Reusing HttpClient for different users

Question

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.

Peridotite

Answer 1

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).

Erlene

Thanks, that's exactly what I was planning to do. Do you know if it's harmless to dispose the HttpRequestMessage object after SendAsync finishes? – Medlin

@raRaRa - You are welcome. The HttpRequestMessage implements IDisposable because the HttpContent type of the Content property is an IDisposable. I do not see any reasons why a dispose should cause any harm (especially for GET calls). But I have not made any first hand experience in disposing the HttpRequestMessage instances directly. – Pouncey