Date: Mon, 30 Aug 2004 20:35:07 -0500 From: "Lucas (a.k.a T-Bird or bsdfan3)" <tbird-contact@cox.net> To: <freebsd-questions@freebsd.org> Subject: Variable length packets? Message-ID: <000301c48efa$bfa00500$c022fc18@yourxu5v9frokn>
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I am trying to implement a custom protocol that sends and receives
variable-length packets on top of TCP/IPv4. The problem is that the length
field of the packet is silently being mangled first becoming 0 and then
getting turned into a very large number (about 2-3 billion). The length
field is a u_int32_t and I am using the byteorder routines. Source code
snippets follow:
--decl of struct packet_t--
struct packet_t
{
u_int16_t num;
u_int32_t len;
char data[0];
};
--receive code--
if (read (s, auth_header, sizeof (struct packet_t)))
{
perror ("srvrmond read: could not read from socket");
exit (2);
}
auth_header -> num = ntohs (auth_header -> num);
auth_header -> len = ntohl (auth_header -> len);
--send code--
struct packet_t *auth_data2 = malloc (sizeof (struct packet_t) +
AUTHCOOKIE_S\
IZE + sizeof (time_t));
auth_data2 -> num = htons (100);
auth_data2 -> len = htonl (AUTHCOOKIE_SIZE + sizeof (time_t));
fprintf (stderr, "Packet payload length: %lu", ntohl (auth_data2 -> len));
long temp = htonl ((long)time (0) & 0xffffff00);
memcpy (auth_data2 -> data, cookie, AUTHCOOKIE_SIZE);
memcpy (auth_data2 -> data + AUTHCOOKIE_SIZE, &temp, sizeof (time_t));
if (write (s, auth_data2, AUTHCOOKIE_SIZE + sizeof (struct packet_t) +
sizeof\
(time_t)) == -1)
{
perror ("srvrmon write");
free (auth_data2);
exit (1);
}
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