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Why is my header data missing from my Azure Function Http Trigger in .Net 5 when calling from HttpClient.GetAsync

I have a client using HttpClient.GetAsync to call into a Azure Function Http Trigger in .Net 5.
When I call the function using PostMan, I get my custom header data.
However, when I try to access my response object (HttpResponseMessage) that is returned from HttpClient.GetAsync, my header data empty.
I have my Content data and my Status Code. But my custom header data are missing.
Any insight would be appreciated since I have looking at this for hours.
Thanks for you help.
Edit: Here is the code where I am making the http call:
public async Task<HttpResponseMessage> GetQuotesAsync(int? pageNo, int? pageSize, string searchText)
{
var requestUri = $"{RequestUri.Quotes}?pageNo={pageNo}&pageSize={pageSize}&searchText={searchText}";
return await _httpClient.GetAsync(requestUri);
}
Edit 8/8/2021: See my comment below. The issue has something to do with using Blazor Wasm Client.

For anyone having problems after following the tips on this page, go back and check the configuration in the host.json file. you need the Access-Control-Expose-Headers set to * or they won't be send even if you add them. Note: I added the "extensions" node below and removed my logging settings for clarity.
host.json (sample file):
{
"version": "2.0",
"extensions": {
"http": {
"customHeaders": {
"Access-Control-Expose-Headers": "*"
}
}
}
}

This is because HttpResponseMessage's Headers property data type is HttpResponseHeaders but HttpResponseData's Headers property data type is HttpHeadersCollection. Since, they are different, HttpResponseHeaders could not bind to HttpHeadersCollection while calling HttpClient.GetAsync(as it returns HttpResponseMessage).
I could not find a way to read HttpHeadersCollection through HttpClient.

As long as your Azure function code is emitting the header value, you should be able to read that in your client code from the Headers collection of HttpResponseMessage. Nothing in your azure function (which is your remote endpoint you are calling) makes it any different. Remember, your client code has no idea how your remote endpoint is implemented. Today it is azure functions, tomorrow it may be a full blown aspnet core web api or a REST endpoint written in Node.js. Your client code does not care. All it cares is whether the Http response it received has your expected header.
Asumming you have an azure function like this where you are adding a header called total-count to the response.
[Function("quotes")]
public static async Task<HttpResponseData> RunAsync(
[HttpTrigger(AuthorizationLevel.Anonymous, "get", "post")] HttpRequestData req,
FunctionContext executionContext)
{
var logger = executionContext.GetLogger("Quotes");
logger.LogInformation("C# HTTP trigger function processed a request for Quotes.");
var quotes = new List<Quote>
{
new Quote { Text = "Hello", ViewCount = 100},
new Quote { Text = "Azure Functions", ViewCount = 200}
};
var response = req.CreateResponse(HttpStatusCode.OK);
response.Headers.Add("total-count", quotes.Count.ToString());
await response.WriteAsJsonAsync(quotes);
return response;
}
Your existing client code should work as long as you read the Headers property.
public static async Task<HttpResponseMessage> GetQuotesAsync()
{
var requestUri = "https://shkr-playground.azurewebsites.net/api/quotes";
return await _httpClient.GetAsync(requestUri);
}
Now your GetQuotesAsync method can be called somewhere else where you will use the return value of it (HttpResponseMessage instance) and read the headers. In the below example, I am reading that value and adding to a string variable. HttpResponseMessage implements IDisposable. So I am using a using construct to implicitly call the Dispose method.
var msg = "Total count from response headers:";
using (var httpResponseMsg = await GetQuotesAsync())
{
if (httpResponseMsg.Headers.TryGetValues("total-count", out var values))
{
msg += values.FirstOrDefault();
}
}
// TODO: use "msg" variable as needed.
The types which Azure function uses for dealing with response headers is more of an implementation concern of azure functions. It has no impact on your client code where you are using HttpClient and HttpResponseMessage. Your client code is simply dealing with standard http call response (response headers and body)

