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Re: [lwip-users] netconn_write, "Flush" functionality

From: Simon Goldschmidt
Subject: Re: [lwip-users] netconn_write, "Flush" functionality
Date: Tue, 14 Jun 2011 14:25:33 +0200

"Walter Saegesser" <address@hidden> wrote:
> Quite a long time ago a read somewhere - don't ask me where, it was not
> on this mailing list - that a statement like "xNewConn->pcb.tcp->flags
> |= TF_NODELAY;" would force the netconn API to write data out
> immediately. 

This is a *very* bad example since you are accessing internals of the stack. 
Please use this code instead:


The tcp_nagle_*() functions were added in 1.4.0 only (I think) but using them 
is strongly encouraged over directly accessing pcb members!

> What is the behavior of netconn_write if this flag is not set, i.e. what
> is the criterion to actually write the data?

The code you stated disables the nagle algorithm, which is enabled by default. 
For details, see:


> Is there in the meantime a more appropriate solution to flush the buffer
> at the end of a sequence of netconn_writes?

No, buffering data is TCP behaviour, not netconn specific. You could leave 
nagle enabled until just before writing the last bytes, which would flush all 
bytes out, but I think that's rather a hack, too.

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