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Санкт-Петербургский государственный электротехнический университет "ЛЭТИ"
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Электротехника
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Jack H.Integration and automation of manufacturing systems.2001.pdf
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page 89

4.Call the Information technology people on campus, and request an IP address. Also ask for the gateway number, netmask, and nameserver numbers. They will add your machine to the campus DNS so that others may find it by name (the number will always work if chosen properly).

5.Connect the computer to the network, then turn it on.

6.Install Windows NT, and when asked provide the network information. Indicate that web serving will be permitted.

7.Modify web pages as required.

4.4.5 Java

•This is a programming language that is supported on most Internet based computers.

•These programs will run on any computer - there is no need for a Mac, PC and Unix version.

•Most users don’t need to program in Java, but the results can be used in your web pages

4.4.6 Javascript

• Simple programs can be written as part of an html file that will add abilities to the HTML page.

4.4.7 CGI

•CGI (Common Gateway Interface) is a very popular technique to allow the html page on the client to run programs on the server.

•Typical examples of these include,

-counters

-feedback forms

-information requests

4.5 NETWORKING IN LINUX

page 90

Configuration files are under /etc

Recompile kernel in some cases, such as a firewall. or new hardware

Loadable modules

DHCP versus static IP

Most modern versions of Linux simplify hardware detection and setup. The steps below can help perform the basic operations, or find problems.

A.Installing a normal ethernet network connection:

1.During the installation process you will be asked for network parameters.

2.Enter a unique name for the machine and the network name.

3.(for DHCP) All that should be required is a setting for DHCP.

3.(for a static IP) You will need to enter the static IP number for the machine, as well as a netmask and gateway. If you are connecting to another network you can get these from a network administrator. If you are connecting your own network (not on the Internet) you can simply pick values like those below. Note that you need some sort of network router with an IP address of 192.168.1.254 for this to work.

IP address: 192.168.1.20 netmask: 255.255.255.0 Gateway: 192.168.1.254 nameserver: none

B.Troubleshooting an ethernet connection to the Internet,

1.Check to see if the network card is recognized with ’more /proc/modules’ The card should be in the list. If not the kernel module must be installed.

2.Check to see if the network is setup with ifconfig. You should see ’eth0’ or something similar. If it is not setup, the network parameters must be checked.

3.Check to see if the network is connected properly with ping to the local gateway, or another local machine - use the IP number, not the name. For example, ’ping 148.61.104.254’. If this fails the gateway or broadcast addresses are probably incorrect.

4.Check the connection to the outside with a ping such as ’ping 148.61.1.10’. If this is not allowed there is probably a problem with the outside connection

5.Verify that the nameserver is working alright with a ping to a named machine such as, ’ping www.linux.org’.

6.If all of these things work the network connection should be alright.

C.Installing a dialup connection

1.During the installation make sure that the location of your modem is correctly identified. Note: Winmodems are very popular because of their low cost, but there are very few Linux drivers. But... you are advised to spend the money for a non-Win- modem anyway, they are more reliable and they don’t use your computers

page 91

resources.

2.

D.Troubleshooting a dialup connection

1.Use a terminal program to dial the Internet service provider’s number manually. If you don’t get a response there is a problem with the modem installation.

2.After connected try providing your login ID and password and see if you get in. Expect to see garbage after this. If login is refused you need to check the user ID and password again.

3.Check ...

E.Setting up a firewall (this requires some work)

1.To set up a firewall the kernel must be recompiled to include network options such as multicasting, and firewall services.

[KERNEL OPTIONS]

2.Shut down the computer and add a second network card in the machine and reboot.

3.Check to see if the card is recognized with ’more /proc/modules’. Both ethernet cards should be listed. If not you will need to edit the network startup files. These are normally in ’/etc/...’ or for slackware ’/etc/rc.d’. An example file follows. Reboot and check for both network cards again.

[NETWORK CONFIG FILES]

4.Use ’ipchains’ to add services to pass, and modify the ’hosts.allow’ and ’hosts.deny’ files to control access.

[ipchains file declarations] [hosts.allow file] [hosts.deny file]

4.5.1 Network Programming in Linux

The following listings show network usage in Linux. The general method of network connection is different for servers and clients.

For servers.....

For clients....

