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The recv() function receives data from a connected socket and places it in a buffer, as follows:
To peek at data that is next in the socket receive queue, use the
IO$_READVBLK function of the $QIO system service and use the
TCPIP$C_MSG_PEEK flag. This allows you to use multiple read operations
on the same data.
2.13 Writing Data
For programs that use TCP, data writing occurs after a client program initiates a connection and after the server program accepts the connection. When using UDP, you also have the option of establishing a default peer address with a specific socket, but this is not required for data transfer.
2.13.1 Writing Data (Sockets API)
Example 2-20 shows a TCP server using the
send()
function to transmit data.
| Example 2-20 Writing Data (Sockets API) |
|---|
#include <in.h> /* define internet related constants, */
/* functions, and structures */
#include <inet.h> /* define network address info */
#include <netdb.h> /* define network database library info */
#include <socket.h> /* define BSD socket api */
#include <stdio.h> /* define standard i/o functions */
#include <stdlib.h> /* define standard library functions */
#include <string.h> /* define string handling functions */
#define SERV_BACKLOG 1 /* server backlog */
#define SERV_PORTNUM 12345 /* server port number */
int main( void )
{
int optval = 1; /* SO_REUSEADDR's option value (on) */
int conn_sockfd; /* connection socket descriptor */
int listen_sockfd; /* listen socket descriptor */
unsigned int cli_addrlen; /* returned length of client socket */
/* address structure */
struct sockaddr_in cli_addr; /* client socket address structure */
struct sockaddr_in serv_addr; /* server socket address structure */
char buf[] = "Hello, world!"; /* data buffer */
/*
* initialize server's socket address structure
*/
memset( &serv_addr, 0, sizeof(serv_addr) );
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons( SERV_PORTNUM );
serv_addr.sin_addr.s_addr = INADDR_ANY;
/*
* create a listen socket
*/
if ( (listen_sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0 )
{
perror( "Failed to create socket" );
exit( EXIT_FAILURE );
}
/*
* bind server's ip address and port number to listen socket
*/
if ( setsockopt(listen_sockfd,
SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) < 0 )
{
perror( "Failed to set socket option" );
exit( EXIT_FAILURE );
}
if ( bind(listen_sockfd,
(struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0 )
{
perror( "Failed to bind socket" );
exit( EXIT_FAILURE );
}
/*
* set socket as a listen socket
*/
if ( listen(listen_sockfd, SERV_BACKLOG) < 0 )
{
perror( "Failed to set socket passive" );
exit( EXIT_FAILURE );
}
/*
* accept connection from a client
*/
printf( "Waiting for a client connection on port: %d\n",
ntohs(serv_addr.sin_port)
);
conn_sockfd = accept( listen_sockfd, (struct sockaddr *) 0, 0 );
if ( conn_sockfd < 0 )
{
perror( "Failed to accept client connection" );
exit( EXIT_FAILURE );
}
/*
* log client connection request
*/
cli_addrlen = sizeof(cli_addr);
memset( &cli_addr, 0, sizeof(cli_addr) );
if ( getpeername(conn_sockfd,
(struct sockaddr *) &cli_addr, &cli_addrlen) < 0 )
{
perror( "Failed to get client name" );
exit( EXIT_FAILURE );
}
printf( "Accepted connection from host: %s, port: %d\n",
inet_ntoa(cli_addr.sin_addr), ntohs(cli_addr.sin_port)
);
/*
* write data to connection
*/
if ( send(conn_sockfd, (1) buf, (2) sizeof(buf),(3) 0 (4)) < 0 )
{
perror( "Failed to write data to connection" );
exit( EXIT_FAILURE );
}
printf( "Data sent: %s\n", buf );
exit( EXIT_SUCCESS );
}
|
The IO$_WRITEVBLK function of the $QIO system service copies data from the address space of the user's process to system dynamic memory and then transfers the data to an internet host or port.
Example 2-21 shows a TCP server using the IO$_WRITEVBLK function to transmit a single data buffer. The $QIO(IO$_ACCESS|IO$M_ACCEPT) function was previously executed to establish the connection with the client.
