在 C# 中以小块下载大文件

问题描述

我需要下载一些超过 25 MB 的文件，但我的网络只允许请求 25 MB 的文件.

I need to download some file which is more than 25 MB large, but my network only allow to request a file of 25 MB only.

我正在使用以下代码

  const long DefaultSize = 26214400;
    long Chunk = 26214400;
    long offset = 0;
    byte[] bytesInStream;
    public void Download(string url, string filename)
    {
        long size = Size(url);
        int blocksize = Convert.ToInt32(size / DefaultSize);
        int remainder = Convert.ToInt32(size % DefaultSize);
        if (remainder > 0) { blocksize++; }

        FileStream fileStream = File.Create(@"D:Download TEST" + filename);
        for (int i = 0; i < blocksize; i++)
        {
            if (i == blocksize - 1)
            {
                Chunk = remainder;

            }

            HttpWebRequest req = (HttpWebRequest)System.Net.WebRequest.Create(url);
            req.Method = "GET";
            req.AddRange(Convert.ToInt32(offset), Convert.ToInt32(Chunk+offset));
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
            // StreamReader sr = new StreamReader(resp.GetResponseStream());


            using (Stream responseStream = resp.GetResponseStream())
            {
                bytesInStream = new byte[Chunk];
                responseStream.Read(bytesInStream, 0, (int)bytesInStream.Length);
                // Use FileStream object to write to the specified file
                fileStream.Seek((int)offset, SeekOrigin.Begin);
                fileStream.Write(bytesInStream,0, bytesInStream.Length);
            }
            offset += Chunk;

        }
        fileStream.Close();

    }
    public long Size(string url)
    {
        System.Net.WebRequest req = System.Net.HttpWebRequest.Create(url);
        req.Method = "HEAD";
        System.Net.WebResponse resp = req.GetResponse();
        resp.Close();
        return resp.ContentLength;

    }

它正在正确地将内容写入磁盘，但内容不起作用

It is properly writing content on disk but content is not working

推荐答案

你应该在写之前检查读了多少，像这样(你不需要记住偏移量来查找，查找是自动的写):

You should check how much was read before write, something like this (and you don't need to remember the offset to seek, the seek is automatic when you write):

int read;
do
{
    read = responseStream.Read(bytesInStream, 0, (int)bytesInStream.Length);
    if (read > 0)
        fileStream.Write(bytesInStream, 0, read);
}
while(read > 0);

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