esu networking class example

client.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netdb.h>
#include <string.h>
#include <unistd.h>

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

int main(int argc, char *argv[]) {
    int sockfd, portno, n;
    
    if (argc<3) {
        fprintf(stdout, "Usage: %s hostname port", argv[0]);
        exit(0);
    }
    portno = atoi(argv[2]);
    const char *hostname = argv[1];

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd <0) error("Error opening client socket");

    //    The gethostbyname*(), gethostbyaddr*(), herror(), and hstrerror()
    //    functions are obsolete.  Applications should use getaddrinfo(3),
    //    getnameinfo(3), and gai_strerror(3) instead.
    // struct hostent {
    //    char  *h_name;            /* official name of host */
    //    char **h_aliases;         /* alias list */
    //    int    h_addrtype;        /* host address type */
    //    int    h_length;          /* length of address */
    //    char **h_addr_list;       /* list of addresses */
    //    }
    //    #define h_addr h_addr_list[0] /* for backward compatibility */
    //    http://man7.org/linux/man-pages/man3/gethostbyname.3.html
    struct hostent *server = gethostbyname(hostname); // resolve IP from hostname
    if (server ==NULL) error("No such host");

    // Open server socket and connect
    struct sockaddr_in serv_addr;
    bzero((char*)&serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    bcopy((char*)server->h_addr_list[0], (char*)&serv_addr.sin_addr.s_addr, server->h_length);
    serv_addr.sin_port = htons(portno);
    

    //while (1) {

        if (connect(sockfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) != 0) error("Error connecting");
        // Read user message
        printf("Please enter the message: ");
        char buffer[256];
        bzero(buffer, 256);
        fgets(buffer, 255, stdin);

        // Send the message to server
        n = write(sockfd, buffer, strlen(buffer));
        if (n <0) error("Error writing to socket");

        // Read response from server
        bzero(buffer, 256);
        n = read(sockfd, buffer, 255);
        if (n < 0) error("Error reading from socket");
        printf("Server responded: %s\n",  buffer);
    //}
    close(sockfd);
    return 0;
}

// This was adapted from https://www.thegeekstuff.com/2011/12/c-socket-programming/?utm_source=feedburner
// Do not use this in production :)

// int main(int argc, char *argv[])
// {
//     if (argc <= 2)
//     {
//         printf("\n Usage: %s <ip of server> <optional message>\n", argv[0]);
//         return 1;
//     }

//     int client_socket = 0;
//     if ((client_socket = socket(AF_INET, SOCK_STREAM, 0)) < 0)
//     {
//         printf("\n Error : Could not create socket \n");
//         return 1;
//     }

//     struct sockaddr_in serv_addr;
//     memset(&serv_addr, '0', sizeof(serv_addr));
//     serv_addr.sin_family = AF_INET;
//     serv_addr.sin_port = htons(5000); // htons: host to network byte order (short)

//     // Here we set the server address in our struct
//     // The inet_pton() function converts an address in its
//     // standard text presentation form into its numeric
//     // binary form. argv[1] is the first command line argument.
//     if (inet_pton(AF_INET, argv[1], &serv_addr.sin_addr) <= 0)
//     {
//         printf("\nClient inet_pton error occurred: couldn't convert %s to IP\n", argv[1]);
//         return 1;
//     }

//     // The connect() function shall attempt to make a connection on our socket.
//     printf("Client: Attempting to connect to server\n");
//     while (connect(client_socket, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
//     {
//         printf("\nClient: Error connecting to %s: %s, retrying in 7 seconds.", argv[1], strerror(errno));
//         for (int i = 0; i < 7; i++)
//         {
//             sleep(1);
//             printf(".");
//             fflush(stdout);
//         }
//         printf("\n");
//     }
//     printf("Client: Connected to server.\n");

//     char *msg = 0;
//     if (argc >= 3)
//         msg = argv[2];
//     else
//         msg = "Hello I am a client!";
//     send(client_socket, msg, strlen(msg), 0); 

//     char buffer[1024];
//     read(client_socket, buffer, sizeof(buffer)); 
//     printf("Client: The server says: \"%s\"\n", buffer ); 