| Example 2-21 Writing Data (System Services) |
|---|
#include <descrip.h> /* define OpenVMS descriptors */
#include <efndef.h> /* define 'EFN$C_ENF' event flag */
#include <in.h> /* define internet related constants, */
/* functions, and structures */
#include <inet.h> /* define network address info */
#include <iodef.h> /* define i/o function codes */
#include <netdb.h> /* define network database library info */
#include <ssdef.h> /* define system service status codes */
#include <starlet.h> /* define system service calls */
#include <stdio.h> /* define standard i/o functions */
#include <stdlib.h> /* define standard library functions */
#include <string.h> /* define string handling functions */
#include <stsdef.h> /* define condition value fields */
#include <tcpip$inetdef.h> /* define tcp/ip network constants, */
/* structures, and functions */
#define SERV_BACKLOG 1 /* server backlog */
#define SERV_PORTNUM 12345 /* server port number */
struct iosb
{ /* i/o status block */
unsigned short status; /* i/o completion status */
unsigned short bytcnt; /* bytes transferred if read/write */
void *details; /* address of buffer or parameter */
};
struct itemlst_2
{ /* item-list 2 descriptor/element */
unsigned short length; /* length */
unsigned short type; /* parameter type */
void *address; /* address of item list */
};
struct itemlst_3
{ /* item-list 3 descriptor/element */
unsigned short length; /* length */
unsigned short type; /* parameter type */
void *address; /* address of item list */
unsigned int *retlen; /* address of returned length */
};
struct sockchar
{ /* socket characteristics */
unsigned short prot; /* protocol */
unsigned char type; /* type */
unsigned char af; /* address format */
};
int main( void )
{
int optval = 1; /* reuseaddr option value (on) */
struct iosb iosb; /* i/o status block */
unsigned int status; /* system service return status */
unsigned short conn_channel; /* connect inet device i/o channel */
unsigned short listen_channel; /* listen inet device i/o channel */
struct sockchar listen_sockchar; /* listen socket characteristics */
unsigned int cli_addrlen; /* returned length of client socket */
/* address structure */
struct sockaddr_in cli_addr; /* client socket address structure */
struct itemlst_3 cli_itemlst; /* client socket address item-list */
struct sockaddr_in serv_addr; /* server socket address structure */
struct itemlst_2 serv_itemlst; /* server socket address item-list */
struct itemlst_2 sockopt_itemlst; /* server socket option item-list */
struct itemlst_2 reuseaddr_itemlst; /* reuseaddr option item-list */
char buf[] = "Hello, world!"; /* data buffer */
int buflen = sizeof( buf ); /* length of data buffer */
$DESCRIPTOR( inet_device, /* string descriptor with logical */
"TCPIP$DEVICE:" ); /* name of network pseudodevice */
/*
* initialize socket characteristics
*/
listen_sockchar.prot = TCPIP$C_TCP;
listen_sockchar.type = TCPIP$C_STREAM;
listen_sockchar.af = TCPIP$C_AF_INET;
/*
* initialize reuseaddr's item-list element
*/
reuseaddr_itemlst.length = sizeof( optval );
reuseaddr_itemlst.type = TCPIP$C_REUSEADDR;
reuseaddr_itemlst.address = &optval;
/*
* initialize setsockopt's item-list descriptor
*/
sockopt_itemlst.length = sizeof( reuseaddr_itemlst );
sockopt_itemlst.type = TCPIP$C_SOCKOPT;
sockopt_itemlst.address = &reuseaddr_itemlst;
/*
* initialize client's item-list descriptor
*/
cli_itemlst.length = sizeof( cli_addr );
cli_itemlst.type = TCPIP$C_SOCK_NAME;
cli_itemlst.address = &cli_addr;
cli_itemlst.retlen = &cli_addrlen;
/*
* initialize server's item-list descriptor
*/
serv_itemlst.length = sizeof( serv_addr );
serv_itemlst.type = TCPIP$C_SOCK_NAME;
serv_itemlst.address = &serv_addr;
/*
* initialize server's socket address structure
*/
memset( &serv_addr, 0, sizeof(serv_addr) );
serv_addr.sin_family = TCPIP$C_AF_INET;
serv_addr.sin_port = htons( SERV_PORTNUM );
serv_addr.sin_addr.s_addr = TCPIP$C_INADDR_ANY;
/*
* assign i/o channels to network device
*/
status = sys$assign( &inet_device, /* device name */
&listen_channel, /* i/o channel */
0, /* access mode */
0 /* not used */
);
if ( status & STS$M_SUCCESS )
status = sys$assign( &inet_device, /* device name */
&conn_channel, /* i/o channel */
0, /* access mode */
0 /* not used */
);
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to assign i/o channel(s)\n" );
exit( status );
}
/*
* create a listen socket
*/
status = sys$qiow( EFN$C_ENF, /* event flag */
listen_channel, /* i/o channel */
IO$_SETMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
&listen_sockchar, /* p1 - socket characteristics */
0, /* p2 */
0, /* p3 */
0, /* p4 */
0, /* p5 */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to create socket\n" );
exit( status );
}
/*
