LWIP 分析二之udp

直接上upd_input

void

udp_input(struct pbuf *p, struct netif *inp)

{

struct udp_hdr *udphdr;

struct udp_pcb *pcb, *prev;

struct udp_pcb *uncon_pcb;

struct ip_hdr *iphdr;

u16_t src, dest;

u8_t local_match;

PERF_START; //看到这个是不是想起来perf.h里的内容了呀

UDP_STATS_INC(udp.recv);

iphdr = p->payload;

/* Check minimum length (IP header + UDP header)

* and move payload pointer to UDP header */

if (p->tot_len < (IPH_HL(iphdr) * 4 + UDP_HLEN) || pbuf_header(p, -(s16_t)(IPH_HL(iphdr) * 4))) { //判断接收的数据符不符合规范, 且将p->payload移到udp头部

/* drop short packets */

LWIP_DEBUGF(UDP_DEBUG,

("udp_input: short UDP datagram (%"U16_F" bytes) discarded\n", p->tot_len));

UDP_STATS_INC(udp.lenerr);

UDP_STATS_INC(udp.drop);

snmp_inc_udpinerrors();

pbuf_free(p);

goto end;

}

udphdr = (struct udp_hdr *)p->payload;

LWIP_DEBUGF(UDP_DEBUG, ("udp_input: received datagram of length %"U16_F"\n", p->tot_len));

/* convert src and dest ports to host byte order */

src = ntohs(udphdr->src);

dest = ntohs(udphdr->dest);

udp_debug_print(udphdr);

/* print the UDP source and destination */

LWIP_DEBUGF(UDP_DEBUG,

("udp (%"U16_F".%"U16_F".%"U16_F".%"U16_F", %"U16_F") <-- "

"(%"U16_F".%"U16_F".%"U16_F".%"U16_F", %"U16_F")\n",

ip4_addr1(&iphdr->dest), ip4_addr2(&iphdr->dest),

ip4_addr3(&iphdr->dest), ip4_addr4(&iphdr->dest), ntohs(udphdr->dest),

ip4_addr1(&iphdr->src), ip4_addr2(&iphdr->src),

ip4_addr3(&iphdr->src), ip4_addr4(&iphdr->src), ntohs(udphdr->src)));

#if LWIP_DHCP

pcb = NULL;

/* when LWIP_DHCP is active, packets to DHCP_CLIENT_PORT may only be processed by

the dhcp module, no other UDP pcb may use the local UDP port DHCP_CLIENT_PORT */

if (dest == DHCP_CLIENT_PORT) {

/* all packets for DHCP_CLIENT_PORT not coming from DHCP_SERVER_PORT are dropped! */

if (src == DHCP_SERVER_PORT) {

if ((inp->dhcp != NULL) && (inp->dhcp->pcb != NULL)) {

/* accept the packe if

(- broadcast or directed to us) -> DHCP is link-layer-addressed, local ip is always ANY!

- inp->dhcp->pcb->remote == ANY or iphdr->src */

if ((ip_addr_isany(&inp->dhcp->pcb->remote_ip) ||

ip_addr_cmp(&(inp->dhcp->pcb->remote_ip), &(iphdr->src)))) {

pcb = inp->dhcp->pcb;

}

}

}

} else

#endif /* LWIP_DHCP */

{

prev = NULL;

local_match = 0;

uncon_pcb = NULL;

/* Iterate through the UDP pcb list for a matching pcb.

* 'Perfect match' pcbs (connected to the remote port & ip address) are

* preferred. If no perfect match is found, the first unconnected pcb that

* matches the local port and ip address gets the datagram. */

for (pcb = udp_pcbs; pcb != NULL; pcb = pcb->next) { //从udp_pcbs里找寻符合目标的udp控制块

local_match = 0;

/* print the PCB local and remote address */

LWIP_DEBUGF(UDP_DEBUG,

("pcb (%"U16_F".%"U16_F".%"U16_F".%"U16_F", %"U16_F") --- "

"(%"U16_F".%"U16_F".%"U16_F".%"U16_F", %"U16_F")\n",

ip4_addr1(&pcb->local_ip), ip4_addr2(&pcb->local_ip),

ip4_addr3(&pcb->local_ip), ip4_addr4(&pcb->local_ip), pcb->local_port,

ip4_addr1(&pcb->remote_ip), ip4_addr2(&pcb->remote_ip),

ip4_addr3(&pcb->remote_ip), ip4_addr4(&pcb->remote_ip), pcb->remote_port));

/* compare PCB local addr+port to UDP destination addr+port */

if ((pcb->local_port == dest) &&

(ip_addr_isany(&pcb->local_ip) ||

ip_addr_cmp(&(pcb->local_ip), &(iphdr->dest)) ||

#if LWIP_IGMP

ip_addr_ismulticast(&(iphdr->dest)) ||

#endif /* LWIP_IGMP */

ip_addr_isbroadcast(&(iphdr->dest), inp)))
{ //判断接收的地址对不对，包括端口

local_match = 1;

if ((uncon_pcb == NULL) &&

((pcb->flags & UDP_FLAGS_CONNECTED) == 0)) {

/* the first unconnected matching PCB */

uncon_pcb = pcb;

