C ++套接字编程（read（）write（））

Question

我正在编写一个程序，将某些文件的内容从客户端传输到服务器，但我遇到了一些问题：

1. 客户端为服务器写入的字节数不等于服务器读取的字节数。
2. 我的解决方案是发送服务器文件的大小吗？

client.cpp

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <iostream>
#include <cstdlib>
#include <sys/stat.h>
#include <errno.h>
#include <dirent.h>
#include <cstdio>
#include <string>
#include <fstream>
#include <stdio.h>
#include <stdlib.h>
#include <sstream>

using namespace std ;

const int BF_SIZE = 2048 ;

void R_directory ( int socket_id ){
    DIR *dir ;
    struct dirent *pent ;
    dir = opendir( "address of files" ) ;
    string path = "address of files" ;

    char BF_read[BF_SIZE] ;
    int n ;

    if ( dir == NULL ){
        cout << "No such directory" << endl ;
    }
    else{
        while (  pent = readdir ( dir ) ){
            if ( pent == NULL ) break ;
            if( !strcmp( pent->d_name , ".") || !strcmp ( pent->d_name , "..") ) continue ;
            string abspath = path , a ;
            for ( int i = 0 ; i < pent->d_name[i] ; i++ ) abspath.push_back( pent->d_name[i] ) ;
            FILE *fi = NULL ;
            fi = fopen ( abspath.c_str() , "r" ) ;
            struct stat fi_sp ;
            stat( abspath.c_str() , &fi_sp );
            if ( fi == NULL ){
                cout << "Can't open file " << abspath << endl ;
                continue ;
            }
            if ( fi_sp.st_size == 0 ){
                cout << "File " << abspath << " is empty" << endl ;
                continue ;
            }
            int file_size = 0 ;
            file_size = fi_sp.st_size ;
            write ( socket_id , &file_size , 4 ) ;
            cout << abspath << " " << file_size << endl ;
            while ( ( n = fread ( BF_read , 1 , BF_SIZE , fi ) ) > 0 && file_size > 0){
                cout << n << endl ;
                file_size -= n ;
                if ( file_size > 0 && n >= BF_SIZE ){
                    write ( socket_id , BF_read , sizeof ( BF_read ) ) ;
                }
                else{
                    write ( socket_id , BF_read , n - 1 ) ;
                }
            }

            cout << "=====================================" << endl ;
            fclose(fi);
        }
        int file_size = 0 ;
        write ( socket_id , &file_size , 4 ) ;
    }
    closedir(dir);
    return ;
}

int main ( int argc , char* argv[] ){
    int sockfd = 0,n = 0;
    struct sockaddr_in serv_addr;

    if((sockfd = socket(AF_INET, SOCK_STREAM, 0))< 0)
    {
        cout << "Error : Could not create socket" << endl ;
        return 1;
    }

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(5000);
    serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

    if(connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr))<0)
    {
        cout << "Error : Connect Failed" << endl ;
        return 1;
    }

    R_directory( sockfd );

    return 0 ;
}

server.cpp

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

using namespace std ;

const int BF_SIZE = 2048 ;

int main(void)
{
    int listenfd = 0,connfd = 0;

    struct sockaddr_in serv_addr;

    char sendBuff[BF_SIZE] , recvBuff[BF_SIZE] ;
    int numrv;

    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    printf("socket retrieve success\n");

    memset(&serv_addr, '0', sizeof(serv_addr));
    memset(sendBuff, '0', sizeof(sendBuff));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(5000);

    bind(listenfd, (struct sockaddr*)&serv_addr,sizeof(serv_addr));

    if(listen(listenfd, 10) == -1){
        printf("Failed to listen\n");
        return -1;
    }

    connfd = accept(listenfd, (struct sockaddr*)NULL ,NULL);
    ofstream cout ( "output.txt" , std::ios::app ) ;

    while(1)
    {    
        int file_size = 0 , n ;
        n = read ( connfd , &file_size , 4 ) ;
        //cout << "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!" << endl ;
        if ( file_size == 0 ) break ;
        while ( file_size > 0 ){
            n = read( connfd , recvBuff, sizeof(recvBuff) ) ;
            cout << n << endl ;
            if ( n == 0 ) break ;
            file_size -= n ;
            /*for ( int i = 0 ; i < n ; i++ ){
                cout << recvBuff[i] ;
            }*/
        }
        cout << endl ;
    }
    close(connfd);

    return 0;
}

在客户端，我发送的字节数等于文件大小（以字节为单位），但在服务器中我有更多的字节 - 为什么？