gprs_ip.cpp

gprs协议实现

#include <stdio.h>
#include <string.h>
#include "GPRS_net.h"
#include "GPRS_ip.h"
#include "GPRS_udp.h"

#define IP_TTL          128     /* Time To Live for an outgoing IP datagram */

IPKT * ip_in;		// 接收的IP 数据包
IPKT * ip_out;		// 要发送的IP 数据包
NODE  locnode;		//本机的节点信息结构(ip,port)



/* Check frame is IP, checksum & byte-swap, return data len */
short is_ip(short len)
{
    short ver, dlen=0, hlen;
    unsigned short sum;
    if (len>=sizeof(IPHDR))
    {
        ver = ip_in->i.vhl >> 4;                /* Get IP version & hdr len */
        hlen = (ip_in->i.vhl & 0xf) << 2;
        sum = ~csum(&ip_in->i, (unsigned short)hlen);     /* Do checksum */
        if (ver==4 && len>=hlen && sum==0)   /* If OK.. */
        {
            dlen = min(ip_in->i.len,len);
            dlen-=hlen;
            if (hlen > sizeof(IPHDR))        /* If IP options present.. */
            {                                /* ..delete them, move data down */
                memmove(ip_in->ipdata, &ip_in->ipdata[hlen-sizeof(IPHDR)], len);
                dlen -= hlen-sizeof(IPHDR);
            }
        }
    }
    return(dlen);
}

/* Make an IP packet, if greater than the MTU, also make fragment (subframe) in
** this frame. Return total length of frame and subframes (if any) */
void make_ip(NODE *srcep, NODE *destp, unsigned char pcol, unsigned short dlen)
{
    static unsigned short ident=0xf0;
    ip_out->i.ident = ident;               	 	/* Set datagram ident */
    ip_out->i.frags = 0;           		 		/* Frag offset in units of 8 bytes */
    ip_out->i.vhl = 0x40+(sizeof(IPHDR)>>2);	/* Version 4, header len 5 LWORDs */
    ip_out->i.service = 0;                  	/* Routine message */
    ip_out->i.ttl = IP_TTL;                 	/* Time To Live */
    ip_out->i.pcol = pcol;                  	/* Set IP protocol */
    ip_out->i.sip = srcep->ip;              	/* Srce, dest IP addrs */
    ip_out->i.dip = destp->ip;
    ip_out->i.len = dlen + sizeof(IPHDR);    	/* Data length */
    #ifdef bigend
    	swap_ip(ip_out);
    #endif	   
    ip_out->i.check = 0;                    	/* Clear checksum */
    ip_out->i.check = ~csum(ip_out, sizeof(IPHDR)); /* ..then set to calc value */
    ident++;                            	/* Increment datagram ident */
}

/* Swap byte order of shorts in IP header */
void swap_ip(IPKT * ip)
{
    ip->i.len = swapw(ip->i.len);
    ip->i.ident = swapw(ip->i.ident);
    ip->i.frags = swapw(ip->i.frags);
    ip->i.sip = swapl(ip->i.sip);
    ip->i.dip = swapl(ip->i.dip);
}
/* Get the frame driver type, source IP and Ethernet addresses
** Returned data does not include port number, netmask or gateway addr */
void getip_srce(NODE *np)
{
	np->ip = ip_in->i.sip;

}
/* Get local node data corresponding to a frame destination IP address
** Data does not include port number. Return 0 if no matching local node */

unsigned short getip_locdest(NODE *np)
{
    unsigned short ok=0;
    if (ip_in->i.dip==locnode.ip)
    {   
    	*np=locnode;
    	ok=1;
    }
    return (ok);
}


/* Return ICMP data length (-1 if no data), 0 if not ICMP */
short is_icmp(short len)
{
    ICMPKT *icmp;
    short dlen=0;

    if (len>=sizeof(ICMPHDR))
    {
        icmp = (ICMPKT *)ip_in;
        if ((csum(&icmp->c, (unsigned short)len)) == 0xffff)
            dlen = len>sizeof(ICMPHDR) ? len-sizeof(ICMPHDR) : -1;
    }
    return(dlen);
}

/* Make an ICMP packet */
void make_icmp(NODE *srcep, NODE *destp, unsigned char type, unsigned char codetype,unsigned char *dat,unsigned short dlen)
{
    ICMPKT *icmp;
    unsigned short len;
    icmp = (ICMPKT *)ip_out;
    memmove((unsigned char *)&icmp->c.ident,dat,dlen+4);
    icmp->c.type = type;
    icmp->c.codetype = codetype;
    icmp->c.check = 0;
    len = (unsigned short)(dlen + sizeof(ICMPHDR));
    icmp->c.check = ~csum(&icmp->c, len);
    make_ip(srcep, destp, PICMP, len);
}

/* Make ICMP 'destination unreachable' for incoming frame */

/*
short icmp_unreach( NODE *srcep, NODE *destp, unsigned char codetype)
{
    unsigned short len;
    ICMPKT *icmp;
    icmp = (ICMPKT *)ip_out;
    len = ((icmp->i.vhl & 0xf) << 2) + 8;
    memmove(icmp->icmpdata, icmp, len);
    return(make_icmp(srcep, destp, ICUNREACH, codetype, (unsigned short)len));
}
*/