UDP多客户端服务器基础知识 [英] UDP multi client server basics

问题描述

我很期待实现这一点:服务器从客户端数量中接收一个字符串(文件名)，该字符串必须从文件夹中获取，并通过在命令行中定义的bufferSize将其返回给客户端.它必须通过UDP通信来实现.我熟悉TCP套接字，但是我不知道如何为udp连接获取fileDescriptor，因为accepts丢失了.

I'm looking forward to achive this: Server recieves from number of clients a string(file name) which he has to take from the folder and return it to the the client by a bufferSize which is defined from the command line. It has to be implemented with UDP communication. i'm familiarized with TCP sockets, but i don't get how can i get a fileDescriptor for the udp connection since accepts is missing.

所以我正在考虑:配置之后，我在服务器中执行一个while循环，在此我得到某种描述符"，我将其发送到一个新线程，该线程知道将数据发送回何处... 有任何想法吗?

So I'm thinking about this: after the config i do a while-loop in the server where i get 'some kind of descriptor' which i'll send to a new thread which knows where to send the data back... Any ideas?

我已经检查过网络，但是没有找到这种操作的具体解释.

I've checked the net but didn't found a concrete explanation for this kind of operation.

推荐答案

我终于找到了一些有用的东西，也许对其他人有用，所以这里是:代码已注释并且非常清晰.PS:抱歉，我粘贴的内容太长了，但是Google不允许我复制链接.

I have finally found something helpful, maybe it will be useful for others so here it is: the code is commented and really clear. PS: sorry for the long paste, but google doesn't let me copy the link.

    /* 
 * udpserver.c - A simple UDP echo server 
 * usage: udpserver <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 sockfd; /* 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 buf */
  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 
   */
  sockfd = socket(AF_INET, SOCK_DGRAM, 0);
  if (sockfd < 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(sockfd, SOL_SOCKET, SO_REUSEADDR, 
         (const void *)&optval , sizeof(int));

  /*
   * build the server's Internet address
   */
  bzero((char *) &serveraddr, sizeof(serveraddr));
  serveraddr.sin_family = AF_INET;
  serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
  serveraddr.sin_port = htons((unsigned short)portno);

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

  /* 
   * main loop: wait for a datagram, then echo it
   */
  clientlen = sizeof(clientaddr);
  while (1) {

    /*
     * recvfrom: receive a UDP datagram from a client
     */
    bzero(buf, BUFSIZE);
    n = recvfrom(sockfd, buf, BUFSIZE, 0,
         (struct sockaddr *) &clientaddr, &clientlen);
    if (n < 0)
      error("ERROR in recvfrom");

    /* 
     * gethostbyaddr: determine who sent the datagram
     */
    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 received datagram from %s (%s)\n", 
       hostp->h_name, hostaddrp);
    printf("server received %d/%d bytes: %s\n", strlen(buf), n, buf);

    /* 
     * sendto: echo the input back to the client 
     */
    n = sendto(sockfd, buf, strlen(buf), 0, 
           (struct sockaddr *) &clientaddr, clientlen);
    if (n < 0) 
      error("ERROR in sendto");
  }
}

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