Edition 0 Updated to asp. Net core 0

Multiple ways to use IHttpClientFactory 
There are several ways that you can use 
IHttpClientFactory
in your application: 
•
Basic usage 
•
Use Named Clients 
•
Use Typed Clients 
•
Use Generated Clients 
For the sake of brevity, this guidance shows the most structured way to use 
IHttpClientFactory
, 
which is to use Typed Clients (Service Agent pattern). However, all options are documented and are 
currently listed in this 
article covering the IHttpClientFactory usage
. 
Note 
If your app requires cookies, it might be better to avoid using 
IHttpClientFactory
 in your app. For 
alternative ways of managing clients, see 
Guidelines for using HTTP clients
 
How to use Typed Clients with IHttpClientFactory 
So, what’s a “Typed Client”? It’s just an 
HttpClient
that’s pre
-configured for some specific use. This 
configuration can include specific values such as the base server, HTTP headers or time outs. 
The following diagram shows how Typed Clients are used with 
IHttpClientFactory
: 

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CHAPTER 7 | Implement resilient applications 
Figure 8-4. Using IHttpClientFactory with Typed Client classes. 
In the above image, a 
ClientService
(used by a controller or client code) uses an 
HttpClient
created by the registered 
IHttpClientFactory
. This factory assigns an 
HttpMessageHandler
from a 
pool to the 
HttpClient
. The 
HttpClient
can be configured with Polly’s policies when registering the 
IHttpClientFactory
in the DI container with the extension method 
AddHttpClient
. 
To configure the above structure, add 
IHttpClientFactory
 in your application by installing the 
Microsoft.Extensions.Http
NuGet package that includes the 
AddHttpClient
 extension method for 
IServiceCollection
. This extension method registers the internal 
DefaultHttpClientFactory
class to 
be used as a singleton for the interface 
IHttpClientFactory
. It defines a transient configuration for 
the 
HttpMessageHandlerBuilder
. This message handler (
HttpMessageHandler
 object), taken from a 
pool, is used by the 
HttpClient
returned from the factory. 
In the next snippet, you can see how 
AddHttpClient()
can be used to register Typed Clients (Service 
Agents) that need to use 
HttpClient
. 
// Program.cs
//Add http client services at ConfigureServices(IServiceCollection services)
builder.
Services
.
AddHttpClient
(); 
builder.
Services
.
AddHttpClient
(); 
builder.
Services
.
AddHttpClient
(); 

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303 
CHAPTER 7 | Implement resilient applications 
Registering the client services as shown in the previous snippet, makes the 
DefaultClientFactory
create a standard 
HttpClient
for each service. The typed client is registered as transient with DI 
container. In the preceding code, 
AddHttpClient()
registers 
CatalogService
, 
BasketService
, 
OrderingService
as transient services so they can be injected and consumed directly without any need 
for additional registrations. 
You could also add instance-specific configuration in the registration to, for example, configure the 
base address, and add some resiliency policies, as shown in the following: 
builder.
Services
.
AddHttpClient
(client => 
{ 
client.
BaseAddress
= 
new
Uri
(builder.
Configuration
[
"BaseUrl"
]); 
}) 
.
AddPolicyHandler
(
GetRetryPolicy
()) 
.
AddPolicyHandler
(
GetCircuitBreakerPolicy
()); 
In this next example, you can see the configuration of one of the above policies: