c#中的文件传输问题

Question

我正在使用 c# 传输文件。我使用了this 代码。问题是像 .txt 文件这样的小文件可以正确传输，但不能正确传输像图像、文档、pdf、ppt 这样的大文件。有时代码运行良好，但大多数时候它传输的数据量较少。

服务器代码：

Socket clientSock = sock.Accept();

byte[] clientData = new byte[1024 * 50000];
int receivedBytesLen = clientSock.Receive(clientData);
int fileNameLen = BitConverter.ToInt32(clientData, 0);
string fileName = Encoding.ASCII.GetString(clientData, 4, fileNameLen);
BinaryWriter bWrite = new BinaryWriter(File.Open(receivedPath + "/" + fileName, FileMode.Append));
bWrite.Write(clientData, 4 + fileNameLen, receivedBytesLen - 4 - fileNameLen);
bWrite.Close();
clientSock.Close();

客户代码：

byte[] fileNameByte = Encoding.ASCII.GetBytes(fileName);
byte[] fileData = File.ReadAllBytes(filePath + fileName);
byte[] clientData = new byte[4 + fileNameByte.Length + fileData.Length];
byte[] fileNameLen = BitConverter.GetBytes(fileNameByte.Length);
fileNameLen.CopyTo(clientData, 0);
fileNameByte.CopyTo(clientData, 4);
fileData.CopyTo(clientData, 4 + fileNameByte.Length);
clientSock.Connect(ipEnd);
clientSock.Send(clientData);
clientSock.Close();

完整的代码在上面的链接中给出。我也看过这个post，但这没有帮助。

Answer 1

有时代码可以正常工作，但大多数时候它传输的数据量较少。

这就是Socket.Receive() 的本质，它并不总是返回发送给它的所有数据。

您必须先执行 Receive(clientData, 4, 0) 以接收指示 size 的字节，然后在循环中调用 Receive(clientData) 直到您收到 size 字节。但请注意，Receive(buffer[], length, offset) 重载就像任何其他重载一样容易返回少于的预期字节数。所以你还必须循环调用它：

类似这样的：

// First receive the size
int sizeSize = 4; // Size of Int32 in bytes
int sizeOffset = 0;
var sizeBytes = new byte[sizeSize];
while (sizeOffset < sizeSize)
{
    sizeOffset += clientSocket.Receive(sizeBytes, sizeSize - sizeOffset, sizeOffset);
}

var size = BitConverter.ToInt32(sizeBytes, 0);

// Then receive the data
byte[] fileData = new byte[size];
byte[] clientData = new byte[8192];
int totalBytes = 0;

while (totalBytes < size)
{
    // This may return anything between 0 and 8192, even if not all sent data has been received yet. It may be in a buffer somewhere, waiting to be picked up. Check for 0, since that's when the client disconnects.
    int bytesReceived = clientSocket.Receive(clientData);

    // You now have received a chunk of data of bytesReceived length. Append it into the fileData array.
    Buffer.BlockCopy(clientData, 0, fileData, totalBytes, bytesReceived);

    totalBytes += bytesReceived;
}

Answer 2

正如 CodeCaster 的 回答 Socket.Receive(), it doesn't always return all data that gets sent to it. 这是 100% 正确且经过测试但发送文件大小的下一步不起作用，我找到了一个简单且正确的解决方案。

Socket.Receive() 方法获取接收数据将被复制到的字节数组，并返回接收到的字节数。所以我们可以很容易地循环它直到接收到的字节数为 0。

byte[] tempData = new byte[1024 * 5000];

BinaryWriter bWrite = null;
int bytes_received;
int fileNamelength = 0;
bool isFirstPacket = true;

do
{
    bytes_received = clientSock.Receive(tempData);
    if(isFirstPacket)
    {
        isFirstPacket = false;
        int fileNameLen = BitConverter.ToInt32(tempData, 0);
        string fileName = Encoding.ASCII.GetString(clientData, 4, fileNameLen);

        bWrite = new BinaryWriter(File.Open(receivedPath + fileName, FileMode.Append))
        bWrite.Write(tempData, 4 + fileNameLength, bytes_received - 4 - fileNamelength);
    }
    else
        bWrite.Write(tempData, 0, bytes_received);
}
while (bytes_received != 0);