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rewrite L4 checksum calculation

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Sergio R. Caprile committed 2026-01-27 10:32:50 -03:00
1 parent b74913ded5
commit 8e0ef3ca5c
3 files changed
+143 -24
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src/net_builtin.c
+24 -12
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@@ -216,6 +216,7 @@ static void mkpay(struct pkt *pkt, void *p) {
mg_str_n((char *) p, (size_t) (&pkt->pay.buf[pkt->pay.len] - (char *) p));
}
// NOTE(): DOES NOT handle reentries after odd length, use last
static uint32_t csumup(uint32_t sum, const void *buf, size_t len) {
size_t i;
const uint8_t *p = (const uint8_t *) buf;
@@ -366,18 +367,25 @@ static bool tx_udp(struct mg_tcpip_if *ifp, uint8_t *l2_dst,
udp->len = mg_htons((uint16_t) (sizeof(*udp) + len));
udp->csum = 0;
cs = csumup(0, udp, sizeof(*udp));
cs = csumup(cs, buf, len);
#if MG_ENABLE_IPV6
if (ip_dst->is_ip6) {
uint32_t pseudo[2];
cs = csumup(cs, &ip6->src, sizeof(ip6->src));
cs = csumup(cs, &ip6->dst, sizeof(ip6->dst));
pseudo[0] = mg_htonl((uint32_t) (sizeof(*udp) + len));
pseudo[1] = mg_htonl(17);
cs = csumup(cs, pseudo, 2 * sizeof(uint32_t));
} else
#endif
{
uint16_t pseudo[2];
cs = csumup(cs, &ip->src, sizeof(ip->src));
cs = csumup(cs, &ip->dst, sizeof(ip->dst));
pseudo[0] = mg_htons(17);
pseudo[1] = udp->len;
cs = csumup(cs, pseudo, 2 * sizeof(uint16_t));
}
cs += (uint32_t) (17 + sizeof(*udp) + len);
cs = csumup(cs, buf, len); // possibly odd length must be last
udp->csum = csumfin(cs);
memmove(udp + 1, buf, len);
l2_len = mg_l2_footer(ifp->l2type, l2_len, l2p);
@@ -694,6 +702,7 @@ static void tx_icmp6(struct mg_tcpip_if *ifp, uint8_t *l2_dst, uint64_t *ip_src,
struct ip6 *ip6;
struct icmp6 *icmp6;
uint32_t cs;
uint16_t pseudo[2];
ip6 = tx_ip6(ifp, l2_dst, 58, ip_src, ip_dst, sizeof(*icmp6) + len);
icmp6 = (struct icmp6 *) (ip6 + 1);
memset(icmp6, 0, sizeof(*icmp6)); // Set csum to 0
@@ -702,10 +711,12 @@ static void tx_icmp6(struct mg_tcpip_if *ifp, uint8_t *l2_dst, uint64_t *ip_src,
memcpy(icmp6 + 1, buf, len); // Copy payload
icmp6->csum = 0; // RFC-4443 2.3, RFC-8200 8.1
cs = csumup(0, icmp6, sizeof(*icmp6));
cs = csumup(cs, buf, len);
cs = csumup(cs, ip_src, 16);
cs = csumup(cs, ip_dst, 16);
cs += (uint32_t) (58 + sizeof(*icmp6) + len);
pseudo[0] = htons(58);
pseudo[1] = htons((uint16_t) (sizeof(*icmp6) + len));
cs = csumup(cs, pseudo, 4);
cs = csumup(cs, buf, len); // possibly odd length must be last
icmp6->csum = csumfin(cs);
driver_output(
ifp, mg_l2_footer(ifp->l2type, sizeof(*ip6) + sizeof(*icmp6) + len, l2p));
@@ -1096,24 +1107,25 @@ static size_t tx_tcp(struct mg_tcpip_if *ifp, uint8_t *l2_dst,
{
uint32_t cs = 0;
uint16_t n = (uint16_t) (sizeof(*tcp) + len);
cs = csumup(cs, tcp, n);
#if MG_ENABLE_IPV6
if (ip_dst->is_ip6) {
uint32_t pseudo[2];
cs = csumup(cs, &ip6->src, sizeof(ip6->src));
cs = csumup(cs, &ip6->dst, sizeof(ip6->dst));
cs += (uint32_t) (6 + n);
pseudo[0] = mg_htonl((uint32_t) n);
pseudo[1] = mg_htonl(6);
cs = csumup(cs, pseudo, 2 * sizeof(uint32_t));
} else
#endif
{
uint8_t pseudo[4];
pseudo[0] = 0;
pseudo[1] = ip->proto;
pseudo[2] = (uint8_t) (n >> 8);
pseudo[3] = (uint8_t) (n & 255);
uint16_t pseudo[2];
cs = csumup(cs, &ip->src, sizeof(ip->src));
cs = csumup(cs, &ip->dst, sizeof(ip->dst));
cs = csumup(cs, pseudo, sizeof(pseudo));
pseudo[0] = mg_htons(6);
pseudo[1] = mg_htons(n);
cs = csumup(cs, pseudo, 2 * sizeof(uint16_t));
}
cs = csumup(cs, tcp, n); // possibly odd length must be last
tcp->csum = csumfin(cs);
}
MG_VERBOSE(("TCP %M -> %M fl %x len %u", mg_print_ip_port, ip_src,