Develop Reference

Blazor Server http headers authorisation throws 400 on attempt to start hub connection

I`ve made a simple Blazor server hub with [Authorize] attribute. Authorisation process is described in specific AuthorizationRequirement and is considered successful only if incoming HTTP request has specified headers.
[Authorize(Policy = EnterpriseServiceBusHub.EsbHubAuthorizationPolicy)]
public class EnterpriseServiceBusHub : Hub
{
public const string EsbHubPath = "/esb-hub";
public const string EsbHubMethod = "InvokeIntegration";
public const string EsbHubAuthorizationPolicy = "EsbHubAuthorizationPolicy";
public const string EsbIntegrationID = "ESB-Integration-ID";
public const string EsbIntegrationName = "ESB-Integration-Channel";
private readonly IEntepriseServiceBus _entepriseServiceBus;
public EnterpriseServiceBusHub(IEntepriseServiceBus entepriseServiceBus)
{
_entepriseServiceBus = entepriseServiceBus;
}
[HubMethodName(EsbHubMethod)]
public async Task InvokeIntegration(string integrationChannel, string encryptedMessage)
{
await Clients.Others.SendAsync(integrationChannel, encryptedMessage);
}
}
public class EsbAuthorizationRequirement : AuthorizationHandler<EsbAuthorizationRequirement>, IAuthorizationRequirement
{
protected override async Task HandleRequirementAsync(AuthorizationHandlerContext context, EsbAuthorizationRequirement requirement)
{
try
{
await EsbAuthorizationChecker.CheckAuthorizationAsync();
context.Succeed(requirement);
}
catch (Exception ex)
{
context.Fail(new AuthorizationFailureReason(this, ex.Message));
}
}
}
static class EsbAuthorizationChecker
{
public static async Task<bool> CheckAuthorizationAsync()
{
var httpContextAccessor = ServicesHolder.GetService<IHttpContextAccessor>();
var requestHeaders = httpContextAccessor.HttpContext.Request.Headers;
if (!requestHeaders.TryGetValue(EnterpriseServiceBusHub.EsbIntegrationID, out var integrationID) ||
!requestHeaders.TryGetValue(EnterpriseServiceBusHub.EsbIntegrationName, out var integrationUrl))
{
var message = $"Headers {EnterpriseServiceBusHub.EsbIntegrationID} or {EnterpriseServiceBusHub.EsbIntegrationName} were not provided";
throw new Exception(message);
}
return await Task.FromResult(true);
}
}
The problem is that even specifying those headers in HubConnectionBuilder, attempt to start hub connection throws 400 (Bad request) exception.
_hubConnection = new HubConnectionBuilder().WithUrl($#"{Url}/{EnterpriseServiceBusHub.EsbHubPath}",
(HttpConnectionOptions options) =>
{
options.Headers.Add(EnterpriseServiceBusHub.EsbIntegrationID, "Value-1");
options.Headers.Add(EnterpriseServiceBusHub.EsbIntegrationName, "Value-2");
}).Build();
await _hubConnection.StartAsync(); // throws 400 Bad request
The specified authorisation policy is included in Program.cs
builder.Services.AddAuthorization(options =>
{
options.AddPolicy(EnterpriseServiceBusHub.EsbHubAuthorizationPolicy, policy =>
{
policy.Requirements.Add(new EsbAuthorizationRequirement());
});
});
builder.Services.AddSignalR(config =>
{
config.EnableDetailedErrors = true;
config.ClientTimeoutInterval = null;
});
What can be the reason for that? Am I specifying headers wrong? Thank you.

