C# System.Net.WebException: 'Too many automatic redirections were attempted.'

Question

I want to download a 68kb zip file using webclient and I have the error: C# System.Net.WebException: 'Too many automatic redirections were attempted.'

About this post is a duplicated post: The solution explained in: Why i'm getting exception: Too many automatic redirections were attempted on webclient? Don't work to make my code below works and download the zip file. How Can I edit to explain better ?

My code:

var url_from = "http://www1.caixa.gov.br/listaweb/Lista_imoveis_RJ.zip";
            var _to = @"F:\folder\file.zip";

            using (var client = new WebClient())
            {
                client.DownloadFile(url_from, _to);
            }

I tried Async ways too but it was generated empty zip file. Like this: How do I download zip file in C#? and this: How can I download a ZIP file from a URL using C#?

The duplicate *is* a duplicate. Redirections have nothing to do with async or the type of the file. The *server* sent so many 302 responses to your client that it gave up once it reached the redirection limit. Perhaps there's a bug in the server, or you need to provide credentials — Panagiotis Kanavos, Aug 01 '18 at 09:39
If you try that link in your browser you'll see that you are redirected to an `https:` URL. Try that instead of `http:`. All sites are switching to `https:` for security reasons, so you might as well avoid the wasted `http:` call — Panagiotis Kanavos, Aug 01 '18 at 09:44
I tried with HTTPS and geve the same error. System.Net.WebException: 'Excessive number of automatic redirect attempts.' — Adriano Frota, Aug 01 '18 at 16:33
It's a server error and a shamefully insecure implementation - both HTTPS and HTTP requests are redirected to HTTP with the `security=true` cookie added. Good thing no hacker will ever think of that, to intercept and alter the contents of that zip file! — Panagiotis Kanavos, Aug 02 '18 at 07:24

score 3 · Accepted Answer · answered Aug 02 '18 at 07:38

This is caused by a bad server implementation. If you use Fiddler, you'll see that the server redirects both HTTPS and HTTP connections to the same HTTP url, adding a security=true cookie.

Calling over HTTP is particulary funny :

The first HTTP redirects to an HTTPS URL
The HTTPS redirects back to the original HTTP with the security=true cookie
If the cookie isn't there, the loop starts again

This means that :

There's no security. Anything can intercept that call and alter or replace the contents of the file. Hope you don't try to download this file over WiFi!
The server will cause an infinite redirection loop unless you store the cookie or add it yourself.

WebClient can't store cookies. It's an obsolete class created back when downloading pages and files was all that's needed. All of its functionality and much more is provided by the HttpClient class.

In this case though, you can add the cookie as a header yourself and avoid the redirections, and still download the file over HTTPS

WebClient is an obsolete class. It was created for simple file and page requests and

var url_from = "https://www1.caixa.gov.br/listaweb/Lista_imoveis_RJ.zip";
using (var client = new System.Net.WebClient())
{
    client.Headers.Add(System.Net.HttpRequestHeader.Cookie, "security=true");
    client.DownloadFile(url_from, _to);
}

This will result in a single call and download the file over HTTP

Thank you very much. Istead of the post appears duplicated your sugestion was simple and Ill help a lot. Thanks. Working after adition of {client.Headers.Add} line code. Great analisys ! — Adriano Frota, Aug 03 '18 at 00:25

C# System.Net.WebException: 'Too many automatic redirections were attempted.'

1 Answers1