User agent null not work

[diandsonc]

When user agent is null, the application not work.

public AccountsController(ApiDbContext dbContext, IDetection detection)
{
    _dbContext = dbContext;
    _detection = detection;
}

{System.NullReferenceException: Object reference not set to an instance of an object.
   at Wangkanai.Detection.Collections.InternetExplorer..ctor(String agent)
   at Wangkanai.Detection.BrowserResolver.GetBrowser()
   at Wangkanai.Detection.BrowserResolver..ctor(IUserAgentService service)
   at lambda_method(Closure , ServiceProvider )
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
   at Microsoft.Extensions.Internal.ActivatorUtilities.GetService(IServiceProvider sp, Type type, Type requiredBy, Boolean isDefaultParameterRequired)
   at lambda_method(Closure , IServiceProvider , Object[] )
   at Microsoft.AspNetCore.Mvc.Controllers.ControllerActivatorProvider.<>c__DisplayClass4_0.<CreateActivator>b__0(ControllerContext controllerContext)
   at Microsoft.AspNetCore.Mvc.Controllers.ControllerFactoryProvider.<>c__DisplayClass5_0.<CreateControllerFactory>g__CreateController|0(ControllerContext controllerContext)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeInnerFilterAsync>d__14.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.<InvokeNextExceptionFilterAsync>d__23.MoveNext()}

[hookkshot]

I am also getting the same issue

Message=Exception : Object reference not set to an instance of an object.
Type : System.NullReferenceException
Source : Wangkanai.Detection.Browser
Stack Trace : at Wangkanai.Detection.Collections.InternetExplorer..ctor(String agent)
at Wangkanai.Detection.BrowserResolver.GetBrowser()
at Wangkanai.Detection.BrowserResolver..ctor(IUserAgentService service)
at lambda_method(Closure , ServiceProvider )
at Microsoft.Extensions.Internal.ActivatorUtilities.GetService(IServiceProvider sp, Type type, Type requiredBy, Boolean isDefaultParameterRequired)
at lambda_method(Closure , IServiceProvider , Object[] )
at Microsoft.AspNetCore.Mvc.Controllers.ControllerFactoryProvider.<>c__DisplayClass5_0.g__CreateController|0(ControllerContext controllerContext)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.d__14.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.d__23.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Rethrow(ExceptionContext context)
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.d__22.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Rethrow(ResourceExecutedContext context)
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.d__17.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.d__15.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Builder.RouterMiddleware.d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Diagnostics.StatusCodePagesMiddleware.d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.d__6.MoveNext()

I think this line may be causing it in InternetExplorer.
_agent = agent.ToLower();

[diandsonc]

Solution: Create a Middleware and set string empty for User-Agent.

public class FixDetectionMiddleware
{
    public FixDetectionMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    readonly RequestDelegate _next;

    public async Task Invoke(HttpContext context, IHostingEnvironment hostingEnviroment)
    {
        var userAgent = context.Request.Headers["User-Agent"].FirstOrDefault();

        if (userAgent == null)
        {
            context.Request.Headers["User-Agent"] = string.Empty;
        }

        await _next.Invoke(context);
    }
}

Startup

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseMiddleware<FixDetectionMiddleware>();
 }

[wangkanai]

Why would the UserAgent be null? this is the web standard and also it in the test coverage that i wrote. #76

[diandsonc]

UserAgent is null when the request is from another API (not from the browser), for example:

var httpClient = new HttpClient();

httpClient.DefaultRequestHeaders.Accept.Clear();
httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

var response = await _httpClient.GetAsync("/url/to/my/private/api");

[wangkanai]

Interesting, but REST is strictly HTTP and subject to RFC7231

So should you do add a useragent to the package header?

[diandsonc]

Yes, I could. But I have no control over another APIs (not mine) that consumes my API.

[wangkanai]

PR #85 merged and closing this issue.