Thread: Help - Tiny Webserver C In UNIX . TCPIP - Big Problem

Hi! I have to make a tiny webserver in C in Unix. I have the first part of the code given by my teacher, and i have to add some extra tasks to it . I dont know why when i compile my code i have some errors. I post now the codes:
1. teacher's first part of the code
[spoiler]

Code:

// skeleton version of a tiny webserver, minimal error handling
// by U. Willers - 07.11.2013
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <strings.h>
#include <stdlib.h>
#include <errno.h> // size_t, pid_t
// accept, bind, listen
// sockaddr_in, htons
// printf
// bzero, strncmp
// exit
// strerror
 
#define BUFSIZE 8096 // size of request buffer
 
// Prototypes, maybe outsource to webserver.h
void handle_request( int s1 );
size_t strlen( const char *s );
int setup_webserver( void );
int respectRequests(char *request);
int SplitTheRequest(char *request);
int main( void )
    {
        int server_socket, client_socket, addrlen;
        struct sockaddr_in client_addr;
       
        printf( "Starting webserver...\n" );
        server_socket = setup_webserver(); // create socket and listen on it
        while( 1 )  // infinite loop
            {
            addrlen = sizeof( client_addr );    // wait for client requests
           
            client_socket = accept( server_socket, (struct sockaddr*) &client_addr, &addrlen ); // process request
           
            handle_request( client_socket );
            }
    }
   
int setup_webserver( void )
    {
        int s, ret;
       
        struct sockaddr_in s_addr;  // create TCP/IP socket
       
        s = socket( AF_INET, SOCK_STREAM, 0 );  // listen on port 80 (http) at localhost for client requests
       
        bzero( &s_addr, sizeof( s_addr ) ); // clear data structure
       
        s_addr.sin_family = AF_INET;    // IP address
       
        s_addr.sin_port = htons( 80 );  // port is 80
       
        s_addr.sin_addr.s_addr = INADDR_ANY; // addr. is 127.0.0.1
        // bind port and addr. to socket
       
        ret = bind( s, (struct sockaddr*) &s_addr, sizeof( s_addr ) );
       
        if( ret < 0 )   // error?
            {
            // Yes, convert into error message
           
            printf( "Bind Error: %s\n", strerror( errno ) );
           
            exit( 1 );      // terminate program and return error code
            }
       
    listen( s, 5 ); // wait for requests, max. 5 requests in queue
   
    return( s );    // return server socket descriptor
   
    }   // Entry: cs is client socket descriptor
   
void handle_request( int cs )
    {
    char request[BUFSIZE];  // buffer for first line of client request
   
    int i = 0;
   
    char c; // buffer for one input character
   
    // read client request and terminate it with 0
   
    printf( "Annalize & Getting request: " );
   
    while( read( cs, &c, 1 ) == 1 && c != '\n' && c != '\r' && i < sizeof( request ) -1 )
   
    request[i++] = c;
   
    request[i] = '\0';  // terminate string
    if(respectRequests(request)==0)
        {
            printf( "%s\n", request );  // print request
            SplitTheRequest(request);
        }
    if (respectRequests(request)==-1)
        {
            printf( " INCORRECT!!!\n"); // print request
        }
       
   
    close( cs );
    }

[/spoiler]


Tasks:


[spoiler]Enhance the web server so that only GET requests will be processed. Extract the file name from the GET request and sent the contents of that file to the client. Map GET / to GET index.html. Prevent absolute paths and the relative path .. being used in the request. This restricts the webserver to the chosen document root folder.[/spoiler]
[spoiler]Update your web server program to use child processes for each client request. Print all error messages to stderr.[/spoiler]
[spoiler]Check if the client request ask for valid file extension. Supply the correct MIME type in the HTTP header of your answer to the client.[/spoiler]


My new code made with my colleague's help:
[spoiler]

Code:

// skeleton version of a tiny webserver, minimal error handling
// by U. Willers - 07.11.2013


#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <string.h>
#include <strings.h>
#include <sys/stat.h>
#include<fcntl.h>
#include<errno.h>