The issue is not with Blazor WASM, rather if that header has been exposed on your API Side. In your azure function, add the following -
Note: Postman will still show the headers even if you don't expose the headers like below. That's because, Postman doesn't care about CORS headers. CORS is just a browser concept and not a strong security mechanism. It allows you to restrict which other web apps may use your backend resources and that's all.
First create a Startup File to inject the HttpContextAccessor
Package Required: Microsoft.Azure.Functions.Extensions
[assembly: FunctionsStartup(typeof(FuncAppName.Startup))]
namespace FuncAppName
{
public class Startup : FunctionsStartup
{
public override void Configure(IFunctionsHostBuilder builder)
{
builder.Services.AddScoped<HttpContextAccessor>();
}
}
}
Next, inject it into your main Function -
using Microsoft.AspNetCore.Http;
namespace FuncAppName
{
public class SomeFunction
{
private readonly HttpContext _httpContext;
public SomeFunction(HttpContextAccessor contextAccessor)
{
_httpContext = contextAccessor.HttpContext;
}
[FunctionName("SomeFunc")]
public override Task<IActionResult> Run([HttpTrigger(AuthorizationLevel.Anonymous, new[] { "post" }, Route = "run")] HttpRequest req)
{
var response = "Some Response"
_httpContext.Response.Headers.Add("my-custom-header", "some-custom-value");
_httpContext.Response.Headers.Add("my-other-header", "some-other-value");
_httpContext.Response.Headers.Add("Access-Control-Expose-Headers", "my-custom-header, my-other-header");
return new OkObjectResult(response)
}
If you want to allow all headers you can use wildcard (I think, not tested) -
_httpContext.Response.Headers.Add("Access-Control-Expose-Headers", "*");
You still need to add your web-app url to the azure platform CORS. You can add * wildcard, more info here - https://iotespresso.com/allowing-all-cross-origin-requests-azure-functions/
to enable CORS for Local Apps during development - https://stackoverflow.com/a/60109518/9276081
Now to access those headers in your Blazor WASM, as an e.g. you can -
protected override async Task OnInitializedAsync()
{
var content = JsonContent.Create(new { query = "" });
using (var client = new HttpClient())
{
var result = await client.PostAsync("https://func-app-name.azurewebsites.net/api/run", content);
var headers = result.Headers.ToList();
}
}

ASP.NET Web-api core: Handling client connections problems and find conflicts

Background
I have a web api server (asp.net core v2.1) that serve some basic operation, like managing entities on the server. This is the interface:
[HttpPost]
[Route("create")]
public async Task<ActionResult<NewEntityResponse>> Create(CreateEntityModel model)
{
// 1) Validate the request.
// 2) Create a new row on the database
// 3) Return the new entity in response.
}
The user running this REST method in this way:
POST https://example.com/create
Content-Type: application/json
{
"firstName": "Michael",
"lastName": "Jorden"
}
And getting response like this:
Status 200
{
"id": "123456" // The newly created entity id
}
The Problem
When sending thousands of requests like this, at some point it will fail because of network connections. When connection fails, it can leads us into two different situations:
The network call was ended on the way to the server - In this case, the server don't know about this request. Therefore, the entity wasn't created. The user just have to send the same message again.
The network call was sent from the server to back to the client but never rich the destination - In this case the request was fulfill completely, but the client don't aware for this. The expected solution is to send the same request again. In this case, it will create the same entity twice - and this is the problem.
The Requested Solution
I want to create an generic solution for web-api that "remmeber" which commands it already done. if he got same request twice, it's return HTTP status code Conflict.
Where I got so far
I thought to add the client an option to add a unique id to the request, in this way:
POST https://example.com/create?call-id=XXX
Add to my server a new filter that check if the key XXX is already fulfill. If yes, return Conflict. Otherwise - continue.
Add another server filter that checks the response of the method and marking it as "completed" for further checks.
The problem with this solution on concurrency calls. If my method takes 5 seconds to be returned and the client sent the same message again after 1 second - it will create two entities with same data.
The Questions:
Do you think that this is good approach to solve this problem?
Do you familiar with ready to use solutions that doing this?
How to solve my "concurrency" problem?
Any other tips will be great!
thanks.

Isnt the easiest solution to make the REST action idempotent?
I mean by that: the call should check if the resource already exists and either create a new resource if it doesnt or return the existing if it does?

