寫入套接字

Question

我正在使用套接字製作一個簡單的1對1服務器 - 客戶端聊天應用程序。基本上有一個服務器可以與單個客戶端進行通信。我試圖做的是客戶端應該發送一個字符串到服務器和服務器必須發送它回到客戶端與更改字符串的情況下（從上到下，反之亦然）。問題是字符串被髮送到服務器，但從服務器的響應從未帳戶該客戶端無法發送其他字符串。 輸出的程序： -

根@用戶：〜/桌面/ Aadil/SystemPracticum /程序/ Assignment5＃./Server 4000

從客戶端該消息是MESSAGE1

根@用戶：〜 /桌面/ Aadil/SystemPracticum /程序/ Assignment5＃./Client本地主機4000

輸入消息MESSAGE1

輸入消息的消息2

謝謝 這裏是我的代碼 Server.c

#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 <time.h> 
void ChangeCase(char *string){ 
    int i = 0; 
    while(string[i]){ 
     // printf("converting\n"); 
     if(string[i] <= 90 && string[i] >= 65) 
      string[i] += 32; 
     else 
      string[i] -= 32; 
     ++i; 
    } 

} 
int main(int counter, char *string[]){ 
    if(counter < 2){ 
     perror("erro! please provide port no.\n"); 
    }else{ 
     int server_socket_file_descriptor,client_socket_file_descriptor, 
     port_no,message_length,client_length; 
     char buffer[256];//buffer to be used for storing messages 
     struct sockaddr_in server_address,client_address; 

     server_socket_file_descriptor = socket(AF_INET,SOCK_STREAM,0); 
     /*it creates new socket the first argument AF_INET is used for internet domain 
      and second argument SOCK_STREAM is used for stream socket 
      third argument 0 means the default protocol for stram socket which is tcp*/ 
     if(server_socket_file_descriptor < 0) 
      perror("\t\t\t\t=====!!!cant create a socket!!!=====\n"); 

     bzero((char*)&server_address,sizeof(server_address));//set all value to 0 

     //set port no. by converting port from char* to integer    
     port_no = atoi(string[1]); 

     /*now initialize the server_address 
      server_address is a struct of sockaddr_in type which has four field in it 
      we need to initialize 3 of them 
     */ 
     server_address.sin_family = AF_INET; 
     //convert port no. to network byte order 
     server_address.sin_port = htons(port_no); 
     //set server ip address to the machines ip address in my case it is 10.8.3.236    
     server_address.sin_addr.s_addr=INADDR_ANY; 

     /*now we need to bind the server with socket created*/ 
     if(bind(server_socket_file_descriptor,(struct sockaddr*)&server_address, 
       sizeof(server_address)) < 0){ 
      perror("\t\t\t\t\t====error in binding====\n"); 
      return 0; 
     } 
     //since socket is bind correctly I am not checking for the error 
     listen(server_socket_file_descriptor,8); 
     /*listening to socket. 8 represent the maximum client that 
     can wait in queue to connect to the server*/ 

     //we are done with the server :D 

     client_length = sizeof(client_address); 
     client_socket_file_descriptor = accept(server_socket_file_descriptor, 
               (struct sockaddr*)&client_address, 
               &client_length); 
     if(client_socket_file_descriptor < 0) 
      perror("\t\t\t\t unable to connect to client"); 

     while(1){ 
      bzero(buffer,256); 
      message_length = read(client_socket_file_descriptor,buffer,255); 

      if(message_length < 0) 
       perror("\t\t\t\t error in reading from socket\n"); 

      printf("\t\t\t\tthe message from client is %s\n",buffer); 
      ChangeCase(buffer); 

      message_length = write(client_socket_file_descriptor,buffer,sizeof(buffer)); 
      if(message_length < 0) 
       perror("\t\t\t\t error writing to socket\n"); 
     } 
     return 0; 
    } 
} 

Client.c

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

    int main(int argc, char *argv[]) 
    { 
     int file_descriptor,message_length,port_no; 
     char Buffer[256];//to store the message 
     //to store the address of the server to  which  we want to connect 
     struct sockaddr_in server_address; 
     struct hostent *server;//hostent defines the host computer on internet 
     if(argc < 3){ 
      printf("\t\t\t please provide ip address and port no.\n"); 
      return 1; 
     } 
     port_no = atoi(argv[2]); 

     if((file_descriptor = socket(AF_INET, SOCK_STREAM, 0)) < 0) 
     { 
      printf("\n Error : Could not create socket \n"); 
      return 1; 
     } 

     memset(&server_address, '0', sizeof(server_address)); 

     server_address.sin_family = AF_INET; 
     //convert port no. to network byte order 
     server_address.sin_port = htons(port_no); 
     //set server ip address to the machines ip address in my case it is 10.8.3.236 
     server_address.sin_addr.s_addr = INADDR_ANY; 

     if(connect(file_descriptor,(struct sockaddr*)&server_address, 
            sizeof(server_address))<0){ 
      perror("error in connection\n"); 
      return 1; 
     } 

     while(1){ 
      memset(Buffer, '0',sizeof(Buffer)); 
      printf("\t\t\t\t\tenter the message\n"); 
      fgets(Buffer,255,stdin); 
      message_length = write(file_descriptor,Buffer,strlen(Buffer)); 

      if(message_length<0) 
       perror("\t\t\t\terror in writing\n"); 

      memset(Buffer,'0',sizeof(Buffer)); 
      message_length = read(file_descriptor,Buffer,255); 

      if(message_length < 0) 
       perror("\t\t\terror in reading from buffer\n"); 
      else{ 
       printf("%s\n",Buffer); 
      } 
     } 

     return 0; 
    } 

Answer 1

我懷疑問題位於這條線在你的服務器代碼：

message_length = write(client_socket_file_descriptor,buffer,sizeof(buffer)); 

請注意，此行始終將256個字節發送回客戶端。對於像「message1」這樣的字符串，這意味着它將發回「MESSAGE1」，然後是248 NUL /零字節。根據TCP堆棧決定如何分解這些字節，客戶端的read（）調用可能會接收到不同部分序列中的那些字節，並且如果接收到的任何部分序列以NUL /零字節開始，它將打印作爲一個空字符串出來。

爲了更好地看到發生了什麼事情，你可能會取代這條線在你的客戶端：

printf("%s\n",Buffer); 

像這樣的東西：

printf("[%s]\n",Buffer); 

我也建議你改變你的服務器指定strlen（buffer）作爲write（）的最終參數而不是sizeof（buffer）。