/*** \addtogroup uip* @{*//*** \file* The uIP TCP/IP stack code.* \author Adam Dunkels <adam@dunkels.com>*//** Copyright (c) 2001-2003, Adam Dunkels.* All rights reserved.** Redistribution and use in source and binary forms, with or without* modification, are permitted provided that the following conditions* are met:* 1. Redistributions of source code must retain the above copyright* notice, this list of conditions and the following disclaimer.* 2. Redistributions in binary form must reproduce the above copyright* notice, this list of conditions and the following disclaimer in the* documentation and/or other materials provided with the distribution.* 3. The name of the author may not be used to endorse or promote* products derived from this software without specific prior* written permission.** THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS* OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE* GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.** This file is part of the uIP TCP/IP stack.** $Id: uip.c,v 1.62.2.10 2003/10/07 13:23:01 adam Exp $**//*This is a small implementation of the IP and TCP protocols (as well assome basic ICMP stuff). The implementation couples the IP, TCP and theapplication layers very tightly. To keep the size of the compiled codedown, this code also features heavy usage of the goto statement.The principle is that we have a small buffer, called the uip_buf, inwhich the device driver puts an incoming packet. The TCP/IP stackparses the headers in the packet, and calls upon the application. Ifthe remote host has sent data to the application, this data is presentin the uip_buf and the application read the data from there. It is upto the application to put this data into a byte stream if needed. Theapplication will not be fed with data that is out of sequence.If the application whishes to send data to the peer, it should put itsdata into the uip_buf, 40 bytes from the start of the buffer. TheTCP/IP stack will calculate the checksums, and fill in the necessaryheader fields and finally send the packet back to the peer.*/#include "uip.h"#include "uipopt.h"#include "uip_arch.h"#include "string.h"/*-----------------------------------------------------------------------------------*//* Variable definitions. *//* The IP address of this host. If it is defined to be fixed (by setting UIP_FIXEDADDR to 1 in uipopt.h), the address is set here. Otherwise, the address */#if UIP_FIXEDADDR > 0const u16_t uip_hostaddr[2] ={HTONS((UIP_IPADDR0 << 8) | UIP_IPADDR1),HTONS((UIP_IPADDR2 << 8) | UIP_IPADDR3)};const u16_t uip_arp_draddr[2] ={HTONS((UIP_DRIPADDR0 << 8) | UIP_DRIPADDR1),HTONS((UIP_DRIPADDR2 << 8) | UIP_DRIPADDR3)};const u16_t uip_arp_netmask[2] ={HTONS((UIP_NETMASK0 << 8) | UIP_NETMASK1),HTONS((UIP_NETMASK2 << 8) | UIP_NETMASK3)};#elseu16_t uip_hostaddr[2];u16_t uip_arp_draddr[2], uip_arp_netmask[2];#endif /* UIP_FIXEDADDR */u8_t uip_buf[UIP_BUFSIZE+2]; /* The packet buffer that containsincoming packets. */volatile u8_t *uip_appdata; /* The uip_appdata pointer points toapplication data. */volatile u8_t *uip_sappdata; /* The uip_appdata pointer points to theapplication data which is to be sent. */#if UIP_URGDATA > 0volatile u8_t *uip_urgdata; /* The uip_urgdata pointer points tourgent data (out-of-band data), ifpresent. */u8_t uip_urglen, uip_surglen;#endif /* UIP_URGDATA > 0 */u16_t uip_len, uip_slen;/* The uip_len is either 8 or 16 bits,depending on the maximum packetsize. */volatile u8_t uip_flags; /* The uip_flags variable is used forcommunication between the TCP/IP stackand the application program. */struct uip_conn *uip_conn; /* uip_conn always points to the currentconnection. */struct uip_conn uip_conns[UIP_CONNS];/* The uip_conns array holds all TCPconnections. */u16_t uip_listenports[UIP_LISTENPORTS];/* The uip_listenports list all currentlylistning ports. */#if UIP_UDPstruct uip_udp_conn *uip_udp_conn;struct uip_udp_conn uip_udp_conns[UIP_UDP_CONNS];#endif /* UIP_UDP */static u16_t ipid; /* Ths ipid variable is an increasingnumber that is used for the IP IDfield. */static u8_t iss[4]; /* The iss variable is used for the TCPinitial sequence number. */#if UIP_ACTIVE_OPENstatic u16_t lastport; /* Keeps track of the last port used fora new connection. */#endif /* UIP_ACTIVE_OPEN *//* Temporary variables. */volatile u8_t uip_acc32[4];static u8_t c, opt;static u16_t tmp16;/* Structures and definitions. */#define TCP_FIN 0x01#define TCP_SYN 0x02#define TCP_RST 0x04#define TCP_PSH 0x08#define TCP_ACK 0x10#define TCP_URG 0x20#define TCP_CTL 0x3f#define ICMP_ECHO_REPLY 0#define ICMP_ECHO 8/* Macros. */#define BUF ((uip_tcpip_hdr *)&uip_buf[UIP_LLH_LEN])#define FBUF ((uip_tcpip_hdr *)&uip_reassbuf[0])#define ICMPBUF ((uip_icmpip_hdr *)&uip_buf[UIP_LLH_LEN])#define UDPBUF ((uip_udpip_hdr *)&uip_buf[UIP_LLH_LEN])#if UIP_STATISTICS == 1struct uip_stats uip_stat;#define