WebRequest.AddRange 不返回正确的 Content-Length

Question

我想部分下载url中的文件。但它返回了错误的内容大小，我不知道为什么。远程文件有Accept-Ranges=bytes如何解决？

long start = 536871935, end = 805306878;
string url = "http://ipv4.download.thinkbroadband.com/1GB.zip";
var request = (HttpWebRequest)WebRequest.Create(url);
request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.102 Safari/537.36 Edge/18.18362";
request.AllowAutoRedirect = true;
request.Method = "GET";
request.Timeout = 5000;
request.ReadWriteTimeout = 3000;
request.AddRange(start, end);
var response = (HttpWebResponse)request.GetResponse();
if (response.ContentLength != end - start + 1)
throw new Exception(string.Format("Returned content size is wrong; start={0}, end={1}, returned = {2}, shouldbe = {3}",
start, end, response.ContentLength, end - start + 1));

中发生类型为"System.exception"的异常Downloadmanager.exe，但未在用户代码中处理

附加信息：返回的内容大小错误起始=536871935，结束=805306878，返回=536869889，应为=268434944

Answer 1

我使用的是HttpClient而不是HttpWebRequest(按照Microsoft的建议(，没有这样的问题。

public class Program
{
private static readonly HttpClient client = new HttpClient();
static async Task Main(string[] args)
{
long start = 536871935, end = 805306878;
try
{
using (HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, "http://ipv4.download.thinkbroadband.com/1GB.zip"))
{
request.Headers.Range = new RangeHeaderValue(start, end);
using (HttpResponseMessage response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead))
{
response.EnsureSuccessStatusCode();
Console.WriteLine(response.Content.Headers.ContentLength);
Console.WriteLine(end - start + 1);
}
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.ReadKey();
}
}

控制台输出

268434944
268434944