[http] provide httpchunk.C tutorial

Shows simple implementation of THttpServer handler
wich spit reply on 1000 smaller pices.
Usable only for single simultaneous request.

Author: linev

tutorials/http/httpchunked.C

@@ -0,0 +1,65 @@
+/// \file
+/// \ingroup tutorial_http
+///  This macro shows implementation of chunked requests
+///  These are special kind of user-defined requests which let
+///  split large http reply on many chunks so that server do not need to allocate
+///  such memory at once
+///
+///  After macro started, try to execute request with
+/// ~~~
+///      wget http://localhost:8080/chunked.txt
+/// ~~~
+///
+///  CAUTION: Example is not able to handle multiple requests at the same time
+///  For this one should create counter for each THttpCallArg instance
+///
+/// \macro_code
+///
+/// \author Sergey Linev
+
+#include "THttpServer.h"
+#include "THttpCallArg.h"
+#include <cstring>
+
+class TChunkedHttpServer : public THttpServer {
+   protected:
+
+      int fCounter = 0;
+
+      /** process only requests which are not handled by THttpServer itself */
+      void MissedRequest(THttpCallArg *arg) override
+      {
+         if (strcmp(arg->GetFileName(), "chunked.txt"))
+            return;
+
+         arg->SetChunked();
+
+         std::string content = "line" + std::to_string(fCounter++) + "   ";
+
+         for (int n = 0; n < 2000; n++)
+            content.append("-");
+         content.append("\n");
+
+         if (fCounter >= 1000) {
+            // to stop chunk transfer either provide empty content or clear chunked flag
+            fCounter = 0;
+            arg->SetChunked(kFALSE);
+         }
+
+         arg->SetTextContent(std::move(content));
+      }
+
+   public:
+      TChunkedHttpServer(const char *engine) : THttpServer(engine) {}
+
+   ClassDefOverride(TChunkedHttpServer, 0)
+};
+
+void httpchunked()
+{
+   // start http server
+   auto serv = new TChunkedHttpServer("http:8080");
+
+   // reduce to minimum timeout for async requests processing
+   serv->SetTimer(1);
+}