Develop Reference

C# in UWP: HTTP Get returns error while the browser returns a correct value

I have a UWP app written in C#.
For some specific users (i.e. specific PCs), the app is not able to perform HTTP requests.
Those PCs are not under any VPN, they turned off any firewall or antivirus, they tried with several connections (e.g. home router, phone hotspot, public wifi, etc.), always with the same result.
Opening a browser and browsing to
https://ltbackend.azurewebsites.net/diagnostic/ping
they are able to see the correct page (actually, a plain text "OK").
But if they use the app (which performs an HTTP GET call using C#), this one fails.
This is the code in C# that we use:
string pingUrl = "https://ltbackend.azurewebsites.net/diagnostic/ping";
HttpRequestMessage req = new HttpRequestMessage(HttpMethod.Get, pingUrl);
using (HttpClient httpClient = new HttpClient())
{
try
{
using (HttpResponseMessage response = await httpClient.SendAsync(req))
{
string stringRes = await response.Content.ReadAsStringAsync();
HttpStatusCode respCode = response.StatusCode;
// .... our biz logic with stringRes and respCode...
}
}
catch (HttpRequestException e)
{
// the ping request for those users throws this exception...
// the error message is "An error occurred while sending the request."
}
}

But if they use the app (which performs an HTTP GET call using C#), this one fails.
I have run your code within UWP platform, it could work well and return 'ok' string. But it looks you used HttpClient under System.Net.Http namespace, and it often used in cross-platform, such as xamarin app.
For sending get request within UWP, we suggest you use Windows.Web.Http.HttpClient. The following is simple get method you could refer to.
Windows.Web.Http.HttpClient httpClient = new Windows.Web.Http.HttpClient();
//Add a user-agent header to the GET request.
var headers = httpClient.DefaultRequestHeaders;
//The safe way to add a header value is to use the TryParseAdd method and verify the return value is true,
//especially if the header value is coming from user input.
string header = "ie";
if (!headers.UserAgent.TryParseAdd(header))
{
throw new Exception("Invalid header value: " + header);
}
header = "Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; WOW64; Trident/6.0)";
if (!headers.UserAgent.TryParseAdd(header))
{
throw new Exception("Invalid header value: " + header);
}
Uri requestUri = new Uri("https://ltbackend.azurewebsites.net/diagnostic/ping");
//Send the GET request asynchronously and retrieve the response as a string.
Windows.Web.Http.HttpResponseMessage httpResponse = new Windows.Web.Http.HttpResponseMessage();
string httpResponseBody = string.Empty;
try
{
//Send the GET request
httpResponse = await httpClient.GetAsync(requestUri);
httpResponse.EnsureSuccessStatusCode();
httpResponseBody = await httpResponse.Content.ReadAsStringAsync();
}
catch (Exception ex)
{
httpResponseBody = "Error: " + ex.HResult.ToString("X") + " Message: " + ex.Message;
}
For more info please refer HttpClient document.

If you are using latest version of .NET try once using WebClient instead of HttpClient.
Ref: https://learn.microsoft.com/en-us/dotnet/api/system.net.webclient.downloadstringasync?view=net-5.0
string pingUrl = "https://ltbackend.azurewebsites.net/diagnostic/ping";
var client = new WebClient();
string stringRes = await client.DownloadStringTaskAsync(pingUrl);

How can I call a web api in c# using HttpClient?

