3

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。

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;

    }

它可以在磁盘上正确写入内容，但内容无法正常工作

4

4 回答 4

4

您应该检查在写入之前读取了多少，如下所示（并且您不需要记住要查找的偏移量，写入时查找是自动的）：

int read;
do
{
    read = responseStream.Read(bytesInStream, 0, (int)bytesInStream.Length);
    if (read > 0)
        fileStream.Write(bytesInStream, 0, read);
}
while(read > 0);
于 2012-11-26T14:03:24.367 回答
1

有一个类似的 SO questions 可能对您有帮助 Segmented C# file downloader

和

如何打开多个连接以下载单个文件？

还有这个代码项目文章 http://www.codeproject.com/Tips/307548/Resume-Suppoert-Downloading

于 2012-11-26T15:38:40.303 回答
0

范围从零开始，您应该从上限中减去 1。

request.Headers.Range = new System.Net.Http.Headers.RangeHeaderValue(offset, chunkSize + offset - 1);

我在以下链接中发布了正确的代码片段： https ://stackoverflow.com/a/48019611/1099716

于 2017-12-29T08:31:53.537 回答
0

Akka 流可以帮助使用多线程从 System.IO.Stream 下载小块文件。https://getakka.net/articles/intro/what-is-akka.html

Download 方法会将字节追加到以 long fileStart 开头的文件中。如果文件不存在，fileStart 值必须为 0。

using Akka.Actor;
using Akka.IO;
using Akka.Streams;
using Akka.Streams.Dsl;
using Akka.Streams.IO;

private static Sink<ByteString, Task<IOResult>> FileSink(string filename)
{
    return Flow.Create<ByteString>()
        .ToMaterialized(FileIO.ToFile(new FileInfo(filename), FileMode.Append), Keep.Right);
}

private async Task Download(string path, Uri uri, long fileStart)
{
    using (var system = ActorSystem.Create("system"))
    using (var materializer = system.Materializer())
    {
       HttpWebRequest request = WebRequest.Create(uri) as HttpWebRequest;
       request.AddRange(fileStart);

       using (WebResponse response = request.GetResponse())
       {
           Stream stream = response.GetResponseStream();

           await StreamConverters.FromInputStream(() => stream, chunkSize: 1024)
               .RunWith(FileSink(path), materializer);
       }
    }
}
于 2018-10-17T10:33:39.173 回答