关于动作memoryStream

Question

我在互联网上找到这段代码，不明白服务器如何为客户端发送完整的文件大小，以及为什么客户端可以知道文件大小。帮助我回应:(

Code server: 
FileStream fs = null;
FileInfo fi = new FileInfo(textBox4.Text);
ulong fileSize = (ulong)fi.Length; 
byte[] buf = new byte[32 * 1024]; 
MemoryStream ms = new MemoryStream(buf);//
BinaryWriter bw = new BinaryWriter(ms);
bw.Write(fileSize);
fs = File.OpenRead(textBox4.Text); 
int ns = socket.Send(buf, sizeof(ulong), SocketFlags.None);//why only 32KB which client 
                                                       //can know file size  
ulong pos = 0;
while (pos < fileSize) 
{   int nr = fs.Read(buf, 0, buf.Length);
    if (nr <= 0) { break; } 
    pos += (ulong)nr;
    ns = socket.Send(buf, nr, SocketFlags.None); 
}

代码客户端：

FileStream fs = null; 
fs = File.Create(saveFileName); 
byte[] buf = new byte[32 * 1024]; 
int nr = socket.Receive(buf, sizeof(ulong), SocketFlags.None); 
MemoryStream ms = new MemoryStream(buf); 
BinaryReader br = new BinaryReader(ms); 
ulong fileSize = br.ReadUInt64(); 
ulong pos = 0; 
while (pos < fileSize)
{      nr = socket.Receive(buf);
   if (nr <= 0) { throw new Exception("Receive 0 byte"); } 
   pos += (ulong)nr; 
   fs.Write(buf, 0, nr); 
}

Answer 1

服务器首先写入以下内容：

bw.Write(fileSize);

客户端首先读取以下内容：

ulong fileSize = br.ReadUInt64(); 

因此，客户端知道要跟多少个字节。