So I am trying to call a api in my C# method and am not getting the response that I would be getting, if I called the api using postman or insomia.
public static async Task GetObject()
{
var httpClient = new HttpClient();
//var t = await httpClient.GetStringAsync("https://ipapi.co/json/");
var y = await httpClient.GetAsync("https://ipapi.co/json/");
var o = await y.Content.ReadAsStringAsync();
var j = y.Content.ReadAsStringAsync();
}
The api is getting my request but its not returning the right result. You should be getting this result. Click on this https://ipapi.co/json/
What am getting is this
{
"error":true,
"reason":"RateLimited",
"message":"Sign up for IP Address Location API # https://ipapi.co"
}
But I don't get it, when am using postman

You need to add the user-agent header.
httpClient.DefaultRequestHeaders.Add("User-Agent", "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/14.0.835.202 Safari/535.1");

Better to Use xNet.dll or Leaf.xNet.dll libraries
Or restsharp one
Google them
I'm also new If ur interesting to contact me
Discord Cyx.#4260

C# WinApp throws (403) Fobidden exception while sending HTTP/GET request

I have ASP.NET website. When I call the url 'http://example.org/worktodo.ashx' from browser it works ok.
I have created one android app and if I call the above url from android app then also it works ok.
I have created windows app in C# and if I call the above url from that windows app then it fails with error 403 forbidden.
Following is the C# code.
try
{
bool TEST_LOCAL = false;
//
// One way to call the url
//
WebClient client = new WebClient();
string url = TEST_LOCAL ? "http://localhost:1805/webfolder/worktodo.ashx" : "http://example.org/worktodo.ashx";
string status = client.DownloadString(url);
MessageBox.Show(status, "WebClient Response");
//
// Another way to call the url
//
WebRequest request = WebRequest.Create(url);
request.Method = "GET";
request.Headers.Add("Accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8");
request.Headers.Add("Connection:keep-alive");
request.Headers.Add("User-Agent:Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.133 Safari/537.36");
request.Headers.Add("Upgrade-Insecure-Requests:1");
request.Headers.Add("Accept-Encoding:gzip, deflate, sdch");
request.ContentType = "text/json";
WebResponse response = request.GetResponse();
string responseString = new System.IO.StreamReader(response.GetResponseStream()).ReadToEnd();
MessageBox.Show(responseString, "WebRequest Response");
}
catch (WebException ex)
{
string error = ex.Status.ToString();
}
The exception thrown is:
The remote server returned an error: (403) Forbidden.
StatusCode value is 'Forbidden'
StatusDescription value is 'ModSecurity Action'
Following is android app code (uses org.apache.http library):
Handler handler = new Handler() {
Context ctx = context; // save context for use inside handleMessage()
#SuppressWarnings("deprecation")
public void handleMessage(Message message) {
switch (message.what) {
case HttpConnection.DID_START: {
break;
}
case HttpConnection.DID_SUCCEED: {
String response = (String) message.obj;
JSONObject jobjdata = null;
try {
JSONObject jobj = new JSONObject(response);
jobjdata = jobj.getJSONObject("data");
String status = URLDecoder.decode(jobjdata.getString("status"));
Toast.makeText(ctx, status, Toast.LENGTH_LONG).show();
} catch (Exception e1) {
Toast.makeText(ctx, "Unexpected error encountered", Toast.LENGTH_LONG).show();
// e1.printStackTrace();
}
}
}
}
};
final ArrayList<NameValuePair> params1 = new ArrayList<NameValuePair>();
if (RUN_LOCALLY)
new HttpConnection(handler).post(LOCAL_URL, params1);
else
new HttpConnection(handler).post(WEB_URL, params1);
}
Efforts / Research done so far to solve the issue:
I found following solutions that fixed 403 forbidden error for them but that could not fix my problem
Someone said, the file needs to have appropriate 'rwx' permissions set, so, I set 'rwx' permissions for the file
Someone said, specifying USER-AGENT worked, I tried (ref. Another way to call)
Someone said, valid header fixed it - used Fiddler to find valid header to be set, I used Chrome / Developer Tools and set valid header (ref.
another way to call)
Someone configured ModSecurity to fix it, but, I don't have ModSecurity installed for my website, so, not an option for me
Many were having problem with MVC and fixed it, but, I don't use MVC, so those solutions are not for me
ModSecurity Reference manual says, to remove it from a website, add <modules><remove name="ModSecurityIIS" /></modules> to web.config. I did but couldn't fix the issue
My questions are:
Why C# WinApp fails where as Android App succeeds?
Why Android App doesn't encounter 'ModSecurity Action' exception?
Why C# WinApp encounter 'ModSecurity Action' exception?
How to fix C# code?
Please help me solve the issue. Thank you all.

