raRaRa raRaRa - 15 days ago 5
ASP.NET (C#) Question

Reusing HttpClient for different users

I've been reading a lot about best practices when using

HttpClient
. Most people recommend reusing it for the lifetime of the application, even though it's
IDisposable
.

My web application is communicating with various APIs, like Facebook Graph API, Twitter API and Instagram API.

The plan is to create an individual HttpClient for each API it communicates to, which is recommended, because then I can reuse some of the headers.

But now to the question, let's take the Twitter API as an example, each user using my web application has its own authorization header (user bound access token). I believe this means that I can't set the authorization header to the DefaultRequestHeaders of the
HttpClient
object.

What is the best practice when it comes to reusing
HttpClient
for multiple users who have different authorization headers?

Could I create a
HttpRequestMessage
object for each request and set the authorization header on the httpRequestMessage object, instead of setting it to the default one,
httpClient.DefaultRequestHeaders.Authorization
?

Thanks.

Answer

Because there is some cost involved in creating a HttpClient (especially the number of sockets) there are some benefits in reusing a HttpClient instance. It is thread-safe as as well.

In order to have no dependencies between multiple concurrent calls with one client instance the key pattern is to use HttpRequestMessage class and invoke the HttpClient.SendAsync method (instead of using the more convenient HttpClient.GetAsync, PostAsync, ...).

Something like this:

var request = new HttpRequestMessage() {
   RequestUri = new Uri("http://api.twitter.com/someapiendpoint"),
   Method = HttpMethod.Get
}
// set the authorization header values for this call
request.Headers.Accept.Add(...);

var response = await client.SendAsync(request);

Now the request headers of the HttpRequestMessage will be used (and not the DefaultRequestHeaders anymore).

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