| Previous | Contents | Index |
Binding a socket associates a local protocol address (that is, a 32-bit IPv4 address and a 16-bit TCP or UDP port number) with a socket. To bind a socket, specify a local interface address and local port number for the socket.
With the TCP protocol, you can specify an IP address, a port number, both an IP address and port number or neither.
If the application is using the UDP protocol and needs to receive
incoming multicast or broadcast datagrams destined for a specific UDP
port, see Section 2.10 for information about specifying the
SO_REUSEPORT option when binding the socket.
2.3.1 Binding a Socket (Sockets API)
Example 2-3 shows an example of a TCP application using the bind() function to bind a socket name.
The process must have a system user identification code (UIC) and the SYSPRV, BYPASS, or OPER privilege to bind port numbers 1 to 1023. |
| Example 2-3 Binding a Socket (Sockets API) |
|---|
#include <in.h> /* define internet related constants, */
/* functions, and structures */
#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 PORTNUM 12345 /* server port number */
int main( void )
{
int sockfd;
struct sockaddr_in addr;
/*
* initialize socket address structure
*/
memset( &addr, 0, sizeof(addr) );
addr.sin_family = AF_INET;
addr.sin_port = htons( PORTNUM );
addr.sin_addr.s_addr = INADDR_ANY;
/*
* create a socket
*/
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0 )
{
perror( "Failed to create socket" );
exit( EXIT_FAILURE );
}
/*
* bind ip address and port number to socket
*/
if ( bind(sockfd,(1) (struct sockaddr *) &addr,(2) sizeof(addr)(3)) < 0 )
{
perror( "Failed to bind socket" );
exit( EXIT_FAILURE );
}
exit( EXIT_SUCCESS );
}
|
In this example, the bind() function:
Use the IO$_SETMODE or IO$_SETCHAR function of the $QIO system service to bind a socket.
The process must have a system user identification code (UIC), SYSPRV, BYPASS, or OPER privileges to bind port numbers 1 to 1023. |
Example 2-4 shows a TCP server using the IO$_SETMODE function to bind sockets.
| Example 2-4 Binding a Socket (System Services) |
|---|
#include <descrip.h> /* define OpenVMS descriptors */
#include <efndef.h> /* define 'EFN$C_ENF' event flag */
#include <in.h> /* define internet related constants, */
/* functions, and structures */
#include <iodef.h> /* define i/o function codes */
#include <ssdef.h> /* define system service status codes */
#include <starlet.h> /* define system service calls */
#include <stdio.h> /* define standard i/o functions */
#include <stdlib.h> /* define standard library functions */
#include <string.h> /* define string handling functions */
#include <stsdef.h> /* define condition value fields */
#include <tcpip$inetdef.h> /* define tcp/ip network constants, */
/* structures, and functions */
#define 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 sockchar
{ /* socket characteristics */
unsigned short prot; /* protocol */
unsigned char type; /* type */
unsigned char af; /* address format */
};
int main( void )
{
struct iosb iosb; /* i/o status block */
unsigned int status; /* system service return status */
unsigned short channel; /* network device i/o channel */
struct sockchar sockchar; /* socket characteristics buffer */
struct sockaddr_in addr; /* socket address structure */
struct itemlst_2 addr_itemlst; /* socket address item-list */
$DESCRIPTOR( inet_device, /* string descriptor with logical */
"TCPIP$DEVICE:" ); /* name of network pseudodevice */
/*
* initialize socket characteristics
*/
sockchar.prot = TCPIP$C_TCP;
sockchar.type = TCPIP$C_STREAM;
sockchar.af = TCPIP$C_AF_INET;
/*
* initialize socket address item-list descriptor
*/
addr_itemlst.length = sizeof( addr );
addr_itemlst.type = TCPIP$C_SOCK_NAME;
addr_itemlst.address = &addr;
/*
* initialize socket address structure
*/
memset( &addr, 0, sizeof(addr) );
addr.sin_family = TCPIP$C_AF_INET;
addr.sin_port = htons( PORTNUM );
addr.sin_addr.s_addr = TCPIP$C_INADDR_ANY;
/*
* assign i/o channel to network device
*/
status = sys$assign( &inet_device, /* device name */
&channel, /* i/o channel */
0, /* access mode */
0 /* not used */
);
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to assign i/o channel\n" );
exit( status );
}
/*
* create a socket
*/
status = sys$qiow( EFN$C_ENF, /* event flag */
channel, /* i/o channel */
IO$_SETMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
&sockchar, /* p1 - socket characteristics */
0, /* p2 */
0, /* p3 */
0, /* p4 */
0, /* p5 */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to create socket\n" );
exit( status );
}
/*
* bind ip address and port number to socket
*/
status = sys$qiow( EFN$C_ENF, /* event flag */
channel, /* i/o channel */
IO$_SETMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
0, /* p1 */
0, /* p2 */
&addr_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 );
}
exit( EXIT_SUCCESS );
}
|
Only server programs that use the TCP protocol need to set a socket to be a listener. This allows the program to receive incoming connection requests. As a connection-oriented protocol, TCP requires a connection; UDP, a connectionless protocol, does not.
