c - 从客户端到服务器的文件传输

Question

我正在尝试将文件从客户端发送到服务器。它有时有效，有时无效。当第一次尝试发送文件时，它发送损坏的文件，并且在服务器端形成的文件端是其大小的两倍。但在第一次尝试后，所有尝试都会成功传输。谁能帮我解决这个问题吗？

客户端.c

     message msg;
        msg.type = SEND_FILE;
        char *username, *filename;

        username = strtok(input+6, " ");
        filename = strtok(NULL, "");

        //Get Picture Size
        printf("Getting Picture Size\n");
        FILE *picture;
        picture = fopen(filename, "r");
        int size;
        fseek(picture, 0, SEEK_END);
        size = ftell(picture);
        fseek(picture, 0, SEEK_SET);

        //Send Picture Size
        printf("Getting Picture Size\n");
        sprintf(msg.data, "%d", size);
        strncpy(msg.username, username, 20);

        if(send(connection->socket, &msg, sizeof(message), 0) < 0)
        {
            perror("Send failed");
            exit(1);
        }
        //Send Picture as Byte Array
        printf("Sending Picture as Byte Array\n");
        char send_buffer[size+1];
        fread(send_buffer, 1, sizeof(send_buffer), picture);
        write(connection->socket, send_buffer, sizeof(send_buffer));
        bzero(send_buffer, sizeof(send_buffer));

服务器.c

  //Read Picture Size
printf("Reading Picture Size\n");
int size = atoi(message_text);

//Read Picture Byte Array
printf("Reading Picture Byte Array\n");
char p_array[size];
printf("Converting Byte Array to Picture %d\n", size);
FILE *image;
image = fopen("c4.png", "w");
int readSize = 0;
while (readSize < size) {
  readSize = readSize + read(clients[sender].socket, p_array, size);
  fwrite(p_array, 1, sizeof(p_array), image);
}

fclose(image);

Answer 1

对于初学者:

您不想在每个 fwrite() 上存储相同数量的字节

fwrite(p_array, 1, sizeof(p_array), image);

但只是实际读取的字节数。

sizeof(p_array) 返回 p_array 的大小，它是 size 乘以 char 的大小。后者被定义为1。

<小时/>

除此之外，对 read() 的调用完全缺乏错误检查，以及测试对方是否关闭连接。这并没有领先太远。

<小时/>

要解决这个问题，你可以这样做:

#include <errno.h> /* for errno */

...

  size_t size = atoi(message_text);
  printf("Reading Picture Byte Array\n");
  char p_array[size];
  size_t readSize = 0;
  while (readSize < size) {
    ssize_t result = read(clients[sender].socket, p_array, size); /* Mind the ssize_t, it's *not* size_t! */
    if (0 >= result)
    {
      if (0 == result)
      {
        fprintf(stderr, "The other end gracefully shut down the connection.\n");

        break;
      }
      else
      {
        if (EINTR == errno)  /* got interrupted, start over */
        {
           continue;
        }

        if (EAGAIN == errno)  /* in case reading from a non-blocking socket: no data available, start over */
        {
           continue;
        }

        /* Something went wrong unrecoverable. */
        perror("read() failed");

        break;
      }
    }
    else
    {
       fwrite(p_array, 1, result, image); 
       /* Also add error checking here! */
       readSize += result;
    }
 }