UIP_STAT(s) s#else#define UIP_STAT(s)#endif /* UIP_STATISTICS == 1 */#if UIP_LOGGING == 1#include <stdio.h>void uip_log(char *msg);#define UIP_LOG(m) uip_log(m)#else#define UIP_LOG(m)#endif /* UIP_LOGGING == 1 *//*-----------------------------------------------------------------------------------*/void uip_init(void){for(c = 0; c < UIP_LISTENPORTS; ++c) {uip_listenports[c] = 0;}for(c = 0; c < UIP_CONNS; ++c) {uip_conns[c].tcpstateflags = CLOSED;}#if UIP_ACTIVE_OPENlastport = 1024;#endif /* UIP_ACTIVE_OPEN */#if UIP_UDPfor(c = 0; c < UIP_UDP_CONNS; ++c) {uip_udp_conns[c].lport = 0;}#endif /* UIP_UDP *//* IPv4 initialization. */#if UIP_FIXEDADDR == 0uip_hostaddr[0] = uip_hostaddr[1] = 0;#endif /* UIP_FIXEDADDR */}/*-----------------------------------------------------------------------------------*/#if UIP_ACTIVE_OPENstruct uip_conn * uip_connect(u16_t *ripaddr, u16_t rport){register struct uip_conn *conn, *cconn;/* Find an unused local port. */again:++lastport;if(lastport >= 32000) {lastport = 4096;}/* Check if this port is already in use, and if so try to findanother one. */for(c = 0; c < UIP_CONNS; ++c) {conn = &uip_conns[c];if(conn->tcpstateflags != CLOSED &&conn->lport == htons(lastport)) {goto again;}}conn = 0;for(c = 0; c < UIP_CONNS; ++c) {cconn = &uip_conns[c];if(cconn->tcpstateflags == CLOSED) {conn = cconn;break;}if(cconn->tcpstateflags == TIME_WAIT) {if(conn == 0 ||cconn->timer > uip_conn->timer) {conn = cconn;}}}if(conn == 0) {return 0;}conn->tcpstateflags = SYN_SENT;conn->snd_nxt[0] = iss[0];conn->snd_nxt[1] = iss[1];conn->snd_nxt[2] = iss[2];conn->snd_nxt[3] = iss[3];conn->initialmss = conn->mss = UIP_TCP_MSS;conn->len = 1; /* TCP length of the SYN is one. */conn->nrtx = 0;conn->timer = 1; /* Send the SYN next time around. */conn->rto = UIP_RTO;conn->sa = 0;conn->sv = 16;conn->lport = htons(lastport);conn->rport = rport;conn->ripaddr[0] = ripaddr[0];conn->ripaddr[1] = ripaddr[1];return conn;}#endif /* UIP_ACTIVE_OPEN *//*-----------------------------------------------------------------------------------*/#if UIP_UDPstruct uip_udp_conn *uip_udp_new(u16_t *ripaddr, u16_t rport){register struct uip_udp_conn *conn;/* Find an unused local port. */again:++lastport;if(lastport >= 32000) {lastport = 4096;}for(c = 0; c < UIP_UDP_CONNS; ++c) {if(uip_udp_conns[c].lport == lastport) {goto again;}}conn = 0;for(c = 0; c < UIP_UDP_CONNS; ++c) {if(uip_udp_conns[c].lport == 0) {conn = &uip_udp_conns[c];break;}}if(conn == 0) {return 0;}conn->lport = HTONS(lastport);conn->rport = HTONS(rport);conn->ripaddr[0] = ripaddr[0];conn->ripaddr[1] = ripaddr[1];return conn;}#endif /* UIP_UDP *//*-----------------------------------------------------------------------------------*/voiduip_unlisten(u16_t port){for(c = 0; c < UIP_LISTENPORTS; ++c) {if(uip_listenports[c] == port) {uip_listenports[c] = 0;return;}}}/*-----------------------------------------------------------------------------------*/voiduip_listen(u16_t port){for(c = 0; c < UIP_LISTENPORTS; ++c) {if(uip_listenports[c] == 0) {uip_listenports[c] = port;return;}}}/*-----------------------------------------------------------------------------------*//* XXX: IP fragment reassembly: not well-tested. */#if UIP_REASSEMBLY#define UIP_REASS_BUFSIZE (UIP_BUFSIZE - UIP_LLH_LEN)static u8_t uip_reassbuf[UIP_REASS_BUFSIZE];static u8_t uip_reassbitmap[UIP_REASS_BUFSIZE / (8 * 8)];static const u8_t bitmap_bits[8] = {0xff, 0x7f, 0x3f, 0x1f,0x0f, 0x07, 0x03, 0x01};static u16_t uip_reasslen;static u8_t uip_reassflags;#define UIP_REASS_FLAG_LASTFRAG 0x01static u8_t uip_reasstmr;#define IP_HLEN 20#define IP_MF 0x20static u8_tuip_reass(void){u16_t offset, len;u16_t i;/* If ip_reasstmr is zero, no packet is present in the buffer, so wewrite the IP header of the fragment into the reassemblybuffer. The timer is updated with the maximum age. */if(uip_reasstmr == 0) {memcpy(uip_reassbuf, &BUF->vhl, IP_HLEN);uip_reasstmr = UIP_REASS_MAXAGE;uip_reassflags = 0;/* Clear the bitmap. */memset(uip_reassbitmap, sizeof(uip_reassbitmap), 0);}/* Check if the incoming fragment matches the one currently presentin the reasembly buffer. If so, we proceed with copying thefragment into the buffer. */if(BUF->srcipaddr[0] == FBUF->srcipaddr[0] &&BUF->srcipaddr[1] == FBUF->srcipaddr[1] &&BUF->destipaddr[0] == FBUF->destipaddr[0] &&BUF->destipaddr[1] == FBUF->destipaddr[1] &&BUF->ipid[0] == FBUF->ipid[0] &&BUF->ipid[1] == FBUF->ipid[1]) {len = (BUF->len[0] << 8) + BUF->len[1] - (BUF->vhl & 0x0f) * 4;offset = (((BUF->ipoffset[0] & 0x3f) << 8) + BUF->ipoffset[1]) * 8;/* If the offset or the offset + fragment length overflows thereassembly buffer, we discard the entire packet. */if(offset > UIP_REASS_BUFSIZE ||offset + len > UIP_REASS_BUFSIZE) {uip_reasstmr = 0;goto nullreturn;}/* Copy the fragment into the reassembly buffer, at the rightoffset. */memcpy(&uip_reassbuf[IP_HLEN + offset],(char *)BUF + (int)((BUF->vhl & 0x0f) * 4),len);/* Update the bitmap. */if(offset / (8 * 8) == (offset + len) / (8 * 8)) {/* If the two endpoints are in the same byte, we only updatethat byte. */uip_reassbitmap[offset / (8 * 8)] |=bitmap_bits[(offset / 8 ) & 7] &~bitmap_bits[((offset + len) / 8 ) & 7];} else {/* If the two endpoints are in different bytes, we update thebytes in the endpoints and fill the stuff inbetween with0xff. */uip_reassbitmap[offset / (8 * 8)] |=bitmap_bits[(offset / 8 ) & 7];for(i = 1 + offset / (8 * 8); i < (offset + len) / (8 * 8); ++i) {uip_reassbitmap[i] = 0xff;}uip_reassbitmap[(offset + len) / (8 * 8)] |=~bitmap_bits[((offset + len) / 8 ) & 7];}/* If this fragment has the More Fragments flag set to zero, weknow that this is the last fragment, so we can calculate thesize of the entire packet. We also set theIP_REASS_FLAG_LASTFRAG flag to indicate that we have receivedthe final fragment. */if((BUF->ipoffset[0] & IP_MF) == 0) {uip_reassflags |= UIP_REASS_FLAG_LASTFRAG;uip_reasslen = offset + len;}/* Finally, we check if we have a full packet in the buffer. We dothis by checking if we have the last fragment and if all bitsin the bitmap are set. */if(uip_reassflags & UIP_REASS_FLAG_LASTFRAG) {/* Check all bytes up to and including all but the last byte inthe bitmap. */for(i = 0; i < uip_reasslen / (8 * 8) - 1; ++i) {if(uip_reassbitmap[i] != 0xff) {goto nullreturn;}}/* Check the last byte in the bitmap. It should contain just theright amount of bits. */if(uip_reassbitmap[uip_reasslen / (8 * 8)] !=(u8_t)~bitmap_bits[uip_reasslen / 8 & 7]) {goto nullreturn;}/* If we have come this far, we have a full packet in thebuffer, so we allocate a pbuf and copy the packet into it. Wealso reset the timer. */uip_reasstmr = 0;memcpy(BUF, FBUF, uip_reasslen);/* Pretend to be a "normal" (i.e., not fragmented) IP packetfrom now on. */BUF->ipoffset[0] = BUF->ipoffset[1] = 0;BUF->len[0] = uip_reasslen >> 8;BUF->len[1] = uip_reasslen & 0xff;BUF->ipchksum = 0;BUF->ipchksum = ~(uip_ipchksum());return uip_reasslen;}}nullreturn:return 0;}#endif /* UIP_REASSEMBL *//*-----------------------------------------------------------------------------------*/static voiduip_add_rcv_nxt(u16_t n){uip_add32(uip_conn->rcv_nxt, n);uip_conn->rcv_nxt[0] = uip_acc32[0];uip_conn->rcv_nxt[1] = uip_acc32[1];uip_conn->rcv_nxt[2] = uip_acc32[2];uip_conn->rcv_nxt[3] = uip_acc32[3];}/*-----------------------------------------------------------------------------------*/voiduip_process(u8_t flag){register struct uip_conn *uip_connr = uip_conn;uip_appdata = &uip_buf[40 + UIP_LLH_LEN];/* Check if we were invoked because of the perodic timer fireing. */if(flag == UIP_TIMER) {#if UIP_REASSEMBLYif(uip_reasstmr != 0) {--uip_reasstmr;}#endif /* UIP_REASSEMBLY *//* Increase the initial sequence number. */if(++iss[3] == 0) {if(++iss[2] == 0) {if(++iss[1] == 0) {++iss[0];}}}uip_len = 0;if(uip_connr->tcpstateflags == TIME_WAIT ||uip_connr->tcpstateflags == FIN_WAIT_2) {++(uip_connr->timer);if(uip_connr->timer == UIP_TIME_WAIT_TIMEOUT) {uip_connr->tcpstateflags = CLOSED;}} else if(uip_connr->tcpstateflags != CLOSED) {/* If the connection has outstanding data, we increase theconnection's timer and see if it has reached the RTO valuein which case we retransmit. */if(uip_outstanding(uip_connr)) {if(uip_connr->timer-- == 0) {if(uip_connr->nrtx == UIP_MAXRTX ||((uip_connr->tcpstateflags == SYN_SENT ||uip_connr->tcpstateflags == SYN_RCVD) &&uip_connr->nrtx == UIP_MAXSYNRTX)) {uip_connr->tcpstateflags = CLOSED;/* We call UIP_APPCALL() with uip_flags set toUIP_TIMEDOUT to inform the application that theconnection has timed out. */uip_flags = UIP_TIMEDOUT;UIP_APPCALL();/* We also send a reset packet to the remote host. */BUF->flags = TCP_RST | TCP_ACK;goto tcp_send_nodata;}/* Exponential backoff. */uip_connr->timer = UIP_RTO << (uip_connr->nrtx > 4?4:uip_connr->nrtx);++(uip_connr->nrtx);/* Ok, so we need to retransmit. We do this differentlydepending on which state we are in. In ESTABLISHED, wecall upon the application so that it may prepare thedata for the retransmit. In SYN_RCVD, we resend theSYNACK that we sent earlier and in LAST_ACK we have toretransmit our FINACK. */UIP_STAT(++uip_stat.tcp.rexmit);switch(uip_connr->tcpstateflags & TS_MASK) {case SYN_RCVD:/* In the SYN_RCVD state, we should retransmit ourSYNACK. */goto tcp_send_synack;#if UIP_ACTIVE_OPENcase SYN_SENT:/* In the SYN_SENT state, we retransmit out SYN. */BUF->flags = 0;goto tcp_send_syn;#endif /* UIP_ACTIVE_OPEN */case ESTABLISHED:/* In the ESTABLISHED state, we call upon the applicationto do the actual retransmit after which we jump intothe code for sending out the packet (the apprexmitlabel). */uip_len = 0;uip_slen = 0;uip_flags = UIP_REXMIT;UIP_APPCALL();goto apprexmit;case FIN_WAIT_1:case CLOSING:case LAST_ACK:/* In all these states we should retransmit a FINACK. */goto tcp_send_finack;}}} else