HttpClient doesn't redirect even when AllowAutoRedirect = true

问题

I'm trying to parse a wikispaces page but I'm not able to get the actual page. I'm not sure if its a HttpClient bug or some missing configuration.

This is my code:

HttpClientHandler handler = new HttpClientHandler();
handler.AllowAutoRedirect = true;
_httpClient = new HttpClient(handler);

HttpResponseMessage response = await _httpClient
    .GetAsync("http://medivia.wikispaces.com/Monsters");

When i run that code I get the StatusCode 302 and get sent to https://session.wikispaces.com/1/auth/auth?authToken=token. I expect the HttpClient to follow a 302 because I have AllowAutoRedirect = true.

This is the first time I've encountered this problem. It works fine with Postman and RestClient which is part of RestSharp.

回答1:

The reason the HttpClient isn't redirecting properly is because the site is redirecting you to HTTPS and then back to HTTP. A quick fix is to GET https://medivia.wikispaces.com/Monsters instead, which is a better idea anyhow:

HttpResponseMessage response = await _httpClient.GetAsync("https://medivia.wikispaces.com/Monsters");
// Works fine! :)

I was curious why it didn't work the first way, so I dug a little deeper. If you watch the network trace in a browser or a network client, this is what happens:

GET http://medivia.wikispaces.com/Monsters
302 https://session.wikispaces.com/1/auth/auth?authToken=token
302 http://medivia.wikispaces.com/Monsters?redirectToken=token

That 302 from an encrypted (HTTPS) connection to an unencrypted one is causing the HttpClientHandler to stop automatically following. From what I can tell, this is a security quirk of the Windows implementation of HttpClientHandler, because the Unix one didn't seem to care about the HTTPS->HTTP redirect in my informal testing.

来源：https://stackoverflow.com/questions/42405183/httpclient-doesnt-redirect-even-when-allowautoredirect-true