将图像从C＃客户端发送到C服务器

Question

如果我发送纯文本没有问题。 一切都好。 但是，如果我尝试从C＃客户端发送一个映像，服务器会收到正确的字节数，但是当我将缓冲区保存到文件（二进制模式 - wb）时，它总是有4个字节。

我通过使用File.ReadAllBytes()函数由C＃客户端发送它。

我的保存代码看起来像

   FILE * pFile;
   char *buf = ReceiveMessage(s);
   pFile = fopen (fileName , "wb");
   fwrite(buf, sizeof(buf[0]), sizeof(buf)/sizeof(buf[0]), pFile);
   fclose (pFile);
   free(buf);

我的接收功能看起来像

static unsigned char *ReceiveMessage(int s)
{
   int prefix;
   recv(s, &prefix, 4, 0);
   int len = prefix;
   char *buffer= (char*)malloc(len + 1);
   int received = 0, totalReceived = 0;
   buffer[len] = '\0';
   while (totalReceived < len)
   {
      if (len - totalReceived > BUFFER_SIZE)
      {
         received = recv(s, buffer + totalReceived, BUFFER_SIZE, 0);
      }
      else
      {
         received = recv(s, buffer + totalReceived, len - totalReceived, 0);
      }
      totalReceived += received;
   }

   return buffer;
}

Answer 1

你初学者犯了使用sizeof(buf)错误。 它不返回缓冲区中的字节数，而是返回指针的大小（如果运行32位或64位平台，则为4或8）。

您需要更改ReceiveMessage函数以“返回”接收数据的大小。

Answer 2

您的C代码需要从ReceiveMessage（）函数传回len 。

char *buf = ReceiveMessage(s);  // buf is a char*
... sizeof(buff)                // sizeof(char*) is 4 or 8

所以你需要类似的东西

 static unsigned char *ReceiveMessage(int s, int* lenOut)
 {
     ...
     *lenOut = totalReceived ;
 }

Answer 3

你没有得到sizeof数组的sizeof 。 改为ie：

int len = 0;
char *buf;

buf = ReceiveMessage(s, &len);

/* then use len to calculate write length */


static unsigned char *ReceiveMessage(int s, int *len) 
/* or return len and pass ptr to buf */
{


  ...
}