dotnet-http-client

name	dotnet-http-client
description	Consumes HTTP APIs. IHttpClientFactory, typed/named clients, resilience, DelegatingHandlers.

dotnet-http-client

Best practices for consuming HTTP APIs in .NET applications using IHttpClientFactory. Covers named and typed clients, resilience pipeline integration, DelegatingHandler chains for cross-cutting concerns, and testing strategies.

Scope

• IHttpClientFactory patterns (named and typed clients)
• DelegatingHandler chains for cross-cutting concerns
• Resilience pipeline integration with HTTP clients
• Testing strategies for HTTP client code

Out of scope

• DI container mechanics and service lifetimes -- see [skill:dotnet-csharp-dependency-injection]
• Async/await patterns and cancellation token propagation -- see [skill:dotnet-csharp-async-patterns]
• Resilience pipeline configuration (Polly v8, retry, circuit breaker) -- see [skill:dotnet-resilience]
• Integration testing frameworks -- see [skill:dotnet-integration-testing]

Cross-references: [skill:dotnet-resilience] for resilience pipeline configuration, [skill:dotnet-csharp-dependency-injection] for service registration, [skill:dotnet-csharp-async-patterns] for async HTTP patterns.

---

Why IHttpClientFactory

Creating HttpClient instances directly causes two problems:

1. Socket exhaustion -- each HttpClient instance holds its own connection pool. Creating and disposing many instances exhausts available sockets (SocketException: Address already in use).
2. DNS staleness -- a long-lived singleton HttpClient caches DNS lookups indefinitely, missing DNS changes during blue-green deployments or failovers.

IHttpClientFactory solves both by managing HttpMessageHandler lifetimes with automatic pooling and rotation (default: 2-minute handler lifetime).

// Do not do this
var client = new HttpClient(); // Socket exhaustion risk

// Do not do this either
static readonly HttpClient _client = new(); // DNS staleness risk

// Do this -- use IHttpClientFactory
builder.Services.AddHttpClient();

```text

---

## Named Clients

Register clients by name for scenarios where you consume multiple APIs with different configurations:

```csharp

// Registration
builder.Services.AddHttpClient("catalog-api", client =>
{
    client.BaseAddress = new Uri("https://catalog.internal");
    client.DefaultRequestHeaders.Add("Accept", "application/json");
    client.Timeout = TimeSpan.FromSeconds(30);
});

builder.Services.AddHttpClient("payment-api", client =>
{
    client.BaseAddress = new Uri("https://payments.internal");
    client.DefaultRequestHeaders.Add("X-Api-Version", "2");
});

// Usage
public sealed class OrderService(IHttpClientFactory clientFactory)
{
    public async Task<Product?> GetProductAsync(
        string productId, CancellationToken ct)
    {
        var client = clientFactory.CreateClient("catalog-api");
        var response = await client.GetAsync($"/products/{productId}", ct);

         (response.StatusCode == HttpStatusCode.NotFound)
        {
             ;
        }

        response.EnsureSuccessStatusCode();
          response.Content
            .ReadFromJsonAsync<Product>(ct);
    }
}

```json

---



Typed clients encapsulate HTTP logic behind a strongly-typed . Prefer typed clients  a service consumes a
single API  multiple operations:

```csharp



{
      Task<Product?> GetProductAsync(
         productId, CancellationToken ct = )
    {
         response =  httpClient.GetAsync(
            , ct);

         (response.StatusCode == HttpStatusCode.NotFound)
        {
             ;
        }

        response.EnsureSuccessStatusCode();
          response.Content
            .ReadFromJsonAsync<Product>(ct);
    }

      Task<PagedResult<Product>> ListProductsAsync(
         page = ,
         pageSize = ,
        CancellationToken ct = )
    {
         response =  httpClient.GetAsync(
            , ct);

        response.EnsureSuccessStatusCode();
         ( response.Content
            .ReadFromJsonAsync<PagedResult<Product>>(ct))!;
    }

