将文件从客户端发送到服务器

Question

I'm developing a client/server program in C. The server send to a client a txt file, but the name is like corrupt. The content is good, only the name is not good.

Can someone tell me why? Thank you!

This is the code who send the file:

fd = open(appoggio1, O_RDONLY);
if (fd < 0) {
  fprintf(stderr, "unable to open '%s': %s\n", appoggio1, strerror(errno));
  exit(1);
}
while ((nread = read(fd, buffer2, sizeof(buffer2))) > 0) 
    {
        write(servers_fd, buffer2, nread);
            read(servers_fd,buffer2,sizeof(char));
    }

    printf("Trasmissione completata con successo\n\n");

    write(servers_fd,fine,strlen(fine)); 
    read(servers_fd,fine,strlen(fine));
close(fd);

This is the code who receive the file:

fd = open(nomefile, O_CREAT | O_WRONLY, 0755);

    if (fd < 0) 
    {
        fprintf(stderr, "errore open(): %s\n", strerror(errno));
        exit(errno);
    }
while ((nread = read(conn_fd, buffer, sizeof(buffer))) > 0)
{
    if(!strncmp(buffer,fine,7))
        break;        
    write(fd, buffer, nread);
    write(conn_fd,buffer,sizeof(char));
}
write(conn_fd,fine,strlen(fine));

}

Answer 1

The problem is with your protocol.

You send the file and then the name. But the client has no way of knowing when the file ends and the name begins.

You can fix it by first sending the length of the name and then the actual name:

#include <arpa/inet.h>

// Write the file name with length marker
uint32_t nameLength = htonl(strlen(fine));
write(servers_fd, &nameLength, sizeof nameLength); 
write(servers_fd, fine, strlen(fine)); 

// Write the actual file.

And in the client:

#include <arpa/inet.h>

uint32_t nameLength;
read(conn_fd, &nameLength, sizeof nameLength);
nameLength = ntohl(nameLength);

read(conn_fd, fine, nameLength);
fine[nameLength] = '\0';  // Add nul-terminator to file name.

// Read the rest of the file

htonl and ntohl convert numbers to network byte order, enabling your code to work even if the client and server use different byte orders (big/little endianness).

Note: Unless you use a size marker for the actual file as well, the client won't know how big it is, and the connection will only be good for one file download.

Note2 : I have ignored the possibility that the size and file names might be divided into more than one network packets.