Xamarin.Forms 中的 HttpClient 抛出“发送请求时发生错误。”

Question

我使用 Xamarin.Forms 在 Windows(UWP) 和 Android 上开发多平台应用程序。此外，我使用在我工作的企业的 LAN 上运行的 ERP 中的 WebService。此 WebService 在 C# 中使用 WebRequest 的正常请求中可用，并且工作正常。但是 Xamarin 更喜欢使用带有异步方法的 HttpClient，有几个平台。 WebRequest 确实不适用于 android，它会将 UI 锁定在 UWP 中。

所以我在 MSDN 中创建了一个像它一样的 RestService 并且无法使请求响应。只要我将 WebRequest 请求放在 HttpClient 请求之前，它就可以正常工作，并且我会收到我想要的 XML。

如果我只放置 HttpClient 请求，它会抛出一个简单的错误 → HttpRequestException，只是（“发送请求时发生错误。”）。 InnerException 是 →“找不到与此错误代码关联的文本。证书颁发机构无效或不正确。”

目标是多平台，所以我认为需要 HttpClient，我已经尝试放置证书验证并在许多论坛上搜索但没有找到答案！！

希望有人可以帮助我！

使用 WebRequest 的请求

public string Request(string uri)
{
     string responseFromServer = "";
     ServicePointManager.ServerCertificateValidationCallback = delegate (object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; };

     WebRequest request = WebRequest.Create(uri);
     request.Credentials = new NetworkCredential(user, pswd);
     request.Method = "GET";

     HttpWebResponse response = (HttpWebResponse)request.GetResponse();

     if (((HttpWebResponse)response).StatusDescription == "OK")
     {
          Stream dataStream;
          using (dataStream = response.GetResponseStream())
          {
               StreamReader reader = new StreamReader(dataStream);
               responseFromServer = reader.ReadToEnd();
          }
     }
     response.Close();

     return responseFromServer;
}

我对 HttpClient 的请求

//Constructor 
public RestService()
{
     //Authentification for the request header
     user = "**";
     pswd = "*****";
     society= "*****";
     user = "%CP1252%" + Base64Encode(user + "@@" + society+ "@@00000");
     pswd = Base64Encode(pswd );
     var authData = string.Format("{0}{1}", user, mdp);

     client = new HttpClient();
     client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", authData);

     //Security protocol
     ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;
     ServicePointManager.ServerCertificateValidationCallback = delegate (object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; };
}

//Request method
public async Task<string> GetDatas(string url)
{
     Uri uri = new Uri(string.Format(url, string.Empty));
     string content = "";

     try
     {
          HttpResponseMessage response = await client.GetAsync(uri);
          response.EnsureSuccessStatusCode();
          content = await response.Content.ReadAsStringAsync();
     }
     catch (HttpRequestException e)
     {
          Console.WriteLine(e.Message);
     }
     return content;
}

我在 MockDataStore 中请求填写对象列表的位置

public async Task<IEnumerable<Operation>> GetItemsAsync(bool forceRefresh = false)
{
     GetOperations(); // call WebRequest Method

     await GetOperationsAsync(); // call HttpClient Method

     return await Task.FromResult(Operations);
}

尝试使用 GetStringAsync 自定义 httpclient 实例的默认标头

client = new HttpClient();

client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", authData);
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/xml"));
client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("Mozilla", "5.0"));
client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("AppleWebKit", "537.36"));
client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("Chrome", "91.0.4472.114"));
client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("Safari", "537.36"));
client.DefaultRequestHeaders.Host = "srverp:****";
client.DefaultRequestHeaders.AcceptEncoding.Add(new StringWithQualityHeaderValue("gzip"));
client.DefaultRequestHeaders.AcceptEncoding.Add(new StringWithQualityHeaderValue("deflate"));
client.DefaultRequestHeaders.AcceptEncoding.Add(new StringWithQualityHeaderValue("br"));
client.DefaultRequestHeaders.AcceptLanguage.Add(new StringWithQualityHeaderValue("fr-FR"));
client.DefaultRequestHeaders.Connection.Add("keep-alive");
client.DefaultRequestHeaders.Pragma.Add(new NameValueHeaderValue("no-cache"));

尝试使用 sendAsync 自定义请求标头

var request = new HttpRequestMessage()
{
     RequestUri = uri,
     Method = HttpMethod.Get,
     Headers = {
          { HttpRequestHeader.Authorization.ToString(), "Basic " + authData},
          { HttpRequestHeader.Accept.ToString(), "application/xml" }
     },
};

var task = client.SendAsync(request).ContinueWith((taskwithmsg) =>
{
     var response = taskwithmsg.Result;
     var tmp = response.Content.ReadAsStringAsync();
     content = tmp.Result;
});
task.Wait();

Answer 1

通过在 Handler 实例中添加 httpClient 的标头来解决问题，如下所示：

public HttpClient HttpclientAccount
{
     get
     {
          client = client ?? new HttpClient
          (
               new HttpClientHandler()
               {
                    ServerCertificateCustomValidationCallback = (sender, cert, chain, sslPolicyErrors) =>
                    {
                         //bypass
                         return true;
                    },
               }
               , false
          );

          // authentification headers
          client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", 
Convert.ToBase64String(Encoding.UTF8.GetBytes($"{user}:{mdp}")));
          return client;
     }
}

使用此方法，认证成功，反响良好！