    
    {
         response =  httpClient.PostAsJsonAsync(
            , request, ct);

        response.EnsureSuccessStatusCode();
         ( response.Content
            .ReadFromJsonAsync<Product>(ct))!;
    }
}


builder.Services.AddHttpClient<CatalogApiClient>(client =>
{
    client.BaseAddress =  Uri();
    client.DefaultRequestHeaders.Add(, );
});

```json



For testability, define an :

```

  
{
    Task<Product?> GetProductAsync( productId, CancellationToken ct = );
    Task<PagedResult<Product>> ListProductsAsync( page = ,  pageSize = , CancellationToken ct = );
}


{
    
}


builder.Services.AddHttpClient<ICatalogApiClient, CatalogApiClient>(client =>
{
    client.BaseAddress =  Uri();
});

```text

---



Apply resilience to HTTP clients  `Microsoft.Extensions.Http.Resilience`. See [skill:dotnet-resilience] 
detailed pipeline configuration, strategy options,  migration guidance.



;
    })
    .AddStandardResilienceHandler();

```text



```csharp

builder.Services
    .AddHttpClient<CatalogApiClient>(client =>
    {
        client.BaseAddress =  Uri();
    })
    .AddStandardResilienceHandler(options =>
    {
        options.Retry.MaxRetryAttempts = ;
        options.Retry.Delay = TimeSpan.FromSeconds();
        options.CircuitBreaker.BreakDuration = TimeSpan.FromSeconds();
        options.AttemptTimeout.Timeout = TimeSpan.FromSeconds();
        options.TotalRequestTimeout.Timeout = TimeSpan.FromSeconds();
    });

```text



For idempotent read operations  tail latency matters:

```csharp

builder.Services
    .AddHttpClient()
    .AddStandardHedgingHandler(options =>
    {
        options.Hedging.MaxHedgedAttempts = ;
        options.Hedging.Delay = TimeSpan.FromMilliseconds();
    });

```text

See [skill:dotnet-resilience]   to use hedging vs standard retry.

---



`DelegatingHandler` provides a pipeline of message handlers that process outgoing requests  incoming responses. Use
them  cross-cutting concerns that apply to HTTP traffic.




{
    
    {
         stopwatch = Stopwatch.StartNew();

        logger.LogInformation(
            ,
            request.Method,
            request.RequestUri);

         response =  .SendAsync(request, cancellationToken);

        stopwatch.Stop();
        logger.LogInformation(
            ,
            request.Method,
            request.RequestUri,
            ()response.StatusCode,
            stopwatch.ElapsedMilliseconds);

         response;
    }
}


builder.Services.AddTransient<RequestLoggingHandler>();
builder.Services
    .AddHttpClient<CatalogApiClient>()
    .AddHttpMessageHandler<RequestLoggingHandler>();

```text



```
{
    
    {
         apiKey = config[]
            ??   InvalidOperationException();

        request.Headers.Add(, apiKey);

         .SendAsync(request, cancellationToken);
    }
}


builder.Services.AddTransient<ApiKeyHandler>();
builder.Services
    .AddHttpClient<CatalogApiClient>()
    .AddHttpMessageHandler<ApiKeyHandler>();

```text



```
{
    
    {
         token = httpContextAccessor.HttpContext?
            .Request.Headers.Authorization
            .ToString()
            .Replace(, );

         (!.IsNullOrEmpty(token))
        {
            request.Headers.Authorization =
                 AuthenticationHeaderValue(, token);
        }

         .SendAsync(request, cancellationToken);
    }
}

```text



```csharp

    : 
{
       HeaderName = ;

    
    {
         (!request.Headers.Contains(HeaderName))
        {
             correlationId = Activity.Current?.Id
                ?? Guid.NewGuid().ToString();
            request.Headers.Add(HeaderName, correlationId);
        }

         .SendAsync(request, cancellationToken);
    }
}

```text



Handlers are added  execution order:

