从Java客户端接收数据（数据包含INT，短，字符串） [英] Receiving data from Java-Client (data contains int, short, string)

问题描述

我在寻找了几个小时，以获取有关我的问题的答案，但没有发现任何东西。也许我得到一些帮助这里。

I was searching for hours to get an answer about my question, but didnt find anything. Maybe I get some help here.

我试图做的事：
一个Java客户端发送消息到C-服务器。该邮件包含不同的类型，如整型，短，也是一个字符串（如消息= INT：total_msg_length;短：手术;字符串：你好 - > total_msg长度= 4（整数大小），操作= 2（短尺寸） ，你好= 5（每封信是1字节= 5）。

What I'm trying to do: A Java-Client sends a message to a C-Server. The message contains different types like integer, short and also a string (e.g. message = int: total_msg_length; short: operation; string: hello --> total_msg-length=4 (size of integer), operation = 2 (size of short), hello = 5 (each letter is 1 byte=5).

那么，怎样才能我在服务器收到消息？下面的code接收一个整数（正常工作）。下一步将收到一个短，然后一个字符串（转换在US-ASCII）。

So, how can I receive the message in my server? The code below receives an Integer (works fine). Next step will be to receive a short and then a string (converted in US-ASCII).

int *msg;
int recv_size;
int final_msg;

if( (recv_size = recv(client_socket, &msg, sizeof(msg), 0 )) < 0 ){
    error_exit("Fehler bei recv(message_len)");
}

final_msg = endian_swap(msg);
printf("Message: %d\n", final_msg);

return final_msg;

有没有使用一个字节数组，而不是字符缓冲区的方法吗？ IM感谢每一个帮助。请原谅我的英语不好，我来自德国:-)

Is there a way to use a byte array instead of char buffer? Im thankful for every help. Please excuse my bad english, I'm from germany :-)

推荐答案

您需要创建一个通用的read_n_bytes功能。

You need to create a generic "read_n_bytes" function.

这可以用来读取邮件大小，操作和文字，在三个连续调用。

This you can use to read the message-size, the operation and the text, in three successive calls.

这三个调用，那么你在函数换到被调用来读整个消息。

Those three calls you then wrap in a function to be called to read an entire message.

一个普通的读者可能会是这样的：

A generic reader might look like this:

/*
 * Reads n bytes from sd into where p points to.
 *
 * returns 0 on succes or -1 on error.
 *
 * Note: 
 * The function's name is inspired by and dedicated to "W. Richard Stevens" (RIP).
 */
int readn(int sd, void * p, size_t n)
{
  size_t bytes_to_read = n;
  size_t bytes_read = 0;

  while (bytes_to_read > bytes_read)
  {
    ssize_t result = read(sd, p + bytes_read, bytes_to_read);
    if (-1 == result)
    {
      if ((EAGAIN == errno) || (EWOULDBLOCK == errno))
      {
        continue;
      }

#     ifdef DEBUG     
      {
        int errno_save = errno;
        perror("read() failed");
        errno = errno_save;
      }
#     endif

      break;
    }
    else if(0 == result)
    {
#     ifdef DEBUG
      {     
        int errno_save = errno;
        fprintf(stderr, "%s: Connection closed by peer.", __FUNCTION__);
        errno = errno_save;
      }
#     endif

      break;
    }

    bytes_to_read -= result;
    bytes_read += result;
  }

  return (bytes_read < bytes_to_read) ?-1 :0; 
}

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