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#include "proto.h"
#include "util.h"
#include <string.h>
enum {
HdrType = 0,
HdrTypeEther = 1,
ProtoType = 2,
HdrALen = 4,
ProtoALen = 5,
Operation = 6,
OpReq = 1,
OpReply = 2,
};
void arp_parse(const uint8_t *buf, size_t len) {
// TODO no bound checks
uint16_t htype = nget16(buf + HdrType);
uint16_t ptype = nget16(buf + ProtoType);
uint16_t op = nget16(buf + Operation);
if (!(htype == HdrTypeEther && ptype == ET_IPv4)) return;
enum { /* only valid for this combination of header + proto */
SrcMAC = 8,
SrcIP = 14,
DstMAC = 18,
DstIP = 24,
};
if (op == OpReq) {
uint32_t daddr = nget32(buf + DstIP);
if (daddr == state.ip) {
uint8_t *pkt = ether_start(30, (struct ethernet){
.dst = (void*)(buf + SrcMAC),
.type = ET_ARP,
});
nput16(pkt + HdrType, 1);
nput16(pkt + ProtoType, ET_IPv4);
pkt[HdrALen] = 6;
pkt[ProtoALen] = 4;
nput16(pkt + Operation, OpReply);
memcpy(pkt + SrcMAC, state.mac, 6);
nput32(pkt + SrcIP, state.ip);
memcpy(pkt + DstMAC, buf + SrcMAC, 10); /* sender's MAC and IP */
ether_finish(pkt);
}
}
}
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