Thread: TCP/IP server/client programm +files

Hello all , i have a homework that is related with tcp/ip server/client. The project says :

We sent from client to server , 2 file names , server opens them and sends back the data from the two files back to client and client prints them on the screen.

The code i made is

//client

Code:

 #include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> 
#define SERVER "127.0.0.1"
#define TCP_PORT 6000

void error(const char *msg)
{
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[])
{
    int sockfd, n;
    struct sockaddr_in serv_addr;
    char buffer[256];
    /*if (argc < 3) {
       fprintf(stderr,"usage %s hostname port\n", argv[0]);
       exit(0);
    }*/
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) 
        error("ERROR opening socket");
    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr=inet_addr(SERVER);
    serv_addr.sin_port = htons(TCP_PORT);
    if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0) 
        error("ERROR connecting");
    //printf("Please enter the message: ");
    bzero(buffer,256);
    //fgets(buffer,255,stdin);
   strcpy(buffer,"file1.txt");
   strcat(buffer," ");
   strcat(buffer,"file2.txt");
    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);
    close(sockfd);
    return 0;
}

//server

Code:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>
#define server 6000

 void dostuff(int); 
void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[])
{
     int sockfd, newsockfd, portno, pid;
     socklen_t clilen;
     struct sockaddr_in serv_addr, cli_addr;

     sockfd = socket(AF_INET, SOCK_STREAM, 0);
     if (sockfd < 0) 
        error("ERROR opening socket");
     bzero((char *) &serv_addr, sizeof(serv_addr));
     portno = server;
     serv_addr.sin_family = AF_INET;
     serv_addr.sin_addr.s_addr = INADDR_ANY;
     serv_addr.sin_port = htons(portno);
     if (bind(sockfd, (struct sockaddr *) &serv_addr,
              sizeof(serv_addr)) < 0) 
              error("ERROR on binding");
     listen(sockfd,5);
     clilen = sizeof(cli_addr);
     while (1) {
         newsockfd = accept(sockfd, 
               (struct sockaddr *) &cli_addr, &clilen);
         if (newsockfd < 0) 
             error("ERROR on accept");
         pid = fork();
         if (pid < 0)
             error("ERROR on fork");
         if (pid == 0)  {
             close(sockfd);
             dostuff(newsockfd);
             exit(0);
         }
         else close(newsockfd);
     } /* end of while */
     close(sockfd);
     return 0; /* we never get here */
}

void dostuff (int sock)
{ 
   int n;
   char buffer[256];
  FILE *pFile1,*pFile2;
  long lSize1,lSize2;
  char * buffer1,*buffer2,*buffer3;
  size_t file1str,file2str;
  char *file1,*file2;
      
   n = read(sock,buffer,255);
   if (n < 0) error("ERROR reading from socket");
   sscanf(buffer,"%s %s",file1,file2);
	
        //opening and writing the first file in a buffer1
	pFile1 = fopen ( file1, "rb" );
	if (pFile1==NULL) {fputs ("File error",stderr); }

  	
  	fseek (pFile1 , 0 , SEEK_END);
  	lSize1 = ftell (pFile1);
 	 rewind (pFile1);

  	
  	buffer1 = (char*) malloc (sizeof(char)*lSize2);
 	 if (buffer1 == NULL) {fputs ("Memory error",stderr);}

 	 file1str = fread (buffer1,1,lSize2,pFile1);
 	 if (file1str!= lSize2) {fputs ("Reading error",stderr);}

	 fclose (pFile1);

        //opening and writing the second  file in  buffer2
	pFile2 = fopen ( file2, "rb" );
 	 if (pFile2==NULL) {fputs ("File error",stderr); }


  	fseek (pFile2 , 0 , SEEK_END);
 	 lSize2 = ftell (pFile2);
  	rewind (pFile2);

  	
  	buffer2 = (char*) malloc (sizeof(char)*lSize2);
  	if (buffer2 == NULL) {fputs ("Memory error",stderr); }

  	file2str = fread (buffer2,1,lSize2,pFile2);
  	if (file2str != lSize2) {fputs ("Reading error",stderr); }
	
	fclose(pFile2);
	
	printf("%s  %s",buffer1, buffer2);

    strcpy(buffer3,buffer1);
    strcat(buffer3,buffer2);
   n = write(sock,buffer3,256);
   if (n < 0) error("ERROR writing to socket");
}

Now my problem is . Server is up and running! No problem with this. When i try to connect the client , client returns me an empty line and after it closes.


