[SOLVED] Handle query strings using socket programming

c00get · 12-07-2009, 10:52 AM

Hi, I need to make a daemon which listens to port 81 for messages like http://localhost/message?command=move&dir=left
So far I made a daemon which serves as a simple stream server: I set up a socket to listen to a non-reserved port (like 9999), but I don't know how to read the query strings.

Linux distro: Kubuntu 9.04
Language: C

David1357 · 12-07-2009, 12:23 PM

Quote:

Originally Posted by c00get

So far I made a daemon which serves as a simple stream server: I set up a socket to listen to a non-reserved port (like 9999), but I don't know how to read the query strings.

What have you written so far? Paste your code inside CODE tags.

theNbomr · 12-07-2009, 12:56 PM

Use netcat (nc) as a listener, and it will print the query that your application will see. From that, you should be able to determine the method you should use to parse the query. The query string will be readable on the standard input stream.
What you are creating is one of the essential ingredients of a web server.
--- rod

c00get · 12-08-2009, 10:31 AM

Thanks for the replies.

Quote:

Originally Posted by David1357

What have you written so far? Paste your code inside CODE tags.

Code:

#include <stdlib.h>
#include <syslog.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

#define PORT		81
#define MAXBUF		64
#define SLEEP_TIME 	3
#define COUNT_MAX	3


int main(void)
{
	pid_t pid, sid;
	int status;

	/* Fork off the parent process */
	pid = fork();
	if (pid < 0)
	{
		syslog(LOG_ERR, "fork(): %m");
		exit(EXIT_FAILURE);
	}
	
    /* If we got a good PID, then
	we can exit the parent process. */
	if (pid > 0)
	{
		exit(EXIT_SUCCESS);
	}

	/* Change the file mode mask */
	umask(0);

	/* Create a new SID for the child process */
	sid = setsid();
	if (sid < 0)
	{
		syslog(LOG_ERR, "setsid(): %m");
		exit(EXIT_FAILURE);
	}

	/* Change the current working directory */
	if ((chdir("/")) < 0)
	{
		syslog(LOG_ERR, "chdir(): %m");
		exit(EXIT_FAILURE);
	}

	/* Close out the standard file descriptors */
	status = close(STDIN_FILENO);
	if (status < 0)
	{
		syslog(LOG_ERR, "close(STDIN_FILENO): %m");
		exit(EXIT_FAILURE);
	}
	
	status = close(STDOUT_FILENO);
	if (status < 0)
	{
		syslog(LOG_ERR, "close(STDOUT_FILENO): %m");
		exit(EXIT_FAILURE);
	}
	
	status = close(STDERR_FILENO);
	if (status < 0)
	{
		syslog(LOG_ERR, "close(STDERR_FILENO): %m");
		exit(EXIT_FAILURE);
	}

	//---------------------------------------------------------------------------
	
	int sockfd, clientfd;
	struct sockaddr_in self, client_addr;
	int addrlen = sizeof(client_addr);
	char buffer[MAXBUF], command[8], param[8];
	int count;

	/* Create streaming socket */
	sockfd = socket(AF_INET, SOCK_STREAM, 0);
	if (sockfd < 0)
	{
		syslog(LOG_ERR, "socket(): %m");
		exit(EXIT_FAILURE);
	}

	/* Initialize address/port structure */
	bzero(&self, sizeof(self));
	self.sin_family = AF_INET;
	self.sin_port = htons(PORT);
	self.sin_addr.s_addr = INADDR_ANY;

	/* Assign a port number to the socket */
	status = bind(sockfd, (struct sockaddr*) &self, sizeof(self));
	if (status < 0)
	{
		syslog(LOG_ERR, "bind(): %m");
		exit(EXIT_FAILURE);
	}
	
	/* Make it a "listening socket" */
	status = listen(sockfd, 20);
	if (status < 0)
	{
		syslog(LOG_ERR, "listen(): %m");
		exit(EXIT_FAILURE);
	}
	
	/* The Big Loop */
	while (1)
	{
		/* Accept a connection (creating a data pipe) */
		count = COUNT_MAX;
		do {
			clientfd = accept(sockfd, (struct sockaddr*) &client_addr, &addrlen);
			if (clientfd < 0)
			{
				syslog(LOG_ERR, "accept(): %m");
				count--;
				sleep(SLEEP_TIME); // Wait
			}
		} while (status < 0 && count > 0);
		if (count <= 0)
			exit(EXIT_FAILURE);

		/* Receive message */
		status = recv(clientfd, buffer, MAXBUF, 0);
		if (status < 0)
			syslog(LOG_ERR, "recv(): %m");
		else if (status > 0)
		{