GRPC-web RPCException Bad gRPC response. Invalid content-type value: text/html; charset=utf-8

I got an error when trying to fetch gRPC API (using C#) to blazor client, at first it worked fine but after adding IdentityServer4 and use CORS for gRPC-Web similar like in the docs. Here's the code relevant to the error.
BackEnd/Startup.cs
namespace BackEnd
{
public class Startup
{
public IWebHostEnvironment Environment { get; }
public IConfiguration Configuration { get; }
private string _clientId = null;
private string _clientSecret = null;
public Startup(IWebHostEnvironment environment, IConfiguration configuration)
{
Environment = environment;
Configuration = configuration;
}
public void ConfigureServices(IServiceCollection services)
{
// Initialize certificate
var cert = new X509Certificate2(Path.Combine(".", "IdsvCertificate.pfx"), "YouShallNotPass123");
var migrationAssembly = typeof(Startup).GetTypeInfo().Assembly.GetName().Name;
// The connection strings is in user secret
string connectionString = Configuration["ConnectionStrings:DefaultConnection"];
_clientId = Configuration["OAuth:ClientId"];
_clientSecret = Configuration["OAuth:ClientSecret"];
services.AddControllersWithViews();
services.AddDbContext<ApplicationDbContext>(options =>
options.UseNpgsql(connectionString));
services.AddIdentity<ApplicationUser, IdentityRole>(options => options.SignIn.RequireConfirmedAccount = true)
.AddRoles<IdentityRole>()
.AddEntityFrameworkStores<ApplicationDbContext>()
.AddClaimsPrincipalFactory<ClaimsFactory>()
.AddDefaultTokenProviders();
var builder = services.AddIdentityServer(options =>
{
options.Events.RaiseErrorEvents = true;
options.Events.RaiseInformationEvents = true;
options.Events.RaiseFailureEvents = true;
options.Events.RaiseSuccessEvents = true;
// see https://identityserver4.readthedocs.io/en/latest/topics/resources.html
options.EmitStaticAudienceClaim = true;
options.UserInteraction = new UserInteractionOptions()
{
LoginUrl = "/Account/Login",
LogoutUrl = "/Account/Logout"
};
})
.AddInMemoryIdentityResources(Config.IdentityResources)
.AddInMemoryApiResources(Config.ApiResources)
.AddInMemoryApiScopes(Config.ApiScopes)
.AddInMemoryClients(Config.Clients)
.AddProfileService<ProfileService>()
.AddAspNetIdentity<ApplicationUser>()
.AddConfigurationStore(options =>
{
options.ConfigureDbContext = b => b.UseNpgsql(connectionString,
sql => sql.MigrationsAssembly(migrationAssembly));
})
.AddOperationalStore(options =>
{
options.ConfigureDbContext = b => b.UseNpgsql(connectionString,
sql => sql.MigrationsAssembly(migrationAssembly));
});
// Add signed certificate to identity server
builder.AddSigningCredential(cert);
JwtSecurityTokenHandler.DefaultInboundClaimTypeMap.Clear();
// Enable CORS for gRPC
services.AddCors(o => o.AddPolicy("AllowAll", builder =>
{
builder.AllowAnyOrigin()
.AllowAnyMethod()
.AllowAnyHeader()
.WithExposedHeaders("Grpc-Status", "Grpc-Message", "Grpc-Encoding", "Grpc-Accept-Encoding");
}));
// Add profile service
services.AddScoped<IProfileService, ProfileService>();
services.AddAuthentication()
.AddGoogle("Google", options =>
{
options.SignInScheme = IdentityServerConstants.ExternalCookieAuthenticationScheme;
options.ClientId = _clientId;
options.ClientSecret = _clientSecret;
options.SaveTokens = true;
options.ClaimActions.MapJsonKey("role", "role");
});
services.AddAuthorization();
services.AddGrpc(options =>
{
options.EnableDetailedErrors = true;
});
}
public void Configure(IApplicationBuilder app)
{
InitializeDatabase(app);
if (Environment.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
app.UseStaticFiles();
app.UseRouting();
app.UseIdentityServer();
