HTTP API – Web request

When you're maintaining scoreboards or other such things that require regular HTTP request access to servers, you can use the HTTP API to perform such web request tasks.

Getting ready

Have a server to which you're allowed to request data via HTTP. You can use a public server of any type to try out HTTP requests if you'd like.

How to do it…

  1. Link to the HTTP API in your ProjectName.Build.cs file.
  2. In the file in which you will send your web request, include the HttpModule.h header file, the HttpManager.h header file, and the HttpRetrySystem.h file, as shown in the following code snippet:
    #include "Runtime/Online/HTTP/Public/HttpManager.h"
#include "Runtime/Online/HTTP/Public/HttpModule.h"
#include "Runtime/Online/HTTP/Public/HttpRetrySystem.h"
  3. Construct an IHttpRequest object from FHttpModule using the following code:
    TSharedRef<IHttpRequest> http=FHttpModule::Get().CreateRequest();

    Tip

    FHttpModule is a singleton object. One copy of it exists for the entire program that you are meant to use for all interactions with the FHttpModule class.

  4. Attach your function to run to the IHttpRequest object's FHttpRequestCompleteDelegate, which has a signature as follows:
    void HttpRequestComplete( FHttpRequestPtr request,
FHttpResponsePtr response, bool success );
  5. The delegate is found inside of the IHttpRequest object as http->OnProcessRequestComplete():
    FHttpRequestCompleteDelegate& delegate = http->OnProcessRequestComplete();

    There are a few ways to attach a callback function to the delegate. You can use the following:

    • A lambda using delegate.BindLambda():
      delegate.BindLambda(
  // Anonymous, inlined code function (aka lambda)
  []( FHttpRequestPtr request, FHttpResponsePtr response, bool success ) -> void
{
  UE_LOG( LogTemp, Warning, TEXT( "Http Response: %d, %s" ),
  request->GetResponse()->GetResponseCode(),
  *request->GetResponse()->GetContentAsString() );
});
    • Any UObject's member function:
      delegate.BindUObject( this, &AChapter12GameMode::HttpRequestComplete );

      Tip

      You cannot attach to UFunction directly here as the .BindUFunction() command requests arguments that are all UCLASS, USTRUCT or UENUM.

    • Any plain old C++ object's member function using .BindRaw:
      PlainObject* plainObject = new PlainObject();
delegate.BindRaw( plainObject, &PlainObject::httpHandler );
// plainObject cannot be DELETED Until httpHandler gets called..

      Tip

      You have to ensure that your plainObject refers to a valid object in memory at the time the HTTP request completes. This means that you cannot use TAutoPtr on plainObject, because that will deallocate plainObject at the end of the block in which it is declared, but that may be before the HTTP request completes.

    • A global C-style static function:
      // C-style function for handling the HTTP response:
void httpHandler( FHttpRequestPtr request, 
FHttpResponsePtr response, bool success )
{
  Info( "static: Http req handled" );
}
delegate.BindStatic( &httpHandler );

    Note

    When using a delegate callback with an object, be sure that the object instance that you're calling back on lives on at least until the point at which the HttpResponse arrives back from the server. Processing the HttpRequest takes real time to run. It is a web request after all—think of waiting for a web page to load.

    You have to be sure that the object instance on which you're calling the callback function has not deallocated on you between the time of the initial call and the invocation of your HttpHandler function. The object must still be in memory when the callback returns after the HTTP request completes.

    You cannot simply expect that the HttpResponse function happens immediately after you attach the callback function and call ProcessRequest()! Using a reference counted UObject instance to attach the HttpHandler member function is a good idea to ensure that the object stays in memory until the HTTP request completes.

  6. Specify the URL of the site you'd like to hit:
    http->SetURL( TEXT( "http://unrealengine.com" ) );
  7. Process the request by calling ProcessRequest:
    http->ProcessRequest();

How it works…

The HTTP object is all you need to send off HTTP requests to a server and get HTTP responses. You can use the HTTP request/response for anything that you wish; for example, submitting scores to a high scores table or to retrieve text to display in-game from a server.

They are decked out with a URL to visit and a function callback to run when the request is complete. Finally, they are sent off via FManager. When the web server responds, your callback is called and the results of your HTTP response can be shown.

There's more…

You can set additional HTTP request parameters via the following member functions:

  • SetVerb() to change whether you are using the GET or POST method in your HTTP request
  • SetHeaders() to modify any general header settings you would like
..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
18.220.163.91