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/* Welcome to spaghetti land. */
#include "proto.h"
#include "util.h"
enum {
SrcPort = 0,
DstPort = 2,
Seq = 4,
AckNum = 8, /* last processed seq + 1 */
Flags = 12,
FlagSize = 0xF000, /* size of header / 4 bytes */
/* 3 bits: 0, still unused
* 3 bits: modern stuff not in the original RFC */
FlagURG = 0x0020, /* urgent */
FlagACK = 0x0010,
FlagPSH = 0x0008, /* force buffer flush */
FlagRST = 0x0004, /* reset connection */
FlagSYN = 0x0002, /* first packet; sync sequence numbers */
FlagFIN = 0x0001, /* last packet */
FlagAll = 0x003F,
WinSize = 14, /* amount of data we're willing to receive */
Checksum = 16,
Urgent = 18,
MinHdr = 20,
};
enum tcp_state {
LISTEN,
SYN_RCVD,
LAST_ACK,
CLOSED,
};
struct tcp_conn {
uint32_t lip, rip;
mac_t rmac;
uint16_t lport, rport;
struct tcp_conn *next, **link;
enum tcp_state state;
uint32_t lack, rack;
uint32_t lseq;
bool uclosed; /* did the user close? */
void (*on_conn)(struct tcp_conn *, void *carg);
void (*on_close)(void *carg);
void *carg;
};
static struct tcp_conn *conns;
static void conns_append(struct tcp_conn *c) {
c->next = conns;
if (c->next)
c->next->link = &c->next;
c->link = &conns;
*c->link = c;
}
static void tcpc_send(struct tcp_conn *c, uint16_t flags) {
uint8_t *pkt = malloc(MinHdr);
memset(pkt, 0, MinHdr);
nput16(pkt + SrcPort, c->lport);
nput16(pkt + DstPort, c->rport);
nput32(pkt + Seq, c->lseq);
nput32(pkt + AckNum, c->lack);
flags |= (MinHdr / 4) << 12;
nput16(pkt + Flags, flags);
nput16(pkt + WinSize, 4096);
nput16(pkt + Checksum, ip_checksumphdr(pkt, MinHdr, c->lip, c->rip, 6));
ipv4_send(pkt, MinHdr, (struct ipv4){
.proto = 6,
.src = c->lip,
.dst = c->rip,
.e.dst = &c->rmac,
});
free(pkt);
}
void tcp_listen(
uint16_t port,
void (*on_conn)(struct tcp_conn *, void *carg),
void (*on_close)(void *carg),
void *carg)
{
struct tcp_conn *c = malloc(sizeof *c);
c->lport = port;
c->lip = state.ip;
c->state = LISTEN;
c->on_conn = on_conn;
c->on_close = on_close;
c->carg = carg;
conns_append(c);
}
void tcpc_close(struct tcp_conn *c) {
/* ONLY FOR USE BY THE USER, drops their reference */
if (!c->uclosed) {
c->uclosed = true;
tcpc_send(c, FlagFIN | FlagACK);
c->state = LAST_ACK;
c->on_conn = NULL;
c->on_close = NULL;
}
}
void tcp_parse(const uint8_t *buf, size_t len, struct ipv4 ip) {
if (len < 20) return;
uint16_t srcport = nget16(buf + SrcPort);
uint16_t dstport = nget16(buf + DstPort);
uint32_t seq = nget32(buf + Seq);
uint32_t acknum = nget32(buf + AckNum);
uint16_t flags = nget16(buf + Flags);
uint16_t winsize = nget16(buf + WinSize);
uint16_t chksum = nget16(buf + Checksum);
uint16_t hdrlen = ((flags & FlagSize) >> 12) * 4;
if (hdrlen > len) return;
uint16_t payloadlen = len - hdrlen;
for (struct tcp_conn *iter = conns; iter; iter = iter->next) {
if (iter->state == CLOSED) continue;
if (iter->lport != dstport) continue;
if (iter->state == LISTEN && (flags & FlagAll) == FlagSYN) {
iter->state = SYN_RCVD;
iter->rip = ip.src;
iter->rport = srcport;
iter->lack = seq + 1;
memcpy(&iter->rmac, ip.e.src, sizeof(mac_t));
tcpc_send(iter, FlagSYN | FlagACK);
iter->lseq++;
if (iter->on_conn) iter->on_conn(iter, iter->carg);
return;
}
if (iter->rip == ip.src && iter->rport == srcport) {
// TODO doesn't handle seq/ack overflows
if (flags & FlagACK) {
if (iter->rack < acknum)
iter->rack = acknum;
if (iter->state == LAST_ACK) {
iter->state = CLOSED; // TODO check if ack has correct number
// TODO free (also after a timeout)
return;
}
}
if (iter->lack != seq && iter->lack - 1 != seq) {
eprintf("remote seq jumped by %d", seq - iter->lack);
tcpc_send(iter, FlagACK);
return;
}
iter->lack = seq + 1;
if (flags & FlagFIN) {
// TODO should resend the packet until an ACK is received
// TODO duplicated in tcpc_close
tcpc_send(iter, FlagFIN | FlagACK);
iter->state = LAST_ACK;
if (iter->on_close) iter->on_close(iter->carg);
return;
}
return;
}
}
uint8_t *pkt = malloc(MinHdr);
memset(pkt, 0, MinHdr);
nput16(pkt + SrcPort, dstport);
nput16(pkt + DstPort, srcport);
nput32(pkt + Seq, acknum);
nput32(pkt + AckNum, seq + 1);
uint16_t pktflags = FlagRST | FlagACK;
pktflags |= (MinHdr / 4) << 12;
nput16(pkt + Flags, pktflags);
nput16(pkt + Checksum, ip_checksumphdr(pkt, MinHdr, ip.src, ip.dst, 6));
ipv4_send(pkt, MinHdr, (struct ipv4){
.proto = 6,
.src = ip.dst,
.dst = ip.src,
.e.dst = ip.e.src,
});
free(pkt);
}
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