10.4 SCTP Streaming Echo Client:
str_cli Function
Figure
10.4 shows our SCTP default client processing function.
Figure 10.4
SCTP sctp_strcli function.
sctp/sctp_strcli.c
1 #include "unp.h"
2 void
3 sctpstr_cli (FILE *fp, int sock_fd, struct sockaddr *to, socklen_t tolen)
4 {
5 struct sockaddr_in peeraddr;
6 struct sctp_sndrcvinfo sri;
7 char sendline [MAXLINE], recvline [MAXLINE];
8 socklen_t len;
9 int out_sz, rd_sz;
10 int msg_flags;
11 bzero (&sri, sizeof (sri) ) ;
12 while (fgets (sendline, MAXLINE, fp) != NULL) {
13 if (sendline [0] != ' [') {
14 printf ("Error, line must be of the form '[streamnum] text '\n");
15 continue;
16 }
17 sri.sinfo_stream = strtol (&sendline [1], NULL, 0);
18 out_sz = strlen (sendline);
19 Sctp_sendmsg (sock_fd, sendline, out_sz,
20 to, tolen, 0, 0, sri.sinfo_stream, 0, 0);
21 len = sizeof (peeraddr) ;
22 rd_sz = Sctp_recvmsg (sock_fd, recvline, sizeof (recvline),
23 (SA *) &peeraddr, &len, &sri, &msg_flags) ;
24 printf ("From str:%d seq:%d (assoc:0x%x):",
25 sri.sinfo_stream, sri.sinfo_ssn, (u_int) sri.sinfo_assoc_id);
26 printf ("%.*s", rd_sz, recvline);
27 }
28 }
Initialize the sri structure
and enter loop
11鈥?2
The client starts by clearing the sctp_sndrcvinfo
structure, sri. The client then enters a loop that reads
from the fp passed by our caller with a blocking call to
fgets. The main program passes stdin to this
function, so user input is read and processed in the loop until the
terminal EOF character (Control-D) is typed by the user. This user
action ends the function and causes a return to the caller.
Validate input
13鈥?6
The client examines the user input to make sure it is of the form
[#] text. If the format is invalid, the client prints an
error message and re-enters the blocking call to the fgets
function.
Translate stream number
17 The
client translates the user requested stream found in the input into
the sinfo_stream field in the sri structure.
Send message
18鈥?0
After initializing the appropriate lengths of the address and the
size of the actual user data, the client sends the message using
the sctp_sendmsg function.
Block while waiting for message
21鈥?3
The client now blocks and waits for the echoed message from the
server.
Display returned message and loop
24鈥?6
The client displays the returned message echoed to it displaying
the stream number, stream sequence number, as well as the text
message. After displaying the message, the client loops back to get
another request from the user.
Running the Code
A user starts the SCTP echo server with no
arguments on a FreeBSD machine. The client is started with just the
address of our server.
|
freebsd4% sctpclient01 10.1.1.5
|
|
|
[0]Hello
|
Send a message on
stream 0
|
|
From str:1 seq:0 (assoc:0xc99e15a0) :
[0]Hello
|
Server echoes on
stream 1
|
|
[4]Message
two
|
Send a message on
stream 4
|
|
From str:5 seq:0 (assoc:0xc99e15a0) :
[4]Message two
|
Server echoes on
stream 5
|
|
[4]Message
three
|
Send a second message
on stream 4
|
|
From str:5 seq:1 (assoc:0xc99e15a0) :
[4]Message three
|
Server echoes on
stream 5
|
|
^D
|
Control-D is our EOF
character
|
|
freebsd4%
|
Notice that the client sends the message on
streams 0 and 4 while our server sends the messages back on streams
1 and 5. This behavior is expected from our server with no
arguments. Also notice that the stream sequence number incremented
on the second message received on stream 5, as expected.
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