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c/tcp socket programming how to send recv

Posted on 2008-10-19
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Last Modified: 2012-05-05
I have two files - client and server. I can get them to connect using tcp sockets but need to know once a connection is established how can i then have the client send a message to the server and the server send a message back? two files are below
/*
** server.c -- a stream socket server demo
*/
 
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <signal.h>
 
#define PORT "3492"  // the port users will be connecting to
#define MAXDATASIZE 100 // max number of bytes we can get at once 
#define BACKLOG 10     // how many pending connections queue will hold
 
void sigchld_handler(int s)
{
    while(waitpid(-1, NULL, WNOHANG) > 0);
}
 
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }
 
    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
 
int main(void)
{
    int sockfd, new_fd;  // listen on sock_fd, new connection on new_fd
    struct addrinfo hints, *servinfo, *p;
    struct sockaddr_storage their_addr; // connector's address information
    socklen_t sin_size;
    struct sigaction sa;
    int yes=1;
    char s[INET6_ADDRSTRLEN];
    int rv;
 
    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE; // use my IP
 
    if ((rv = getaddrinfo(NULL, PORT, &hints, &servinfo)) == -1) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }
 
    // loop through all the results and bind to the first we can
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("server: socket");
            continue;
        }
 
        if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,
                sizeof(int)) == -1) {
            perror("setsockopt");
            exit(1);
        }
 
        if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            close(sockfd);
            perror("server: bind");
            continue;
        }
 
        break;
    }
 
    if (p == NULL)  {
        fprintf(stderr, "server: failed to bind\n");
        return 2;
    }
 
    freeaddrinfo(servinfo); // all done with this structure
 
    if (listen(sockfd, BACKLOG) == -1) {
        perror("listen");
        exit(1);
    }
 
    sa.sa_handler = sigchld_handler; // reap all dead processes
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    if (sigaction(SIGCHLD, &sa, NULL) == -1) {
        perror("sigaction");
        exit(1);
    }
 
    printf("server: waiting for connections...\n");
 
    while(1) {  // main accept() loop
        sin_size = sizeof their_addr;
        new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
        if (new_fd == -1) {
            perror("accept");
            continue;
        }
 
        inet_ntop(their_addr.ss_family,
            get_in_addr((struct sockaddr *)&their_addr),
            s, sizeof s);
        printf("server: got connection from %s\n", s);
 
        if (!fork()) { // this is the child process
            close(sockfd); // child doesn't need the listener
            if (send(new_fd, "Hello, world!", 13, 0) == -1)
                perror("send");
            close(new_fd);
            exit(0);
        }
 
        close(new_fd);  // parent doesn't need this
       	
        
    }
 
    return 0;
}
 
 
 
 
 
-------------------------------------------------------------------------
 
 
 
 
 
 
 
/*
** client.c -- a stream socket client demo
*/
 
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
 
#include <arpa/inet.h>
 
#define PORT "3492" // the port client will be connecting to 
 
#define MAXDATASIZE 100 // max number of bytes we can get at once 
 
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }
 
    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
 
int queryServer(char* hostname, char *searchterm) {
    int sockfd, numbytes;  
    char buf[MAXDATASIZE];
    struct addrinfo hints, *servinfo, *p;
    int rv;
    char s[INET6_ADDRSTRLEN];
 
/*
    if (argc != 2) {
        fprintf(stderr,"usage: client hostname\n");
        exit(1);
    }
*/
 
    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
 
    if ((rv = getaddrinfo(hostname, PORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }
 
    // loop through all the results and bind to the first we can
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("client: socket");
            continue;
        }
 
        if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            close(sockfd);
            perror("client: connect");
            continue;
        }
 
        break;
    }
 
    if (p == NULL) {
        fprintf(stderr, "client: failed to connect\n");
        return 2;
    }
 
    inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr),
            s, sizeof s);
    printf("client: connecting to %s\n", s);
 
    freeaddrinfo(servinfo); // all done with this structure
 
    if ((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1) {
        perror("recv");
        exit(1);
    }
 
    buf[numbytes] = '\0';
 
    printf("client: received '%s'\n",buf);
 
    close(sockfd);    
  
  	return 0;
  
