This is the IPv4 packet segmentation and reassembly implementation.

#include "lwip/opt.h"
#include "lwip/ip_frag.h"
#include "lwip/def.h"
#include "lwip/inet_chksum.h"
#include "lwip/netif.h"
#include "lwip/snmp.h"
#include "lwip/stats.h"
#include "lwip/icmp.h"
#include <string.h>

Data Structures
struct	ip_reass_helper
	This is a helper struct which holds the starting offset and the ending offset of this fragment to easily chain the fragments. More...

Macros
#define	IP_ADDRESSES_AND_ID_MATCH(iphdrA, iphdrB)

#define	IP_REASS_CHECK_OVERLAP 1
	The IP reassembly code currently has the following limitations: More...

#define	IP_REASS_FLAG_LASTFRAG 0x01

#define	IP_REASS_FREE_OLDEST 1
	Set to 0 to prevent freeing the oldest datagram when the reassembly buffer is full (IP_REASS_MAX_PBUFS pbufs are enqueued). More...

Functions
err_t	ip_frag (struct pbuf p, struct netif netif, ip_addr_t *dest)
	Fragment an IP datagram if too large for the netif. More...

struct pbuf *	ip_reass (struct pbuf *p)
	Reassembles incoming IP fragments into an IP datagram. More...

static int	ip_reass_chain_frag_into_datagram_and_validate (struct ip_reassdata ipr, struct pbuf new_p)
	Chain a new pbuf into the pbuf list that composes the datagram. More...

static void	ip_reass_dequeue_datagram (struct ip_reassdata ipr, struct ip_reassdata prev)
	Dequeues a datagram from the datagram queue. More...

static struct ip_reassdata *	ip_reass_enqueue_new_datagram (struct ip_hdr *fraghdr, int clen)
	Enqueues a new fragment into the fragment queue. More...

static int	ip_reass_free_complete_datagram (struct ip_reassdata ipr, struct ip_reassdata prev)
	Free a datagram (struct ip_reassdata) and all its pbufs. More...

static int	ip_reass_remove_oldest_datagram (struct ip_hdr *fraghdr, int pbufs_needed)
	Free the oldest datagram to make room for enqueueing new fragments. More...

void	ip_reass_tmr (void)
	Reassembly timer base function for both NO_SYS == 0 and 1 (!). More...

Variables
static u16_t	ip_reass_pbufcount

PACK_STRUCT_BEGIN struct ip_reass_helper	PACK_STRUCT_STRUCT

static struct ip_reassdata *	reassdatagrams

#define IP_ADDRESSES_AND_ID_MATCH	(	iphdrA,
		iphdrB
	)

Value:

(ip_addr_cmp(&(iphdrA)->src, &(iphdrB)->src) && \
   ip_addr_cmp(&(iphdrA)->dest, &(iphdrB)->dest) && \
   IPH_ID(iphdrA) == IPH_ID(iphdrB)) ? 1 : 0

Referenced by ip_reass(), and ip_reass_remove_oldest_datagram().

#define IP_REASS_CHECK_OVERLAP 1

The IP reassembly code currently has the following limitations:

IP header options are not supported
fragments must not overlap (e.g. due to different routes), currently, overlapping or duplicate fragments are thrown away if IP_REASS_CHECK_OVERLAP=1 (the default)!

Todo:: : work with IP header options

Setting this to 0, you can turn off checking the fragments for overlapping regions. The code gets a little smaller. Only use this if you know that overlapping won't occur on your network!

#define IP_REASS_FLAG_LASTFRAG 0x01

Referenced by ip_reass(), and ip_reass_chain_frag_into_datagram_and_validate().

#define IP_REASS_FREE_OLDEST 1

Set to 0 to prevent freeing the oldest datagram when the reassembly buffer is full (IP_REASS_MAX_PBUFS pbufs are enqueued).

