Download large file in small chunks in C# - asp.net

Question

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.
I am using following code
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;
}
It is properly writing content on disk but content is not working

Answer 1

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);

Answer 2

There is a similar SO questions that might help you
Segmented C# file downloader
and
How to open multiple connections to download single file?
Also this code project article
http://www.codeproject.com/Tips/307548/Resume-Suppoert-Downloading

Answer 3

Range is zero based and you should subtract 1 from upper bound.
request.Headers.Range = new System.Net.Http.Headers.RangeHeaderValue(offset, chunkSize + offset - 1);
I published correct code fragment at the following link:
https://stackoverflow.com/a/48019611/1099716

Answer 4

Akka streams can help download file in small chunks from a System.IO.Stream using multithreading. https://getakka.net/articles/intro/what-is-akka.html
The Download method will append the bytes to the file starting with long fileStart. If the file does not exist, fileStart value must be 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);
}
}
}