Develop Reference

Suppress "The controller for path '/' was not found or does not implement IController." Server-Side with Application Insights

I am aware of this discussion (with no exception-source-side resolution): https://social.msdn.microsoft.com/Forums/vstudio/en-US/cb944fc4-4410-4e49-ba0b-43e675fe2173/ignoring-certain-exeptions-not-implementing-icontroller-bad-url?forum=ApplicationInsights
I have the same problem in that I don't want to pollute my exception log with traffic generated by bots (we only have Web API controllers). I was able to ignore those for server requests (usually showing in "Failed Requests") using a telemetry processor and simply return'ing on 404.
However, wasn't able to get rid of the exception entries - does anyone know of a setting / filter / you-name-it that would allow me to decide server-side (before they are sent off) which exceptions are delivered to Application Insights?

You would need to implement a custom ITelemetryProcessor as outlined here:
https://learn.microsoft.com/en-gb/azure/azure-monitor/app/api-filtering-sampling#filtering
public class ControllerNotImplementedTelemetryProcessor : ITelemetryProcessor
{
private ITelemetryProcessor Next { get; }
public void Process(ITelemetry item)
{
var exception = item as ExceptionTelemetry;
if (exception != null && exception.Exception.GetType() == typeof(HttpException) && exception.Exception.Message.Contains("was not found or does not implement IController"))
return;
Next.Process(item);
}
public ControllerNotImplementedTelemetryProcessor(ITelemetryProcessor next)
{
Next = next;
}
}
Registering the custom processor happens in Global.ascx:
TelemetryConfiguration.Active.TelemetryProcessorChainBuilder
.Use(next => new ControllerNotImplementedTelemetryProcessor(next))
.Build();
Note that this is obviously a very crude filter, depending on the language of the error message to be English might be acceptable but could also cause false positives.

Easy tables with Xamarin Forms - InvalidOperationException

I am using this tutorial in order to connect a xamarin.forms app with easy tables. I cannot add data to the database in Azure as i get
System.InvalidOperationException
The error message is the following
An insert operation on the item is already in the queue.
The exception happends in the following line of code.
await usersTable.InsertAsync(data);
In order to add a user
var user = new User { Username = "username", Password = "password" };
bool x = await AddUser(user);
AddUser
public async Task<bool> AddUser(User user)
{
try
{
await usersTable.InsertAsync(user);
await SyncUsers();
return true;
}
catch (Exception x)
{
await new MessageDialog(x.Message.ToString()).ShowAsync();
return false;
}
}
SyncUsers()
public async Task SyncUsers()
{
await usersTable.PullAsync("users", usersTable.CreateQuery());
await client.SyncContext.PushAsync();
}
where
IMobileServiceSyncTable<User> usersTable;
MobileServiceClient client = new MobileServiceClient("url");
Initialize
var path = Path.Combine(MobileServiceClient.DefaultDatabasePath, "DBNAME.db");
var store = new MobileServiceSQLiteStore(path);
store.DefineTable<User>();
await client.SyncContext.InitializeAsync(store, new MobileServiceSyncHandler());
usersTable = client.GetSyncTable<User>();

Please check your table. You probably have added the item already. Also, I would suggest that you don't set the Id property for your entity, because you might be inserting a same ID that's already existing in your table. It's probably the reason why the exception is appearing.
Hope it helps!

Some debugging you can do:
1) Turn on diagnostic logging in the backend and debug the backend: https://adrianhall.github.io/develop-mobile-apps-with-csharp-and-azure/chapter8/developing/#debugging-your-cloud-mobile-backend
2) Add a logging delegating handler in your MobileServiceClient setup: https://adrianhall.github.io/develop-mobile-apps-with-csharp-and-azure/chapter3/server/#turning-on-diagnostic-logs
The MobileServicePushFailedException contains an inner exception that contains the actual error. Normally, it is one of the 409/412 HTTP errors, which indicates a conflict. However, it can also be a 404 (which means there is a mismatch between what your client is asking for and the table name in Easy Tables) or 500 (which means the server crashed, in which case the server-side diagnostic logs indicate why).
Easy Tables is just a Node.js service underneath the covers.