}

}

/* compare PCB remote addr+port to UDP source addr+port */

if ((local_match != 0) &&

(pcb->remote_port == src) &&

(ip_addr_isany(&pcb->remote_ip) ||

ip_addr_cmp(&(pcb->remote_ip), &(iphdr->src)))) {

/* the first fully matching PCB */

if (prev != NULL) {

/* move the pcb to the front of udp_pcbs so that is

found faster next time */

prev->next = pcb->next;

pcb->next = udp_pcbs;

udp_pcbs = pcb;

} else {

UDP_STATS_INC(udp.cachehit);

}

break;

}

prev = pcb;

}

/* no fully matching pcb found? then look for an unconnected pcb */

if (pcb == NULL) {

pcb = uncon_pcb;

}

}

/* Check checksum if this is a match or if it was directed at us. */

if (pcb != NULL || ip_addr_cmp(&inp->ip_addr, &iphdr->dest)) {

LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_input: calculating checksum\n"));

#if LWIP_UDPLITE

if (IPH_PROTO(iphdr) == IP_PROTO_UDPLITE) {

/* Do the UDP Lite checksum */

#if CHECKSUM_CHECK_UDP

u16_t chklen = ntohs(udphdr->len);

if (chklen < sizeof(struct udp_hdr)) {

if (chklen == 0) {

/* For UDP-Lite, checksum length of 0 means checksum

over the complete packet (See RFC 3828 chap. 3.1) */

chklen = p->tot_len;

} else {

/* At least the UDP-Lite header must be covered by the

checksum! (Again, see RFC 3828 chap. 3.1) */

UDP_STATS_INC(udp.chkerr);

UDP_STATS_INC(udp.drop);

snmp_inc_udpinerrors();

pbuf_free(p);

goto end;

}

}

if (inet_chksum_pseudo_partial(p, (struct ip_addr *)&(iphdr->src),

(struct ip_addr *)&(iphdr->dest),

IP_PROTO_UDPLITE, p->tot_len, chklen) != 0) {

LWIP_DEBUGF(UDP_DEBUG | 2,

("udp_input: UDP Lite datagram discarded due to failing checksum\n"));

UDP_STATS_INC(udp.chkerr);

UDP_STATS_INC(udp.drop);

snmp_inc_udpinerrors();

pbuf_free(p);

goto end;

}

#endif /* CHECKSUM_CHECK_UDP */

} else

#endif /* LWIP_UDPLITE */

{

#if CHECKSUM_CHECK_UDP

if (udphdr->chksum != 0) {

if (inet_chksum_pseudo(p, (struct ip_addr *)&(iphdr->src),

(struct ip_addr *)&(iphdr->dest),

IP_PROTO_UDP, p->tot_len) != 0) {

LWIP_DEBUGF(UDP_DEBUG | 2,

("udp_input: UDP datagram discarded due to failing checksum\n"));

UDP_STATS_INC(udp.chkerr);

UDP_STATS_INC(udp.drop);

snmp_inc_udpinerrors();

pbuf_free(p);

goto end;

}

}

#endif /* CHECKSUM_CHECK_UDP */

}

if(pbuf_header(p, -UDP_HLEN)) { //将p->payload移到数据区域

/* Can we cope with this failing? Just assert for now */

LWIP_ASSERT("pbuf_header failed\n", 0);

UDP_STATS_INC(udp.drop);

snmp_inc_udpinerrors();

pbuf_free(p);

goto end;

}

if (pcb != NULL) {

snmp_inc_udpindatagrams();

/* callback */

if (pcb->recv != NULL) {

/* now the recv function is responsible for freeing p */

pcb->recv(pcb->recv_arg, pcb, p, &(iphdr->src), src); //这里调用udp回调函数，通过udp_accept函数实现

} else {

/* no recv function registered? then we have to free the pbuf! */

pbuf_free(p);

goto end;

}

} else {

LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_input: not for us.\n"));

#if LWIP_ICMP

/* No match was found, send ICMP destination port unreachable unless

destination address was broadcast/multicast. */

if (!ip_addr_isbroadcast(&iphdr->dest, inp) &&

!ip_addr_ismulticast(&iphdr->dest)) {

/* move payload pointer back to ip header */

pbuf_header(p, (IPH_HL(iphdr) * 4) + UDP_HLEN);

LWIP_ASSERT("p->payload == iphdr", (p->payload == iphdr));

icmp_dest_unreach(p, ICMP_DUR_PORT); //如果不是，发送ICMP报文

}

#endif /* LWIP_ICMP */

UDP_STATS_INC(udp.proterr);

UDP_STATS_INC(udp.drop);

snmp_inc_udpnoports();

pbuf_free(p);

}

} else {

pbuf_free(p);

}

end:

PERF_STOP("udp_input");

}