app.UseGrpcWeb(new GrpcWebOptions { DefaultEnabled = true });
app.UseAuthentication();
app.UseCors("AllowAll");
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapGrpcService<UserService>().RequireCors("AllowAll");
endpoints.MapDefaultControllerRoute().RequireAuthorization();
});
}
// Based on IdentityServer4 document
private void InitializeDatabase(IApplicationBuilder app)
{
using (var serviceScope = app.ApplicationServices.GetService<IServiceScopeFactory>().CreateScope())
{
serviceScope.ServiceProvider.GetRequiredService<ApplicationDbContext>().Database.Migrate();
var context = serviceScope.ServiceProvider.GetRequiredService<ConfigurationDbContext>();
context.Database.Migrate();
if (!context.Clients.Any())
{
foreach (var client in Config.Clients)
{
context.Clients.Add(client.ToEntity());
}
context.SaveChanges();
}
if (!context.IdentityResources.Any())
{
foreach (var resource in Config.IdentityResources)
{
context.IdentityResources.Add(resource.ToEntity());
}
context.SaveChanges();
}
if (!context.ApiScopes.Any())
{
foreach (var resource in Config.ApiScopes)
{
context.ApiScopes.Add(resource.ToEntity());
}
context.SaveChanges();
}
}
}
}
}
BackEnd/Services/UserService.cs
namespace BackEnd
{
[Authorize(Roles="User")]
public class UserService : User.UserBase
{
private readonly ILogger<UserService> _logger;
private readonly ApplicationDbContext _dataContext;
public UserService(ILogger<UserService> logger, ApplicationDbContext dataContext)
{
_logger = logger;
_dataContext = dataContext;
}
public override async Task<Empty> GetUser(UserInfo request, ServerCallContext context)
{
var response = new Empty();
var userList = new UserResponse();
if (_dataContext.UserDb.Any(x => x.Sub == request.Sub))
{
var newUser = new UserInfo(){ Id = userList.UserList.Count, Sub = request.Sub, Email = request.Email };
_dataContext.UserDb.Add(newUser);
userList.UserList.Add(newUser);
await _dataContext.SaveChangesAsync();
}
else
{
var user = _dataContext.UserDb.Single(u => u.Sub == request.Sub);
userList.UserList.Add(user);
}
return await Task.FromResult(response);
}
public override async Task<ToDoItemList> GetToDoList(UuidParameter request, ServerCallContext context)
{
var todoList = new ToDoItemList();
var userInfo = new UserInfo();
var getTodo = (from data in _dataContext.ToDoDb
where data.Uuid == userInfo.Sub
select data).ToList();
todoList.ToDoList.Add(getTodo);
return await Task.FromResult(todoList);
}
public override async Task<Empty> AddToDo(ToDoStructure request, ServerCallContext context)
{
var todoList = new ToDoItemList();
var userInfo = new UserInfo();
var newTodo = new ToDoStructure()
{
Id = todoList.ToDoList.Count,
Uuid = request.Uuid,
Description = request.Description,
IsCompleted = false
};
todoList.ToDoList.Add(newTodo);
await _dataContext.ToDoDb.AddAsync(newTodo);
await _dataContext.SaveChangesAsync();
return await Task.FromResult(new Empty());
}
public override async Task<Empty> PutToDo(ToDoStructure request, ServerCallContext context)
{
var response = new Empty();
_dataContext.ToDoDb.Update(request);
await _dataContext.SaveChangesAsync();
return await Task.FromResult(response);
}
public override async Task<Empty> DeleteToDo(DeleteToDoParameter request, ServerCallContext context)
{
var item = (from data in _dataContext.ToDoDb
where data.Id == request.Id
select data).First();
_dataContext.ToDoDb.Remove(item);
var result = await _dataContext.SaveChangesAsync();
return await Task.FromResult(new Empty());
}
}
}
FrontEnd/Program.cs
namespace FrontEnd
{
public class Program
{
public static async Task Main(string[] args)
{
var builder = WebAssemblyHostBuilder.CreateDefault(args);
