I'm using a .Net MVC application as a simplified web service.
I've got an async method that I call:
public void RunQueue()
{
QueueDelegate queue = new QueueDelegate(Queue);
AsyncCallback completedCallback = new AsyncCallback(QueueCompleteCallback);
lock (_sync)
{
if (!queueIsRunning)
{
AsyncOperation async = AsyncOperationManager.CreateOperation(null);
queue.BeginInvoke(QueueCompleteCallback, async);
queueIsRunning = true;
}
}
}
and the hope is that when I call it, it starts the queue and then lets the user continue on with their day (they'll get an email when the queue's done).
As it stands right now, everything works fine except that instead of letting the user continue on, the webpage calling the "web service" just hangs and the request eventually times out.
How do I build an HttpWebResponse and send it back to the other server so that the user can continue on?
I've tried having it return things other than "void" but that doesn't do much.
Here's the Controller that's calling it.
public ActionResult StartQueue()
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://localhost:2394/Home/RunQueue/");
HttpWebResponse response;
string r = "";
try
{
response = (HttpWebResponse)request.GetResponse();
Stream stream = response.GetResponseStream();
StreamReader reader = new StreamReader(stream);
r = reader.ReadToEnd();
}
catch (WebException ex) // A WebException is not fatal. Record the status code.
{
response = (HttpWebResponse)ex.Response;
if (response != null) // timeout
{
r = response.StatusCode.ToString();
}
}
ViewData["message"] = r;
return View();
}
What is the QueueDelegate class? My guess would be that the request is waiting for the other thread to complete (maybe something like Thread.Join()?). I don't think sending a response is the solution you want - I'd suggest either finding a way to spawn a thread that is disconnected from the current request so that it ends naturally, or move the logic out completely into something like a Windows Service.
Hosting your long-running processes in the web context will be complicated at best :(
Related
I am calling UploadStringTaskAsync on a restful Web API 2 post method I wrote and it is failing with no exceptions. If I change the call to be UploadString, it works as expected. I've tried a number of different approaches. With UploadStringTaskAsync attempt Fiddler does show the post being issued but with a content-length mismatch (see below). I am running this call from a class library included in a test console app. .Net 4.5.2 So far just running in debug mode from VS 2015. here's my code:
private async Task PostLoggingItem(SmgLoggingItem loggingItem)
{
try
{
//using (WebClient client = new WebClient())
//{
//WebClient client = new WebClient();
const string authToken = "mytoken";
loggingItem.AuthToken = Encryptor.GenerateSecurityToken(authToken);
client.Encoding = Encoding.UTF8;
//client.Credentials = CredentialCache.DefaultNetworkCredentials;
//client.UseDefaultCredentials = true;
client.Credentials = new NetworkCredential("user","mypwd","mydom");
// set content type to JSon
client.Headers.Add("Content-Type", "application/json");
var jsonItem = JsonConvert.SerializeObject(loggingItem);
var response = await client.UploadStringTaskAsync(new Uri(ConfigurationManager.AppSettings["WebLogAPI"]), jsonItem);
//string response = client.UploadString(new Uri(ConfigurationManager.AppSettings["SMGWebLogAPI"]), "POST", jsonItem);
string result = JsonConvert.DeserializeObject<string>(response);
if (result != "ok")
{
await SMTPSendEmailAsync.SendEmail("brownp#spectrummg.com", "logging failed WebAPI call",
"Error return from WebAPI call in PostLoggingItem");
}
return;
//}
}
catch (Exception e)
{
await SMTPSendEmailAsync.SendEmail("brownp#spectrummg.com", "logging failed WebAPI call",
"Exception in PostLoggingItem" + e.Message);
return;
}
}
You can see where I have commented out the working UploadString call. Also, I have a theory problem related to "lifetime" of the WebClient object, so played around with creating it in the method (see commented using), but now create it with the object instantiation to which method PostLoggingItem belongs.
here's fiddler:
I'd sure like to know why the Async does not work. Also, I have used aync methods and awaits all the way up the call tree - to no avail.
I previously had a small VBScript that would test if a specific website was accessible by sending a GET request. The script itself was extremely simple and did everything I needed:
Function GETRequest(URL) 'Sends a GET http request to a specific URL
Dim objHttpRequest
Set objHttpRequest = CreateObject("MSXML2.XMLHTTP.3.0")
objHttpRequest.Open "GET", URL, False
On Error Resume Next 'Error checking in case access is denied
objHttpRequest.Send
GETRequest = objHttpRequest.Status
End Function
I now want to include this sort of functionality in an expanded C# application. However I've been unable to get the same results my previous script provided.