```csharp

builder.Services.AddTransient<CorrelationIdHandler>();
builder.Services.AddTransient<BearerTokenHandler>();
builder.Services.AddTransient<RequestLoggingHandler>();

builder.Services
    .AddHttpClient<CatalogApiClient>(client =>
    {
        client.BaseAddress =  Uri();
    })
    .AddHttpMessageHandler<CorrelationIdHandler>()   
    .AddHttpMessageHandler<BearerTokenHandler>()     
    .AddHttpMessageHandler<RequestLoggingHandler>()  
    .AddStandardResilienceHandler();                 

```text

**Note:** In `IHttpClientFactory`, handlers registered first are outermost. `.AddStandardResilienceHandler()` added last
 innermost -- it wraps the actual HTTP call directly. This means retries happen inside the resilience handler without
re-executing the outer DelegatingHandlers. This  typically correct: correlation IDs  auth tokens are  once 
the outer handlers,  the resilience layer retries the raw HTTP call. If you need per-;
    client.BaseAddress =  Uri(baseUrl);
});

```text

```json

{
  : {
    : {
      : 
    }
  }
}

```text



The  handler lifetime   minutes. Adjust  services  different DNS characteristics:

```csharp

builder.Services
    .AddHttpClient<CatalogApiClient>()
    .SetHandlerLifetime(TimeSpan.FromMinutes());

```csharp

**Shorter lifetime** ( min):  services behind load balancers  frequent DNS changes. **Longer lifetime** (
min):  stable  services  connection reuse improves performance.

---





Test typed clients  providing a mock handler that returns controlled responses:

```csharp

   
{
    []
    
    {
        
         expectedProduct =  Product { Id = , Name =  };
         handler =  MockHttpMessageHandler(
             HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = JsonContent.Create(expectedProduct)
            });

         httpClient =  HttpClient(handler)
        {
            BaseAddress =  Uri()
        };

         client =  CatalogApiClient(httpClient);

        
         result =  client.GetProductAsync();

        
        Assert.NotNull(result);
        Assert.Equal(, result.Name);
    }

    []
    
    {
         handler =  MockHttpMessageHandler(
             HttpResponseMessage(HttpStatusCode.NotFound));

         httpClient =  HttpClient(handler)
        {
            BaseAddress =  Uri()
        };

         client =  CatalogApiClient(httpClient);

         result =  client.GetProductAsync();

        Assert.Null(result);
    }
}



{
     HttpRequestMessage? _lastRequest;

     HttpRequestMessage? LastRequest => _lastRequest;

    
    {
        _lastRequest = request;
         Task.FromResult(response);
    }
}

```text



Test handlers  isolation  providing an inner handler:

```csharp

   
{
    []
    
    {
        
         config =  ConfigurationBuilder()
            .AddInMemoryCollection( Dictionary<, ?>
            {
                [] = 
            })
            .Build();

         innerHandler =  MockHttpMessageHandler(
             HttpResponseMessage(HttpStatusCode.OK));

         handler =  ApiKeyHandler(config)
        {
            InnerHandler = innerHandler
        };

         client =  HttpClient(handler)
        {
            BaseAddress =  Uri()
        };

        
         client.GetAsync();

        
        Assert.NotNull(innerHandler.LastRequest);
        Assert.Equal(
            ,
            innerHandler.LastRequest.Headers
                .GetValues().Single());
    }
}

```text



Test the full HTTP client pipeline including DI registration:

```csharp



```csharp

---



| Factor         | Named Client                  | Typed Client                        |
| -------------- | ----------------------------- | ----------------------------------- |
| API surface    | Simple ( calls)            | Rich (multiple operations)          |
| Type safety    | Requires  name          | Strongly typed                      |
| Encapsulation  | HTTP logic  consuming  |               |
|     |  ``     |               |
|    |                  |                       |
|  | -           |      |

**   .**      , -         
 .

---

##  

- **  ** --  ` ()`   
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- **   ** --  `()` ( [:-])  
    
- **  ** --  ``     (, , )
- **   ** --    --     
   
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- **  / ** --     ``

---

##  

1. **     ``** --   ``    .  
     .
2. **    ** --     .   ``  
    (     ),     ``  .
3. **   ``    ** -- ` (":
      .  ` (":
   .
4. **      ** -- `()`  
   ``      .    -  . 
        (/   ).    -  ,   
             .
5. **     ** --      ``  
     .

---

## 

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