How to generalize login, action, and logout when using Web API HttpClient

Question

I am using HttpClient (aka Web API client) to consume RESTfull services. Services require session to be established (via login) and then destroyed (via logout) upon each operation. So the call to consume service A looks something like this (pseudocode)

// setup create auth dictionary authDict create authenticationContent using FormUrlEndodeContent(authDict) create cookieContainer create HttpClientHandler... create HttpClient // login await httpClient.PostAsync(LoginUrl, authenticationContent); do error checking // perform Operation A await httpClient.....post...or...get... extract data, process it, tranform it, get a cup of coffee, etc, etc populate OperationAResult // logout await httpClient.GetAsync(LogoutUrl); // return result return OperationAResult

My question is, how can I easily reuse setup, login, and logout for different operations? Should I be creating some method that will take in Action<> and if so how do I make sure that operations occur in order?

Erik Philips · Accepted Answer · 2012-10-24 01:32:28Z

Probably the easiest way is to just write a wrapper class.

public class MyHttpClient { private HttpClient _client = new HttpClient(); private MyHttpClientSetup _setup; public MyHttpClient(MyHttpClientSetup setup) { this._setup = setup; } private void HttpLogin() { // .. custom login stuff that uses this._setup } private void HttpLogout() { // .. custom logout stuff that uses this._setup } public void Reset() { this._client = new HttpClient(); } // Wrapped Properties from the private HttpClient (1 example) public Uri BaseAddress { get{ return this._client.BaseAddress;} set{ this._client.BaseAddress = value;} } // Wrapped HttpMethods (1 example) // Extremely poorly written, should be delegated properly // This is just a bad example not using Task properly public Task<HttpResponseMessage> DeleteAsync(string requestUri) { this.HttpLogin(); Task<HttpResponseMessage> result = this._client.DeleteAsync(requestUri); this.HttpLogout(); return result; } public class MyHttpClientSetup { // Properties required for setup; } }

Darrel Miller · Accepted Answer · 2012-10-24 15:12:01Z

You may be able to create a new MessageHandler to handle this stuff for you transparently.

public class ConnectionHandler : DelegatingHandler { public HttpClient HttpClient {get;set;} public TestHandler(HttpMessageHandler handler) { this.InnerHandler = handler; } protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) { // Do your login stuff here return base.SendAsync(request, cancellationToken) // Make your actual request .ContinueWith(t => { // Do your logout stuff here } } }

Then you can just use a single instance of a HttpClient to do all your requests. To add your handler to the request/response pipeline you just need to create a regular HttpClientHandler, assign it to the InnerHandler property of your DelegatingHandler and then pass your new handler into the constructor of the HttpClient. From that point on, all requests made via the HttpClient will be routed through your ConnnectionHandler.

 var connectionHandler = new ConnectionHandler(new HttpClientHandler()); var client = new HttpClient(connectionHandler); connectionHandler.HttpClient = client; var response = client.GetAsync("http://example.org/request").Result;

The advantage of using a single HttpClient instance is that you don't have to keep re-specifying the DefaultRequestHeaders. Also, disposing the HttpClient will kill the TCP Connection so the next request will have to re-open it.

I have seen this approach with creating custom handler in the HttpClient examples on codeplex, and it is nice. But I need to "hit" 3 different URLs (login, service, logout) during same "operation". in SendAsync override I only have request so a separate HttpClient instance would have to be created right? Which is what I am trying to avoid...Take a look at BingTranslate example, they did almost similar approach where a separate client was used to get Azure data token...
...To make things "easier" once I hit /login a cookie is created (encypted autho) that needs to be "carried over" to the next call (operation) as well as to /logout call (so that I don't exceed max number of sessions).....
@zam6ak Add a HttpClient property to the ConnectionHandler and give it a reference to your Httpclient instance. There is no problem making multiple simultaneous requests with the same HttpClient.
@zam6ak If you enable the CookieContainer on the HttpClientHandler then it may take care of the re-sending the auth token on each request.
So I need to create a client using ConnectionHandler which in turn needs to reference that client :)? I may not have had enough coffee this morning, but wouldn't you have to 1) create connectionHandler, 2) create client using connectionHandler, and then 3) pass client back to connectionHandler....Does that sound right? Could you perhaps modify example to show this? Tnx

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