Using code similar to what I've posted below sort of gets me a proper result, but fails to run if my network connection has failed.
public static void GETRequest()
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://url");
request.Method = "GET";
HttpStatusCode status;
HttpWebResponse response;
try
{
response = (HttpWebResponse)request.GetResponse();
status = response.StatusCode;
Console.WriteLine((int)response.StatusCode);
Console.WriteLine(status);
}
catch (WebException e)
{
status = ((HttpWebResponse)e.Response).StatusCode;
Console.WriteLine(status);
}
}
But as I said, I need to know if the site is accessible, not matter the reason: the portal could be down, or the problem might reside on the side of the PC that's trying to access it. Either way: I don't care.
When I used MSXML2.XMLHTTP.3.0 in the script I was able to get values ranging from 12000 to 12156 if I was having network problems. I would like to have the same functionality in my C# app, that way I could at least write a minimum of information to a log and let the computer act accordingly. Any ideas?
A direct translation of your code would be something like this:
static void GetStatusCode(string url)
{
dynamic httpRequest = Activator.CreateInstance(Type.GetTypeFromProgID("MSXML2.XMLHTTP.3.0"));
httpRequest.Open("GET", url, false);
try { httpRequest.Send(); }
catch { }
finally { Console.WriteLine(httpRequest.Status); }
}
It's as small and simple as your VBScript script, and uses the same COM object to send the request.
This code happily gives me error code like 12029 ERROR_WINHTTP_CANNOT_CONNECT or 12007 ERROR_WINHTTP_NAME_NOT_RESOLVED etc.
If the code is failing only when you don't have an available network connection, you can use GetIsNetworkAvailable() before executing your code. This method will return a boolean indicating if a network connection is available or not. If it returns false, you could execute an early return / notify the user, and if not, continue.
System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable()
using the code you provided above:
public static void GETRequest()
{
if (!System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable())
return; //or alert the user there is no connection
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://url");
request.Method = "GET";
HttpStatusCode status;
HttpWebResponse response;
try
{
response = (HttpWebResponse)request.GetResponse();
status = response.StatusCode;
Console.WriteLine((int)response.StatusCode);
Console.WriteLine(status);
}
catch (WebException e)
{
status = ((HttpWebResponse)e.Response).StatusCode;
Console.WriteLine(status);
}
}
This should work for you, i've used it many times before, cut it down a bit for your needs: -
private static string GetStatusCode(string url)
{
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
req.Method = WebRequestMethods.Http.Get;
req.ProtocolVersion = HttpVersion.Version11;
req.UserAgent = "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)";
try
{
HttpWebResponse response = (HttpWebResponse)req.GetResponse();
StringBuilder sb = new StringBuilder();
foreach (string header in response.Headers)
{
sb.AppendLine(string.Format("{0}: {1}", header, response.GetResponseHeader(header)));
}
return string.Format("Response Status Code: {0}\nServer:{1}\nProtocol: {2}\nRequest Method: {3}\n\n***Headers***\n\n{4}", response.StatusCode,response.Server, response.ProtocolVersion, response.Method, sb);
}
catch (Exception e)
{
return string.Format("Error: {0}", e.ToString());
}
}
Feel free to ignore the section that gets the headers
I'm currently writing a simple app that performs a series of requests to the web server and I've encountered a strange... feature?
I don't need response stream of the request, but only status code. So, for each piece of my data I call my own "Send" method:
public static int Send(string uri)
{
HttpWebRequest request = null;
HttpWebResponse response = null;
try
{
request = (HttpWebRequest)WebRequest.Create(uri);
response = (HttpWebResponse)request.GetResponse();
if (response.StatusCode == HttpStatusCode.OK) return 0;
}
catch (Exception e)
{
if (request != null) request.Abort();
}
return -1;
}
Works fine? Yes, unless I call this function at least twice. Second call of such a function in a row (with the same uri) will ALWAYS result in timeout.
Now, that's odd: if I add request.Abort(); when I return zero (here, when status code is 200) - everything ALWAYS works fine.
So my question is - why? Is it some kind of framework restriction, or maybe the some kind of anti-DOS protection on the particular server (unfortunately, the server is a black box for me)? Or maybe I just don't understand smth in how it all works?