Static variable value lost in IIS6

I'm using a Webservice coded in C# using .Net Framework 3.5.
The WebMethods of this Webservice besides their main workload also connect to Salesforce to retrieve and write data, so I'm using a static variable for keeping the Salesforce api login object alive between requests, this way I only log in once (on Salesforce) and then reuse this variable for subsequent calls, avoiding the need to login on each request.
This static object is evaluated on the main ctor of the Webservice, to check if some properties inside the login object are valid (for example, the validity of the session), if not, the login method is called again.
This works with no problems at all on my development environment (Windows 7 and VS2012 IIS7.5? Dev server) and in a test server (Win Server 2003, IIS6), but it doesn't work at all on the production box which is also a Windows Server 2003 with IIS6, because the static variable value is null on each request, logging in Salesforce on every request, giving long response times for each call and also hitting some limits on Salesforce, locking the account and blocking any following logins.
Sadly both machines (test and production) don't have the same configuration and the production box is currently unreachable for me, so the recycling time of the App Pool and other specifics are unknown to me at the moment.
I think this is a configuration issue, but anyway here is my code, firstly i started only by having a static variable inside the Webservice main class and then (current version) creating a whole static class with static variables.
All of the following code is under the same namespace
Static class (Salesforce login logic):
public static class Srv
{
public static SFHelpers helper = new SFHelpers(); // own class, Holds Salesforce logic and data related to this requirement
public static SforceService SFserv = new SforceService(); // Salesforce class that handles login (and other Salesforce data manipulation methods)
public static DateTime NextLoginSF = DateTime.MinValue; // Determines when does the Salesforce session expires
public static void LoginSalesforce()
{ // Simplified salesforce login steps, removed try-catch and other conditions to facilitate comprehension
SFserv.Url = helper.URLSalesforce;
LoginResult loginResult = SFserv.login(SFuser, SFpass);
NextLoginSF = DateTime.Now.AddSeconds(loginResult.userInfo.sessionSecondsValid);
SFserv.Url = loginResult.serverUrl;
SFserv.SessionHeaderValue = new SessionHeader { sessionId = loginResult.sessionId };
}
}
Main ctor and sample Webmethod:
[WebService(Namespace = "http://helloSO.com/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
public class WsSFTest : System.Web.Services.WebService
{
public WsSFTest()
{
try
{
if (Srv.SFserv.SessionHeaderValue == null || DateTime.Now >= Srv.NextLoginSF) // any of this will trigger a login to renew Salesforce session
{
Srv.LoginSalesforce();
}
}
catch (SoapException se)
{
if (se.Code.Name == ExceptionCode.INVALID_SESSION_ID.ToString())
{ // Login again because Salesforce invalidated my session somehow
Srv.LoginSalesforce();
}
else
{
// Irrelevant
}
}
catch (Exception e)
{
// Irrelevant
}
}
[WebMethod]
public SampleResult SampleMethod(int param)
{
try
{
//irrelevant code gathers values here
var something = Srv.helper.Method(param, anotherParam);
return something;
}
catch (Exception e)
{
// Irrelevant
}
}
}
Serializing the login object to a local file or persistance database are my last options since quick response times are a must.
I think what's left for me to try are Session variables but given this behavior odds that something similar could happen seem high.
Any clues? Thanks in advance

At the end I realized some evaluation value in this line (Specifically Srv.NextLoginSF)
if (Srv.SFserv.SessionHeaderValue == null || DateTime.Now >= Srv.NextLoginSF) // any of this will trigger a login to renew Salesforce session
Was returning with a different value than expected, and that the static variable wasn't losing its value

