C 中的简单回声服务器和UNIX中的C

Question

我编写了一台服务器，该服务器从客户端获取消息，并用其字典中的单词对其进行响应（我在文件中有字典）。例如：

Client wrote: cat
Server got: cat, Server wrote: miauuu! (and client can see the massege 
from server in his window)

我的dict.txt文件看起来像这样：

cat
miauuu!
dog
raw,raw!
etc...

我的代码有一些问题，因为我的服务器从客户端获取消息，但是仍然有问题向客户端发送消息...（在我的客户端窗口中，我看不到服务器的消息）。作为客户，我使用telnet。有什么想法吗？

我的意思是，我运行服务器：./server 9999和telnet：telnet 127.0.0.1 9999，并且可以将消息发送到服务器（并且服务器可以看到它们），但是在Telnets side上，我看不到服务器（也可以看到任何消息）服务器似乎发送一个空字符串（或什么都不知道，我真的不知道））

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netdb.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <map>
#include <string>
#include <iostream>
#include <fstream>
using namespace std;
map <string, string> dict;
void* clients_service(void * arg)
{
    int client_fd = *((int*)&arg), buffsize = 1024, bytes_num = 0;
    char buffer[1024];
    char word[1024];
    while(1)
        {
            if ((bytes_num = read(client_fd, buffer, buffsize)) == -1)
            {
                perror("read error");
                exit(1);
            }
            else if (bytes_num == 0)
            {
                fprintf(stdout, "connection closed.n");
                break;
            }
            buffer[bytes_num] = '';
            fprintf(stdout, "Got: %s", buffer);
            string from_client(buffer);
            string to_client = dict[from_client];
            char buff[1024];
            strncpy(buff, to_client.c_str(), strlen(buff));
            buff[strlen(buff) - 1] = '';
            if ((write(client_fd, buff, strlen(buff))) == -1)
            {
                fprintf(stderr, "write errorn");
                close(client_fd);
                break;
            }
            fprintf(stdout, "I wrote: %s", buff);
        }
        close(client_fd);
}
void loadDictionary(map <string, string> &dict)
{
    dict.clear();
    ifstream file("dict.txt");
    string s1, s2;
    if(file.is_open())
    {
        while(file.good())
        {
            getline(file, s1);
            getline(file, s2);
            dict.insert(pair<string, string>(s1, s2));
        }
    }
    file.close();
}
int main(int argc, char **argv)
{
    int server_soc_fd, port, buffsize = 1024;
    char buffer[buffsize];
    struct sockaddr_in addr;
    socklen_t addrlen = sizeof(addr);
    loadDictionary(dict);
    if (argc < 2)
    {
        fprintf(stderr, "Use : ./server {port number}n");
        exit(1);
    }
    port = atoi(argv[1]);
    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    addr.sin_addr.s_addr = INADDR_ANY;
    server_soc_fd = socket(AF_INET, SOCK_STREAM, 0);
    if(server_soc_fd < 0)
    {
        perror("socket");
        exit(1);
    }
    if(bind(server_soc_fd,(struct sockaddr *)&addr, addrlen) < 0)
    {
        perror("bind");
        exit(1);
    }
    if(listen(server_soc_fd, 10) < 0)
    {
        perror("listen");
        exit(1);
    }
    fprintf(stdout, "nWorking...nn");
    while(true)
    {
        int client_soc_fd = accept(server_soc_fd, NULL, NULL);
        pthread_t thread;
        pthread_create(&thread, NULL, clients_service, (void*)client_soc_fd);
    }
    return 0;
}

Answer 1

this：

char buff[1024];
strncpy(buff, to_client.c_str(), strlen(buff));
buff[strlen(buff) - 1] = '';

不会填充buff。

char *strncpy(char *dest, const char *src, size_t n);

复制n字节从src到dest。

所以你最好做：

const char * cstr = to_client.c_str();
size_t len = strlen(cstr);
strncpy(buff, cstr, max(len, sizeof(buff)-1));
buff[len] = 0;

甚至更好的做：

const char * cstr = to_client.c_str();
size_t len = strlen(cstr);
if (!len)
  continue;
if ((write(client_fd, cstr, len) == -1)
{
  ...

您也不应立即依靠write()编写所有数据。

因此，您可以像这样扩展它：

...
const char * cstr = to_client.c_str();
size_t len = strlen(cstr);
size_t lenWrittenTotal = 0;
while (lenWrittenTotal < len);
{
  ssize_t lenWritten = write(client_fd, cstr + lenWrittenTotal , len - lenWrittenTotal);
  if (lenWritten < 0)
  {
    perror("write");
    break;
  } 
  else if (lenWritten > 0)
  {
    lenWrittenTotal += lenWritten;
  }
  else
  {
    ... 
    break;
  }
};
...