The code gets a little smaller. Datagrams will be freed by timeout only. Especially useful when MEMP_NUM_REASSDATA is set to 1, so one datagram can be reassembled at a time, only.

err_t ip_frag	(	struct pbuf *	p,
		struct netif *	netif,
		ip_addr_t *	dest
	)

Fragment an IP datagram if too large for the netif.

Chop the datagram in MTU sized chunks and send them in order by using a fixed size static memory buffer (PBUF_REF) or point PBUF_REFs into p (depending on IP_FRAG_USES_STATIC_BUF).

Parameters

p	ip packet to send
netif	the netif on which to send
dest	destination ip address to which to send

Returns: ERR_OK if sent successfully, err_t otherwise

References ERR_MEM, ERR_OK, htons, if(), inet_chksum(), ip_frag(), IP_HLEN, IP_MF, IP_OFFMASK, IP_REASS_DEBUG, IPFRAG_STATS_INC, IPH_CHKSUM_SET, IPH_LEN_SET, IPH_OFFSET, IPH_OFFSET_SET, iphdr, pbuf::len, LWIP_ASSERT, LWIP_DEBUGF, LWIP_MEM_ALIGN, netif::mtu, pbuf::next, ntohs, NULL, netif::output, pbuf::payload, pbuf_alloc(), pbuf_cat(), pbuf_chain(), pbuf_copy_partial(), pbuf_free(), pbuf_header(), PBUF_IP, PBUF_LINK, PBUF_RAM, PBUF_RAW, pbuf_realloc(), PBUF_REF, pbuf_ref(), snmp_inc_ipfragcreates, snmp_inc_ipfragoks, and pbuf::tot_len.

Referenced by ip_frag(), ip_reass(), and ip_reass_enqueue_new_datagram().

struct pbuf* ip_reass ( struct pbuf * p )

Reassembles incoming IP fragments into an IP datagram.

Parameters

p	points to a pbuf chain of the fragment

Returns: NULL if reassembly is incomplete, ? otherwise

References ip_reassdata::datagram_len, ip_reassdata::flags, htons, if(), inet_chksum(), IP_ADDRESSES_AND_ID_MATCH, ip_frag(), IP_HLEN, IP_MF, IP_OFFMASK, ip_reass_chain_frag_into_datagram_and_validate(), IP_REASS_DEBUG, ip_reass_dequeue_datagram(), ip_reass_enqueue_new_datagram(), IP_REASS_FLAG_LASTFRAG, ip_reass_pbufcount, ip_reass_remove_oldest_datagram(), IPFRAG_STATS_INC, IPH_CHKSUM_SET, IPH_HL, IPH_ID, IPH_LEN, IPH_LEN_SET, IPH_OFFSET, IPH_OFFSET_SET, ip_reassdata::iphdr, LWIP_DEBUGF, ip_reassdata::next, ntohs, NULL, ip_reassdata::p, pbuf::payload, pbuf_cat(), pbuf_clen(), pbuf_free(), pbuf_header(), PP_NTOHS, S16_F, snmp_inc_ipreasmreqds, and X16_F.

Referenced by ip_input().

static int ip_reass_chain_frag_into_datagram_and_validate	(	struct ip_reassdata *	ipr,
		struct pbuf *	new_p
	)

static

Chain a new pbuf into the pbuf list that composes the datagram.

The pbuf list will grow over time as new pbufs are rx. Also checks that the datagram passes basic continuity checks (if the last fragment was received at least once).

Parameters

root_p	points to the 'root' pbuf for the current datagram being assembled.
new_p	points to the pbuf for the current fragment

Returns: 0 if invalid, >0 otherwise

References ip_reassdata::datagram_len, ip_reassdata::flags, if(), IP_HLEN, IP_OFFMASK, IP_REASS_FLAG_LASTFRAG, ip_reass_pbufcount, IPH_HL, IPH_LEN, IPH_OFFSET, pbuf::len, LWIP_ASSERT, ntohs, NULL, ip_reassdata::p, pbuf::payload, pbuf_clen(), and pbuf_free().