Listing X.1 - network_io.cpp

page 92

#include "network_io.h"

#include <sys/poll.h> #include <sys/ioctl.h> #include <linux/tcp.h>

#include <stdio.h> #include <string.h> #include <unistd.h> #include <fcntl.h>

network_io::network_io(){ type = _READ; level = 0;

}

network_io::~network_io(){

if(type == _READ){

if(level > 1){

if(level > 2){

end_read_connection();

}

deinit_read();

}

} else if (type == _WRITE){

}

}

int network_io::set_remote_host(char *_host_name, int host_socket){

static

int

error;

static

int

nm_a,

nm_b, nm_c, nm_d;

struct hostent*hp; unsigned charaddress[4];

error = NO_ERROR; strcpy(host_name, _host_name); host_socket_number = host_socket;

// Set up server descriptor, get host reference and error trap write_connection.sin_family = AF_INET;

if((host_name[0] > ’9’) ||(host_name[0]<’0’)){ hp = gethostbyname(host_name);

} else {

sscanf(host_name, "%d.%d.%d.%d", &nm_a, &nm_b, &nm_c, &nm_d);

address[0] = (unsigned char)(nm_a); address[1] = (unsigned char)(nm_b); address[2] = (unsigned char)(nm_c); address[3] = (unsigned char)(nm_d);

hp = gethostbyaddr((char *)address, 4, AF_INET);

}

if(hp != 0){

/* complete descriptor set up. */ bcopy((char *)hp->h_addr,

page 93

(char *)&(write_connection.sin_addr), hp->h_length);

} else {

error_log(MINOR, "ERROR: unknown network host"); error = ERROR;

}

return error;

}

int network_io::set_local_host(int socket_num){ static int error;

error = NO_ERROR; socket_number = socket_num;

return error;

}

int network_io::writer(char *string){

static int

error;

error = NO_ERROR;

 

// Open a new socket for the write, and check for errors.

error = init_write();

 

if(error == NO_ERROR) error

= open_write_connection();

if(error == NO_ERROR) error

= write_to_connection(string);

if(error == NO_ERROR) error

= end_write_connection();

if(deinit_write() == ERROR)

error = ERROR;

return(error);

 

}

 

int network_io::reader(char *buf, int length){

static interror;

// Error return variable

error = NO_ERROR;

// Wait for a socket connection request, then get its reference. buf[0] = 0;

if(wait_read_connection() == NO_ERROR){

if(read_from_connection(buf, length) == ERROR){

}

// Close socket connection to remote write client. end_read_connection();

}

return(error);

}

int network_io::init_write(){

static int

error;

struct hostent

*gethostbyname();

error =

NO_ERROR;

/* Open

a new

socket for the write, and check for errors. */

if((rw_socket

= socket(AF_INET, SOCK_STREAM, 0)) >= 0){

page 94

write_connection.sin_port = htons(host_socket_number);

} else {

error_log(MINOR, "ERROR: opening stream socket"); error = ERROR;

}

return error;

}

int network_io::open_write_connection(){

static int error;

error = NO_ERROR;

if(connect(rw_socket, (struct sockaddr *) &(write_connection), sizeof(write_connection))

< 0){

error = ERROR;

error_log(MINOR, "ERROR: Connecting stream Socket");

}

return error;

}

int network_io::write_to_connection(char *text){

static int error;

error = NO_ERROR;

if(write(rw_socket, text, strlen(text) /* +1 */) < 0){

error_log(MINOR, "ERROR: writing on stream socket"); error = ERROR;

}

return error;

}

int network_io::write_stuff_done(){ int error;

error = NO_ERROR; return error;

}

int network_io::check_connection(){

int

error;

int

count;

struct pollfd ufds;

error = NO_ERROR; ufds.fd = rw_socket;

ufds.events = POLLOUT | POLLIN | POLLPRI | POLLERR | POLLHUP | POLLNVAL; count = poll(&ufds, 1, 0);

if((ufds.revents & 16) != 0) error = ERROR;

return error;

}

int network_io::end_write_connection(){ static int error;

error = NO_ERROR;

page 95

return error;

}

 

 

int network_io::deinit_write(){

 

 

static int error;

 

 

error = NO_ERROR;

 

 

close(rw_socket);

 

 

rw_socket = ANY;

 

 

return error;

 

 

}

 

 

int network_io::init_read(){

 

 

static int

error;

// low level socket number

unsigned

length;

// temporary work variable

static struct sockaddr_inserver; // read socket descriptor

static struct hostent*hp;

 

 

char

text[100];

// Open internet socket, and check for error.

error = ERROR;

 

 

gethostname(text, 100);

/* who are we? */

hp = gethostbyname(text);

if((hp != NULL) && (read_socket = socket(AF_INET, SOCK_STREAM, 0)) >= 0){

//Set up server descriptor for binding name. memset(&server, 0, sizeof(struct sockaddr_in)); server.sin_family = hp->h_addrtype; server.sin_port = htons(socket_number);

//Bind the socket, and check for error.

level = 1; int flag = 1;

setsockopt(read_socket, SOL_SOCKET, SO_REUSEADDR, (char *)&flag, sizeof(int)); if(bind(read_socket, (struct sockaddr *)&server, sizeof(struct sockaddr_in)) >=