builder.RootComponents.Add<App>("#app");
builder.Services.AddScoped(sp => new HttpClient()
{ BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) });
// Connect server to client
builder.Services.AddScoped(services =>
{
var baseAddressMessageHandler = services.GetRequiredService<AuthorizationMessageHandler>()
.ConfigureHandler(
authorizedUrls: new[] { "https://localhost:5001" },
scopes: new[] { "todoApi" }
);
baseAddressMessageHandler.InnerHandler = new HttpClientHandler();
var httpHandler = new GrpcWebHandler(GrpcWebMode.GrpcWeb, new HttpClientHandler());
var channel = GrpcChannel.ForAddress("https://localhost:5000", new GrpcChannelOptions
{
HttpHandler = httpHandler
});
return new User.UserClient(channel);
});
// Add Open-ID Connect authentication
builder.Services.AddOidcAuthentication(options =>
{
builder.Configuration.Bind("Authentication:Google", options.ProviderOptions);
options.ProviderOptions.DefaultScopes.Add("role");
options.UserOptions.RoleClaim = "role"; // Important to get role claim
}).AddAccountClaimsPrincipalFactory<CustomUserFactory>();
builder.Services.AddOptions();
builder.Services.AddAuthorizationCore();
await builder.Build().RunAsync();
}
}
}
FrontEnd/Pages/ToDoList.razor.cs
namespace FrontEnd.Pages
{
public partial class TodoList
{
[Inject]
private User.UserClient UserClient { get; set; }
[Inject]
private IJSRuntime JSRuntime { get; set; }
[CascadingParameter]
public Task<AuthenticationState> authenticationStateTask { get; set; }
public string Description { get; set; }
public string ToDoDescription { get; set; }
public RepeatedField<ToDoStructure> ServerToDoResponse { get; set; } = new RepeatedField<ToDoStructure>();
protected override async Task OnInitializedAsync()
{
var authState = await authenticationStateTask;
var user = authState.User;
Console.WriteLine($"IsAuthenticated: {user.Identity.IsAuthenticated} | IsUser: {user.IsInRole("User")}");
if (user.Identity.IsAuthenticated && user.IsInRole("User"))
{
await GetUser(); // Error when trying to call this function
}
}
// Fetch usser from server
public async Task GetUser()
{
var authState = await authenticationStateTask;
var user = authState.User;
var userRole = user.IsInRole("User");
var userUuid = user.Claims.FirstOrDefault(c => c.Type == "preferred_username").Value;
var subjectId = user.Claims.FirstOrDefault(c => c.Type == "sub").Value;
var userEmail = user.Claims.FirstOrDefault(c => c.Type == "email").Value;
var request = new UserInfo(){ Sub = subjectId, Email = userEmail };
await UserClient.GetUserAsync(request);
await InvokeAsync(StateHasChanged);
await GetToDoList();
}
// Fetch to-do list from server
private async Task GetToDoList()
{
var authState = await authenticationStateTask;
var user = authState.User;
var userUuid = user.Claims.FirstOrDefault(c => c.Type == "preferred_username").Value;
var request = new UuidParameter(){ Uuid = userUuid };
var response = await UserClient.GetToDoListAsync(request);
ServerToDoResponse = response.ToDoList;
}
// Add to-do list to the server
public async Task AddToDo(KeyboardEventArgs e)
{
var authState = await authenticationStateTask;
var user = authState.User;
var userUuid = user.Claims.FirstOrDefault(c => c.Type == "Sub").Value;
if (e.Key == "Enter" && !string.IsNullOrWhiteSpace(Description) ||
e.Key == "NumpadEnter" && !string.IsNullOrWhiteSpace(Description))
{
var request = new ToDoStructure()
{
Uuid = userUuid,
Description = this.Description,
};
await UserClient.AddToDoAsync(request);
await InvokeAsync(StateHasChanged);
await GetToDoList();
}
}
// Update the checkbox state of the to-do list
public async Task PutToDoIsCompleted(int id, string description, bool isCompleted, MouseEventArgs e)
