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#include <llarp/endian.h>
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#include <algorithm>
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#include <llarp/ip.hpp>
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#include "llarp/buffer.hpp"
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#include "mem.hpp"
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#ifndef _WIN32
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#include <netinet/in.h>
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#endif
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#include <llarp/endian.h>
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#include <map>
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#include <algorithm>
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namespace llarp
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{
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namespace net
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{
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bool
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IPv4Packet::Load(llarp_buffer_t pkt)
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{
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sz = std::min(pkt.sz, sizeof(buf));
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memcpy(buf, pkt.base, sz);
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return true;
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}
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llarp_buffer_t
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IPv4Packet::Buffer()
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{
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return llarp::InitBuffer(buf, sz);
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}
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static uint32_t
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ipchksum_pseudoIPv4(nuint32_t src_ip, nuint32_t dst_ip, uint8_t proto,
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uint16_t innerlen)
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{
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#define IPCS(x) ((uint32_t)(x & 0xFFFF) + (uint32_t)(x >> 16))
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uint32_t sum = IPCS(src_ip.n) + IPCS(dst_ip.n) + (uint32_t)proto
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+ (uint32_t)htons(innerlen);
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#undef IPCS
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return sum;
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}
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static uint16_t
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ipchksum(const byte_t *buf, size_t sz, uint32_t sum = 0)
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{
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while(sz > 1)
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{
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sum += *(const uint16_t *)buf;
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sz -= sizeof(uint16_t);
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buf += sizeof(uint16_t);
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}
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if(sz > 0)
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sum += *(const byte_t *)buf;
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while(sum >> 16)
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sum = (sum & 0xffff) + (sum >> 16);
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return ~sum;
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}
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static uint16_t
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deltachksum(uint16_t old_sum, huint32_t old_src_ip, huint32_t old_dst_ip,
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huint32_t new_src_ip, huint32_t new_dst_ip)
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{
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#define ADDIPCS(x) ((uint32_t)(x.h & 0xFFFF) + (uint32_t)(x.h >> 16))
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#define SUBIPCS(x) ((uint32_t)((~x.h) & 0xFFFF) + (uint32_t)((~x.h) >> 16))
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uint32_t sum = ntohs(old_sum) + ADDIPCS(old_src_ip) + ADDIPCS(old_dst_ip)
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+ SUBIPCS(new_src_ip) + SUBIPCS(new_dst_ip);
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#undef ADDIPCS
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#undef SUBIPCS
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while(sum >> 16)
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sum = (sum & 0xffff) + (sum >> 16);
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return htons(sum);
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}
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static std::map<
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byte_t,
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std::function< void(const ip_header *ohdr, byte_t *pld, size_t psz,
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huint32_t oSrcIP, huint32_t oDstIP,
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huint32_t nSrcIP, huint32_t nDstIP) > >
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protoDstCheckSummer = {
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// {RFC3022} says that IPv4 hdr isn't included in ICMP checksum calc
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// and that we don't need to modify it
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{// TCP
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6,
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[](const ip_header *ohdr, byte_t *pld, size_t psz,
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huint32_t oSrcIP, huint32_t oDstIP, huint32_t nSrcIP,
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huint32_t nDstIP) {
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uint16_t *check = (uint16_t *)(pld + 16);
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*check = deltachksum(*check, oSrcIP, oDstIP, nSrcIP, nDstIP);
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}},
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{// UDP
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17,
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[](const ip_header *ohdr, byte_t *pld, size_t psz,
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huint32_t oSrcIP, huint32_t oDstIP, huint32_t nSrcIP,
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huint32_t nDstIP) {
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uint16_t *check = (uint16_t *)(pld + 6);
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if(*check != 0xFFff)
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{
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if(*check == 0x0000)
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return; // don't change zero
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*check = deltachksum(*check, oSrcIP, oDstIP, nSrcIP, nDstIP);
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if(*check == 0x0000)
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*check = 0xFFff;
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}
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else
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{
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// such checksum can mean 2 things: 0x0000 or 0xFFff
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// we can only know by looking at data :<
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auto pakcs = *check; // save
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*check = 0; // zero checksum before calculation
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auto cs = ipchksum(
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pld, psz,
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ipchksum_pseudoIPv4(nuint32_t{ohdr->saddr},
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nuint32_t{ohdr->daddr}, 17, psz));
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auto new_cs = deltachksum(cs, oSrcIP, oDstIP, nSrcIP, nDstIP);