OK, I just figure it up how to make it right. So, I implemented it by myself and share it with you.
In order to sync all requests between different servers, I used Redis as cache service. If you have only one server, you can use Dictionary<string, string> instead.
This filter do:
Before processing the request - add a new empty value key to Redis.
After the server processed the request - store the server response in Redis. This data will be used when the user will ask again for same request.
public class ConflictsFilter : ActionFilterAttribute
{
const string CONFLICT_KEY_NAME = "conflict-checker";
static readonly TimeSpan EXPIRE_AFTER = TimeSpan.FromMinutes(30);
private static bool ShouldCheck(ActionDescriptor actionDescription, IQueryCollection queries)
{
return queries.ContainsKey(CONFLICT_KEY_NAME);
}
private string BuildKey(string uid, string requestId)
{
return $"{uid}_{requestId}";
}
public override void OnActionExecuting(ActionExecutingContext context)
{
if (ShouldCheck(context.ActionDescriptor, context.HttpContext.Request.Query))
{
using (var client = RedisConnectionPool.ConnectionPool.GetClient())
{
string key = BuildKey(context.HttpContext.User.GetId(), context.HttpContext.Request.Query[CONFLICT_KEY_NAME]);
string existing = client.Get<string>(key);
if (existing != null)
{
var conflict = new ContentResult();
conflict.Content = existing;
conflict.ContentType = "application/json";
conflict.StatusCode = 409;
context.Result = conflict;
return;
}
else
{
client.Set(key, string.Empty, EXPIRE_AFTER);
}
}
}
base.OnActionExecuting(context);
}
public override void OnResultExecuted(ResultExecutedContext context)
{
base.OnResultExecuted(context);
if (ShouldCheck(context.ActionDescriptor, context.HttpContext.Request.Query) && context.HttpContext.Response.StatusCode == 200)
{
string key = BuildKey(context.HttpContext.User.GetId(), context.HttpContext.Request.Query[CONFLICT_KEY_NAME]);
using (var client = RedisConnectionPool.ConnectionPool.GetClient())
{
var responseBody = string.Empty;
if (context.Result is ObjectResult)
{
ObjectResult result = context.Result as ObjectResult;
responseBody = JsonConvert.SerializeObject(result.Value);
}
if (responseBody != string.Empty)
client.Set(key, responseBody, EXPIRE_AFTER);
}
}
}
}
The code is executed only if the query ?conflict-checker=XXX is exists.
This code is provide you under MIT license.
Enjoy the ride :)

Grapevine Rest Server Route Pathinfo with dynamic values

I'm pretty new to C# and need to realise a REST Service so i stumbled over Grapevine.
I need to have parts of the URL of the service handed over on service start via config file but I don't manage to hand over the value "clientId" of the config file to the Route's Pathinfo because it's not constant.
Here's the part of the code:
[RestResource(BasePath = "/RestService/")]
public class Rest_Resource
{
public string clientId = ConfigurationManager.AppSettings["ClientId"];
[RestRoute(PathInfo = clientId + "/info")]//<-how do I fill Pathinfo with dynamic values?
public IHttpContext GetVersion(IHttpContext context)
{....}
}
I'm using grapevine v4.1.1 as nuget package in visual studio.

While it is possible to change attribute values at runtime, or even use dynamic attributes, an easier solution in this case might be to not use the auto discovery feature exclusively, but use a hybrid approach to route registration.
Consider the following class that contains two rest routes, but only one of them is decorated with the attribute:
[RestResource(BasePath = "/RestService/")]
public class MyRestResources
{
public IHttpContext ManuallyRegisterMe(IHttpContext context)
{
return context;
}
[RestRoute(PathInfo = "/autodiscover")]
public IHttpContext AutoDiscoverMe(IHttpContext context)
{
return context;
}
}
Since you want to register the first route using a value that is not known until runtime, we can manually register that route:
// Get the runtime value
var clientId = "someValue";
// Get the method info
var mi = typeof(MyRestResources).GetMethod("ManuallyRegisterMe");
// Create the route
var route = new Route(mi, $"/RestService/{clientId}");
// Register the route
server.Router.Register(route);
This takes care of manually registering our route that needs a runtime value, but we still want the other routes to be automatically discovered. Since the router will only autodiscover if the routing table is empty when the server starts, we'll have to tell the router when to scan the assemblies. You can do this either before or after you manually register the route:
server.Router.ScanAssemblies();

C# WCF Service Get Status Code

I have a very basic WCF service which has a method named SaveSchoolName(string SchoolName) which basically returns as boolean value of True if the operation is good.
.
I added a service reference to my client application and is consuming the service as follows:
MyService.WebServicesClient svc = new MyService.WebServicesClient();
bool dataSaved = false;
dataSaved = svc.SaveSchoolName("School Name");
if(dataSaved){
// do something.
}
else{
// log not saved.
}
I want to know how do I determine the Http Status Code (200 - OK) for the WCF Service call. I have tried to search but none seems to provide any detailed info on how I would be able to get the response headers from invoking the method.