{
if (isCompleted == false && e.Button== 0)
{
isCompleted = true;
}
else if (isCompleted == true && e.Button == 0)
{
isCompleted = false;
}
var request = new ToDoStructure()
{
Id = id,
Description = description,
IsCompleted = isCompleted
};
await UserClient.PutToDoAsync(request);
await GetToDoList();
}
// Edit mode function
private async Task EditToDo(int todoId, string description, bool isCompleted)
{
var authState = await authenticationStateTask;
var user = authState.User;
var userUuid = user.Claims.FirstOrDefault(c => c.Type == "Sub").Value;
// Get the index of the to-do list
int grpcIndex = ServerToDoResponse.IndexOf(new ToDoStructure()
{
Id = todoId,
Uuid = userUuid,
Description = description,
IsCompleted = isCompleted
});
ToDoDescription = ServerToDoResponse[grpcIndex].Description;
// Make text area appear and focus on text area and edit icon dissapear based on the to-do list index
await JSRuntime.InvokeVoidAsync("editMode", "edit-icon", "todo-description", "edit-todo", grpcIndex);
await JSRuntime.InvokeVoidAsync("focusTextArea", todoId.ToString(), ToDoDescription);
}
// Update the to-do description
public async Task PutToDoDescription(int id, string htmlId, string oldDescription, string newDescription, bool isCompleted)
{
var authState = await authenticationStateTask;
var user = authState.User;
var userUuid = user.Claims.FirstOrDefault(c => c.Type == "Sub").Value;
var request = new ToDoStructure()
{
Id = id,
Uuid = userUuid,
Description = newDescription,
};
int grpcIndex = ServerToDoResponse.IndexOf(new ToDoStructure()
{
Id = id,
Description = oldDescription,
IsCompleted = isCompleted
});
// Text area auto resize function
await JSRuntime.InvokeVoidAsync("theRealAutoResize", htmlId);
// Make text area display to none and edit icon appear base on the to-do list index
await JSRuntime.InvokeVoidAsync("initialMode", "edit-icon", "todo-description", "edit-todo", grpcIndex);
await UserClient.PutToDoAsync(request);
await GetToDoList();
}
// Delete to-do
public async Task DeleteToDo(int id)
{
var request = new DeleteToDoParameter(){ Id = id };
await UserClient.DeleteToDoAsync(request);
await GetToDoList();
}
}
}
This is the output of the console
Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
Unhandled exception rendering component: Status(StatusCode="Cancelled", Detail="Bad gRPC response. Invalid content-type value: text/html; charset=utf-8")
Grpc.Core.RpcException: Status(StatusCode="Cancelled", Detail="Bad gRPC response. Invalid content-type value: text/html; charset=utf-8")
at FrontEnd.Pages.TodoList.GetUser() in C:\Users\bryan\source\repos\Productivity_App\frontend\Pages\TodoList.razor.cs:line 50
at FrontEnd.Pages.TodoList.OnInitializedAsync() in C:\Users\bryan\source\repos\Productivity_App\frontend\Pages\TodoList.razor.cs:line 35
at Microsoft.AspNetCore.Components.ComponentBase.RunInitAndSetParametersAsync()
at Microsoft.AspNetCore.Components.RenderTree.Renderer.GetErrorHandledTask(Task taskToHandle)
This is the output in the terminal when trying to authenticate with IdentityServer4 (the authentication and authorization is working fine though)
[21:11:15 Debug] Grpc.AspNetCore.Web.Internal.GrpcWebMiddleware
Detected gRPC-Web request from content-type 'application/grpc-web'.
[21:11:15 Information] Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationHandler
AuthenticationScheme: Identity.Application was challenged.
[21:11:15 Debug] IdentityServer4.Hosting.CorsPolicyProvider
CORS request made for path: /Account/Login from origin: https://localhost:5001 but was ignored because path was not for an allowed IdentityServer CORS endpoint