I found the answer. Below is the code that works as expected.
bool TEST_LOCAL = false;
string url = TEST_LOCAL ? "http://localhost:1805/webfolder/worktodo.ashx" : "http://example.org/worktodo.ashx";
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
request.Method = "GET";
request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.133 Safari/537.36";
request.ContentType = "text/json";
WebResponse response = request.GetResponse();
string responseString = new System.IO.StreamReader(response.GetResponseStream()).ReadToEnd();
MessageBox.Show(responseString, "WebRequest Response");
NOTE: requires using System.Net;

How do I make a case request from the Pacer.gov API?

I am trying to make a request to an API called Pacer.gov. I'm expecting a file to be returned, but I'm not getting it. Can someone help me with what I'm missing?
So my C# Rest call looks like this:
(The variable PacerSession is the authentication cookie I got (with help from #jonathon-reinhart); read more about that here: How do I use RestSharp to POST a login and password to an API?)
var client = new RestClient("https://pcl.uscourts.gov/dquery");
client.CookieContainer = new System.Net.CookieContainer();
//var request = new RestRequest("/dquery", Method.POST);
var request = new RestRequest(Method.POST);
request.AddParameter("download", "1");
request.AddParameter("dl_fmt", "xml");
request.AddParameter("party", "Moncrief");
request.AddHeader("user-agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36");
request.AddHeader("content-type", "text/plain; charset=utf-8");
request.AddHeader("accept", "*/*");
request.AddHeader("accept-encoding", "gzip, deflate, sdch");
request.AddHeader("accept-language", "en-US,en;q=0.8");
request.AddHeader("cookie", "PacerSession=" + PacerSession);
IRestResponse response = client.Execute(request);
If I just type the URL https://pcl.uscourts.gov/dquery?download=1&dl_fmt=xml&party=Moncrief into Chrome, I get back an XML file. When I look at the IRestResponse, I don't see anything that looks like a file. Is there something wrong with my request or am I getting the file back and just need to know how to retrieve it?
Here's part of the file I get back if I use the URL directly in the browser:
Here's what I see in VS when I debug it and look at the IRestResponse variable:
UPDATE - 6/3/16
Received this response from Pacer tech support:
In the Advanced REST Client, you will see a HTTP 302 response (a redirect to another page). In a normal browser, the redirect is automatically followed without the user seeing anything (even on the URL in the browser).
The ARC does not automatically follow that redirect to the target page.
You can see in the header of the response the target URL that has the results.
If you manually cut and paste this URL to the ARC as a HTTP GET request, you will get the XML results. I have never used C#, but there is usually a property associated with web clients that will force the client to follow the redirect.
I tried adding this:
client.FollowRedirects = true;
but I'm still not seeing an xml file when I debug this code:
IRestResponse response = client.Execute(request);
How do I get the file? Is there something I have to do to get the file from the URL it's being redirected to?