if((uip_connr->tcpstateflags & TS_MASK) == ESTABLISHED) {/* If there was no need for a retransmission, we poll theapplication for new data. */uip_len = 0;uip_slen = 0;uip_flags = UIP_POLL;UIP_APPCALL();goto appsend;}}goto drop;}#if UIP_UDPif(flag == UIP_UDP_TIMER) {if(uip_udp_conn->lport != 0) {uip_appdata = &uip_buf[UIP_LLH_LEN + 28];uip_len = uip_slen = 0;uip_flags = UIP_POLL;UIP_UDP_APPCALL();goto udp_send;} else {goto drop;}}#endif/* This is where the input processing starts. */UIP_STAT(++uip_stat.ip.recv);/* Start of IPv4 input header processing code. *//* Check validity of the IP header. */if(BUF->vhl != 0x45) { /* IP version and header length. */UIP_STAT(++uip_stat.ip.drop);UIP_STAT(++uip_stat.ip.vhlerr);UIP_LOG("ip: invalid version or header length.");goto drop;}/* Check the size of the packet. If the size reported to us inuip_len doesn't match the size reported in the IP header, therehas been a transmission error and we drop the packet. */if(BUF->len[0] != (uip_len >> 8)) { /* IP length, high byte. */uip_len = (uip_len & 0xff) | (BUF->len[0] << 8);}if(BUF->len[1] != (uip_len & 0xff)) { /* IP length, low byte. */uip_len = (uip_len & 0xff00) | BUF->len[1];}/* Check the fragment flag. */if((BUF->ipoffset[0] & 0x3f) != 0 ||BUF->ipoffset[1] != 0) {#if UIP_REASSEMBLYuip_len = uip_reass();if(uip_len == 0) {goto drop;}#elseUIP_STAT(++uip_stat.ip.drop);UIP_STAT(++uip_stat.ip.fragerr);UIP_LOG("ip: fragment dropped.");goto drop;#endif /* UIP_REASSEMBLY */}/* If we are configured to use ping IP address configuration andhasn't been assigned an IP address yet, we accept all ICMPpackets. */#if UIP_PINGADDRCONFif((uip_hostaddr[0] | uip_hostaddr[1]) == 0) {if(BUF->proto == UIP_PROTO_ICMP) {UIP_LOG("ip: possible ping config packet received.");goto icmp_input;} else {UIP_LOG("ip: packet dropped since no address assigned.");goto drop;}}#endif /* UIP_PINGADDRCONF *//* Check if the packet is destined for our IP address. */if(BUF->destipaddr[0] != uip_hostaddr[0]) {UIP_STAT(++uip_stat.ip.drop);UIP_LOG("ip: packet not for us.");goto drop;}if(BUF->destipaddr[1] != uip_hostaddr[1]) {UIP_STAT(++uip_stat.ip.drop);UIP_LOG("ip: packet not for us.");goto drop;}#if 0// IP checksum is wrong through Netgear DSL routerif (uip_ipchksum() != 0xffff) { /* Compute and check the IP headerchecksum. */UIP_STAT(++uip_stat.ip.drop);UIP_STAT(++uip_stat.ip.chkerr);UIP_LOG("ip: bad checksum.");goto drop;}#endifif(BUF->proto == UIP_PROTO_TCP) /* Check for TCP packet. If so, jumpto the tcp_input label. */goto tcp_input;#if UIP_UDPif(BUF->proto == UIP_PROTO_UDP)goto udp_input;#endif /* UIP_UDP */if(BUF->proto != UIP_PROTO_ICMP) { /* We only allow ICMP packets fromhere. */UIP_STAT(++uip_stat.ip.drop);UIP_STAT(++uip_stat.ip.protoerr);UIP_LOG("ip: neither tcp nor icmp.");goto drop;}#if UIP_PINGADDRCONFicmp_input:#endifUIP_STAT(++uip_stat.icmp.recv);/* ICMP echo (i.e., ping) processing. This is simple, we only changethe ICMP type from ECHO to ECHO_REPLY and adjust the ICMPchecksum before we return the packet. */if(ICMPBUF->type != ICMP_ECHO) {UIP_STAT(++uip_stat.icmp.drop);UIP_STAT(++uip_stat.icmp.typeerr);UIP_LOG("icmp: not icmp echo.");goto drop;}/* If we are configured to use ping IP address assignment, we usethe destination IP address of this ping packet and assign it toourself. */#if UIP_PINGADDRCONFif((uip_hostaddr[0] | uip_hostaddr[1]) == 0) {uip_hostaddr[0] = BUF->destipaddr[0];uip_hostaddr[1] = BUF->destipaddr[1];}#endif /* UIP_PINGADDRCONF */ICMPBUF->type = ICMP_ECHO_REPLY;if(ICMPBUF->icmpchksum >= HTONS(0xffff - (ICMP_ECHO << 8))) {ICMPBUF->icmpchksum += HTONS(ICMP_ECHO << 8) + 1;} else {ICMPBUF->icmpchksum += HTONS(ICMP_ECHO << 8);}/* Swap IP addresses. */tmp16 = BUF->destipaddr[0];BUF->destipaddr[0] = BUF->srcipaddr[0];BUF->srcipaddr[0] = tmp16;tmp16 = BUF->destipaddr[1];BUF->destipaddr[1] = BUF->srcipaddr[1];BUF->srcipaddr[1] = tmp16;UIP_STAT(++uip_stat.icmp.sent);goto send;/* End of IPv4 input header processing code. */#if UIP_UDP/* UDP input processing. */udp_input:/* UDP processing is really just a hack. We don't do anything to theUDP/IP headers, but let the UDP application do all the hardwork. If the application sets uip_slen, it has a packet tosend. */#if UIP_UDP_CHECKSUMSif(uip_udpchksum() != 0xffff) {UIP_STAT(++uip_stat.udp.drop);UIP_STAT(++uip_stat.udp.chkerr);UIP_LOG("udp: bad checksum.");goto drop;}#endif /* UIP_UDP_CHECKSUMS *//* Demultiplex this UDP packet between the UDP "connections". */for(uip_udp_conn = &uip_udp_conns[0];uip_udp_conn < &uip_udp_conns[UIP_UDP_CONNS];++uip_udp_conn) {if(uip_udp_conn->lport != 0 &&UDPBUF->destport == uip_udp_conn->lport &&(uip_udp_conn->rport == 0 ||UDPBUF->srcport == uip_udp_conn->rport) &&BUF->srcipaddr[0] == uip_udp_conn->ripaddr[0] &&BUF->srcipaddr[1] == uip_udp_conn->ripaddr[1]) {goto udp_found;}}goto drop;udp_found:uip_len = uip_len - 28;uip_appdata = &uip_buf[UIP_LLH_LEN + 28];uip_flags = UIP_NEWDATA;uip_slen = 0;UIP_UDP_APPCALL();udp_send:if(uip_slen == 0) {goto drop;}uip_len = uip_slen + 28;BUF->len[0] = (uip_len >> 8);BUF->len[1] = (uip_len & 0xff);BUF->proto = UIP_PROTO_UDP;UDPBUF->udplen = HTONS(uip_slen + 8);UDPBUF->udpchksum = 0;#if UIP_UDP_CHECKSUMS/* Calculate UDP checksum. */UDPBUF->udpchksum = ~(uip_udpchksum());if(UDPBUF->udpchksum == 0) {UDPBUF->udpchksum = 0xffff;}#endif /* UIP_UDP_CHECKSUMS */BUF->srcport = uip_udp_conn->lport;BUF->destport = uip_udp_conn->rport;BUF->srcipaddr[0] = uip_hostaddr[0];BUF->srcipaddr[1] = uip_hostaddr[1];BUF->destipaddr[0] = uip_udp_conn->ripaddr[0];BUF->destipaddr[1] = uip_udp_conn->ripaddr[1];uip_appdata = &uip_buf[UIP_LLH_LEN + 40];goto ip_send_nolen;#endif /* UIP_UDP *//* TCP input processing. */tcp_input:UIP_STAT(++uip_stat.tcp.recv);/* Start of TCP input header processing code. */#if 1 // FIXMEif(uip_tcpchksum() != 0xffff) { /* Compute and check the TCPchecksum. */UIP_STAT(++uip_stat.tcp.drop);UIP_STAT(++uip_stat.tcp.chkerr);UIP_LOG("tcp: bad checksum.");goto drop;}#endif/* Demultiplex this segment. *//* First check any active connections. */for(uip_connr = &uip_conns[0]; uip_connr < &uip_conns[UIP_CONNS]; ++uip_connr) {if(uip_connr->tcpstateflags != CLOSED &&BUF->destport == uip_connr->lport &&BUF->srcport == uip_connr->rport &&BUF->srcipaddr[0] == uip_connr->ripaddr[0] &&BUF->srcipaddr[1] == uip_connr->ripaddr[1]) {goto found;}}/* If we didn't find and active connection that expected the packet,either this packet is an old duplicate, or this is a SYN packetdestined for a connection in LISTEN. If the SYN flag isn't set,it is an old packet and we send a RST. */if((BUF->flags & TCP_CTL) != TCP_SYN)goto reset;tmp16 = BUF->destport;/* Next, check listening connections. */for(c = 0; c < UIP_LISTENPORTS; ++c) {if(tmp16 == uip_listenports[c])goto found_listen;}/* No matching connection found, so we send a RST packet. */UIP_STAT(++uip_stat.tcp.synrst);reset:/* We do not send resets in response to resets. */if(BUF->flags & TCP_RST)goto drop;UIP_STAT(++uip_stat.tcp.rst);BUF->flags = TCP_RST | TCP_ACK;uip_len = 40;BUF->tcpoffset = 5 << 4;/* Flip the seqno and ackno fields in the TCP header. */c = BUF->seqno[3];BUF->seqno[3] = BUF->ackno[3];BUF->ackno[3] = c;c = BUF->seqno[2];BUF->seqno[2] = BUF->ackno[2];BUF->ackno[2] = c;c = BUF->seqno[1];BUF->seqno[1] = BUF->ackno[1];BUF->ackno[1] = c;c = BUF->seqno[0];BUF->seqno[0] = BUF->ackno[0];BUF->ackno[0] = c;/* We also have to increase the sequence number we areacknowledging. If the least significant byte overflowed, we needto propagate the carry to the other bytes as well. */if(++BUF->ackno[3] == 0) {if(++BUF->ackno[2] == 0) {if(++BUF->ackno[1] == 0) {++BUF->ackno[0];}}}/* Swap port numbers. */tmp16 = BUF->srcport;BUF->srcport = BUF->destport;BUF->destport = tmp16;/* Swap IP addresses. */tmp16 = BUF->destipaddr[0];BUF->destipaddr[0] = BUF->srcipaddr[0];BUF->srcipaddr[0] = tmp16;tmp16 = BUF->destipaddr[1];BUF->destipaddr[1] = BUF->srcipaddr[1];BUF->srcipaddr[1] = tmp16;/* And send out the RST packet! */goto tcp_send_noconn;/* This label will be jumped to if we matched the incoming packetwith a connection in LISTEN. In that case, we should create a newconnection and send a SYNACK in return. */found_listen:/* First we check if there are any connections avaliable. Unusedconnections are kept in the same table as used connections, butunused ones have the tcpstate set to CLOSED. Also, connections inTIME_WAIT are kept track of and we'll use the oldest one if noCLOSED connections are found. Thanks to Eddie C. Dost for a verynice algorithm for the TIME_WAIT search. */uip_connr = 0;for(c = 0; c < UIP_CONNS; ++c) {if(uip_conns[c].tcpstateflags == CLOSED) {uip_connr = &uip_conns[c];break;}if(uip_conns[c].tcpstateflags == TIME_WAIT) {if(uip_connr == 0 ||uip_conns[c].timer > uip_connr->timer) {uip_connr = &uip_conns[c];}}}if(uip_connr == 0) {/* All connections are used already, we drop packet and hope thatthe remote end will retransmit the packet at a time when wehave more spare connections. */UIP_STAT(++uip_stat.tcp.syndrop);UIP_LOG("tcp: found no unused connections.");goto drop;}uip_conn = uip_connr;/* Fill in the necessary fields for the new connection. */uip_connr->rto = uip_connr->timer = UIP_RTO;uip_connr->sa = 0;uip_connr->sv = 4;uip_connr->nrtx = 0;uip_connr->lport = BUF->destport;uip_connr->rport = BUF->srcport;uip_connr->ripaddr[0] = BUF->srcipaddr[0];uip_connr->ripaddr[1] = BUF->srcipaddr[1];uip_connr->tcpstateflags = SYN_RCVD;uip_connr->snd_nxt[0] = iss[0];uip_connr->snd_nxt[1] = iss[1];uip_connr->snd_nxt[2] = iss[2];uip_connr->snd_nxt[3] = iss[3];uip_connr->len = 1;/* rcv_nxt should be the seqno from the incoming packet + 1. */uip_connr->rcv_nxt[3] = BUF->seqno[3];uip_connr->rcv_nxt[2] = BUF->seqno[2];uip_connr->rcv_nxt[1] = BUF->seqno[1];uip_connr->rcv_nxt[0] = BUF->seqno[0];uip_add_rcv_nxt(1);/* Parse