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if(cs != 0x0000 && cs != 0xFFff)
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{
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// packet was bad - sabotage new checksum
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new_cs += pakcs - cs;
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}
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// 0x0000 is reserved for no checksum
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if(new_cs == 0x0000)
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new_cs = 0xFFff;
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// put it in
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*check = new_cs;
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}
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}},
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};
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void
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IPv4Packet::UpdatePacketOnDst(huint32_t nSrcIP, huint32_t nDstIP)
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{
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auto hdr = Header();
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auto oSrcIP = xntohl(nuint32_t{hdr->saddr});
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auto oDstIP = xntohl(nuint32_t{hdr->daddr});
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// IPv4 checksum
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hdr->check = deltachksum(hdr->check, oSrcIP, oDstIP, nSrcIP, nDstIP);
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// L4 checksum
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auto proto = hdr->protocol;
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auto itr = protoDstCheckSummer.find(proto);
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size_t ihs;
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if(itr != protoDstCheckSummer.end() && (ihs = size_t(hdr->ihl * 4)) <= sz)
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{
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itr->second(hdr, buf + ihs, sz - ihs, oSrcIP, oDstIP, nSrcIP, nDstIP);
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}
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// write new IP addresses
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hdr->saddr = xhtonl(nSrcIP).n;
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hdr->daddr = xhtonl(nDstIP).n;
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}
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static std::map<
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byte_t,
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std::function< void(const ip_header *ohdr, byte_t *pld, size_t psz,
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huint32_t oSrcIP, huint32_t oDstIP) > >
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protoSrcCheckSummer = {
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{// TCP
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6,
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[](const ip_header *ohdr, byte_t *pld, size_t psz,
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huint32_t oSrcIP, huint32_t oDstIP) {
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uint16_t *check = (uint16_t *)(pld + 16);
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*check = deltachksum(*check, oSrcIP, oDstIP, huint32_t{0},
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huint32_t{0});
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}},
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{// UDP
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17,
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[](const ip_header *ohdr, byte_t *pld, size_t psz,
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huint32_t oSrcIP, huint32_t oDstIP) {
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uint16_t *check = (uint16_t *)(pld + 6);
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if(*check != 0xFFff)
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{
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if(*check == 0x0000)
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return; // don't change zero
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*check = deltachksum(*check, oSrcIP, oDstIP, huint32_t{0},
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huint32_t{0});
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if(*check == 0x0000)
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*check = 0xFFff;
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}
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else
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{
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// such checksum can mean 2 things: 0x0000 or 0xFFff
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// we can only know by looking at data :<
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auto pakcs = *check; // save
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*check = 0; // zero checksum before calculation
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auto cs = ipchksum(
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pld, psz,
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ipchksum_pseudoIPv4(nuint32_t{ohdr->saddr},
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nuint32_t{ohdr->daddr}, 17, psz));
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auto new_cs = deltachksum(cs, oSrcIP, oDstIP, huint32_t{0},
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huint32_t{0});
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if(cs != 0x0000 && cs != 0xFFff)
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{
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// packet was bad - sabotage new checksum
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new_cs += pakcs - cs;
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}
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// 0x0000 is reserved for no checksum
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if(new_cs == 0x0000)
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new_cs = 0xFFff;
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// put it in
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*check = new_cs;
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}
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}},
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};
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void
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IPv4Packet::UpdatePacketOnSrc()
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{
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auto hdr = Header();
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auto oSrcIP = xntohl(nuint32_t{hdr->saddr});
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auto oDstIP = xntohl(nuint32_t{hdr->daddr});
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// L4
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auto proto = hdr->protocol;
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auto itr = protoSrcCheckSummer.find(proto);
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size_t ihs;
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if(itr != protoSrcCheckSummer.end() && (ihs = size_t(hdr->ihl * 4)) <= sz)
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{
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itr->second(hdr, buf + ihs, sz - ihs, oSrcIP, oDstIP);
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}
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// IPv4
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hdr->check =
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deltachksum(hdr->check, oSrcIP, oDstIP, huint32_t{0}, huint32_t{0});
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// clear addresses
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hdr->saddr = 0;
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hdr->daddr = 0;
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}
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} // namespace net
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} // namespace llarp
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