There's one major problem with your code. You're only carrying one of the three cookies that checp-pacer-passwd.pl returns. You need to preserve all three. The following code is a possible implementation of this, with some notes afterwards.
public class PacerClient
{
private CookieContainer m_Cookies = new CookieContainer();
public string Username { get; set; }
public string Password { get; set; }
public PacerClient(string username, string password)
{
this.Username = username;
this.Password = password;
}
public void Connect()
{
var client = new RestClient("https://pacer.login.uscourts.gov");
client.CookieContainer = this.m_Cookies;
RestRequest request = new RestRequest("/cgi-bin/check-pacer-passwd.pl", Method.POST);
request.AddParameter("loginid", this.Username);
request.AddParameter("passwd", this.Password);
IRestResponse response = client.Execute(request);
if (response.Cookies.Count < 1)
{
throw new WebException("No cookies returned.");
}
}
public XmlDocument SearchParty(string partyName)
{
string requestUri = $"/dquery?download=1&dl_fmt=xml&party={partyName}";
var client = new RestClient("https://pcl.uscourts.gov");
client.CookieContainer = this.m_Cookies;
var request = new RestRequest(requestUri);
IRestResponse response = client.Execute(request);
if (!String.IsNullOrEmpty(response.Content))
{
XmlDocument result = new XmlDocument();
result.LoadXml(response.Content);
return result;
}
else return null;
}
}
It's easiest to just keep a hold of the CookieContainer throughout the entire time you're working with Pacer. I wrapped the functionality into a class, just to make it a little easier to package up with this answer, but you can implement it however you want. I didn't put in any real error checking, so you probably want to check that response.ResponseUri is actually the search page and not the logon page, and that the content is actually well-formed XML.
I've tested this using my own Pacer account, like so:
PacerClient client = new PacerClient(Username, Password);
client.Connect();
var document = client.SearchParty("Moncrief");

C# HttpClient.SendAsync always returns 404 but URL works in browser

I am developing an C# console application for testing whether a URL is valid or not. It works well for most of URLs. But we found that there are some cases the application always got 404 response from target site but the URLs actually work in the browser. And those URLs also works when I tried them in the tools such as DHC (Dev HTTP Client).
In the beginning, I though that this could be the reason of not adding right headers. But after tried using Fiddler to compose a http request with same headers, it works in Fiddler.
So what's wrong with my code? Is there any bug in .NET HttpClient?
Here are the simplified code of my test application:
class Program
{
static void Main(string[] args)
{
var urlTester = new UrlTester("http://www.hffa.it/short-master-programs/fashion-photography");
Console.WriteLine("Test is started");
Task.WhenAll(urlTester.RunTestAsync());
Console.WriteLine("Test is stoped");
Console.ReadKey();
}
public class UrlTester
{
private HttpClient _httpClient;
private string _url;
public UrlTester(string url)
{
_httpClient = new HttpClient
{
Timeout = TimeSpan.FromMinutes(1)
};
// Add headers
_httpClient.DefaultRequestHeaders.Add("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2490.80 Safari/537.36");
_httpClient.DefaultRequestHeaders.Add("Accept-Encoding", "gzip,deflate,sdch");
_httpClient.DefaultRequestHeaders.Add("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8");
_httpClient.DefaultRequestHeaders.Add("Accept-Language", "sv-SE,sv;q=0.8,en-US;q=0.6,en;q=0.4");
_url = url;
}
public async Task RunTestAsync()
{
var httpRequestMsg = new HttpRequestMessage(HttpMethod.Get, _url);
try
{
using (var response = await _httpClient.SendAsync(httpRequestMsg, HttpCompletionOption.ResponseHeadersRead))
{
Console.WriteLine("Response: {0}", response.StatusCode);
}
}
catch (HttpRequestException e)
{
Console.WriteLine(e.InnerException.Message);
}
}
}
}

This appears to be an issue with the accepted languages. I got a 200 response when using the following Accept-Language header value
_httpClient.DefaultRequestHeaders.Add("Accept-Language", "en-GB,en-US;q=0.8,en;q=0.6,ru;q=0.4");
p.s. I assume you know in your example _client should read _httpClient in the urlTester constructor or it wont build.

Another possible cause of this problem is if the url you are sending is over approx 2048 bytes long. At that point the content (almost certainly the query string) can become truncated and this in turn means that it may not be matched correctly with a server side route.
Although these urls were processed correctly in the browser, they also failed using the get command in power shell.
This issue was resolved by using a POST with key value pairs instead of using a GET with a long query string.