Re: [lwip-users] What is pbuf's payload?

[Pomeroy, Marty]

 

Well, assuming "unsigned char * packet" is a pointer to your received byte array:

 

if ( (*(short *)&packet[12]) == 0x0800  && packet[23] == 0x11)  // 0x800 is IP packet, 0x11 is UDP protocol byte in IP header

 

you have a UDP packet (verify those offsets are correct).  You can look at this before it gets passed in to tcpip_input().

 

Was this what you were looking for?

 

Marty

 

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From: address@hidden [mailto:address@hidden On Behalf Of Chen
Sent: Friday, August 03, 2012 10:58 AM
To: address@hidden
Subject: Re: [lwip-users] What is pbuf's payload?

Sorry, but I am answering my own question 
again...

1) tcpip_input posts the message TCPIP_MSG_INPUT with pbuf, 
along with its payload
2) tcpip_thread picks up the message and calls 
ethernet_input because NETIF_FLAG_ETHARP was set in low_level_init during 
ethernetif_init
3) ethernet_input 
looks at pbuf's payload, which starts with Ethernet header, and based on the 
type, it calls ip_input or others

I'd like to catch an UDP packet without parcing it all the way. If anyone 
has any pointer, please suggest, thanks


> Date: Thu, 02 Aug 2012 16:53:57 
>   -0400
> From: Chen <address@hidden>
> To: 
>   address@hidden
> Subject: [lwip-users] What is pbuf's 
>   payload?
> Message-ID: 
>   <address@hidden>
> Content-Type: text/plain; 
>   charset="us-ascii"; Format="flowed"
>
> Hi there,
>
> I am trying to 
>   understand pbuf's payload referenced in 
> tcpip_input(struct pbuf *p, struct 
>   netif *inp)
>
> pbuf's payload is defined as void *, what are the possible 
>   structures 
> it can be under tcpip_input()?
>
> since tcpip_input deals 
>   with udp and tcp only, is it just the actual 
> data from udp and tcp 
>   packets?
>
> thanks for any 
> pointer
>
> Chen