ELMAH exceptions generating generic "The service is unavailable" message

I'm trying to create an availability page which checks all the services that a site uses, wrapping each check in a try/catch and then displaying any failures to the users. One of those services is ELMAH, so I am calling that to double check that we can log errors there successfully.
Controller:
var a = new AvailabilityModel();
try {
a.ElmahConnectionString = ConfigurationManager.ConnectionStrings["elmah-sqlserver"].ConnectionString;
Elmah.ErrorSignal.FromCurrentContext().Raise(new Exception("Elmah availability test"));
a.ElmahSuccess = true;
} catch (Exception ex) {
a.ElmahSuccess = false;
a.ElmahException = ex;
Response.StatusCode = 503;
}
return View(a);
When ELMAH succeeds, all is well. When it throws any kind of error (DB permissions, etc.), I get an error which is not captured by the try/catch OR by any of the normal error-capturing pieces: ASP.NET MVC HandleError, customErrors redirects, or even httpErrors in system.webServer. The display is not the normal IIS generic message, instead I see a single line saying "The service is unavailable."
Response:
LTSB-W34511 C:\s\d\build % curl -i http://server/test/availability
HTTP/1.1 503 Service Unavailable
Cache-Control: public, max-age=14400, s-maxage=0
Content-Type: text/html
Server: Microsoft-IIS/7.5 X-AspNetMvc-Version: 4.0
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Wed, 06 Aug 2014 15:46:55 GMT
Content-Length: 27
The service is unavailable.
And that's it. At least I know my availability is not working, but I want to at least display to the user that it's ELMAH causing the problem, and show the connection string it's trying to use. So, I need to capture this exception somehow.
I've tried tweaking my web.config a number of different ways, but I suspect there's something about the way ELMAH inserts itself into the module pipeline which stops me from handling the issue.
Edit:
To clarify, this is a simplified example. I am not planning to expose this information to end users. This availability page will only be available to internal users who are troubleshooting future issues.
ELMAH is only one of the services/databases used by the application in question, and I want to give administrators a quick dashboard-like view of what is up and down. I can't do that if ELMAH errors lead to this insta-503.

Ok, basically this is not possible without any code. The Raise method in Elmah will not let you see any error except if you trace it:
// ErrorLogModule.LogException
try
{
Error error = new Error(e, context);
ErrorLog errorLog = this.GetErrorLog(context);
error.ApplicationName = errorLog.ApplicationName;
string id = errorLog.Log(error);
errorLogEntry = new ErrorLogEntry(errorLog, id, error);
}
catch (Exception value)
{
Trace.WriteLine(value);
}
However when the event is successfully logged the ErrorLogModule will call the logged event in order to let potential listeners know that the logging was a success. So let's quickly write a custom class that will override some methods from the ErrorLogModule and will allow us to notice that the event was not logged:
public class CustomErrorLogModule: Elmah.ErrorLogModule
{
public Boolean SomethingWasLogged { get; set; }
protected override void OnLogged(Elmah.ErrorLoggedEventArgs args)
{
SomethingWasLogged = true;
base.OnLogged(args);
}
protected override void LogException(Exception e, HttpContext context)
{
SomethingWasLogged = false;
base.LogException(e, context);
if (!SomethingWasLogged)
{
throw new InvalidOperationException("An error was not logged");
}
}
}
Swap the ErrorLogModule with the CustomErrorLogModule in your configuration file and Elmah will complain when something wrong is happening; calling Elmah.ErrorSignal.FromCurrentContext().Raise(new Exception("test")); in a test page lets the InvalidOperationException("An error was not logged") be thrown out of the call.
If you want to get back the exact exception that occured when trying to log the exception, you can use the fact that the ErrorLogModule traces the exception when it occurs. Create a listener class:
public class ExceptionInterceptor : DefaultTraceListener
{
public Exception TracedException { get; set; }
public override void WriteLine(object o)
{
var exception = o as Exception;
if (exception != null)
{
TracedException = exception;
}
}
}
Then your LogException method becomes
protected override void LogException(Exception e, HttpContext context)
{
var exceptionListener = new ExceptionInterceptor();
Trace.Listeners.Add(exceptionListener);
try
{
SomethingWasLogged = false;
base.LogException(e, context);
if (!SomethingWasLogged)
{
throw exceptionListener.TracedException;
}
}
finally
{
Trace.Listeners.Remove(exceptionListener);
}
}
EDIT: or even if you want to be as terse as possible
public class ExceptionInterceptor : DefaultTraceListener
{
public override void WriteLine(object o)
{
var exception = o as Exception;
if (exception != null)
{
throw exception;
}
}
}
// snip... LogException in your CustomErrorLogModule
protected override void LogException(Exception e, HttpContext context)
{
var exceptionListener = new ExceptionInterceptor();
Trace.Listeners.Add(exceptionListener);
try
{
base.LogException(e, context);
}
finally
{
Trace.Listeners.Remove(exceptionListener);
}
}
One final word: There is a smell in this way of checking for service availability, and you are going to pepper your error database with test exceptions which may not be the desired behavior. I understand that you aim to check the whole logging chain but perhaps there could be some other way to do it; I don't really know your context so I won't comment any further but don't hesitate to think on it.
Anyway, these changes should let you receive the exception you will need.
important edit: very important point: you may want to add a trigger to your CustomErrorLogModule so it doesn't throw when you are not testing. The resilience you are observing in Elmah is generally a good thing because you don't want a diagnostic platform to cause problems that may necessitate other diagnostics. That's why Elmah or logging frameworks don't throw, and that's why you should make the exception rethrowing mechanism triggerable so your program doesn't have to watch its step when raising exceptions in Elmah.