You need to create a client message inspector for this.
Check the below code out ... to make it work just add the inspector to your client. BTW, obviously this only works for HTTP :)
public class HttpStatusCodeMessageInspector : IClientMessageInspector
{
public void AfterReceiveReply(ref Message reply, object correlationState)
{
if (reply.Properties.ContainsKey(HttpResponseMessageProperty.Name))
{
var httpResponseProperty = (HttpResponseMessageProperty)reply.Properties[HttpResponseMessageProperty.Name];
Console.WriteLine($"Response status is {(int)httpResponseProperty.StatusCode}");
}
}
public object BeforeSendRequest(ref Message request, IClientChannel channel)
{
return null;
}
}

To extend #Jorge's answer, I started by implementing the IClientMessageInspector and IEndpointBehavior from the example here. I replaced the contents of IClientMessageInspector.AfterReceiveReply with the code provided by Jorge:
public void AfterReceiveReply(ref Message reply, object correlationState)
{
if (reply.Properties.ContainsKey(HttpResponseMessageProperty.Name))
{
var httpResponseProperty = (HttpResponseMessageProperty)reply.Properties[HttpResponseMessageProperty.Name];
Console.WriteLine($"Response status is {(int)httpResponseProperty.StatusCode}");
}
}
Now, you can choose to continue inheriting BehaviorExtensionElement and add the behavior to your client configuration file. If you take this approach you'll be done.
However, since my client configuration was created programmatically, I needed a few additional steps here.
In the docs you can see that an Endpoint Behavior can be added by using the ServiceEndpoint.Behaviors.Add method. But how do we get access to the ServiceEndpoint object?
This can be done by first creating your service client object, and then using its Endpoint property like so:
''' VB.NET
'' Creating the binding obj
Dim objMyBinding As New System.ServiceModel.WSHttpBinding()
objMyBinding.Name = "YOUR_BINDING_NAME"
'' Other details of binding added here ''
'' Creating the endpoint address obj
Dim objMyEndpoint As System.ServiceModel.EndpointAddress
objMyEndpoint = New System.ServiceModel.EndpointAddress(New Uri(ENDPOINT_ADDR_HERE))
'' Creating the Service obj
Dim objWebServices As CalculatorService = New CalculatorService(objMyBinding, objMyEndpoint)
'' Finally adding the behavior to the Service Endpoint (CustomEndpointBehavior is implementation of IEndpointBehavior)
objWebServices.Endpoint.EndpointBehaviors.Add(New CustomEndpointBehavior)
/// C#.NET
// Creating the binding obj
System.ServiceModel.WSHttpBinding objMyBinding = New System.ServiceModel.WSHttpBinding();
objMyBinding.Name = "YOUR_BINDING_NAME";
// Other details of binding added here //
// Creating the endpoint address obj
System.ServiceModel.EndpointAddress objMyEndpoint;
objMyEndpoint = New System.ServiceModel.EndpointAddress(New Uri(ENDPOINT_ADDR_HERE));
// Creating the Service obj
CalculatorService objWebServices = New CalculatorService(objMyBinding, objMyEndpoint);
// Finally adding the behavior to the Service Endpoint (CustomEndpointBehavior is implementation of IEndpointBehavior)
objWebServices.Endpoint.EndpointBehaviors.Add(New CustomEndpointBehavior());

How to return 302 redirect from Web service environment

I am in a restful service environment and we are using ServiceStack as our service Framework. At this moment, I need to do a redirect directly from the service and as soon as I try to do it from my Get method it fails because I think my Get function looks somethinglike this:
public override object OnGet(ShareDTO request)
{
HttpContext.Current.Response.Redirect(#"http://www.google.com");
return new object();
}
May be because first it is trying to redirect and then it is trying to return a value but this is just wild guess. I am not sure if it is even possible in service environment because all the time whenever I have used Response.Redirect, it was always always a .NET aspx page and never tried in service environment.
Any thoughts?

The easiest way is to just return a custom HttpResult, e.g:
public object Any(Request request)
{
return HttpResult.Redirect("http://www.google.com");
}
Which is equivalent to the more explicit:
return new HttpResult
{
StatusCode = HttpStatusCode.Found,
Headers =
{
{ HttpHeaders.Location, "http://www.google.com" },
}
};
Alternatively you can write directly to the Response, either in a Request Filter or within a Service, e.g:
public object Any(Request request)
{
base.Response.StatusCode = 302;
base.Response.AddHeader(HttpHeaders.Location, "");
base.Response.EndRequest();
return null;
}