0){

// Check for valid socket binding length = sizeof(server);

if(getsockname(read_socket, (struct sockaddr *)&server, &length) >=

0){

error = NO_ERROR;

//Set up variables for success

//Zero because anything higher would allow

//messages to arrive out of sequence. listen(read_socket, 0);

} else {

error_log(MINOR, "ERROR: getting socket name");

}

} else {

error_log(MINOR, "ERROR: binding stream socket");

}

} else {

error_log(MINOR, "ERROR: opening stream socket");

}

return(error);

}

int network_io::read_stuff_waiting(){ int error,

count; struct pollfd ufds;

page 96

error = ERROR; ufds.fd = read_socket;

ufds.events = POLLIN | POLLPRI | POLLOUT; count = poll(&ufds, 1, 0); if((ufds.revents & 1) > 0){

error = NO_ERROR;

}

return error;

}

int network_io::wait_read_connection(){

static int error;

unsigned size;

static struct sockaddr addr;

error = NO_ERROR;

size = sizeof(struct sockaddr); fcntl(read_socket, F_SETFL, O_NONBLOCK); rw_socket = accept(read_socket, &addr, &size);

level = 2; if(rw_socket < 0){

error = ERROR;

// error_log("ERROR: warning:accept");

}

return error;

}

int network_io::read_from_connection(char *buf, int length){

int

error;

int

len;

error = NO_ERROR;

//Empty input buffer buf[0] = 0;

//Read string into buffer from socket fcntl(rw_socket, F_SETFL, O_NONBLOCK); len = read(rw_socket, buf, length); if(len < 0){

//error_log("ERROR: reading stream message");

//error = ERROR;

if(errno != 11){

printf("errno=%d ", errno);

}

} else {

buf[len] = 0;

}

return error;

}

int network_io::end_read_connection(){

int

error;

int

a;

error = NO_ERROR;

a = close(rw_socket); level = 1;

page 97

return error;

}

int network_io::deinit_read(){

int

error;

int

a;

error = NO_ERROR;

a = close(read_socket); level = 0;

return error;

}

char *network_io::get_address(){

static char

work[MAXIMUM_HOST_NAME_LENGTH];

struct sockaddr_inaddress;

int

i,

 

addr[4];

long

int_address;

#ifndef SGI

// Sun Version get_myaddress(&address);

int_address = address.sin_addr.s_addr;

#else

// SGI Version int_address = gethostid();

#endif

// SUN & SGI version for(i = 0; i < 4; i++){

addr[i]=int_address & 0xFF; int_address >>= 8;

}

#ifdef OTHER_UNIX

sprintf(work, "%d.%d.%d.%d",

(int)addr[3], (int)addr[2], (int)addr[1], (int)addr[0]);

#else

// This is for linux sprintf(work, "%d.%d.%d.%d",

(int)addr[0], (int)addr[1], (int)addr[2], (int)addr[3]);

#endif

return work;

}

char *network_io::get_remote_client(){

staticchar

work[100];

struct sockaddr

address;

socklen_t

len;

len = sizeof(address);

if(getpeername(rw_socket, &address, &len) == 0){

sprintf(work, "%u.%u.%u.%u", address.sa_data[2], address.sa_data[3], address.sa_data[4], address.sa_data[5]);

// printf("Got address [%s]\n", work); //strcpy(work, address);

} else {

strcpy(work, "unknown network address");

}

return work;

}

page 98

Listing X.2 - network_io.h

#ifndef _NETWORK_IO #define _NETWORK_IO

#include <errno.h> #include <linux/socket.h> #include <sys/types.h> #include <netdb.h> #include <rpc/rpc.h> #include <unistd.h>

#define ANY

0

 

// Indicates no socket number prechosen

#define

MAXIMUM_HOST_NAME_LENGTH100

class network_io{

 

 

public:

 

 

 

 

int

 

socket_number;

 

int

 

rw_socket;

 

// int

 

read_connection;

 

char

host_name[MAXIMUM_HOST_NAME_LENGTH];

 

int

 

host_socket_number;

 

int

 

read_socket;

 

struct sockaddr_inwrite_connection;

 

// char

incoming_string[MAXIMUM_STRING_SIZE];

 

int

 

type;

 

int

 

level;

 

#define

_READ

200

 

#define

_WRITE

201

 

 

 

network_io();

 

 

 

~network_io();

 

int

 

set_remote_host(char*, int);

 

int

 

set_local_host(int);

 

int

 

reader(char*, int);

 

int

 

writer(char*);

 

int

 

init_write();

 

int

 

open_write_connection();

 

int

 

write_to_connection(char*);

 

// int

 

write_to_read_connection(char*);

