自上而下理解内核网络(一)---TCP应用层介绍

gcc server.c -o server
gcc client.c -o client

/*
 * tcpserver.c - A simple TCP echo server
 * usage: tcpserver <port>
 */

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

#define BUFSIZE 1024


/*
 * error - wrapper for perror
 */
void error(char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char **argv)
{
    int parentfd;                  /* parent socket */
    int childfd;                   /* child socket */
    int portno;                    /* port to listen on */
    int clientlen;                 /* byte size of client's address */
    struct sockaddr_in serveraddr; /* server's addr */
    struct sockaddr_in clientaddr; /* client addr */
    struct hostent *hostp;         /* client host info */
    char buf[BUFSIZE];             /* message buffer */
    char *hostaddrp;               /* dotted decimal host addr string */
    int optval;                    /* flag value for setsockopt */
    int n;                         /* message byte size */

    /*
     * check command line arguments
     */
    if (argc != 2)
    {
        fprintf(stderr, "usage: %s <port>\n", argv[0]);
        exit(1);
    }
    portno = atoi(argv[1]);

    /*
     * socket: create the parent socket
     */
    parentfd = socket(AF_INET, SOCK_STREAM, 0);
    if (parentfd < 0)
        error("ERROR opening socket");

    /* setsockopt: Handy debugging trick that lets
     * us rerun the server immediately after we kill it;
     * otherwise we have to wait about 20 secs.
     * Eliminates "ERROR on binding: Address already in use" error.
     */
    // optval = 1;
    // setsockopt(parentfd, SOL_SOCKET, SO_REUSEADDR,
    //            (const void *)&optval, sizeof(int));

    /*
     * build the server's Internet address
     */
    bzero((char *)&serveraddr, sizeof(serveraddr));

    /* this is an Internet address */
    serveraddr.sin_family = AF_INET;

    /* let the system figure out our IP address */
    serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);

    /* this is the port we will listen on */
    serveraddr.sin_port = htons((unsigned short)portno);

    /*
     * bind: associate the parent socket with a port
     */
    if (bind(parentfd, (struct sockaddr *)&serveraddr,
             sizeof(serveraddr)) < 0)
        error("ERROR on binding");

    /*
     * listen: make this socket ready to accept connection requests
     */
    if (listen(parentfd, 5) < 0) /* allow 5 requests to queue up */
        error("ERROR on listen");

    /*
     * main loop: wait for a connection request, echo input line,
     * then close connection.
     */
    clientlen = sizeof(clientaddr);
    while (1)
    {

        /*
         * accept: wait for a connection request
         */
        childfd = accept(parentfd, (struct sockaddr *)&clientaddr, &clientlen);
        if (childfd < 0)
            error("ERROR on accept");

        /*
         * gethostbyaddr: determine who sent the message
         */
        hostp = gethostbyaddr((const char *)&clientaddr.sin_addr.s_addr,
                              sizeof(clientaddr.sin_addr.s_addr), AF_INET);
        if (hostp == NULL)
            error("ERROR on gethostbyaddr");
        hostaddrp = inet_ntoa(clientaddr.sin_addr);
        if (hostaddrp == NULL)
            error("ERROR on inet_ntoa\n");
        printf("server established connection with %s (%s)\n",
               hostp->h_name, hostaddrp);

        /*
         * read: read input string from the client
         */
        bzero(buf, BUFSIZE);
        n = read(childfd, buf, BUFSIZE);
        if (n < 0)
            error("ERROR reading from socket");
        printf("server received %d bytes: %s", n, buf);

        /*
         * write: echo the input string back to the client
         */
        n = write(childfd, buf, strlen(buf));
        if (n < 0)
            error("ERROR writing to socket");

        close(childfd);
    }
}

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

#define BUFSIZE 1024

/*
 * error - wrapper for perror
 */
void error(char *msg) {
    perror(msg);
    exit(0);
}

int main(int argc, char **argv) {
    int sockfd, portno, n;
    struct sockaddr_in serveraddr;
    struct hostent *server;
    char *hostname;
    char buf[BUFSIZE];

    /* check command line arguments */
    if (argc != 3) {
       fprintf(stderr,"usage: %s <hostname> <port>\n", argv[0]);
       exit(0);
    }
    hostname = argv[1];
    portno = atoi(argv[2]);

    /* socket: create the socket */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
        error("ERROR opening socket");

    /* gethostbyname: get the server's DNS entry */
    server = gethostbyname(hostname);
    if (server == NULL) {
        fprintf(stderr,"ERROR, no such host as %s\n", hostname);
        exit(0);
    }

    /* build the server's Internet address */
    bzero((char *) &serveraddr, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    bcopy((char *)server->h_addr,
          (char *)&serveraddr.sin_addr.s_addr, server->h_length);
    serveraddr.sin_port = htons(portno);

    /* connect: create a connection with the server */
    if (connect(sockfd, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) < 0)
      error("ERROR connecting");

    /* get message line from the user */
    printf("Please enter msg: ");
    bzero(buf, BUFSIZE);
    fgets(buf, BUFSIZE, stdin);

    /* send the message line to the server */
    n = write(sockfd, buf, strlen(buf));
    if (n < 0)
      error("ERROR writing to socket");

    /* print the server's reply */
    bzero(buf, BUFSIZE);
    n = read(sockfd, buf, BUFSIZE);
    if (n < 0)
      error("ERROR reading from socket");
    printf("Echo from server: %s", buf);
    close(sockfd);
    return 0;
}