//     return 0;
// }

server.c

#include <arpa/inet.h>
#include <errno.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>

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

int main(int argc, char **argv) {
    const int MAX_CLIENTS = 5;
    const int BUF_SIZE = 256;
    char buffer[BUF_SIZE];
    struct sockaddr_in serv_addr, cli_addr;

    if (argc < 2) {
        fprintf(stderr, "ERROR NO PORT PROVIDED\n");
        exit(1);
    }
    int portno = atoi(argv[1]);

    int 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_port = htons(portno);
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY); // IPv4 address
    if (bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) error("error on binding");


    //while (1) {
            listen(sockfd, MAX_CLIENTS);

        socklen_t clilen = sizeof(cli_addr);
        int newsockfd = accept(sockfd, (struct sockaddr*)&cli_addr, &clilen);
        if (newsockfd < 0) error("ERROR on accept");

        bzero(buffer, BUF_SIZE);
        int n = read(newsockfd, buffer, BUF_SIZE - 1);
        if (n < 0) error("Error reading form socket");
        
        printf("Client sent %s\n", buffer);
        
        n = write(newsockfd, "I got your message", 18);
        if (n < 0) error("Error writing to socket");
    //}
    close(sockfd);
    return 0;
}

// int main(int argc, char *argv[])
// {
//     printf("Server: starting...\n");

//     // Structure for handling internet addresses
//     // We will bind this to our socket later
//     struct sockaddr_in serv_addr;
//     memset(&serv_addr, '0', sizeof(serv_addr)); // Zero out serv_addr

//     // The socket address will be IPv4
//     // sin_family is always set to AF_INET.  This is required; in Linux 2.2
//     // most networking functions return EINVAL when this setting is missing.
//     serv_addr.sin_family = AF_INET;

//     // Set the IP address of the socket
//     // htonl() converts hostlong from host byte order to network byte order.
//     serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
//     serv_addr.sin_port = htons(5000);

//     // These 'file descriptors' will be used for our sockets, which
//     // like everything in Linux are treated as files.
//     // A socket is a combination of IP address and port on one system
//     // The call to the function ‘socket()’ creates an UN-named socket
//     // inside the kernel and returns an integer known as socket descriptor.
//     // AF_INET: Internet family of IPv4 addresses we use .
//     // SOCK_STREAM: specifies that the transport layer be reliable (have
//     // acknowledgement techniques) The protocol is generally left zero to let the
//     // kernel decide; it will be TCP
//     int server_socket = socket(AF_INET, SOCK_STREAM, 0);

//     // Attempt to prevent 'bind failed. Error: Address already in use'
//     // by setting the 'reuse address' socket option
//     if (setsockopt(server_socket, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int)) < 0)
//         printf("Server: setsockopt(SO_REUSEADDR) failed\n");

//     // bind() assigns the details specified in the structure ‘serv_addr’
//     // to the socket created in the step above:
//     // the family/domain, the interface to listen on, and the port on which
//     // the server will wait for the client requests to come.
//     while (bind(server_socket, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) != 0)
//     {
//         printf("\nServer: bind() failed: error %s, retrying in 7 seconds", strerror(errno));
//         for (int i = 0; i < 7; i++)
//         {
//             sleep(1);
//             printf(".");
//             fflush(stdout);
//         }
//         printf("\n");
//     }

//     // This call finishes setup of the socket. The second argument is
//     // the maximum number of client connections the server will accept.
//     listen(server_socket, 10);

//     char *msg = "Hi, I am a server!";
//     char buffer[1024];
//     while (1)
//     {
//         // accept() puts the server to sleep until client completes TCP handshake
//         // At which point the server awakens and connfd is assigned the client's
//         // socket descriptor.
//         int client_socket = accept(server_socket, (struct sockaddr *)NULL, NULL);

//         // Read client message
//         read(client_socket, buffer, sizeof(buffer));
//         printf("Server: The client said \"%s\"\n", buffer);

//         // Send back a message
//         send(client_socket, msg, strlen(msg), 0); 

//         close(client_socket);
//         sleep(0.1);
//     }
// }