Asc*_*caL 12 c sockets linux file
我试图在服务器和客户端之间进行文件传输,但工作非常糟糕.基本上需要发生的是:
1)客户端将txt文件发送到服务器(我称之为"quotidiani.txt")
2)服务器将其保存在另一个txt文件中("receive.txt")
3)服务器运行它上面的一个脚本修改它并用另一个名字保存它("output.txt")
4)服务器将文件发送回客户端,保存它(在同一个套接字上)名称(final.txt)
问题是第一个文件(quotidi.txt)只是读取了一小部分,然后有一些错误.我希望有人帮助我理解并纠正我的错误.
这是我的代码:
client.c:
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <signal.h>
#include <ctype.h>
#include <arpa/inet.h>
#include <netdb.h>
#define PORT 20000
#define LENGTH 512
void error(const char *msg)
{
perror(msg);
exit(1);
}
int main(int argc, char *argv[])
{
/* Variable Definition */
int sockfd;
int nsockfd;
char revbuf[LENGTH];
struct sockaddr_in remote_addr;
/* Get the Socket file descriptor */
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
fprintf(stderr, "ERROR: Failed to obtain Socket Descriptor! (errno = %d)\n",errno);
exit(1);
}
/* Fill the socket address struct */
remote_addr.sin_family = AF_INET;
remote_addr.sin_port = htons(PORT);
inet_pton(AF_INET, "127.0.0.1", &remote_addr.sin_addr);
bzero(&(remote_addr.sin_zero), 8);
/* Try to connect the remote */
if (connect(sockfd, (struct sockaddr *)&remote_addr, sizeof(struct sockaddr)) == -1)
{
fprintf(stderr, "ERROR: Failed to connect to the host! (errno = %d)\n",errno);
exit(1);
}
else
printf("[Client] Connected to server at port %d...ok!\n", PORT);
/* Send File to Server */
//if(!fork())
//{
char* fs_name = "/home/aryan/Desktop/quotidiani.txt";
char sdbuf[LENGTH];
printf("[Client] Sending %s to the Server... ", fs_name);
FILE *fs = fopen(fs_name, "r");
if(fs == NULL)
{
printf("ERROR: File %s not found.\n", fs_name);
exit(1);
}
bzero(sdbuf, LENGTH);
int fs_block_sz;
while((fs_block_sz = fread(sdbuf, sizeof(char), LENGTH, fs)) > 0)
{
if(send(sockfd, sdbuf, fs_block_sz, 0) < 0)
{
fprintf(stderr, "ERROR: Failed to send file %s. (errno = %d)\n", fs_name, errno);
break;
}
bzero(sdbuf, LENGTH);
}
printf("Ok File %s from Client was Sent!\n", fs_name);
//}
/* Receive File from Server */
printf("[Client] Receiveing file from Server and saving it as final.txt...");
char* fr_name = "/home/aryan/Desktop/progetto/final.txt";
FILE *fr = fopen(fr_name, "a");
if(fr == NULL)
printf("File %s Cannot be opened.\n", fr_name);
else
{
bzero(revbuf, LENGTH);
int fr_block_sz = 0;
while((fr_block_sz = recv(sockfd, revbuf, LENGTH, 0)) > 0)
{
int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
if(write_sz < fr_block_sz)
{
error("File write failed.\n");
}
bzero(revbuf, LENGTH);
if (fr_block_sz == 0 || fr_block_sz != 512)
{
break;
}
}
if(fr_block_sz < 0)
{
if (errno == EAGAIN)
{
printf("recv() timed out.\n");
}
else
{
fprintf(stderr, "recv() failed due to errno = %d\n", errno);
}
}
printf("Ok received from server!\n");
fclose(fr);
}
close (sockfd);
printf("[Client] Connection lost.\n");
return (0);
}
server.c
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <signal.h>
#include <ctype.h>
#include <arpa/inet.h>
#include <netdb.h>
#define PORT 20000
#define BACKLOG 5
#define LENGTH 512
void error(const char *msg)
{
perror(msg);
exit(1);
}
int main ()
{
/* Defining Variables */
int sockfd;
int nsockfd;
int num;
int sin_size;
struct sockaddr_in addr_local; /* client addr */
struct sockaddr_in addr_remote; /* server addr */
char revbuf[LENGTH]; // Receiver buffer
/* Get the Socket file descriptor */
