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HP OpenVMS systems documentation |
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You can use a read operation to look at data in a socket receive queue
without removing the data from the buffer. This is called
peeking.
2.12.1 Peeking at Data (Sockets API)
Use the MSG_PEEK flag with the recv() function to peek at data in the socket receive queue.
Example 2-19 shows a TCP server using the recv() function with the MSG_PEEK flag to peek at received data.
| Example 2-19 Peeking at 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 */
#include <unixio.h> /* define unix i/o */
#define BUFSZ 128 /* user input buffer size */
#define SERV_BACKLOG 1 /* server backlog */
#define SERV_PORTNUM 1234 /* server port number */
int main( void )
{
char buf[BUFSIZ]; /* user input buffer */
int conn_sockfd; /* connection socket descriptor */
int listen_sockfd; /* listen socket descriptor */
int optval = 1; /* SO_REUSEADDR'S option value (on) */
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 */
/*
* initialize client's socket address structure
*/
memset( &cli_addr, 0, sizeof(cli_addr) );
/*
* 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)
);
cli_addrlen = sizeof(cli_addr);
conn_sockfd = accept( listen_sockfd,
(struct sockaddr *) &cli_addr,
&cli_addrlen
);
if ( conn_sockfd < 0 )
{
perror( "Failed to accept client connection" );
exit( EXIT_FAILURE );
}
/*
* ask client to pick a character
*/
sprintf( buf, "Please pick a character:\r\n");
if ( send(conn_sockfd, buf, strlen(buf), 0) != strlen(buf) )
{
perror( "Failed to write data to connection" );
exit( EXIT_FAILURE );
}
/*
* peek at client's reply
*/
if ( recv(conn_sockfd (1), buf (2), 1 (3), MSG_PEEK (4)) != 1 )
{
perror( "Failed to read data from connection" );
exit( EXIT_FAILURE );
}
sprintf( buf, "Before receiving, I see you picked '%c'.\r\n", buf[0] );
if ( send(conn_sockfd, buf, strlen(buf), 0) != strlen(buf) )
{
perror( "Failed to write data to connection" );
exit( EXIT_FAILURE );
}
/*
* now, read client's reply
*/
if ( recv(conn_sockfd, buf, 1, 0) != 1 )
{
perror( "Failed to read data from connection" );
exit( EXIT_FAILURE );
}
sprintf( buf, "Sure enough, I received '%c'.\r\n", buf[0] );
if ( send(conn_sockfd, buf, strlen(buf), 0) != strlen(buf) )
{
perror( "Failed to write data to connection" );
exit( EXIT_FAILURE );
}
/*
* close sockets
*/
if ( close(conn_sockfd) < 0 )
{
perror( "Failed to close socket" );
exit( EXIT_FAILURE );
}
if ( close(listen_sockfd) < 0 )
{
perror( "Failed to close socket" );
exit( EXIT_FAILURE );
}
exit( EXIT_SUCCESS );
}
|
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. The code is similar to the example shown in
Section 2.11.2.
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 );
}
|
In this example, the send() function include the following arguments:
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.
| 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$M_SUCCESS) )
{
printf( "Failed to set socket passive\n" );
exit( status );
}
/*
* accept connection from a client
*/
printf( "Waiting for a client connection on port: %d\n",
ntohs(serv_addr.sin_port)
);
(1)
status = sys$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$_WRITEVBLK, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
(2) buf, /* p1 - buffer address */
buflen, /* p2 - buffer length */
0, /* p3 */
0, /* p4 */
(3) 0, /* p5 */
(4) 0 /* p6 */
);
if ( status & STS$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 );
}
|
This example uses OpenVMS system services to transmit a single buffer of data.
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