Try to dispose of the web response, you may leak some resources
public static int Send(string uri)
{
HttpWebRequest request = null;
try
{
request = (HttpWebRequest)WebRequest.Create(uri);
using (var response = (HttpWebResponse)request.GetResponse())
{
if (response.StatusCode == HttpStatusCode.OK) return 0;
}
}
catch (Exception e)
{
if (request != null) request.Abort();
}
return -1;
}
There is also a default number of connections (2 I think, but you can configure this) you can make to a domain simultaneously, please see this SO question. You're probably hitting this limit with your unclosed responses.
First of all I'd make a series of changes in order to get to the root of this:
take out that try..catch{} (you're likely swallowing an exception)
return a boolean instead of a number
You should then get your exception information you need.
Also you should be using "HEAD" as your method as you only want the status code:
request.Method = "HEAD";
read the difference here.
I use this code snippet that verifies if the file specified in the URL exists and keep trying it every few seconds for every user. Sometimes (mostly when there are large number of users using the site) the code doesn't work.
[WebMethod()]
public static string GetStatus(string URL)
{
bool completed = false;
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
try
{
if (response.StatusCode == HttpStatusCode.OK)
{
completed = true;
}
}
catch (Exception)
{
//Just don't do anything. Retry after few seconds
}
}
return completed.ToString();
}
When I look at the Windows Event logs there are several errors:
Unable to read data from the transport connection. An existing connection was forcibly closed
The Operation has timed out
The remote host closed the connection. The error code is 0x800703E3
When I restart the IIS, things work fine until the next time this happens.
You are putting the try/catch inside the using statement while it's the request.GetResponse method that might throw:
bool completed = false;
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);
try
{
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
if (response.StatusCode == HttpStatusCode.OK)
{
completed = true;
}
}
}
catch (Exception)
{
//Just don't do anything. Retry after few seconds
}
return completed.ToString();
I wrote this method to check if a page exists or not:
protected bool PageExists(string url)
{
try
{
Uri u = new Uri(url);
WebRequest w = WebRequest.Create(u);
w.Method = WebRequestMethods.Http.Head;
using (StreamReader s = new StreamReader(w.GetResponse().GetResponseStream()))
{
return (s.ReadToEnd().Length >= 0);
}
}
catch
{
return false;
}
}
I am using it to check a set of pages (iterates from AAAA-AAAZ), and it takes between 3 and 7 seconds to run the entire loop. Is there a faster or more efficient way to do this?
I think your approach is rather good, but would change it into only downloading the headers by adding w.Method = WebRequestMethods.Http.Head; before calling GetResponse.
This could do it:
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.example.com");
request.Method = WebRequestMethods.Http.Head;
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
bool pageExists = response.StatusCode == HttpStatusCode.OK;
You may probably want to check for other status codes as well.
static bool GetCheck(string address)
{
try
{
HttpWebRequest request = WebRequest.Create(address) as HttpWebRequest;
request.Method = "GET";
request.CachePolicy = new RequestCachePolicy(RequestCacheLevel.NoCacheNoStore);
var response = request.GetResponse();
return (response.Headers.Count > 0);
}
catch
{
return false;
}
}
static bool HeadCheck(string address)
{
try
{
HttpWebRequest request = WebRequest.Create(address) as HttpWebRequest;
request.Method = "HEAD";
request.CachePolicy = new RequestCachePolicy(RequestCacheLevel.NoCacheNoStore);
var response = request.GetResponse();
return (response.Headers.Count > 0);
}
catch
{
return false;
}
}
Beware, certain pages (eg. WCF .svc files) may not return anything from a head request. I know because I'm working around this right now.
EDIT - I know there are better ways to check the return data than counting headers, but this is a copy/paste from stuff where this is important to us.
One obvious speedup is to run several requests in parallel - most of the time will be spent on IO, so spawning 10 threads to each check a page will complete the whole iteration around 10 times faster.
You could do it using asynchronous way, because now you are waiting for results after each request. For few pages, you could just throw your function in ThreadPool, and wait for all requests to finish. For more requests, you could use asynchronous methods for your ResponseStream() (BeginRead etc.).
The other thing that can help you (help me for sure) is to clear .Proxy property:
w.Proxy = null;
Without this, at least 1st request is much slower, at least on my machine.
3. You can not download whole page, but download only header, by setting .Method to "HEAD".
I simply used Fredrik Mörk answer above but placed it within a method:
private bool checkURL(string url)
{
bool pageExists = false;
try
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.Method = WebRequestMethods.Http.Head;
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
pageExists = response.StatusCode == HttpStatusCode.OK;
}
catch (Exception e)
{
//Do what ever you want when its no working...
//Response.Write( e.ToString());
}
return pageExists;
}