Socket Programming - Readline

    在我們撰寫網路應用程式的時候，通常我們對於字串上都要另外去特別處理，因為網路不一定是穩定的狀況下，就算是TCP connection都會有所謂的delay，如果我們就僅只是直接呼叫
read(int fd, void *buf, size_t count)
的話，只要有封包延遲的狀況下，回傳的buf裡面所存的值就不會是原本另外一端想要傳輸的了。

  所以我們必須要自己implement一個readline的funciton，只要還沒讀到換行符號的狀況下就繼續等待一直讀，如果被其他signal interrupt的話也不能停，一直到結束為止。

int readline(int fd, void *vptr, size_t maxlen )
{
     ssize_t     n, rc;
     char        c, *ptr;

     ptr = (char*)vptr;
     for (n = 1; n < maxlen; n++) {
 again:
         if ( (rc = read(fd, &c, 1)) == 1) {
             *ptr++ = c;
             if (c == '\n')
                 break;  /* newline is stored, like fgets() */
         } else if (rc == 0) {
             *ptr = 0;
             return(n - 1);      /* EOF, n - 1 bytes were read */
         } else {
             if (errno == EINTR) /* This is when read has been interrupt*/
                 goto again;
             return(-1);         /* error, errno set by read() */
         }
     }

     *ptr = 0;   /* null terminate like fgets() */
     return n;
 }

在Unix Network Programming一書上的版本與此差不多，然而還有更快的版本，這個相對比較慢。

Network Programming - Simple Socket Echo Server

這學期做網程設的助教，我想應該作業要寫一遍的前提下，紀錄一下也讓以後如果自己要寫的話不用再從頭抓資料多麻煩XD

Client.c

#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>

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

int main(int argc, char *argv[])
{
    int sockfd, n;
    struct sockaddr_in serv_addr;
    struct hostent *server;

    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");
    server = gethostbyname(argv[1]);

    if (server == NULL) {
        fprintf(stderr,"ERROR, no such host\n");
        exit(0);
    }
    bzero((char *) &serv_addr, sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    bcopy((char *)server->h_addr,
         (char *)&serv_addr.sin_addr.s_addr,
         server->h_length);
    serv_addr.sin_port = htons(atoi(argv[2]));

    if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
        error("ERROR connecting");

    printf("Connected!\necho-Server >");
    fflush(stdout);
    bzero(buffer,256);
    fgets(buffer,255,stdin);

    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.c

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

#define LISTENQLEN 10

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

int main(int argc, char *argv[])
{
    int sockfd, newsockfd, portno;
    socklen_t clilen;
    char buffer[256];
    struct sockaddr_in serv_addr, cli_addr;
    int n;

    if (argc != 2) {
        fprintf(stderr,"ERROR, no port provided\n");
        exit(1);
    }

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    //socket():
    //argument 1:                       argument 2:
    //AF_INET : IPv4                    SOCK_STREAM : stream socket
    //AF_INET6: IPv6                    SOCK_DGRAM  : datagram socket
    //AF_LOCAL: Unix domain protocols   SOCK_SEQPACKET: sequenced packet socket
    //AF_ROUTE: Routing socket          SOCK_RAW    : raw socket
    //AF_KEY  : Key socket
    //
    //argument 3:
    // IPPROTO_TCP : TCP
    // IPPROTO_UDP : UDP
    // IPPROTO_SCTP: SCTP

    if (sockfd < 0)
        errmsg("ERROR opening socket");

    bzero((char *) &serv_addr, sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;   // listen where
    serv_addr.sin_port = htons(atoi(argv[1]));// port number

    if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
        errmsg("ERROR on binding");

    listen(sockfd,LISTENQLEN);

    clilen = sizeof(cli_addr);

    newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);

    if (newsockfd < 0)
        errmsg("ERROR on accept");

    bzero(buffer,256);
    n = read(newsockfd,buffer,255);
    if (n < 0)
        errmsg("ERROR reading from socket");

    printf("Recieved string: %s\n",buffer);
    n = write(newsockfd,buffer,strlen(buffer));
    if (n < 0)
        errmsg("ERROR writing to socket");

    close(newsockfd);
    close(sockfd);

    return 0;
}

Makefile

all : client.c server.c
 gcc -Wall -g -o client client.c
 gcc -Wall -g -o server server.c
 
clean : 
 rm client
 rm server

直接make完以後就可以使用。

Ubuntu 12.04 hostname

Ubuntu 12.04
通常一安裝完以後，基本上應該不太會是你自己所想要設定的hostname，安裝時候會試著去抓你的Domain name，不然就會直接設定成localhost如下：

21:48 jdchen@localhost [~] >

要調整在安裝時候的所誤設的hostname的話，依照下面步驟


先去修改系統內部所設定的hostname：

sudo vim /etc/hostname

改成你自己想要的名字以後:wq離開，在使用init.d重讀hostname

sudo /etc/init.d/hostname restart

這樣基本上應該就可以了~