Can you help me with this? I think i have made some mistakes passing the string in fopen or something and i am not familiar with debugging >.>

Your server is not fine. Yes it runs, but it has a number of problems, mostly in dostuff. Your client, on the other hand, seems to be fine. A couple of notes first:

1. Don't cast malloc
2. bzero is deprecated. Use memset(foo, 0, size) instead
3. You can resue the same code for reading file1 and file2 in dostuff() since it's basically identical. Move everything from the file open to file close, with appropriate error checks, into a function. Have it return the contents of the file in a malloc'ed buffer, or NULL on error.

Can you help me with this? I think i have made some mistakes passing the string in fopen or something and i am not familiar with debugging >.>

You need to get familiar with debugging. There's no two ways about it. You would have solved this in about 10 minutes if you knew how to use a debugger instead of waiting 5 hours for me to help you. Good debugging skills, including using a debugger like GDB, are invaluable to a programmer. Check out our tutorial, and Google around for some others. The GDB website has a lot of good info too.

//server

Code:

void dostuff (int sock)
{ 
   int n;
   char buffer[256];
  FILE *pFile1,*pFile2;
  long lSize1,lSize2;
  char * buffer1,*buffer2,*buffer3;
  size_t file1str,file2str;
  char *file1,*file2;  // You need a place to store the file names.  Try file1[100]
      
   n = read(sock,buffer,255);
   if (n < 0) error("ERROR reading from socket");
   sscanf(buffer,"%s %s",file1,file2);
    
        //opening and writing the first file in a buffer1
    pFile1 = fopen ( file1, "rb" );
    if (pFile1==NULL) {fputs ("File error",stderr); }
    // You shouldn't check the size of or read from a NULL file pointer.
    // skip all this if pFile1 is NULL
      
      fseek (pFile1 , 0 , SEEK_END);
      lSize1 = ftell (pFile1);
      rewind (pFile1);

      
      buffer1 = (char*) malloc (sizeof(char)*lSize2);  // lSize1
      if (buffer1 == NULL) {fputs ("Memory error",stderr);}
      // Again, you need to skip the following code if buffer1 is NULL
      // otherwise you will probably seg fault, trying to read into a NULL buffer

      file1str = fread (buffer1,1,lSize2,pFile1);  // lSize1
      if (file1str!= lSize2) {fputs ("Reading error",stderr);}  // lSize1

     fclose (pFile1);

        //opening and writing the second  file in  buffer2
    pFile2 = fopen ( file2, "rb" );
      if (pFile2==NULL) {fputs ("File error",stderr); }
     // You shouldn't check the size of or read from a NULL file pointer.
     // skip all this if pFile1 is NULL

      fseek (pFile2 , 0 , SEEK_END);
      lSize2 = ftell (pFile2);
      rewind (pFile2);

      
      buffer2 = (char*) malloc (sizeof(char)*lSize2);
      if (buffer2 == NULL) {fputs ("Memory error",stderr); }
      // Again, you need to skip the following code if buffer1 is NULL
      // otherwise you will probably seg fault, trying to read into a NULL buffer
 
      file2str = fread (buffer2,1,lSize2,pFile2);
      if (file2str != lSize2) {fputs ("Reading error",stderr); }
    
    fclose(pFile2);
    
    printf("%s  %s",buffer1, buffer2);

    // You need to allocate sufficient space for buffer3 before writing to it
    strcpy(buffer3,buffer1);
    strcat(buffer3,buffer2);
   n = write(sock,buffer3,256);  // You want to write strlen(buffer3)
   if (n < 0) error("ERROR writing to socket");
}