the TCP MSS option, if present. */if((BUF->tcpoffset & 0xf0) > 0x50) {for(c = 0; c < ((BUF->tcpoffset >> 4) - 5) << 2 ;) {opt = uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + c];if(opt == 0x00) {/* End of options. */break;} else if(opt == 0x01) {++c;/* NOP option. */} else if(opt == 0x02 &&uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == 0x04) {/* An MSS option with the right option length. */tmp16 = ((u16_t)uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 2 + c] << 8) |(u16_t)uip_buf[40 + UIP_LLH_LEN + 3 + c];uip_connr->initialmss = uip_connr->mss =tmp16 > UIP_TCP_MSS? UIP_TCP_MSS: tmp16;/* And we are done processing options. */break;} else {/* All other options have a length field, so that we easilycan skip past them. */if(uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == 0) {/* If the length field is zero, the options are malformedand we don't process them further. */break;}c += uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c];}}}/* Our response will be a SYNACK. */#if UIP_ACTIVE_OPENtcp_send_synack:BUF->flags = TCP_ACK;tcp_send_syn:BUF->flags |= TCP_SYN;#else /* UIP_ACTIVE_OPEN */tcp_send_synack:BUF->flags = TCP_SYN | TCP_ACK;#endif /* UIP_ACTIVE_OPEN *//* We send out the TCP Maximum Segment Size option with ourSYNACK. */BUF->optdata[0] = 2;BUF->optdata[1] = 4;BUF->optdata[2] = (UIP_TCP_MSS) / 256;BUF->optdata[3] = (UIP_TCP_MSS) & 255;uip_len = 44;BUF->tcpoffset = 6 << 4;goto tcp_send;/* This label will be jumped to if we found an active connection. */found:uip_conn = uip_connr;uip_flags = 0;/* We do a very naive form of TCP reset processing; we just acceptany RST and kill our connection. We should in fact check if thesequence number of this reset is wihtin our advertised windowbefore we accept the reset. */if(BUF->flags & TCP_RST) {uip_connr->tcpstateflags = CLOSED;UIP_LOG("tcp: got reset, aborting connection.");uip_flags = UIP_ABORT;UIP_APPCALL();goto drop;}/* Calculated the length of the data, if the application has sentany data to us. */c = (BUF->tcpoffset >> 4) << 2;/* uip_len will contain the length of the actual TCP data. This iscalculated by subtracing the length of the TCP header (inc) and the length of the IP header (20 bytes). */uip_len = uip_len - c - 20;/* First, check if the sequence number of the incoming packet iswhat we're expecting next. If not, we send out an ACK with thecorrect numbers in. */if(uip_len > 0 &&(BUF->seqno[0] != uip_connr->rcv_nxt[0] ||BUF->seqno[1] != uip_connr->rcv_nxt[1] ||BUF->seqno[2] != uip_connr->rcv_nxt[2] ||BUF->seqno[3] != uip_connr->rcv_nxt[3])) {goto tcp_send_ack;}/* Next, check if the incoming segment acknowledges any outstandingdata. If so, we update the sequence number, reset the length ofthe outstanding data, calculate RTT estimations, and reset theretransmission timer. */if((BUF->flags & TCP_ACK) && uip_outstanding(uip_connr)) {uip_add32(uip_connr->snd_nxt, uip_connr->len);if(BUF->ackno[0] == uip_acc32[0] &&BUF->ackno[1] == uip_acc32[1] &&BUF->ackno[2] == uip_acc32[2] &&BUF->ackno[3] == uip_acc32[3]) {/* Update sequence number. */uip_connr->snd_nxt[0] = uip_acc32[0];uip_connr->snd_nxt[1] = uip_acc32[1];uip_connr->snd_nxt[2] = uip_acc32[2];uip_connr->snd_nxt[3] = uip_acc32[3];/* Do RTT estimation, unless we have done retransmissions. */if(uip_connr->nrtx == 0) {signed char m;m = uip_connr->rto - uip_connr->timer;/* This is taken directly from VJs original code in his paper */m = m - (uip_connr->sa >> 3);uip_connr->sa += m;if(m < 0) {m = -m;}m = m - (uip_connr->sv >> 2);uip_connr->sv += m;uip_connr->rto = (uip_connr->sa >> 3) + uip_connr->sv;}/* Set the acknowledged flag. */uip_flags = UIP_ACKDATA;/* Reset the retransmission timer. */uip_connr->timer = uip_connr->rto;}}/* Do different things depending on in what state the connection is. */switch(uip_connr->tcpstateflags & TS_MASK) {/* CLOSED and LISTEN are not handled here. CLOSE_WAIT is notimplemented, since we force the application to close when thepeer sends a FIN (hence the application goes directly fromESTABLISHED to LAST_ACK). */case SYN_RCVD:/* In SYN_RCVD we have sent out a SYNACK in response to a SYN, andwe are waiting for an ACK that acknowledges the data we sentout the last time. Therefore, we want to have the UIP_ACKDATAflag set. If so, we enter the ESTABLISHED state. */if(uip_flags & UIP_ACKDATA) {uip_connr->tcpstateflags = ESTABLISHED;uip_flags = UIP_CONNECTED;uip_connr->len = 0;if(uip_len > 0) {uip_flags |= UIP_NEWDATA;uip_add_rcv_nxt(uip_len);}uip_slen = 0;UIP_APPCALL();goto appsend;}goto drop;#if UIP_ACTIVE_OPENcase SYN_SENT:/* In SYN_SENT, we wait for a SYNACK that is sent in response toour SYN. The rcv_nxt is set to sequence number in the SYNACKplus one, and we send an ACK. We move into the ESTABLISHEDstate. */if((uip_flags & UIP_ACKDATA) &&BUF->flags == (TCP_SYN | TCP_ACK)) {/* Parse the TCP MSS