 

int

 

end_write_connection();

 

int

 

deinit_write();

 

int

 

init_read();

 

int

 

wait_read_connection();

 

int

 

read_from_connection(char*, int);

 

// int

 

read_from_write_connection(char*, int);

 

int

 

end_read_connection();

 

int

 

deinit_read();

 

int

 

read_stuff_waiting();

 

int

 

write_stuff_done();

 

int

 

check_connection();

 

char*

get_remote_client();

 

char

*get_address();

};

 

 

 

page 99

#endif

Listing X.3 - network.cpp

#include "../network_io/network_io.h" #include <time.h>

network_io *network;

 

int

mode;

 

char

*params;

 

char

received_temp[200];

int

connect_flag;

time_t

now_time;

 

time_t

last_time;

int

timeout;

 

int main(){

 

 

timeout = 5;

// the default timeout

return 1;

 

 

}

 

 

int deinit(){

 

 

int

error;

 

error = NO_ERROR;

if(network != NULL) delete network;

return error;

}

int process_command(); int check_network();

int step(){

int error;

error = NO_ERROR;

error = check_network();

if(error == NO_ERROR) error = process_command();

return error;

}

int check_network(){

int

error;

error = NO_ERROR;

if(*state == WAITINGFORCONNECTION){ if(connect_flag == TRUE){

page 100

if(mode == LISTENER){

if(network->wait_read_connection() == NO_ERROR){ char text[200];

*state = CONNECTIONESTABLISHED; *received_flag = FALSE; *send_flag = FALSE;

sprintf(text, "Got a connection from %s", network-

>get_remote_client());

error_log(WARNING, text); time(&last_time);

}

} else if(mode == TALKER){ if(network->open_write_connection() == NO_ERROR){

*state = CONNECTIONESTABLISHED; *received_flag = FALSE; *send_flag = FALSE; time(&last_time);

}

}

}

} else if(*state == CONNECTIONESTABLISHED){ if(*send_flag == TRUE){

network->write_to_connection(send_buf);

//printf("Sending String [%s]\n", send_buf); send_buf[0] = 0;

*send_flag = FALSE;

//time(&last_time); // You can keep the connection alive by writing

//but this doesn’t guarantee that the remote client is still there

}

if(*received_flag == FALSE){ if(network->read_from_connection(received_temp, 199) != ERROR){

if(strlen(received_temp) > 0){ strcpy(received, received_temp); *received_flag = TRUE; time(&last_time);

// printf("Got String [%s]\n", received);

}

}

}

time(&now_time);

if((network->check_connection() == ERROR) || ((mode == LISTENER) && (difftime(now_time, last_time) > timeout))){

if(mode == LISTENER){ network->end_read_connection();

} else if(mode == TALKER){ network->end_write_connection();

}

*state = WAITINGFORCONNECTION; connect_flag = FALSE;

}

}

return error;

}

int process_command(){

int

error;

int

i, len;

int

port;

error = NO_ERROR; if(*change_lock == TRUE){

if(*command == INITIALIZE){

page 101

if(*state == NOTINITIALIZED){ if(mode == LISTENER){

port = atoi(params); if(port > 0){

network = new network_io(); network->set_local_host(port); network->init_read();

//now ready to listen

*state = WAITINGFORCONNECTION; connect_flag = FALSE;

} else {

error_log(MINOR, "Parameter did not hold

a valid port");

*error_flag = ERROR;

}

} else if(mode == TALKER){

len = strlen(params); for(i = 0; i < len; i++){

if(params[i] == ’:’){ params[i] = 0;

port = atoi(&(params[i+1])); break;

}

}

if((i < len) && (port > 0)){

network = new network_io(); network->set_remote_host(params, port); network->init_write();

*state = WAITINGFORCONNECTION; connect_flag = FALSE;

} else {

error_log(MINOR, "Address string was not

properly formed");

*error_flag = ERROR;

}

} else {

error_log(MINOR, "ERROR: Mode not defined yet"); *error_flag = ERROR;

}

} else {

error_log(MINOR, "Network talker initialize command in wrong

state");

*error_flag = ERROR;

}

} else if(*command == CONNECT){

if(*state == WAITINGFORCONNECTION){ connect_flag = TRUE;

}

} else if(*command == DISCONNECT){

if(*state == CONNECTIONESTABLISHED){ if(mode == TALKER){

network->end_write_connection(); } else if (mode == LISTENER){

network->end_read_connection();

}

*state = WAITINGFORCONNECTION; connect_flag = FALSE;

} else {

error_log(MINOR, "Cannot disconnect network unless

connected");

*error_flag = ERROR;

}

} else if(*command == UNINITIALIZE){ if(*state == WAITINGFORCONNECTION){

if(mode == TALKER){

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