HttpClient timeout - data response vs request completion

Question

I have an application that has to download a large payload (a few hundred MB), and in some circumstances on a device with a slow connection.

So I have this:

using (var client = new HttpClient())
{
    client.BaseAddress = new Uri(activeResource.Content);
    client.Timeout = TimeSpan.FromHours(6);
    binary = await client.GetByteArrayAsync(activeResource.Content);
}

I've set the Timeout to be 6 hours to be safe - in realistic terms we have seem instances where it has taken up to an hour to download.

My question is: Does this Timeout specify the timeout for the entire transaction, or is it the timeout while waiting for a response?

In other words, what I want is, to allow for up to 6 hours (or thereabouts) for the entire download to complete, but if, say there is no data coming through, due to, say a dropped connection, I don't want the user to have to wait 6 hours to find out.

And if it's the former, how do I set a short timeout for waiting for a response from the server, but allow a long time for the download to complete?

Answer 1

What ended up doing the trick was a variation of Jeevan Abi's answer

I ditched the TimeOut property altogether and put the read into a cancellable task.

{
    var downloadTimeout = TimeSpan.FromHours(6);
    var inactivityTimeout = TimeSpan.FromSeconds(30);

    using (var client = new HttpClient())
    {
        client.Timeout = Timeout.InfiniteTimeSpan;

        var cancellationTokenSource = new CancellationTokenSource(downloadTimeout);
        using (var response = await client.GetAsync(resource.ResourceUrl, HttpCompletionOption.ResponseHeadersRead, cancellationTokenSource.Token))
        {
            response.EnsureSuccessStatusCode();
            
            using (var contentStream = await response.Content.ReadAsStreamAsync())
            {
                using (var fileStream = new FileStream(tempFile, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true))
                {
                    var buffer = new byte[8192];
                    int bytesRead;
                    long totalBytesRead = 0;

                    while ((bytesRead = await ReadDataAsync(contentStream, buffer, 0, buffer.Length, inactivityTimeout, cancellationTokenSource.Token)) > 0)
                    {
                        await fileStream.WriteAsync(buffer, 0, bytesRead);
                        totalBytesRead += bytesRead;
                    }
                }
            }

        }
    }
}


private async Task<int> ReadDataAsync(Stream stream, byte[] buffer, int offset, int count, TimeSpan timeout, CancellationToken cancelToken)
{
    var readTask = Task.Run(() => stream.ReadAsync(buffer, offset, count), cancelToken);

    if (await Task.WhenAny(readTask, Task.Delay(timeout)) == readTask)
    {
        return await readTask;
    }
    else
    {
        throw new TimeoutException("Connection timed out during download.");
    }
}