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#include "netlib.h"
/* tcp - a minimal TCP client over SLIP (milestone C). Connects to 10.0.0.1:7,
sends a line, prints the reply, closes. No retransmission: the GB<->gateway
link is lossless, and the gateway's real socket handles the lossy side.
Us = 10.0.0.2, peer = 10.0.0.1. */
static unsigned char pkt[256];
static unsigned long snd_nxt, rcv_nxt;
#define LPORT 40000u
#define RPORT 7u
/* SYN 0x02, ACK 0x10, FIN 0x01, PSH 0x08, RST 0x04 */
static unsigned int sum16(unsigned char *d, unsigned int len, unsigned int sum) {
unsigned int w, i = 0;
while (i + 1 < len) { w = ((unsigned int)d[i] << 8) | d[i + 1]; sum += w; if (sum < w) sum++; i += 2; }
if (len & 1) { w = (unsigned int)d[len - 1] << 8; sum += w; if (sum < w) sum++; }
return sum;
}
static void put32(unsigned char *p, unsigned long v) {
p[0] = (unsigned char)(v >> 24); p[1] = (unsigned char)(v >> 16);
p[2] = (unsigned char)(v >> 8); p[3] = (unsigned char)v;
}
static unsigned long get32(unsigned char *p) {
return ((unsigned long)p[0] << 24) | ((unsigned long)p[1] << 16)
| ((unsigned long)p[2] << 8) | p[3];
}
/* build+send IP+TCP with 'flags' and 'dlen' payload bytes already at pkt[40..] */
static void tcp_send(unsigned char flags, unsigned char dlen) {
unsigned int c, psum, tcplen = 20 + dlen, total = 20 + tcplen;
pkt[0] = 0x45; pkt[1] = 0; pkt[2] = (unsigned char)(total >> 8); pkt[3] = (unsigned char)total;
pkt[4] = 0; pkt[5] = 1; pkt[6] = 0x40; pkt[7] = 0; pkt[8] = 64; pkt[9] = 6;
pkt[10] = 0; pkt[11] = 0;
pkt[12] = 10; pkt[13] = 0; pkt[14] = 0; pkt[15] = 2;
pkt[16] = 10; pkt[17] = 0; pkt[18] = 0; pkt[19] = 1;
pkt[20] = LPORT >> 8; pkt[21] = (unsigned char)LPORT;
pkt[22] = RPORT >> 8; pkt[23] = (unsigned char)RPORT;
put32(pkt + 24, snd_nxt);
put32(pkt + 28, rcv_nxt);
pkt[32] = 0x50; pkt[33] = flags; pkt[34] = 2; pkt[35] = 0; /* window 512 */
pkt[36] = 0; pkt[37] = 0; pkt[38] = 0; pkt[39] = 0;
psum = sum16(pkt + 12, 8, 0);
c = 6; psum += c; if (psum < c) psum++;
c = tcplen; psum += c; if (psum < c) psum++;
c = ~sum16(pkt + 20, tcplen, psum);
pkt[36] = (unsigned char)(c >> 8); pkt[37] = (unsigned char)c;
c = ~sum16(pkt, 20, 0);
pkt[10] = (unsigned char)(c >> 8); pkt[11] = (unsigned char)c;
slip_send((char *)pkt, (unsigned char)total);
}
/* receive the next TCP segment for our connection; returns TCP header offset,
sets *flags,*seq,*dlen,*doff. */
static unsigned char tcp_recv(unsigned char *flags, unsigned long *seq,
unsigned char *dlen, unsigned char *doff) {
unsigned char len, ihl, hl;
for (;;) {
len = slip_recv((char *)pkt, 255);
if (len < 40 || (pkt[0] >> 4) != 4 || pkt[9] != 6) continue;
ihl = (pkt[0] & 0x0f) << 2;
if (((unsigned int)pkt[22] << 8 | pkt[23]) != LPORT) continue; /* not our port */
hl = (pkt[ihl + 12] >> 4) << 2;
*flags = pkt[ihl + 13];
*seq = get32(pkt + ihl + 4);
*doff = (unsigned char)(ihl + hl);
*dlen = (unsigned char)(len - ihl - hl);
return ihl;
}
}
void main(void) {
unsigned char flags, dlen, doff, i;
unsigned long seq;
puts("tcp: SYN -> 10.0.0.1:7"); nl();
snd_nxt = 1000; rcv_nxt = 0;
tcp_send(0x02, 0); /* SYN */
snd_nxt = 1001;
tcp_recv(&flags, &seq, &dlen, &doff); /* expect SYN|ACK */
if (!(flags & 0x02)) { puts("tcp: no SYN-ACK"); nl(); return; }
rcv_nxt = seq + 1;
tcp_send(0x10, 0); /* ACK -> ESTABLISHED */
pkt[40] = 'h'; pkt[41] = 'i'; pkt[42] = ' '; pkt[43] = 'g'; pkt[44] = 'b';
tcp_send(0x18, 5); /* PSH|ACK "hi gb" */
snd_nxt += 5;
for (;;) {
tcp_recv(&flags, &seq, &dlen, &doff);
if (dlen) {
puts("tcp: recv '");
for (i = 0; i < dlen; i++) putc(pkt[doff + i]);
puts("'"); nl();
rcv_nxt = seq + dlen;
tcp_send(0x10, 0); /* ACK the data */
tcp_send(0x11, 0); /* FIN|ACK - start closing */
snd_nxt += 1;
}
if (flags & 0x01) { /* their FIN */
rcv_nxt = seq + dlen + 1;
tcp_send(0x10, 0); /* ACK it */
puts("tcp: closed"); nl();
return;
}
}
}
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