使用HttpClient的Async NancyFX - fbcdn的GetAsync返回403 forbidden？

Question

注意:我已经改变了这个问题,试图让它更多地指出问题所在.以下评论不再反映这个问题.

我想从fbcdn获取这个图像:

https://scontent.xx.fbcdn.net/v/t1.0-1/c15.0.50.50/p50x50/10354686_10150004552801856_220367501106153455_n.jpg?oh=6c801f82cd5a32fd6e5a4258ce00a314&oe=589AAD2F

浏览器得到它就好了.这是我的代码:

public class ReverseProxyController : NancyModule
{
    public ReverseProxyController()
    {
        Get["/", true] = async (parameters, ct) =>
        {
            var result = await GetResult(parameters, ct);
            return result;
        };
    }

    private async Task<Response> GetResult(dynamic parameters, CancellationToken ct)
    {
        var client = new HttpClient();
        string url = Request.Query["url"].Value.ToString();
        if (url == null) return null;

        client.DefaultRequestHeaders.Add("Access-Control-Allow-Origin", "*");
        client.DefaultRequestHeaders.Add("User-Agent",
            "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.71 Safari/537.36");
        client.DefaultRequestHeaders.Add("Upgrade-Insecure-Requests", "1");
        client.DefaultRequestHeaders.Add("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8");
        client.DefaultRequestHeaders.Add("Accept-Encoding", "gzip, deflate, sdch, br");
        client.DefaultRequestHeaders.Add("Accept-Language", "en-US,en;q=0.8,ru;q=0.6");
        var response = await client.GetAsync(url, ct);

        ct.ThrowIfCancellationRequested();


        switch (response.StatusCode)
        {
            case HttpStatusCode.OK:
                var stream = await response.Content.ReadAsStreamAsync();

                return Response.FromStream(stream, response.Content.Headers.ContentType != null
                    ? response.Content.Headers.ContentType.ToString()
                    : "application/octet-stream");

            default:
                return Response.AsText("\nError " + response.StatusCode);
        }
    }
}

我每次都收到403 Forbidden响应.我认为添加标题会使它工作但不会去.

此代码适用于其他主机上的其他图像,如下所示:

https://s-media-cache-ak0.pinimg.com/564x/ff/f0/c9/fff0c988a4516659d4009f60e0694cb6.jpg

Answer 1

问题出在 Nancy 请求的 URL 检索中，而不是使用HttpClient.

我假设您正在向 nancy 发送请求，例如：

http://localhost/?url= ...

因此对于 Facebook 来说，它将是：

http://localhost/?url=https://scontent.xx.fbcdn.net/v/t1.0-1/c15.0.50.50/p50x50/10354686_10150004552801856_220367501106153455_n.jpg?oh=6c801f82cd5a32fd6e5a4258ce 00a314&oe=589AAD2F

但这个 urlstring url = Request.Query["url"].Value.ToString();不完整并且缺少最后一部分 (&oe=589AAD2F)，因此服务器响应为 Forbidden。

这是演示问题的简单更改：

private async Task<Response> GetResult(dynamic parameters, CancellationToken ct)
{
    var client = new HttpClient();
    var req = Request.Url.ToString();
    var queryStart = req.IndexOf("url=");
    if (queryStart == -1)
        return Nancy.HttpStatusCode.BadRequest;

    var url = req.Substring(queryStart + 4);
    if (string.IsNullOrEmpty(url))
        return Nancy.HttpStatusCode.BadRequest;

    client.DefaultRequestHeaders.Add("Access-Control-Allow-Origin", "*");
    client.DefaultRequestHeaders.Add("User-Agent",
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.71 Safari/537.36");
    client.DefaultRequestHeaders.Add("Upgrade-Insecure-Requests", "1");
    client.DefaultRequestHeaders.Add("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8");
    client.DefaultRequestHeaders.Add("Accept-Encoding", "gzip, deflate, sdch, br");
    client.DefaultRequestHeaders.Add("Accept-Language", "en-US,en;q=0.8,ru;q=0.6");
    var response = await client.GetAsync(url, ct);

    ct.ThrowIfCancellationRequested();


    switch (response.StatusCode)
    {
        case System.Net.HttpStatusCode.OK:
            var stream = await response.Content.ReadAsStreamAsync();

            return Response.FromStream(stream, response.Content.Headers.ContentType != null
                ? response.Content.Headers.ContentType.ToString()
                : "application/octet-stream");

        default:
            return Response.AsText("\nError " + response.StatusCode);
    }
}

解决方案

实际上，我们可以在发送 URL 之前对其进行编码，Nancy 会自动为我们解码 URL，因此无需在服务器端进行任何更改。

HttpUtility.UrlEncode这是使用Applied on生成的链接示例

https://scontent.xx.fbcdn.net/v/t1.0-1/c15.0.50.50/p50x50/10354686_10150004552801856_220367501106153455_n.jpg?oh=6c801f82cd5a32fd6e5a4258ce00a314& oe=589AAD2F

结果：

https%3a%2f%2fscontent.xx.fbcdn.net%2fv%2ft1.0-1%2fc15.0.50.50%2fp50x50%2f10354686_10150004552801856_220367501106153455_n.jpg%3foh%3d6c801f82cd5 a32fd6e5a4258ce00a314%26oe%3d589AAD2F

对此特定链接的实际请求将是：

http://localhost:9876/?url=https%3a%2f%2fscontent.xx.fbcdn.net%2fv%2ft1.0-1%2fc15.0.50.50%2fp50x50%2f10354686_10150004552801856_220367501106153455_n.jpg%3foh% 3d6c801f82cd5a32fd6e5a4258ce00a314%26oe %3d589AAD2F

替代解决方案

在这种情况下，我个人更喜欢 POST 而不是 GET，所以这里是：

public class ReverseProxyController : NancyModule
{
    class ProxyRequest
    {
        public string Url { get; set; }
    }

    public ReverseProxyController()
    {
        Post["/", true] = async (parameters, ct) =>
        {
            var result = await GetResult(parameters, ct);
            return result;
        };
    }

    private async Task<Response> GetResult(dynamic parameters, CancellationToken ct)
    {
        var pReq = this.Bind<ProxyRequest>();
        var url = pReq.Url;
        if (string.IsNullOrEmpty(url))
            return null;

        var client = new HttpClient();
        client.DefaultRequestHeaders.Add("Access-Control-Allow-Origin", "*");
        client.DefaultRequestHeaders.Add("User-Agent",
            "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.71 Safari/537.36");
        client.DefaultRequestHeaders.Add("Upgrade-Insecure-Requests", "1");
        client.DefaultRequestHeaders.Add("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8");
        client.DefaultRequestHeaders.Add("Accept-Encoding", "gzip, deflate, sdch, br");
        client.DefaultRequestHeaders.Add("Accept-Language", "en-US,en;q=0.8,ru;q=0.6");
        var response = await client.GetAsync(url, ct);

        ct.ThrowIfCancellationRequested();


        switch (response.StatusCode)
        {
            case System.Net.HttpStatusCode.OK:
                var stream = await response.Content.ReadAsStreamAsync();

                return Response.FromStream(stream, response.Content.Headers.ContentType != null
                    ? response.Content.Headers.ContentType.ToString()
                    : "application/octet-stream");

            default:
                return Response.AsText("\nError " + response.StatusCode);
        }
    }
}