Referenced by ip_reass().

static void ip_reass_dequeue_datagram	(	struct ip_reassdata *	ipr,
		struct ip_reassdata *	prev
	)

static

Dequeues a datagram from the datagram queue.

Doesn't deallocate the pbufs.

Parameters

ipr	points to the queue entry to dequeue

References LWIP_ASSERT, memp_free(), ip_reassdata::next, and NULL.

Referenced by ip_reass(), and ip_reass_free_complete_datagram().

static struct ip_reassdata* ip_reass_enqueue_new_datagram	(	struct ip_hdr *	fraghdr,
		int	clen
	)

static

Enqueues a new fragment into the fragment queue.

Parameters

fraghdr	points to the new fragments IP hdr
clen	number of pbufs needed to enqueue (used for freeing other datagrams if not enough space)

Returns: A pointer to the queue location into which the fragment was enqueued

References ip_frag(), IP_HLEN, IP_REASS_DEBUG, ip_reass_remove_oldest_datagram(), IPFRAG_STATS_INC, ip_reassdata::iphdr, LWIP_DEBUGF, memp_malloc(), ip_reassdata::next, NULL, reassdatagrams, and ip_reassdata::timer.

Referenced by ip_reass().

static int ip_reass_free_complete_datagram	(	struct ip_reassdata *	ipr,
		struct ip_reassdata *	prev
	)

static

Free a datagram (struct ip_reassdata) and all its pbufs.

Updates the total count of enqueued pbufs (ip_reass_pbufcount), SNMP counters and sends an ICMP time exceeded packet.

Parameters

ipr	datagram to free
prev	the previous datagram in the linked list

Returns: the number of pbufs freed

References ICMP_TE_FRAG, icmp_time_exceeded(), if(), IP_HLEN, ip_reass_dequeue_datagram(), ip_reass_pbufcount, ip_reassdata::iphdr, LWIP_ASSERT, ip_reassdata::next, NULL, ip_reassdata::p, pbuf::payload, pbuf_clen(), pbuf_free(), and snmp_inc_ipreasmfails.

Referenced by ip_reass_remove_oldest_datagram(), and ip_reass_tmr().

static int ip_reass_remove_oldest_datagram	(	struct ip_hdr *	fraghdr,
		int	pbufs_needed
	)

static

Free the oldest datagram to make room for enqueueing new fragments.

The datagram 'fraghdr' belongs to is not freed!

Parameters

fraghdr	IP header of the current fragment
pbufs_needed	number of pbufs needed to enqueue (used for freeing other datagrams if not enough space)

Returns: the number of pbufs freed

References IP_ADDRESSES_AND_ID_MATCH, ip_reass_free_complete_datagram(), ip_reassdata::iphdr, ip_reassdata::next, NULL, reassdatagrams, and ip_reassdata::timer.

Referenced by ip_reass(), and ip_reass_enqueue_new_datagram().

void ip_reass_tmr ( void )

Reassembly timer base function for both NO_SYS == 0 and 1 (!).

Should be called every 1000 msec (defined by IP_TMR_INTERVAL).

References IP_REASS_DEBUG, ip_reass_free_complete_datagram(), LWIP_DEBUGF, ip_reassdata::next, NULL, reassdatagrams, ip_reassdata::timer, and U16_F.

Referenced by ip_reass_timer().

u16_t ip_reass_pbufcount

static

Referenced by ip_reass(), ip_reass_chain_frag_into_datagram_and_validate(), and ip_reass_free_complete_datagram().

PACK_STRUCT_BEGIN struct ip_reass_helper PACK_STRUCT_STRUCT

struct ip_reassdata* reassdatagrams

static

Referenced by ip_reass_enqueue_new_datagram(), ip_reass_remove_oldest_datagram(), and ip_reass_tmr().

Microchip® Advanced Software Framework

Data Structures

Macros

Functions

Variables