如何在c#中将大文件拆分成块? [英] How to split a large file into chunks in c#?

问题描述

我正在通过网络制作一个简单的文件传输发送方和接收方应用程序.到目前为止，我所知道的是发送方将文件转换为字节数组并将该数组的块发送给接收方.

I'm making a simple file transfer sender and receiver app through the wire. What I have so far is that the sender converts the file into a byte array and sends chunks of that array to the receiver.

这适用于最大 256mb 的文件，但是这一行会抛出系统内存不足"以上内容除外:

This works with file of up to 256mb, but this line throws a "System out of memory" exception for anything above:

byte[] buffer = StreamFile(fileName); //This is where I convert the file

我正在寻找一种方法以分块读取文件，然后写入该块，而不是将整个文件加载到 byte 中.如何使用 FileStream 执行此操作?

I'm looking for a way to read the file in chunks then write that chunk instead of loading the whole file into a byte. How can I do this with a FileStream?

抱歉，这是我目前的蹩脚代码:

Sorry, heres my crappy code so far:

    private void btnSend(object sender, EventArgs e)
    {
        Socket clientSock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);


        byte[] fileName = Encoding.UTF8.GetBytes(fName); //file name
        byte[] fileData = null;
        try
        {
             fileData = StreamFile(textBox1.Text); //file
        }
        catch (OutOfMemoryException ex)
        {
            MessageBox.Show("Out of memory");
            return;
        }

        byte[] fileNameLen = BitConverter.GetBytes(fileName.Length); //length of file name
        clientData = new byte[4 + fileName.Length + fileData.Length];
        fileNameLen.CopyTo(clientData, 0);
        fileName.CopyTo(clientData, 4);
        fileData.CopyTo(clientData, 4 + fileName.Length);
        clientSock.Connect("172.16.12.91", 9050);
        clientSock.Send(clientData, 0, 4 + fileName.Length, SocketFlags.None);

        for (int i = 4 + fileName.Length; i < clientData.Length; i++)
        {
            clientSock.Send(clientData, i, 1 , SocketFlags.None);
        }

        clientSock.Close();
    }

这是我收到的方式(代码来自教程)

And here's how I receive (the code was from a tutorial)

   public void ReadCallback(IAsyncResult ar)
    {

        int fileNameLen = 1;
        String content = String.Empty;
        StateObject state = (StateObject)ar.AsyncState;
        Socket handler = state.workSocket;
        int bytesRead = handler.EndReceive(ar);
        if (bytesRead > 0)
        {

            if (flag == 0)
            {
                Thread.Sleep(1000);
                fileNameLen = BitConverter.ToInt32(state.buffer, 0);
                string fileName = Encoding.UTF8.GetString(state.buffer, 4, fileNameLen);
                receivedPath = fileName;
                flag++;
            }
                if (flag >= 1)
                {
                    BinaryWriter writer = new BinaryWriter(File.Open(receivedPath, FileMode.Append));
                    if (flag == 1)
                    {
                        writer.Write(state.buffer, 4 + fileNameLen, bytesRead - (4 + fileNameLen));
                        flag++;
                    }
                    else
                        writer.Write(state.buffer, 0, bytesRead);
                        writer.Close();
                        handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
                        new AsyncCallback(ReadCallback), state);
                }
        }
        else
        {
            Invoke(new MyDelegate(LabelWriter));
        }

    }

我真的很想知道如何分块读取文件，这样我就不需要将其转换为字节.

I just really want to know how I can read the file in chunks so that I dont need to convert it to a byte.

感谢到目前为止的回复，我想我开始明白了:D

Thanks for the responses so far, I think I'm starting to get it :D

推荐答案

只需使用小缓冲区(我倾向于使用 16K 之类的东西)重复调用 Read.请注意，对 Read 的调用最终可能会读取比您请求的较小的数量.如果您使用固定的块大小并且需要将整个块保存在内存中，那么您当然可以只使用该大小的数组.

Just call Read repeatedly with a small buffer (I tend to use something like 16K). Note that the call to Read may end up reading a smaller amount than you request. If you're using a fixed chunk size and need the whole chunk in memory, you could just use an array of that size of course.

在不知道如何发送文件的情况下，很难就如何构建代码给出很多建议，但它可能是这样的:

Without knowing how you're sending the file, it's hard to give much advice about how to structure your code, but it could be something like this:

byte[] chunk = new byte[MaxChunkSize];
while (true)
{
    int index = 0;
    // There are various different ways of structuring this bit of code.
    // Fundamentally we're trying to keep reading in to our chunk until
    // either we reach the end of the stream, or we've read everything we need.
    while (index < chunk.Length)
    {
        int bytesRead = stream.Read(chunk, index, chunk.Length - index);
        if (bytesRead == 0)
        {
            break;
        }
        index += bytesRead;
    }
    if (index != 0) // Our previous chunk may have been the last one
    {
        SendChunk(chunk, index); // index is the number of bytes in the chunk
    }
    if (index != chunk.Length) // We didn't read a full chunk: we're done
    {
        return;
    }
}

如果我更清醒，我可能会找到一种更易读的方式来写这篇文章，但现在就可以了.一种选择是从中间部分提取另一种方法:

If I was more awake I'd probably find a more readable way of writing this, but it'll do for now. One option is to extract another method from the middle section:

// Attempts to read an entire chunk into the given array; returns the size of
// chunk actually read.
int ReadChunk(Stream stream, byte[] chunk)
{
    int index = 0;
    while (index < chunk.Length)
    {
        int bytesRead = stream.Read(chunk, index, chunk.Length - index);
        if (bytesRead == 0)
        {
            break;
        }
        index += bytesRead;
    }
    return index;
}

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