You can't do OpenID Connect authentication as part of gRPC, the user must have first authenticated on your web site and you should then have received the access token.
Then you can send the access token with gRPC to the API. If you then get a 401 http status back, then you need to refresh(get a new one) the access token.
To make your life easier and to reduce complexity and your sanity, I recommend that you put IdentityServer in its own service, standalone from the client/api. Otherwise its hard to reason about the system and it will be very hard to debug.
My recommendation is that you have this architecture, in three different services:
gRPC is just a transport, similar to HTTP and in the API, you have this basic architecture (slide taken from one of my training classes):
The JwtBearer will examine the access token to verify who you are and after that the authorization module takes over and check if you are allowed in.

Receiving two messages from .net core SignalR and react

I am trying to set up a WebSocket connection using the .net SignalR and React app as a client to be able to send private messages.
Here is my code on the client side:
const setUpSignalRConnection = async () => {
const connection = new HubConnectionBuilder()
.withUrl("http://localhost:5000/messaginghub")
.build();
setConnection(connection);
connection.on("ReceiveMessage", (message: string) => {
console.log("Recieved Message", message);
setChatMessages((oldArray) => [...oldArray, message]);
});
try {
await connection.start();
} catch (err) {
console.log("Errors", err);
}
return connection;
};
const SendMessage = async () => {
if (connection) {
try {
console.log("sending message");
await connection.send("SendPrivateMessage", user.user.email, message);
} catch (e) {
console.log("Errors sending message", e);
}
} else {
alert("No connection to server yet.");
}
};
and my server side code
public async Task SendPrivateMessage(string userEmail, string message)
{
var RecivingMessageUser = _unitOfWork.UserRepository.GetByEmail(userEmail);
var currUserEmail = Context.User.FindFirstValue(ClaimTypes.NameIdentifier);
var sender = _unitOfWork.UserRepository.GetByEmail(currUserEmail);
var newMessage = new MessagesDto
{
FromId = sender.UserId,
ToId = RecivingMessageUser.UserId,
MessageBody = message,
SentAt = DateTime.UtcNow,
};
await Clients.Group(userEmail).SendAsync("ReceiveMessage", message);
_unitOfWork.MessagingRepository.Insert(_mapper.Map<MessagesDto, Messages>(newMessage));
_unitOfWork.SaveChanges();
}
public override Task OnConnectedAsync()
{
var groupName = Context.User.FindFirstValue(ClaimTypes.NameIdentifier);
Groups.AddToGroupAsync(Context.ConnectionId, groupName);
return base.OnConnectedAsync();
}
public override Task OnDisconnectedAsync(Exception ex)
{
Groups.RemoveFromGroupAsync(Context.ConnectionId, Context.User.FindFirstValue(ClaimTypes.NameIdentifier));
return base.OnDisconnectedAsync(ex);
}
With console.logs I see that I am sending a message once and the message is stored in DB once but somehow on the other end, I am getting two received messages.
I am testing it on my local machine in two separate browsers.
What am I doing wrong?

Which method on your back-end is calling twice?
You are telling your message saved in to the DB once so it shouldn't be the SendPrivateMessage method which is calling towice.

Bot Framework, conversation in another conversation

I created a bot using QnA Maker, which depending on the answer I should return the same answer or call another service, which in my case is to assemble a form flow from a JSON.
But when calling this service I start a new Conversation, so it does not return to the emulator.
I'm creating a conversation in another conversation. There must be something missing.
RootDialog.cs:
[Serializable]
public class RootDialog : QnAMakerDialog
{
public RootDialog() : base(
new QnAMakerService(
new QnAMakerAttribute(
ConfigurationManager.AppSettings["QnaSubscriptionKey"],
ConfigurationManager.AppSettings["QnaKnowledgebaseId"],
"Não encontrei sua resposta",
0.5
)
)
)
{
}
protected override async Task RespondFromQnAMakerResultAsync(IDialogContext context, IMessageActivity message, QnAMakerResults result)
{
var primeiraResposta = result.Answers.First().Answer;
if (primeiraResposta.IndexOf("form") == -1)
{
await context.PostAsync(primeiraResposta);
return;
}
await Conversation.SendAsync(message, () => Chain.From(() => FormDialog.FromForm(() => Formulario.JsonForm.BuildJsonForm(), FormOptions.PromptFieldsWithValues)));
return;
}
}
MessagesController.cs
public async Task<HttpResponseMessage> Post([FromBody]Activity activity)
{
var connector = new ConnectorClient(new Uri(activity.ServiceUrl));
if (activity.Type == ActivityTypes.ConversationUpdate)
{
if (activity.MembersAdded.Any(o => o.Id == activity.Recipient.Id))
{
var reply = activity.CreateReply();
reply.Text = "Hello...";
await connector.Conversations.ReplyToActivityAsync(reply);
}
}
else if (activity.Type == ActivityTypes.Message)
{
// HEREE!!!
await Conversation.SendAsync(activity, () => new Dialogs.RootDialog());
}
else
{
HandleSystemMessage(activity);
}
var response = Request.CreateResponse(HttpStatusCode.OK);
return response;
}
The response of emulator:
I could not send, Repeat

