Network Programming - NC Client Like Program

[Danikar]

I used fgets in my C program to read from STDIN. Whenever it comes to that line it stops the program and waits for input. Is there a way that I can set it up so that it only does this when there is something in STDIN for it to send.

The program basicly works like a client only form of netcat.

I am very noob to network programming that is why I am practicing with this type of program.

My program source is as below.



#include <stdio.h>
#include <netinet/in.h>

#define MAXLINE 255

int main(int argc, char *argv[])
{
int socketfd, n, r;
char buffer[MAXLINE + 1];
struct sockaddr_in servaddr;

// Exit if not 1 argument, IP
if(argc != 3)
{
printf("Usage: %s IP_ADDRESS PORT\n", argv[0]);
exit(-1);
}

// Creates socket and file descriptor, exit if error
if( (socketfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
printf("Socket Error\n");

// Clear Struct for writing
memset(&servaddr, '\0', sizeof(servaddr));

// Set family and port
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(atoi(argv[2]));

// Set Address
if( inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0 )
printf("inet_pton error for %s.", argv[1]);

// Connect to server
if( connect(socketfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0 )
{
printf("Could not connect\n");
exit(-1);
}

printf("Type you request, then type . and return on a single");
printf(" line to signify the end of your request.\n\n");

printf("Enter data to send: \n");
do
{
memset(&buffer, '\0', sizeof(buffer));
fgets(buffer, MAXLINE, stdin);
if(strcmp(buffer, ".\n") == 0)
break;
n = write(socketfd, buffer, MAXLINE);
} while(n > 0);
if(n < 0)
printf("Error reading or writing to stream.\n");

printf("Recieving Data... (Press CTRL-C to End Connection)\n");
do
{
memset(&buffer, '\0', sizeof(buffer));
n = read(socketfd, buffer, MAXLINE);
fputs(buffer, stdout);
} while(n > 0);
if(n < 0)
printf("Error reading or writing to stream.\n");

return 0;
}

[dwhitney67]

The stdin you are using is a file descriptor; thus you can use it with a select() call. When select() detects activity, you will be notified and you can do something similar to what you have now (i.e. capture stdin input and look for the single line with a dot).

Btw, select() will block unless you provide it a non-zero timeout period. Thus without a timeout period, you are exactly where you are now. Give a timeout period of say 1/4 of a second and your program will humm along nicely when there is no user input.

P.S. I've had a few beers, thus don't blame me for inaccurate information.

[Danikar]

The stdin you are using is a file descriptor; thus you can use it with a select() call. When select() detects activity, you will be notified and you can do something similar to what you have now (i.e. capture stdin input and look for the single line with a dot).

Btw, select() will block unless you provide it a non-zero timeout period. Thus without a timeout period, you are exactly where you are now. Give a timeout period of say 1/4 of a second and your program will humm along nicely when there is no user input.

P.S. I've had a few beers, thus don't blame me for inaccurate information.

Thanks =) I'll play it like Vegas. Always play the drunk guys numbers.

[dwhitney67]

I'm not drunk yet... 8 x 6% is still the beginning for me. But I'm lazy to verify what I have posted.

[Danikar]

Fair enough.

Does anyone know of a good guide that deals with the select() function specificly?

[dwhitney67]

Guild? Do you mean guide? There's an example of the usage in the man-page.


$ man select