Re: [lwip-devel] pbuf_cat() does not update total_len

[Bill Auerbach]

Hello,

My understanding is that the head is pbuf to reference for total length and
is how I've used it for years.  I pbuf_cat on each recv callback to create a
"stream" of pbufs.  I have a routine to pull data off the front keeping the
chain intact.  The head is used for the total length in the chain.

Bill

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf
Of Laurenz Kamp
Sent: Tuesday, February 03, 2015 11:37 AM
To: address@hidden
Subject: [lwip-devel] pbuf_cat() does not update total_len

Hello,

let's assume I want to merge two pbufs into one and I use pbuf_cat() for the
task.
a and b are the pbufs I want to merge:

First pbuf:     a.len = 10;
                a.total_len = 10;
                a.next = NULL;
Second pbuf:    b.len = 15;
                b.total_len = 15;
                b.next = NULL;

After I call pbuf_cat(a, b), I have the following setup:

First pbuf:     a.len = 10;
                a.total_len = 25;
                a.next = b;
Second pbuf:    b.len = 15;
                b.total_len = 15;  <-- Should be 25.
                b.next = NULL;


As far as I understand, all pbufs in a chain have the same total_len value,
but pbuf_cat doesn't update b.total_len. Is this behavior intentioned or a
bug?


Best regards,

Laurenz Kamp

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