TCP/IP - Sockets appear to be restricted to maximum 65,535 byte transfers
From: Roy Omond (Roy.Omond_at_BlueBubble.UK.Com)
Date: 03/07/05
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Date: Mon, 07 Mar 2005 15:51:56 +0000
Gentle colleagues,
this is becoming a bit of a showstopper for me:
A very simple pair of programs (Server and Client) are setup
to transfer a quantity of data via a TCP Socket. The background
to this is actually in trying to get this to work in UCX v3.3 ECO 3,
whereas it worked flawlessly (and as per the documentation) in
vanilla UCX v3.3 (without ECO), running under VAX VMS 6.2.
The problem is easily demonstrated on VMS 7.3-2 (Alpha) with
TCP/IP Services v5.4 ECO 4, as well as all the versions after
UCX v3.3 ECO 3 and above (both VAX and Alpha).
The Server process establishes a socket, listens for an accept on the
socket (which the Client sends), and sends an amount of data down the
socket to the client. That's it. It works fine with data up to and
including 65,535 bytes. Beyond this, it returns an error
("%system-f-ivbuflen, invalid buffer length").
I can find no mention in the documentation "TCP/IP Sockets API
and System Services Programming" of any such restriction on the
amount of data to transfer.
Here are the 2 small programs:
--- cut here ---
$ create client.c
#include <errno.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include "sys/ioctl.h"
#include <netdb.h>
/*
struct hostent
*VGetHostByName(char *name)
{
struct hostent *h;
int i;
if (name == NULL)
{
return(NULL);
}
sethostent( 1 );
while ((h = gethostent()) != NULL)
{
if (strcmp(name,h->h_name) == 0) {
endhostent();
return(h);
}
i = 0;
while (h->h_aliases[i] != NULL) {
if (strcmp(name,h->h_aliases[i]) == 0) {
endhostent();
return(h);
}
i++;
}
}
endhostent();
return( NULL );
}*/
main (int argc, char ** argv)
{
int sock;
int byte_count;
int bcount;
char data[1000000];
int sendbuf;
int len;
static struct hostent *mh,master_host;
static struct sockaddr_in sin;
if ((sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1)
{
perror ("Create Socket:");
printf ("errno in CreateSock is %d\n", errno);
return(-1);
}
if (argc > 1)
{
printf ("Connecting to host %s\n", argv[1]);
mh = GetHostByName(argv[1]);
if (mh == NULL)
{
perror ("GetHostByName:");
printf ("Can't get host name %s\n", argv[1]);
close(sock);
return (-1);
}
}
else
{
printf ("Need a host name\n");
return (-1);
}
master_host = *mh;
sin.sin_family = master_host.h_addrtype;
sin.sin_port = 50000;
memcpy(&sin.sin_addr, master_host.h_addr, master_host.h_length);
if (connect(sock, &sin, sizeof(struct sockaddr_in)) == -1)
{
perror ("Connect:");
return (-1);
}
len = sizeof(sendbuf);
if (getsockopt(sock,SOL_SOCKET,SO_SNDBUF,&sendbuf,&len) < 0)
{
perror("getsockopt SO_SNDBUF");
}
printf("Send buffer %d bytes\n",sendbuf);
while (1)
{
ioctl(sock, FIONREAD, &bcount);
if (bcount > 0)
{
int cnt = 0;
if ((bcount = read (sock, (char *)&byte_count,sizeof(int))) == -1)
{
perror ("Read data size");
return (-1);
}
printf ("Read %d bytes, count is %d\n", bcount, byte_count);
bcount = 0;
while (cnt < byte_count)
{
if ((bcount = read (sock, data, byte_count - cnt)) == -1)
{
perror ("Read data");
return (-1);
}
printf ("Read %d\n", bcount);
cnt += bcount;
}
printf ("Read %d bytes total\n", cnt);
break;
}
}
}
$ create server.c
#include <errno.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <ucx$inetdef.h>
int
writevv (int fd, struct iovec * iov, int iovcnt)
{
int total_bytes = 0, bytes, i;
for (i = 0; i < iovcnt; i++)
{
bytes = write (fd, iov[i].iov_base, iov[i].iov_len);
if (bytes == -1)
{
perror ("write:");
return (-1);
}
else
{
total_bytes += bytes;
}
}
return (total_bytes);
}
main (int argc, char ** argv)
{
int serv_sock = -1;
int client_sock = -1;
int len;
int data_size = 1000;
if (argc >= 2) data_size = atoi(argv[1]);
if ((serv_sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1)
{
perror ("Create Socket:");
printf ("errno in CreateSock is %d\n", errno);
return(-1);
}
len=sizeof(data_size);
if (setsockopt(serv_sock,SOL_SOCKET,SO_SNDBUF,&data_size,len) < 0)
{
perror("setsockopt SO_SNDBUF");
}
if (setsockopt(serv_sock,SOL_SOCKET,SO_RCVBUF,&data_size,len) < 0)
{
perror("setsockopt SO_RCVBUF");
}
printf("Send/Receive buffer %d bytes\n",data_size);
{
static struct sockaddr_in sin;
sin.sin_family = htons(AF_INET);
sin.sin_port = 50000;
sin.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(serv_sock, &sin, sizeof(sin)) == -1)
{
printf("cannot bind socket to port");
perror ("Bind:");
return(-1);
}
}
if (listen(serv_sock, 20) == -1)
{
printf("cannot set listen(s,20)");
perror ("Listen:");
return(-1);
}
if ((client_sock = accept(serv_sock, NULL, NULL)) > 0)
{
struct iovec iov[2];
int count;
static char data[1000000];
if (data_size > 1000000) data_size = 1000000;
iov[0].iov_base = (char *) &data_size;
iov[0].iov_len = sizeof(int);
iov[1].iov_base = &data;
iov[1].iov_len = data_size;
if (writevv(client_sock,iov,2) == -1)
{
perror ("writev:");
return (-1);
}
sleep(10);
}
}
$ server:=$u:[xxxx]server
$ client:=$u:[xxxx]client
$ spawn/nowait server 65536
$ client my-node-name
Any comments ? Any suggestions ? I thinks this, at worst, a
bug in the Socket implementation, or, at "best", a serious
omission in the documentation.
Note, as mentioned above, this worked fine in UCX v3.3, but
not in UCX v3.3 ECO 3 or later.
Many thanks in advance,
Roy Omond
Blue Bubble Ltd.
- Next message: John Smith: "[OT]: AMD virtualization"
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- Next in thread: Dan Allen: "RE: TCP/IP - Sockets appear to be restricted to maximum 65,535 byte transfers"
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- Reply: Thierry USO: "Re: TCP/IP - Sockets appear to be restricted to maximum 65,535 byte transfers"
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