		}

		/* Close data connection */
		count = COUNT_MAX;
		do {
			status = close(clientfd);
			if (status < 0)
			{
				syslog(LOG_ERR, "close(clientfd): %m");
				count--;
				sleep(SLEEP_TIME); // Wait
			}
		} while (status < 0 && count > 0);
		if (count <= 0)
			exit(EXIT_FAILURE);
	}

	/* Clean up */
	count = COUNT_MAX;
	do {
		status = close(sockfd);
		if (status < 0)
		{
			syslog(LOG_ERR, "close(sockfd): %m");
			count--;
			sleep(SLEEP_TIME); // Wait
		}
	} while (status < 0 && count > 0);
	if (count <= 0)
		exit(EXIT_FAILURE);

	/* Everything went well */
	exit(EXIT_SUCCESS);
}

Thanks theNbomr, I'll try that.

David1357 · 12-08-2009, 12:07 PM

You would put your code to handle GET requests in the "else if" clause that you left empty:

Code:

		/* Receive message */
		status = recv(clientfd, buffer, MAXBUF, 0);
		if (status < 0)
			syslog(LOG_ERR, "recv(): %m");
		else if (status > 0)
		{
			/****************************************
			 * Put GET request processing here 
			 ***************************************/
		}

"buffer" will contain text that looks like

Code:

GET /message?command=move&dir=left HTTP/1.1
Host: 192.168.1.164

I verified this by modifying your program to look like

Code:

#include <stdlib.h>
#include <syslog.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

#define PORT            80
#define MAXBUF          64
#define SLEEP_TIME      3
#define COUNT_MAX       3


int main(void)
{
        pid_t pid, sid;
        int status;

        int sockfd, clientfd;
        struct sockaddr_in self, client_addr;
        int addrlen = sizeof(client_addr);
        char buffer[MAXBUF], command[8], param[8];
        int count;

        /* Create streaming socket */
        sockfd = socket(AF_INET, SOCK_STREAM, 0);
        if (sockfd < 0)
        {
                syslog(LOG_ERR, "socket(): %m");
                exit(EXIT_FAILURE);
        }

        /* Initialize address/port structure */
        bzero(&self, sizeof(self));
        self.sin_family = AF_INET;
        self.sin_port = htons(PORT);
        self.sin_addr.s_addr = INADDR_ANY;

        /* Assign a port number to the socket */
        status = bind(sockfd, (struct sockaddr*) &self, sizeof(self));
        if (status < 0)
        {
                syslog(LOG_ERR, "bind(): %m");
                exit(EXIT_FAILURE);
        }

        /* Make it a "listening socket" */
        status = listen(sockfd, 20);
        if (status < 0)
        {
                syslog(LOG_ERR, "listen(): %m");
                exit(EXIT_FAILURE);
        }

        /* The Big Loop */
        while (1)
        {
                /* Accept a connection (creating a data pipe) */
                count = COUNT_MAX;
                do {
                        clientfd = accept(sockfd, (struct sockaddr*) &client_addr, &addrlen);
                        if (clientfd < 0)
                        {
                                syslog(LOG_ERR, "accept(): %m");
                                count--;
                                sleep(SLEEP_TIME); // Wait
                        }
                } while (status < 0 && count > 0);
                if (count <= 0)
                        exit(EXIT_FAILURE);

                /* Receive message */
                status = recv(clientfd, buffer, MAXBUF, 0);
                if (status < 0)
                        syslog(LOG_ERR, "recv(): %m");
                else if (status > 0)
                {
                        printf("%s\n", buffer);
                }

                /* Close data connection */
                count = COUNT_MAX;
                do {
                        status = close(clientfd);
                        if (status < 0)
                        {
                                syslog(LOG_ERR, "close(clientfd): %m");
                                count--;
                                sleep(SLEEP_TIME); // Wait
                        }
                } while (status < 0 && count > 0);
                if (count <= 0)
                        exit(EXIT_FAILURE);
        }

        /* Clean up */
        count = COUNT_MAX;
        do {
                status = close(sockfd);
                if (status < 0)
                {
                        syslog(LOG_ERR, "close(sockfd): %m");
                        count--;
                        sleep(SLEEP_TIME); // Wait
                }
        } while (status < 0 && count > 0);
        if (count <= 0)
                exit(EXIT_FAILURE);

        /* Everything went well */
        exit(EXIT_SUCCESS);
}

c00get · 12-09-2009, 12:50 PM

I finally managed to get the query string. I wasn't reading the buffer correctly because I didn't know the format. Thank you for your help.