP server problems.
>
> The root cause issue is TCP delayed ACKs. When a packet arrives at the FTP
> server the server will wait for 200 ms to send out an ACK if another packet
> is not received.
>
> We can stop this behavior using the TcpAckFrequence setting in the FTP XP or
> W2K server, but I am worried this might affect other applications running on
> that server.
>
> Does anyone know of a way to increase curl's buffer size from 0x4000 to, say
> 0xffff? Or is there a way for curl to open up the TCP window?

So libcurl's choice of application level buffer size can cause this flaw to
trigger? Seems like a blatant flaw in the TCP/IP stack to me. But of course
that doesn't help at all...

Increasing the buffer size is of course easy but requires a recompile: change
the CURL_MAX_WRITE_SIZE define in curl/curl.h and recompile.

Chaning the TCP window or any other socket-layer things can be done by setting
a CURLOPT_SOCKOPTFUNCTION callback and do whatever you deem necessary.

Please let us know if you figure out a combo of these that makes things run
better!

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