The listen() function:
Example 2-5 shows how a TCP server uses the listen() function to set a socket to listen for connection requests and to specify the number of incoming requests that can wait to be queued for processing.
| Example 2-5 Setting a Socket to Listen (Sockets API) |
|---|
#include <in.h> /* define internet related constants, */
/* functions, and structures */
#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 BACKLOG 1 /* server backlog */
#define PORTNUM 12345 /* server port number */
int main( void )
{
int sockfd;
struct sockaddr_in addr;
/*
* initialize socket address structure
*/
memset( &addr, 0, sizeof(addr) );
addr.sin_family = AF_INET;
addr.sin_port = htons( PORTNUM );
addr.sin_addr.s_addr = INADDR_ANY;
/*
* create a socket
*/
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0 )
{
perror( "Failed to create socket" );
exit( EXIT_FAILURE );
}
/*
* bind ip address and port number to socket
*/
if ( bind(sockfd, (struct sockaddr *) &addr, sizeof(addr)) < 0 )
{
perror( "Failed to bind socket" );
exit( EXIT_FAILURE );
}
/*
* set socket as a listen socket
*/
if ( listen(sockfd, (1) BACKLOG (2) ) < 0 )
{
perror( "Failed to set socket passive" );
exit( EXIT_FAILURE );
}
exit( EXIT_SUCCESS );
}
|
In this example of a listen() function:
Example 2-6 shows how to use the IO$_SETMODE function to set the socket to listen for requests.
| Example 2-6 Setting a Socket to Listen (System Services) |
|---|
#include <descrip.h> /* define OpenVMS descriptors */
#include <efndef.h> /* define 'EFN$C_ENF' event flag */
#include <in.h> /* define internet related constants, */
/* functions, and structures */
#include <iodef.h> /* define i/o function codes */
#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 BACKLOG 1 /* server backlog */
#define 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 sockchar
{ /* socket characteristics */
unsigned short prot; /* protocol */
unsigned char type; /* type */
unsigned char af; /* address format */
};
int main( void )
{
struct iosb iosb; /* i/o status block */
unsigned int status; /* system service return status */
unsigned short channel; /* network device i/o channel */
struct sockchar sockchar; /* socket characteristics buffer */
struct sockaddr_in addr; /* socket address structure */
struct itemlst_2 addr_itemlst; /* socket address item-list */
$DESCRIPTOR( inet_device, /* string descriptor with logical */
"TCPIP$DEVICE:" ); /* name of network pseudodevice */
/*
* initialize socket characteristics
*/
sockchar.prot = TCPIP$C_TCP;
sockchar.type = TCPIP$C_STREAM;
sockchar.af = TCPIP$C_AF_INET;
/*
* initialize socket address item-list descriptor
*/
addr_itemlst.length = sizeof( addr );
addr_itemlst.type = TCPIP$C_SOCK_NAME;
addr_itemlst.address = &addr;
/*
* initialize socket address structure
*/
memset( &addr, 0, sizeof(addr) );
addr.sin_family = TCPIP$C_AF_INET;
addr.sin_port = htons( PORTNUM );
addr.sin_addr.s_addr = TCPIP$C_INADDR_ANY;
/*
* assign i/o channel to network device
*/
status = sys$assign( &inet_device, /* device name */
&channel, /* i/o channel */
0, /* access mode */
0 /* not used */
);