if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1 )
{
fprintf(stderr, "ERROR: Failed to obtain Socket Descriptor. (errno = %d)\n", errno);
exit(1);
}
else
printf("[Server] Obtaining socket descriptor successfully.\n");
/* Fill the client socket address struct */
addr_local.sin_family = AF_INET; // Protocol Family
addr_local.sin_port = htons(PORT); // Port number
addr_local.sin_addr.s_addr = INADDR_ANY; // AutoFill local address
bzero(&(addr_local.sin_zero), 8); // Flush the rest of struct
/* Bind a special Port */
if( bind(sockfd, (struct sockaddr*)&addr_local, sizeof(struct sockaddr)) == -1 )
{
fprintf(stderr, "ERROR: Failed to bind Port. (errno = %d)\n", errno);
exit(1);
}
else
printf("[Server] Binded tcp port %d in addr 127.0.0.1 sucessfully.\n",PORT);
/* Listen remote connect/calling */
if(listen(sockfd,BACKLOG) == -1)
{
fprintf(stderr, "ERROR: Failed to listen Port. (errno = %d)\n", errno);
exit(1);
}
else
printf ("[Server] Listening the port %d successfully.\n", PORT);
int success = 0;
while(success == 0)
{
sin_size = sizeof(struct sockaddr_in);
/* Wait a connection, and obtain a new socket file despriptor for single connection */
if ((nsockfd = accept(sockfd, (struct sockaddr *)&addr_remote, &sin_size)) == -1)
{
fprintf(stderr, "ERROR: Obtaining new Socket Despcritor. (errno = %d)\n", errno);
exit(1);
}
else
printf("[Server] Server has got connected from %s.\n", inet_ntoa(addr_remote.sin_addr));
/*Receive File from Client */
char* fr_name = "/home/aryan/Desktop/receive.txt";
FILE *fr = fopen(fr_name, "a");
if(fr == NULL)
printf("File %s Cannot be opened file on server.\n", fr_name);
else
{
bzero(revbuf, LENGTH);
int fr_block_sz = 0;
while((fr_block_sz = recv(nsockfd, revbuf, LENGTH, 0)) > 0)
{
int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
if(write_sz < fr_block_sz)
{
error("File write failed on server.\n");
}
bzero(revbuf, LENGTH);
if (fr_block_sz == 0 || fr_block_sz != 512)
{
break;
}
}
if(fr_block_sz < 0)
{
if (errno == EAGAIN)
{
printf("recv() timed out.\n");
}
else
{
fprintf(stderr, "recv() failed due to errno = %d\n", errno);
exit(1);
}
}
printf("Ok received from client!\n");
fclose(fr);
}
/* Call the Script */
system("cd ; chmod +x script.sh ; ./script.sh");
/* Send File to Client */
//if(!fork())
//{
char* fs_name = "/home/aryan/Desktop/output.txt";
char sdbuf[LENGTH]; // Send buffer
printf("[Server] Sending %s to the Client...", fs_name);
FILE *fs = fopen(fs_name, "r");
if(fs == NULL)
{
fprintf(stderr, "ERROR: File %s not found on server. (errno = %d)\n", fs_name, errno);
exit(1);
}
bzero(sdbuf, LENGTH);
int fs_block_sz;
while((fs_block_sz = fread(sdbuf, sizeof(char), LENGTH, fs))>0)
{
if(send(nsockfd, sdbuf, fs_block_sz, 0) < 0)
{
fprintf(stderr, "ERROR: Failed to send file %s. (errno = %d)\n", fs_name, errno);
exit(1);
}
bzero(sdbuf, LENGTH);
}
printf("Ok sent to client!\n");
success = 1;
close(nsockfd);
printf("[Server] Connection with Client closed. Server will wait now...\n");
while(waitpid(-1, NULL, WNOHANG) > 0);
//}
}
}
一些评论没有特别的顺序:
您放弃了经常知道确切错误的机会:
if(listen(sockfd,BACKLOG) == -1)
{
printf("ERROR: Failed to listen Port %d.\n", PORT);
return (0);
}
这个块肯定应该包含一个perror("listen")或类似的东西.当通过报告错误详细信息时,始终包含perror()或包含strerror()在每个错误处理块中errno.确切的故障原因可以节省您编程的时间,并且可以节省您和您的用户在将来无法正常工作的时间.
