[rsyslog] Help requested: UDP max message size?

[Rainer Gerhards]

oh my... Please disregard this question. I was working on a tcpdump file, and
the message length actually *is* 1024 bytes. I was confused by Wireshark's
(correct!) indication that the frame is 1066 octets in length. Of course,
this is correct, if you take the 42 octets of UDP header into account...

I guess the dump file was created with a max of 1K... 

Sometimes it is sooo easy ... and yet so hard to see ;)

Sorry for the interruption,
Rainer

> -----Original Message-----
> From: rsyslog-bounces at lists.adiscon.com [mailto:rsyslog-
> bounces at lists.adiscon.com] On Behalf Of Rainer Gerhards
> Sent: Tuesday, September 08, 2009 1:23 PM
> To: rsyslog at lists.adiscon.com
> Subject: [rsyslog] Help requested: UDP max message size?
> 
> Hi all,
> 
> I am really banging my head on a problem which sounds too easy. I have
> seen that my systems (and some others as well), seem to not provide
> more
> than 1024 bytes on a recvfrom() call. With wireshark, I see that the
> system itself, at the IP layer, receives more data. I am a bit puzzled,
> to phrase it lightly. I did not find any information on such a
> limitation.
> 
> I have created a strip-down version of a receiver, even built it on top
> of the Linux man pages samples. Out of desperation, I even set the
> receivebuf size, which I think has no effect on datagram sockets.
> Still... I only get 1024 bytes. Code is after my sig.
> 
> Does anybody have an idea what is going on OR a good place where to ask
> this question?
> 
> Thanks,
> Rainer
> 
>        #include <sys/types.h>
>        #include <stdio.h>
>        #include <stdlib.h>
>        #include <unistd.h>
>        #include <string.h>
>        #include <sys/socket.h>
>        #include <netdb.h>
> 
>        #define BUF_SIZE 2048
> 
>        int
>        main(int argc, char *argv[])
>        {
>            struct addrinfo hints;
>            struct addrinfo *result, *rp;
>            int sfd, s;
>            struct sockaddr_storage peer_addr;
>            socklen_t peer_addr_len;
>            ssize_t nread;
>            char buf[BUF_SIZE];
> 
>            if (argc != 2) {
>                fprintf(stderr, "Usage: %s port\n", argv[0]);
>                exit(EXIT_FAILURE);
>            }
> 
>            memset(&hints, 0, sizeof(struct addrinfo));
>            hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
>            hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
>            hints.ai_flags = AI_PASSIVE;    /* For wildcard IP address
> */
>            hints.ai_protocol = 0;          /* Any protocol */
>            hints.ai_canonname = NULL;
>            hints.ai_addr = NULL;
>            hints.ai_next = NULL;
> 
>            s = getaddrinfo(NULL, argv[1], &hints, &result);
>            if (s != 0) {
>                fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
>                exit(EXIT_FAILURE);
>            }
> 
>            /* getaddrinfo() returns a list of address structures.
>               Try each address until we successfully bind(2).
>               If socket(2) (or bind(2)) fails, we (close the socket
>               and) try the next address. */
> 
>            for (rp = result; rp != NULL; rp = rp->ai_next) {
>                sfd = socket(rp->ai_family, rp->ai_socktype,
>                        rp->ai_protocol);
>                if (sfd == -1)
>                    continue;
> 
> 
> int result2;
> int bufSize = 2048;
> result2 = setsockopt(sfd, SOL_SOCKET, SO_RCVBUF, &bufSize,
> sizeof(bufSize));
> printf("result of setsockopt: %d\n", result2);
> 
>                if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0)
>                    break;                  /* Success */
> 
>                close(sfd);
>            }
> 
>            if (rp == NULL) {               /* No address succeeded */
>                fprintf(stderr, "Could not bind\n");
>                exit(EXIT_FAILURE);
>            }
> 
>            freeaddrinfo(result);           /* No longer needed */
> 
>            /* Read datagrams and echo them back to sender */
>            for (;;) {
>                peer_addr_len = sizeof(struct sockaddr_storage);
> 	       memset(buf, 0, BUF_SIZE);
>                nread = recvfrom(sfd, buf, BUF_SIZE, 0,
>                        (struct sockaddr *) &peer_addr, &peer_addr_len);
> 	       if(nread > 1024)
> 	       	printf("NREAD > 1024!");
>                if (nread == -1)
>                    continue;               /* Ignore failed request */
> 
>                char host[NI_MAXHOST], service[NI_MAXSERV];
> 
>                s = getnameinfo((struct sockaddr *) &peer_addr,
>                                peer_addr_len, host, NI_MAXHOST,
>                                service, NI_MAXSERV, NI_NUMERICSERV);
>               if (s == 0)
>                    printf("Received %ld bytes from %s:%s, msg:'%s'\n",
>                            (long) nread, host, service, buf);
>                else
>                    fprintf(stderr, "getnameinfo: %s\n",
> gai_strerror(s));
>            }
>        }
> 
> 
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