#define BUFSIZE 8096




// Prototypes, maybe outsource to webserver.h




void handle_request( int client_socket, int server_socket);
int setup_webserver( void );
void makeHeader(int type, char * request,int client_socket);
void * openFile(char *request, int client_socket, char * read);
char * readFile(char *uri);
int prevent(char *request);
char *withoutBar ( char * uri );
char * checkUri (char * request);


int main( void )
{
	int server_socket, client_socket, addrlen;
	struct sockaddr_in server_addr, client_addr;


	printf( "Starting webserver...\n" );
	server_socket = setup_webserver(); // create socket and listen on it
	while( 1 )
	{
		addrlen = sizeof( server_addr ); // wait for client requests
		client_socket = accept( server_socket, (struct sockaddr*) &server_addr, &addrlen ); // process request
		printf("Client connected ...\n");
		handle_request( client_socket, server_socket);
	}
}


int setup_webserver( void )
{
	int server_socket;
	int on = 1;
	struct sockaddr_in server_addr;


	server_socket = socket( AF_INET, SOCK_STREAM, 0 );


	setsockopt(server_socket, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(int));


	bzero( &server_addr, sizeof( server_addr ) );
	server_addr.sin_family = AF_INET;
	server_addr.sin_addr.s_addr = INADDR_ANY;
	server_addr.sin_port = htons( 80 );


	if(bind(server_socket, (struct sockaddr *) &server_addr, sizeof(server_addr)) == -1)
	{
		perror("bind");
		close(server_socket);
		exit(1);
	}
	if(listen(server_socket,5) == -1 )
	{
		perror("listen");
		close(server_socket);
		exit(1);
	}


	return( server_socket );
}




void handle_request( int client_socket , int server_socket)
{
	char request[2048]; // buffer for first line of client request
	int i = 0;
	int status;
	char c; // buffer for one input character


	// read client request and terminate it with 0
	printf( "Getting request: \n" );


	read(client_socket,request,2047);
	//printf( "Client request: %s\n", request );


	waitpid(-1,&status,WNOHANG);
	if(!fork())
	{
		// child process 
		if(prevent(request) == 0)
		{
			close(server_socket);
			makeHeader ( 200, request, client_socket );
			exit(0);
		}
		else
		{
			makeHeader( 403, request, client_socket );
		}




	}
	//parent process
	waitpid(-1,&status,WNOHANG);
	close( client_socket );
}


void * openFile(char *request, int client_socket, char * read)
{
	int fdimg;


	if(!strncmp(request,"GET /favicon.ico", 16))
	{
		fdimg = open("icon.png", O_RDONLY);
		sendfile(client_socket, fdimg, NULL, 4000);
		close(fdimg);
	}


	else if(!strncmp(request,"GET /image.jpg", 14))
	{
		fdimg = open("image.jpg", O_RDONLY);
		sendfile(client_socket, fdimg, NULL, 50000);
		close(fdimg);
	}
	else
	{
		write(client_socket, read, strlen(read));
	}
		


}


void makeHeader(int type, char * request,int client_socket)
{
	if(type == 200)// ok
	{
		if(!strncmp(request,"GET / ",5))
		{
			char * read;
			read = readFile("index.html");
			openFile( request, client_socket, read );
		}
		else
		{
			char * file;
			char * read;
			
			file = withoutBar(checkUri(request));
			read = readFile(file);
			openFile( request, client_socket, read );
		}
	}
	else if(type == 403) // forbbiden
	{
		char *read;
		read = readFile("forbidden.html");
		openFile( request, client_socket, read );
	}
	else if(type == 404) // not found
	{
		char *read;
		read = readFile("notfound.html");
	}
}


char * readFile(char *uri)
{
	FILE *fp;
	fp = fopen(uri,"r");
	char *out = NULL;
	char arquivo[1024], buffer[1024] = {""};


	if(fp != NULL)
	{
		while(fgets(arquivo, sizeof(arquivo), (FILE*)fp) != NULL)
			strcat(buffer, arquivo);
		fclose(fp);
		out = buffer;
		return out;
	}
	else
		return NULL;
}




int prevent(char *request)
{
	char verifica[4];
	int i;
	if(strncmp(request, "GET ", 4) == 0)
	{
		for(i = 0; i < strlen(request) - 1; i++)
		{
			verifica[0] = request[i];
			verifica[1] = request[i+1];
			if(strncmp(verifica, "..", 2) == 0)
				return -1;
		}
		return 0;
	}
	else
	{
		return -1;
	}


