c#传输文件 断点续传

在 C# 中实现文件传输的断点续传功能，需要了解以下几个步骤：

1. 建立连接：使用 TCP 或 UDP 协议建立客户端与服务器之间的连接。
2. 发送文件信息：客户端向服务器发送文件名、大小、最后修改时间等信息。
3. 接收文件信息：服务器接收到文件信息后，根据文件名创建或打开文件，并记录已经传输的字节数。
4. 发送文件数据：客户端将文件数据拆分成多个数据块，每个数据块带上序号，发送给服务器。
5. 接收文件数据：服务器接收到数据块后，将其写入文件对应的位置，并记录已经接收到的字节数。
6. 检查数据是否完整：客户端和服务器都需要检查每个数据块是否已经成功接收，并进行重传或者继续传输剩余数据。
7. 断点续传：如果传输过程中出现异常，客户端和服务器可以记录已经传输的字节数，并在恢复连接后从该位置继续传输。

下面是一个简单的 C# 文件传输的断点续传示例代码：

// 客户端代码
TcpClient client = new TcpClient();
client.Connect("127.0.0.1", 8888);

NetworkStream stream = client.GetStream();
byte[] fileNameBytes = Encoding.UTF8.GetBytes(fileName);
byte[] fileInfoBytes = BitConverter.GetBytes(fileSize);
byte[] fileData = File.ReadAllBytes(fileName);

stream.Write(fileNameBytes, 0, fileNameBytes.Length);
stream.Write(fileInfoBytes, 0, fileInfoBytes.Length);

int bufferSize = 1024;
byte[] buffer = new byte[bufferSize];
int bytesSent = 0;
int totalBytesSent = 0;
while (totalBytesSent < fileSize)
{
    int bytesToSend = Math.Min(bufferSize, fileSize - totalBytesSent);
    Buffer.BlockCopy(fileData, totalBytesSent, buffer, 0, bytesToSend);

    stream.Write(buffer, 0, bytesToSend);
    totalBytesSent += bytesToSend;

    Console.WriteLine("Sent {0} bytes.", totalBytesSent);
}

stream.Close();
client.Close();

// 服务器端代码
TcpListener server = new TcpListener(IPAddress.Any, 8888);
server.Start();

while (true)
{
    TcpClient client = server.AcceptTcpClient();
    NetworkStream stream = client.GetStream();

    byte[] fileNameBytes = new byte[1024];
    stream.Read(fileNameBytes, 0, fileNameBytes.Length);
    string fileName = Encoding.UTF8.GetString(fileNameBytes).Trim('\0');

    byte[] fileSizeBytes = new byte[8];
    stream.Read(fileSizeBytes, 0, fileSizeBytes.Length);
    long fileSize = BitConverter.ToInt64(fileSizeBytes, 0);

    FileStream fileStream = new FileStream(fileName, FileMode.Create);
    int bufferSize = 1024;
    byte[] buffer = new byte[bufferSize];
    int bytesReceived = 0;
    int totalBytesReceived = 0;
    while (totalBytesReceived < fileSize)
    {
        int bytesToReceive = Math.Min(bufferSize, (int)(fileSize - totalBytesReceived));
        bytesReceived = stream.Read(buffer, 0, bytesToReceive);

        fileStream.Write(buffer, 0, bytesReceived);
        totalBytesReceived += bytesReceived;

        Console.WriteLine("Received {0} bytes.", totalBytesReceived);
    }

    stream.Close();
    client.Close();
}