* bind server's ip address and port number to listen socket
*/
status = sys$qiow( EFN$C_ENF, /* event flag */
listen_channel, /* i/o channel */
IO$_SETMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
0, /* p1 */
0, /* p2 */
0, /* p3 */
0, /* p4 */
&sockopt_itemlst, /* p5 - socket options */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to set socket option\n" );
exit( status );
}
status = sys$qiow( EFN$C_ENF, /* event flag */
listen_channel, /* i/o channel */
IO$_SETMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
0, /* p1 */
0, /* p2 */
&serv_itemlst, /* p3 - local socket name */
0, /* p4 */
0, /* p5 */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to bind socket\n" );
exit( status );
}
/*
* set socket as a listen socket
*/
status = sys$qiow( EFN$C_ENF, /* event flag */
listen_channel, /* i/o channel */
IO$_SETMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
0, /* p1 */
0, /* p2 */
0, /* p3 */
SERV_BACKLOG, /* p4 - connection backlog */
0, /* p5 */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to set socket passive\n" );
exit( status );
}
/*
* accept connection from a client
*/
printf( "Waiting for a client connection on port: %d\n",
ntohs(serv_addr.sin_port)
);
status = sys$qiow( EFN$C_ENF, /* event flag */
listen_channel, /* i/o channel */
IO$_ACCESS|IO$M_ACCEPT,
/* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
0, /* p1 */
0, /* p2 */
0, /* p3 */
&conn_channel, /* p4 - i/o channel for new */
/* connection */
0, /* p5 */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to accept client connection\n" );
exit( status );
}
/*
* log client connection request
*/
memset( &cli_addr, 0, sizeof(cli_addr) );
status = sys$qiow( EFN$C_ENF, /* event flag */
conn_channel, /* i/o channel */
IO$_SENSEMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
0, /* p1 */
0, /* p2 */
0, /* p3 */
&cli_itemlst, /* p4 - peer socket name */
0, /* p5 */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to get client name\n" );
exit( status );
}
printf( "Accepted connection from host: %s, port: %d\n",
inet_ntoa(cli_addr.sin_addr), ntohs(cli_addr.sin_port)
);
/*
* write data to connection
*/
status = sys$qiow( EFN$C_ENF, /* event flag */
conn_channel, /* i/o channel */
IO$_WRITEVBLK, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
buf, /* p1 - buffer address */
buflen, /* p2 - buffer length */
0, /* p3 */
0, /* p4 */
0, /* p5 */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to write data to connection\n" );
exit( status );
}
printf( "Data sent: %s\n", buf );
exit( EXIT_SUCCESS );
}
|
You can also specify a list of write buffers by omitting the
p1 and p2 parameters and instead
passing the list of buffers as the p5 parameter. Note
that, when writing a list of buffers, the p5 parameter
is used; when reading a list, the p6 parameter is
used. For more information, see Section 5.5.1.
2.14 Writing OOB Data (TCP Protocol)
If your application uses TCP, you can send OOB data to a remote
process. At the remote process, the message is delivered to the user
through either the data receive or the out-of-band data receive
mechanism. You can write only 1 byte of OOB data at a time.
2.14.1 Writing OOB Data (Sockets API)
To send OOB data to a remote process, use the MSG_OOB flag with the send() , sendmsg() , and sendto() functions.
Example 2-22 shows a TCP server using the MSG_OOB flag with the send() function.
| Example 2-22 Writing OOB Data (Sockets API) |
|---|
/* This program accepts a connection on TCP port 1234, sends the string,
"Hello, world!", waits two seconds, sends an urgent BEL (^G), waits
another two seconds, repeats the Hello message, and terminates. */
#include <types.h>
#include <in.h>
#include <socket.h>
#include <unixio.h>
#define PORTNUM 123
main() {
struct sockaddr_in lcladdr;
int r, s, one = 1;
char *message = "Hello, world!\r\n",
*oob_message = "\007";
memset()
lcladdr.sin_family = AF_INET;
lcladdr.sin_addr.s_addr = INADDR_ANY;
lcladdr.sin_port = htons(PORTNUM);
if ((s = socket(AF_INET, SOCK_STREAM, 0)) < 0) perror("socket");
if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)))
perror("setsockopt");
if (bind(s, &lcladdr, sizeof(lcladdr))) perror("bind");
if (listen(s, 1)) perror("listen");
if ((r = accept(s, 0, 0)) < 0) perror("accept");
if (send(r, message, strlen(message), 0) != strlen(message))
perror("send");
sleep(2);
if (send(r,(1) oob_message,(2) strlen(oob_message),(3) MSG_OOB (4)) !=
strlen(oob_message)) perror("send");
sleep(2);
if (send(r, message, strlen(message), 0) != strlen(message))
perror("send");
sleep(2);
if (close(r)) perror("close");
if (close(s)) perror("close");
}
|
The send() function is used to send OOB data to a remote socket, as follows:
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