您的错误处理需要进一步标准化:
if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1 )
{
printf("ERROR: Failed to obtain Socket Descriptor.\n");
return (0);
}
这应该不是 return 0,因为这将标志着该程序运行完成没有错误的壳.您应该return 1(或使用EXIT_SUCCESS和EXIT_FAILURE)发出异常退出的信号.
else
printf("[Server] Server has got connected from %s.\n", inet_ntoa(addr_remote.sin_addr));
/*Receive File from Client */
在前面的块中,您已经出现错误情况但仍然继续执行.这是一种快速获取非常不良行为的方法.这应该重新启动主服务器循环或退出子进程或类似的东西.(取决于您是否保留多进程服务器.)
if(!fork())
{
前面的块忘了说明fork() 失败了.fork()可以,并且确实失败 - 特别是在大学常见的共享托管环境中 - 所以你应该准备好完整,复杂的三个可能的返回值fork():failure,child,parent.
你似乎在fork()不分青红皂白地使用; 您的客户端和服务器都非常简单,它们的运行方式意味着它们不能用于同时为多个客户端提供服务.你可能应该坚持每个进程只有一个,至少在算法完美调试之前你想出了一些同时运行多个客户端的方法.我希望这是你现在遇到的问题的根源.
您需要使用函数来封装细节; 编写一个连接服务器的函数,一个发送文件的函数,一个写文件的函数等.编写一个函数来处理复杂的部分写操作.(我特别建议在Unix环境书的源代码中writen使用高级编程中的功能.文件lib/writen.c.)如果正确编写函数,可以在客户端和服务器中重复使用它们.(比如将它们放入utils.c并编译程序之类的东西gcc -o server server.c utils.c.)
拥有较小的函数,每个函数都可以执行一项操作,这样您就可以一次专注于少量代码,并为每个代码编写一些测试,这将有助于缩小哪些代码段仍需要改进.
这里似乎缺少一个讨论点,所以我想在这里提一下.
让我们非常快速地了解TCP的数据传输.有三个步骤:a)连接建立,b)数据传输,c)连接终止
现在,客户端通过TCP套接字将文件发送到服务器.
服务器对文件进行一些处理并将其发送回客户端.
现在需要完成所有3个步骤.通过调用connect完成连接建立.通过recv/send在此处完成数据读取/写入,并通过关闭完成连接终止.
这里的服务器使用recv在循环中读取数据.现在循环结束了吗？当recv返回0或错误时可能小于0. 当recv返回0时？ - >当另一侧关闭连接时. (当此方收回TCP FIN分段时).
所以在这个代码中,当客户端完成发送文件时,我使用了一个shutdown函数,它从客户端发送FIN segement,服务器的recv现在可以返回0并且程序继续.(中途关闭,因为客户端还需要随后读取数据).
(只是为了理解请注意TCP的连接Establisment是一种3路握手和连接终止是一种4路握手.)
同样,如果您忘记关闭服务器端的连接套接字,客户端的recv也将永久阻止.我认为这就是使用ctrl c有时会停止客户端的原因.
你可以.请参阅任何标准网络书籍或rfc http://www.ietf.org/rfc/rfc793.txt以了解有关TCP的更多信息
我已粘贴修改后的代码,也很少添加一些评论,
希望这个解释会有所帮助.
修改客户端代码:
while((fs_block_sz = fread(sdbuf, sizeof(char), LENGTH, fs)) > 0)
{
if(send(sockfd, sdbuf, fs_block_sz, 0) < 0)
{
fprintf(stderr, "ERROR: Failed to send file %s. (errno = %d)\n", fs_name, errno);
exit(1);
}
bzero(sdbuf, LENGTH);
}
/*Now we have sent the File's data, what about server's recv?
Recv is blocked and waiting for data to arrive or if the protocol
stack receives a TCP FIN segment ..then the recv will return 0 and
the server code can continue */
/*Sending the TCP FIN segment by shutdown and this is half way
close, since the client also needs to read data subsequently*/
shutdown(sockfd, SHUT_WR);
printf("Ok File %s from Client was Sent!\n", fs_name);