option, if present. */if((BUF->tcpoffset & 0xf0) > 0x50) {for(c = 0; c < ((BUF->tcpoffset >> 4) - 5) << 2 ;) {opt = uip_buf[40 + UIP_LLH_LEN + c];if(opt == 0x00) {/* End of options. */break;} else if(opt == 0x01) {++c;/* NOP option. */} else if(opt == 0x02 &&uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == 0x04) {/* An MSS option with the right option length. */tmp16 = (uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 2 + c] << 8) |uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 3 + c];uip_connr->initialmss =uip_connr->mss = tmp16 > UIP_TCP_MSS? UIP_TCP_MSS: tmp16;/* And we are done processing options. */break;} else {/* All other options have a length field, so that we easilycan skip past them. */if(uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == 0) {/* If the length field is zero, the options are malformedand we don't process them further. */break;}c += uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c];}}}uip_connr->tcpstateflags = ESTABLISHED;uip_connr->rcv_nxt[0] = BUF->seqno[0];uip_connr->rcv_nxt[1] = BUF->seqno[1];uip_connr->rcv_nxt[2] = BUF->seqno[2];uip_connr->rcv_nxt[3] = BUF->seqno[3];uip_add_rcv_nxt(1);uip_flags = UIP_CONNECTED | UIP_NEWDATA;uip_connr->len = 0;uip_len = 0;uip_slen = 0;UIP_APPCALL();goto appsend;}goto reset;#endif /* UIP_ACTIVE_OPEN */case ESTABLISHED:/* In the ESTABLISHED state, we call upon the application to feeddata into the uip_buf. If the UIP_ACKDATA flag is set, theapplication should put new data into the buffer, otherwise we areretransmitting an old segment, and the application should put thatdata into the buffer.If the incoming packet is a FIN, we should close the connection onthis side as well, and we send out a FIN and enter the LAST_ACKstate. We require that there is no outstanding data; otherwise thesequence numbers will be screwed up. */if(BUF->flags & TCP_FIN) {if(uip_outstanding(uip_connr)) {goto drop;}uip_add_rcv_nxt(1 + uip_len);uip_flags = UIP_CLOSE;if(uip_len > 0) {uip_flags |= UIP_NEWDATA;}UIP_APPCALL();uip_connr->len = 1;uip_connr->tcpstateflags = LAST_ACK;uip_connr->nrtx = 0;tcp_send_finack:BUF->flags = TCP_FIN | TCP_ACK;goto tcp_send_nodata;}/* Check the URG flag. If this is set, the segment carries urgentdata that we must pass to the application. */if(BUF->flags & TCP_URG) {#if UIP_URGDATA > 0uip_urglen = (BUF->urgp[0] << 8) | BUF->urgp[1];if(uip_urglen > uip_len) {/* There is more urgent data in the next segment to come. */uip_urglen = uip_len;}uip_add_rcv_nxt(uip_urglen);uip_len -= uip_urglen;uip_urgdata = uip_appdata;uip_appdata += uip_urglen;} else {uip_urglen = 0;#endif /* UIP_URGDATA > 0 */uip_appdata += (BUF->urgp[0] << 8) | BUF->urgp[1];uip_len -= (BUF->urgp[0] << 8) | BUF->urgp[1];}/* If uip_len > 0 we have TCP data in the packet, and we flag thisby setting the UIP_NEWDATA flag and update the sequence numberwe acknowledge. If the application has stopped the dataflowusing uip_stop(), we must not accept any data packets from theremote host. */if(uip_len > 0 && !(uip_connr->tcpstateflags & UIP_STOPPED)) {uip_flags |= UIP_NEWDATA;uip_add_rcv_nxt(uip_len);}/* Check if the available buffer space advertised by the other endis smaller than the initial MSS for this connection. If so, weset the current MSS to the window size to ensure that theapplication does not send more data than the other end canhandle.If the remote host advertises a zero window, we set the MSS tothe initial MSS so that the application will send an entire MSSof data. This data will not be acknowledged by the receiver,and the application will retransmit it. This is called the"persistent timer" and uses the retransmission mechanim.*/tmp16 = ((u16_t)BUF->wnd[0] << 8) + (u16_t)BUF->wnd[1];if(tmp16 > uip_connr->initialmss ||tmp16 == 0) {tmp16 = uip_connr->initialmss;}uip_connr->mss = tmp16;/* If this packet constitutes an ACK for outstanding data (flaggedby the UIP_ACKDATA flag, we should call the application since itmight want to send more data. If the incoming packet had datafrom the peer (as flagged by the UIP_NEWDATA flag), theapplication must also be notified.When the application is called, the global variable uip_lencontains the length of the incoming data. The application canaccess the incoming data through the global pointeruip_appdata, which usually points 40 bytes into the uip_bufarray.If the application wishes to send any data, this data should beput into the uip_appdata and the length of the data should beput into uip_len. If the application don't have any data tosend, uip_len must be set to 0. */if(uip_flags & (UIP_NEWDATA | UIP_ACKDATA)) {uip_slen = 0;UIP_APPCALL();appsend:if(uip_flags & UIP_ABORT) {uip_slen = 0;uip_connr->tcpstateflags = CLOSED;BUF->flags = TCP_RST | TCP_ACK;goto tcp_send_nodata;}if(uip_flags & UIP_CLOSE) {uip_slen = 0;uip_connr->len = 1;uip_connr->tcpstateflags = FIN_WAIT_1;uip_connr->nrtx = 0;BUF->flags = TCP_FIN | TCP_ACK;goto tcp_send_nodata;}/* If uip_slen > 0, the application has data to be sent. */if(uip_slen > 0) {/* If the connection has acknowledged data, the contents ofthe ->len variable should be discarded. */if((uip_flags & UIP_ACKDATA) != 0) {uip_connr->len = 0;}/* If the ->len variable is non-zero the connection hasalready data in transit and cannot send anymore rightnow. */if(uip_connr->len == 0) {/* The application cannot send more than what is allowed bythe mss (the minumum of the MSS and the availablewindow). */if(uip_slen > uip_connr->mss) {uip_slen = uip_connr->mss;}/* Remember how much data we send out now so that we knowwhen everything has been acknowledged. */uip_connr->len = uip_slen;} else {/* If the application already had unacknowledged data, wemake sure that the application does not send (i.e.,retransmit) out more than it previously sent out. */uip_slen = uip_connr->len;}} else {uip_connr->len = 0;}uip_connr->nrtx = 0;apprexmit:uip_appdata = uip_sappdata;/* If the application has data to be sent, or if the incomingpacket had new data in it, we must send out a packet. */if(uip_slen > 0 && uip_connr->len > 0) {/* Add the length of the IP and TCP headers. */uip_len = uip_connr->len + UIP_TCPIP_HLEN;/* We always set the ACK flag in response packets. */BUF->flags = TCP_ACK | TCP_PSH;/* Send the packet. */goto tcp_send_noopts;}/* If there is no data to send, just send out a pure ACK ifthere is newdata. */if(uip_flags & UIP_NEWDATA) {uip_len = UIP_TCPIP_HLEN;BUF->flags = TCP_ACK;goto tcp_send_noopts;}}goto drop;case LAST_ACK:/* We can close this connection if the peer has acknowledged ourFIN. This is indicated by the UIP_ACKDATA flag. */if(uip_flags & UIP_ACKDATA) {uip_connr->tcpstateflags = CLOSED;uip_flags = UIP_CLOSE;UIP_APPCALL();}break;case FIN_WAIT_1:/* The application has closed the connection, but the remote hosthasn't closed its end yet. Thus we do nothing but wait for aFIN from the other side. */if(uip_len > 0) {uip_add_rcv_nxt(uip_len);}if(BUF->flags & TCP_FIN) {if(uip_flags & UIP_ACKDATA) {uip_connr->tcpstateflags = TIME_WAIT;uip_connr->timer = 0;uip_connr->len = 0;} else {uip_connr->tcpstateflags = CLOSING;}uip_add_rcv_nxt(1);uip_flags = UIP_CLOSE;UIP_APPCALL();goto tcp_send_ack;} else if(uip_flags & UIP_ACKDATA) {uip_connr->tcpstateflags = FIN_WAIT_2;uip_connr->len = 0;goto drop;}if(uip_len > 0) {goto tcp_send_ack;}goto drop;case FIN_WAIT_2:if(uip_len > 0) {uip_add_rcv_nxt(uip_len);}if(BUF->flags & TCP_FIN) {uip_connr->tcpstateflags = TIME_WAIT;uip_connr->timer = 0;uip_add_rcv_nxt(1);uip_flags = UIP_CLOSE;UIP_APPCALL();goto tcp_send_ack;}if(uip_len > 0) {goto tcp_send_ack;}goto drop;case TIME_WAIT:goto tcp_send_ack;case CLOSING:if(uip_flags & UIP_ACKDATA) {uip_connr->tcpstateflags = TIME_WAIT;uip_connr->timer = 0;}}goto drop;/* We jump here when we are ready to send the packet, and just wantto set the appropriate TCP sequence numbers in the TCP header. */tcp_send_ack:BUF->flags = TCP_ACK;tcp_send_nodata:uip_len = 40;tcp_send_noopts:BUF->tcpoffset = 5 << 4;tcp_send:/* We're done with the input processing. We are now ready to send areply. Our job is to fill in all the fields of the TCP and IPheaders before calculating the checksum and finally send thepacket. */BUF->ackno[0] = uip_connr->rcv_nxt[0];BUF->ackno[1] = uip_connr->rcv_nxt[1];BUF->ackno[2] = uip_connr->rcv_nxt[2];BUF->ackno[3] = uip_connr->rcv_nxt[3];BUF->seqno[0] = uip_connr->snd_nxt[0];BUF->seqno[1] = uip_connr->snd_nxt[1];BUF->seqno[2] = uip_connr->snd_nxt[2];BUF->seqno[3] = uip_connr->snd_nxt[3];BUF->proto = UIP_PROTO_TCP;BUF->srcport = uip_connr->lport;BUF->destport = uip_connr->rport;BUF->srcipaddr[0] = uip_hostaddr[0];BUF->srcipaddr[1] = uip_hostaddr[1];BUF->destipaddr[0] = uip_connr->ripaddr[0];BUF->destipaddr[1] = uip_connr->ripaddr[1];if(uip_connr->tcpstateflags & UIP_STOPPED) {/* If the connection has issued uip_stop(), we advertise a zerowindow so that the remote host will stop sending data. */BUF->wnd[0] = BUF->wnd[1] = 0;} else {BUF->wnd[0] = ((UIP_RECEIVE_WINDOW) >> 8);BUF->wnd[1] = ((UIP_RECEIVE_WINDOW) & 0xff);}tcp_send_noconn:BUF->len[0] = (uip_len >> 8);BUF->len[1] = (uip_len & 0xff);/* Calculate TCP checksum. */BUF->tcpchksum = 0;BUF->tcpchksum = ~(uip_tcpchksum());#if UIP_UDPip_send_nolen:#endifBUF->vhl = 0x45;BUF->tos = 0;BUF->ipoffset[0] = BUF->ipoffset[1] = 0;BUF->ttl = UIP_TTL;++ipid;BUF->ipid[0] = ipid >> 8;BUF->ipid[1] = ipid & 0xff;/* Calculate IP checksum. */BUF->ipchksum = 0;BUF->ipchksum = ~(uip_ipchksum());UIP_STAT(++uip_stat.tcp.sent);send:UIP_STAT(++uip_stat.ip.sent);/* Return and let the caller do the actual transmission. */return;drop:uip_len = 0;return;}/*-----------------------------------------------------------------------------------*/u16_thtons(u16_t val){return HTONS(val);}/*-----------------------------------------------------------------------------------*//** @} */