}


char * checkUri (char * request)
{
	char aux[256];
	char *out;
	int i;
	
	for(i = 5; strlen (request); i++)
	{
		if(request[i] != ' ')
		{
			aux[i-5] = request[i];
		}
		else
		{
			
			out = aux;
			return out;
		}
	}
	return out;
}


char *withoutBar ( char * uri )
{
	int i;
	char aux[256];
	char * out;
	for(i =1; i<strlen(uri);i++)
	{
		aux[i-1] = uri[i];
	}
	out = aux;
	return out;
	
}

[/spoiler]


IF somebody has any ideeas how to solve this i am waiting for it !
Thanks !!!

Do you have a specific question or problem?

Does your "instructor's" code compile without errors or warnings?

Does your code compile without errors or warnings?

Originally Posted by jonsvici

Code:

int setup_webserver( void )
    {
        int s, ret;
    ...    
    return( s );    // return server socket descriptor
   
    }   // Entry: cs is client socket descriptor

The local automatic variable s is allocated on the stack. When the function returns, the stack allocated storage is destroyed. It appears your teacher is not teaching you about lifetime of variables. You can read a little about that here. For an int, you could pass a reference to it as a parameter. You also had some arrays allocated on the stack that you referenced later. You could allocate them on the heap instead with malloc.

Originally Posted by christophergray

The local automatic variable s is allocated on the stack. When the function returns, the stack allocated storage is destroyed. It appears your teacher is not teaching you about lifetime of variables. You can read a little about that here. For an int, you could pass a reference to it as a parameter. You also had some arrays allocated on the stack that you referenced later. You could allocate them on the heap instead with malloc.

It's funny that you mention the "setup_webserver" function, since that's one case where the return value is OK. The functions that return pointers to automatic variables ("readFile", "checkUri", and "withoutBar") are buggy, though.

Originally Posted by christop

It's funny that you mention the "setup_webserver" function, since that's one case where the return value is OK. The functions that return pointers to automatic variables ("readFile", "checkUri", and "withoutBar") are buggy, though.

Are you saying it is not an error?

Originally Posted by christophergray

Are you saying it is not an error?

This code is not an error (which resembles the setup_webserver function that you quoted):

Code:

int foo(void)
{
    int s = 42;
    // ...    
    return s;
}

This code is an error:

Code:

int *foo(void)
{
    int s = 42;
    // ...    
    return &s;
}

Originally Posted by christop

This code is not an error (which resembles the setup_webserver function that you quoted):

Code:

int foo(void)
{
    int s = 42;
    // ...    
    return s;
}

I took a look at the assembler output from gcc. Although I found it hard to read because it is a different format than MASM which also I haven't looked at for 32 years, it looks like your first example just pushes 42 onto the stack and returns. Whereas the second example pushes an address, and the compiler issues a warning.

it looks like your first example just pushes 42 onto the stack and returns.

Yes the function is just returning a value. So no problem, will work as expected.

Whereas the second example pushes an address, and the compiler issues a warning.

Yes, here the function is trying to return a pointer to a local variable which invokes undefined behaviour. Your compiler properly warns you about this issue, good.

You can't return a pointer to a local variable since the variable is destroyed when the function returns.

Originally Posted by jimblumberg

You can't return a pointer to a local variable since the variable is destroyed when the function returns.

But I can return a pointer to an address on the heap, right? So...

Code:

static char *withoutBar ( char * uri )
{
    char *out = malloc(256);
    if (out != NULL) {
        size_t i;
        for(i =1; i<strlen(uri);i++)
        {
            out[i-1] = uri[i];
        }
    }
    return out;
}