checking Internet connection with HttpClient

I am having difficulties to understand on how the bellow code could handle occasional internet connection loss. Ideally I would like to pause the app, once the connection is lost, and resume when it is up again. Is there any guideline on how to do it?
HttpClientHandler clientHandler = new HttpClientHandler();
clientHandler.UseDefaultCredentials = true;
HttpClient client = new HttpClient(clientHandler) { MaxResponseContentBufferSize = 1000000 };
HttpResponseMessage response = await client.GetAsync(Url, ct);

The following example is not a direct solution, but it is an example I built to show how to return "pre-canned" content to requests whilst offline and then return back online when connectivity is restored. If you can get what I'm doing here, building what you want should be fairly easy.
[Fact]
public async Task Getting_a_response_when_offline()
{
var offlineHandler = new OfflineHandler(new HttpClientHandler(), new Uri("http://oak:1001/status"));
offlineHandler.AddOfflineResponse(new Uri("http://oak:1001/ServerNotRunning"),
new HttpResponseMessage(HttpStatusCode.NonAuthoritativeInformation)
{
Content = new StringContent("Here's an old copy of the information while we are offline.")
});
var httpClient = new HttpClient(offlineHandler);
var retry = true;
while (retry)
{
var response = await httpClient.GetAsync(new Uri("http://oak:1001/ServerNotRunning"));
if (response.StatusCode == HttpStatusCode.OK) retry = false;
Thread.Sleep(10000);
}
}
public class OfflineHandler : DelegatingHandler
{
private readonly Uri _statusMonitorUri;
private readonly Dictionary<Uri, HttpResponseMessage> _offlineResponses = new Dictionary<Uri, HttpResponseMessage>();
private bool _isOffline = false;
private Timer _timer;
public OfflineHandler(HttpMessageHandler innerHandler, Uri statusMonitorUri)
{
_statusMonitorUri = statusMonitorUri;
InnerHandler = innerHandler;
}
public void AddOfflineResponse(Uri uri, HttpResponseMessage response)
{
_offlineResponses.Add(uri,response);
}
protected async override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
if (_isOffline == true) return OfflineResponse(request);
try
{
var response = await base.SendAsync(request, cancellationToken);
if (response.StatusCode == HttpStatusCode.ServiceUnavailable || response.StatusCode == HttpStatusCode.BadGateway)
{
MonitorOfflineState();
return OfflineResponse(request);
}
return response;
}
catch (WebException ex)
{
MonitorOfflineState();
return OfflineResponse(request);
}
}
private void MonitorOfflineState()
{
_isOffline = true;
_timer = new Timer( async state =>
{
var request = new HttpRequestMessage() {RequestUri = _statusMonitorUri};
try
{
var response = await base.SendAsync(request, new CancellationToken());
if (response.StatusCode == HttpStatusCode.OK)
{
_isOffline = false;
_timer.Dispose();
}
}
catch
{
}
}, null, new TimeSpan(0,0,0),new TimeSpan(0,1,0));
}
private HttpResponseMessage OfflineResponse(HttpRequestMessage request)
{
if (_offlineResponses.ContainsKey(request.RequestUri))
{
return _offlineResponses[request.RequestUri];
}
return new HttpResponseMessage(HttpStatusCode.ServiceUnavailable);
}
}
}