No, no no! Never display the connection string to the user and never tell them what the problem is. Doing so is a serious security vulnerability. Simply put, don't do it. Fix your underlying problems with Elmah.
Problems in your error handling pipeline are very bad, because it'll cause it to try to handle the new error that's generated, which basically causes a loop. The ASP.NET engine recognizes that something serious has gone wrong, so it gives a generic "the service is unavailable" message. Check the event logs on your server to find out the underlying Elmah error and correct it.

Error from class

I'm a IT student, second year. We just learned to program with 3 layers, one for getting data with a class, one for manipulating stuff with requests (all of the methods go in here) and one for the working of the program itself. Seeing as the first two go into classes instead of a form I dont know how to show errors.
Example:
We need to make a login system with a webbrowser and some other stuff behind it. So I make the login in a class, but how to check back for errors? I don't think it's normal or even possible to do MessageBox.Show(error); from a class, I can only return stuff, but I want the username/id to be returned if possible.
So in short, what is the best/most accepted way to report errors that are caused by data, so from a class?

Your framework level API's (eg. your layers) should use Exceptions for real errors, and return values to report non-critical errors.
public class Login
{
public bool AccountExists(string name) {
bool exists;
// do checking
return exists;
}
public LoginResult Login(string name, string password) {
// Try login
// If successful
return LoginResult.Success;
// What if the user does not exist?
return LoginResult.AccountNotFound;
// What about an error?
return LoginResult.Error;
}
}
public enum LoginResult
{
None,
AccountNotFound,
Error,
Success
}
In the example above, you can report the status of operations through return values. For LoginResult this could even be a value type (struct) that contains more information about the result (eg. a string message or something). Because these types of operations on non-critical, there is no necessity for exceptions here. Exceptions are costly and not always necessary to report errors.
Now let's talk about a different type of error. Logical developer errors. These should be handled by throwing exceptions. Take this example (assume we have some type Account that has a Role property).
public class Foo
{
public bool IsAdmin(Account account) {
if (account == null) {
throw new System.ArgumentNullException("You cannot pass a null account!");
}
return account.Role == "Admin";
}
}
We know as a developer that the account should not be null, so we should check for it and throw an exception if it is. If this exception is ever thrown, its a bug in the calling code and should be fixed not to pass in a null value.
Now that I've given two rough scenarios, how does this apply to your question? These are API's. Whatever your UI layer is, whether it be a WinForm, WPF Window, WebForm, or some other UI, the UI only has to use the API. The API is responsible for reporting information that can be usable by the UI, and the UI is responsible for displaying info in whatever way is best suited for that UI.
The framework API layers should never be responsible for reporting an error to the user with a UI. They should only be responsible for reporting errors to the developer who can take the result, and wire it up to the UI layer in some fashion. You would never display a message box or write to a console from a framework API for example. You would return some result that the UI can use to display its own message.
I highly recommend that you read Framework Design Guidelines. It covers a lot of this material and is an extremely great read.

You should have a class which validates the data object and returns error information. Then your front-end code can ask this class to validate the data and show any error messages that get returned.
var username = GetUserName();
var password = GetPassword();
var validationResult = new Validator().ValidateLogin(username, password);
if(validationResult.ErrorMessage != null) {
MessageBox.Show(validationResult.ErrorMessage);
} else {
// Do what you would have done.
}
If any errors occur that are outside of the expected logic flow, they should throw an exception.

Well you can use Exceptions. You Just throw the exception, it is up to the caller on what to do with the exception.
class Login
{
public Login()
{
}
public bool CheckLogin(string userName, string password)
{
// Do your validation here.
If every thing goes fine
return True.
else
throw Exception("custom message.");
}
}
class Input //class which takes input.
{
Login login = new Login();
public void TakeInput(string username, string password)
{
try
{
login.CheckLogin(username, password);
}
catch(Exception ex)
{
MessageBox.show(ex.message);
}
}
}