}
 
int main(int argc, char *argv[])
{
    if (argc != 3) {
        fprintf(stderr,"usage: client hostname searchterm\n");
        exit(1);
    }
	
 
	queryServer(argv[1], argv[2]);
 
    return 0;
}

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Question by:mstrelan
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5 Comments
 
LVL 45

Accepted Solution

by:
sunnycoder earned 500 total points
ID: 22751446
>the client send a message to the server and the server send a message back?
Right now your server is sending Hello World to the client. In same fashion, you can add a send in the client and a corresponding recv in the server followed by a send in the server and a recv in the client

client()
{
      connect
      send  -- send a message to server
      recv   -- recv the response
}

server()
{
       listen
       accept
       recv   -- recv client request
       send  -- send response
}

Also, you dont need a fork in the server
0
 
LVL 10

Author Comment

by:mstrelan
ID: 22751483
more details please? i need to know exactly where to add these send and receives, and also how does the client know the new socket number? do i need to rebind or anything?
0
 
LVL 10

Author Closing Comment

by:mstrelan
ID: 31507542
thanks i worked it out. i was trying to send back to the server after the socket was closed :P
0
 
LVL 17

Expert Comment

by:sweetfa2
ID: 22754042
You have two problems here.  Is it guaranteed that after a send you will always get a response.  If so you can just do a recv immediately after you do a send in your client.

Likewise, immediately after you receive a recv in the server you can do a send to forward it back again.

If however you cannot guarantee that a response will always be received then you need to set up separate threads to handle the recv and send parts of the code.
0
 

Expert Comment

by:Hemanth_hm
ID: 23062554

//CLIENT
 
#include<sys/socket.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<unistd.h>
#include<stdlib.h>
#include<stdio.h>
 
int main(int argc,char *argv[])
{
  int create_socket,cont;
  int bufsize = 1024;
  char *buffer = malloc(bufsize);
  char fname[256];
  struct sockaddr_in address;
 
  if ((create_socket = socket(AF_INET,SOCK_STREAM,0)) > 0)
    printf("The Socket was created\n");
  address.sin_family = AF_INET;
  address.sin_port = htons(15000);
  inet_pton(AF_INET,argv[1],&address.sin_addr);
 
  if (connect(create_socket,(struct sockaddr *) &address,
              sizeof(address)) == 0)
    printf("The connection was accepted with the server %s...\n",
            argv[1]);
  printf("Enter The Filename to Request : "); scanf("%s",fname);
  send(create_socket, fname, sizeof(fname), 0);
  printf("Request Accepted... Receiving File...\n\n");
  printf("The contents of file are...\n\n");
  while((cont=recv(create_socket, buffer, bufsize, 0))>0) {
    write(1, buffer, cont);
  }
  printf("\nEOF\n");
  return close(create_socket);
}
 
 
 
//Server
 
/*Server*/
 
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<sys/stat.h>
#include<unistd.h>
#include<stdlib.h>
#include<stdio.h>
#include<fcntl.h>
 
int main()
{
  int cont,create_socket,new_socket,addrlen,fd;
  int bufsize = 1024;
  char *buffer = malloc(bufsize);
  char fname[256];
  struct sockaddr_in address;
 
  if ((create_socket = socket(AF_INET,SOCK_STREAM,0)) > 0)
    printf("The socket was created\n");
 
  address.sin_family = AF_INET;
  address.sin_addr.s_addr = INADDR_ANY;
  address.sin_port = htons(15000);
 
  if (bind(create_socket,(struct sockaddr *)&address,sizeof(address)) == 0)
    printf("Binding Socket\n");
  listen(create_socket,3);
  addrlen = sizeof(struct sockaddr_in);
  new_socket = accept(create_socket,(struct sockaddr *)&address,&addrlen);
 
  if (new_socket > 0)
     printf("The Client %s is Connected...\n",
             inet_ntoa(address.sin_addr));
  recv(new_socket,fname, 255,0);
  printf("A request for filename %s Received..\n", fname);
  if ((fd=open(fname, O_RDONLY))<0)
    {perror("File Open Failed"); exit(0);}
  while((cont=read(fd, buffer, bufsize))>0) {
     send(new_socket,buffer,cont,0);
  }
  printf("Request Completed\n");
  close(new_socket);
  return close(create_socket);
}

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