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to assign i/o channel\n" );
exit( status );
}
/*
* create a socket
*/
status = sys$qiow( EFN$C_ENF, /* event flag */
channel, /* i/o channel */
IO$_SETMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
&sockchar, /* p1 - socket characteristics */
0, /* p2 */
0, /* p3 */
0, /* p4 */
0, /* p5 */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to create socket\n" );
exit( status );
}
/*
* bind ip address and port number to socket
*/
status = sys$qiow( EFN$C_ENF, /* event flag */
channel, /* i/o channel */
IO$_SETMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
0, /* p1 */
0, /* p2 */
&addr_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 */
channel, /* i/o channel */
IO$_SETMODE, /* i/o function code */
&iosb, /* i/o status block */
0, /* ast service routine */
0, /* ast parameter */
0, /* p1 */
0, /* p2 */
0, /* p3 */
BACKLOG, /* p4 - connection backlog */
0, /* p5 */
0 /* p6 */
);
if ( status & STS$M_SUCCESS )
status = iosb.status;
if ( !(status & STS$M_SUCCESS) )
{
printf( "Failed to set socket passive\n" );
exit( status );
}
exit( EXIT_SUCCESS );
}
|
Although you can use separate $QIO calls for socket create, bind, and listen operations, you can also perform these operations with one $QIO call. |
A TCP client establishes a connection with a TCP server by issuing the
connect()
function. The
connect()
function initiates a three-way handshake between the client and the
server. This must be successful to establish the connection.
2.5.1 Initiating a Connection (Sockets API)
To initiate a connection to a a TCP server, use the connect() function. Example 2-7 shows a TCP client using the connect() function to initiate a connection to a TCP server.
| Example 2-7 Initiating a Connection (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 BUFSZ 1024 /* user input buffer size */
#define PORTNUM 12345 /* server port number */
void get_servaddr( void *addrptr )
{
char buf[BUFSIZ];
struct in_addr val;
struct hostent *host;
while ( TRUE )
{
printf( "Enter remote host: " );
if ( fgets(buf, sizeof(buf), stdin) == NULL )
{
printf( "Failed to read user input\n" );
exit( EXIT_FAILURE );
}
buf[strlen(buf)-1] = 0;
val.s_addr = inet_addr( buf );
if ( val.s_addr != INADDR_NONE )
{
memcpy( addrptr, &val, sizeof(struct in_addr) );
break;
}
if ( (host = gethostbyname(buf)) )
{
memcpy( addrptr, host->h_addr, sizeof(struct in_addr) );
break;
}
}
}
int main( void )
{
int sockfd;
struct sockaddr_in addr;
/*
* initialize socket address structure
*/
memset( &addr, 0, sizeof(addr) );
addr.sin_family = AF_INET;
addr.sin_port = htons( PORTNUM );
get_servaddr( &addr.sin_addr );
/*
* create a socket
*/
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0 )
{
perror( "Failed to create socket" );
exit( EXIT_FAILURE );
}
/*
* connect to specified host and port number
*/
printf( "Initiated connection to host: %s, port: %d\n",
inet_ntoa(addr.sin_addr), ntohs(addr.sin_port)
);
if ( connect(sockfd, (struct sockaddr *) &addr, sizeof(addr)) < 0 )
{
perror( "Failed to connect to server" );
exit( EXIT_FAILURE );
}
exit( EXIT_SUCCESS );
}
|
| Previous | Next | Contents | Index |